download - Enea

Proceedings of the International Conference“Enrico Fermi and the Universe of Physics”Rome, September 29 – October 2, 20012003 ENEAEnte per le Nuove tecnologie, l’Energia e l’AmbienteLungotevere Thaon di Revel, 7600196 - RomaISBN 88-8286-032-9

Honour CommitteeRettore dell’Università di Roma “La Sapienza”Rettore dell’Università degli Studi di Roma “Tor Vergata”Rettore della Terza Università degli Studi di RomaPresidente del Consiglio Nazionale delle Ricerche (CNR)Presidente dell’Ente per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA)Presidente dell’Istituto Nazionale di Fisica Nucleare (INFN)Direttore Generale del Consiglio Europeo di Ricerche Nucleari (CERN)Presidente dell’Istituto Nazionale di Fisica della Materia (INFM)Presidente dell’Agenzia Italiana Nucleare (AIN)Presidente della European Physical Society (EPS)Presidente dell’Accademia Nazionale dei LinceiPresidente dell’Accademia Nazionale delle Scienze detta dei XLPresidente della Società Italiana di Fisica (SIF)Presidente della Società Italiana per il Progresso delle Scienze (SIPS)Direttore del Dipartimento di Fisica dell’Università di Roma“La Sapienza”

Index009 A Short Presentation of the Fermi Centennial ConferenceCarlo Bernardini013 Enrico Fermi: a Guiding Light in an Anguished CenturyGiorgio Salvini033 Fermi’s Contribution to the World Energy SupplyCarlo Rubbia043 Enrico Fermi and his FamilyAlice Caton053 The Birth and Early Days of the Fermi Group in RomeGerald Holton071 Fermi toward Quantum Statistics (1923-1925)Fabio Sebastiani, Francesco Cordella097 The Evolution of Fermi’s Statistical Theory of AtomsJan Philip Solovej105 Nuclear Physics at the Cavendish Laboratory in the ThirtiesJeff Hughes119 Cooperation and Competition among Nuclear Physics Laboratoriesduring the Thirties: the Role of Frédéric JoliotMichel Pinault133 From Fermi to Fission: Meitner, Hahn and Strassmann in BerlinRuth Lewin Sime145 Slow Neutrons at Via Panisperna: the Discovery, the Production ofIsotopes and the Birth of Nuclear MedicineUgo Amaldi169 Funds and Failures: the Political Economy of Fermi’s GroupGiovanni Battimelli185 Fermi and Quantum Electrodynamics (QED)Sam Schweber7

217 Fermi and Applied Nuclear Physics during the War (1939-1945)Michelangelo De Maria219 New Large Accelerators in the World in the Forties and Early FiftiesDominique Pestre221 Enrico Fermi and the Birth of High-Energy Physics after World War IIGiulio Maltese259 Enrico Fermi, High-Energy Physics and High Speed ComputingRobert Seidel269 Women in Physics in Fermi’s TimeNina Byers289 Documents on Fermi’s LifeHarold Agnew295 Fermi and the Ergodic ProblemGiovanni Gallavotti303 Fermi and General RelativityTullio Regge305 Fermi’s Tentativo and Weak InteractionsNicola Cabibbo317 Enrico Fermi, the Man. Excerpts from some documentsJay Orear341 Experimental Nuclear Physics in the Thirties and FortiesJohn L. Heilbron361 The Beginnings of Pion and Muon PhysicsLeon Lederman365 Perspectives in High Energy Particle PhysicsLuciano Maiani389 Enrico FermiChen Ning Yang395 Concluding RemarksGiorgio Salvini399 Report on the Celebrations for the Centenary of Enrico Fermi’s BirthCarlo Bernardini, Rocco Capasso8

A Short Presentationof the Fermi Centennial ConferenceCarlo BernardiniEnrico Fermi was born on September 29, 1901; he died on November 28,1954: a very short life indeed. Nevertheless, his scientific legacy is by farricher than that of most physicists in the last century. This can be easilyappreciated by the extremely frequent recurrence of his name in most topicsof the so called “modern” physics: Fermi coordinates, Fermi-Dirac statistics,fermions, Fermi-Thomas atom, Fermi motion, Fermi surface, Fermi energy,Fermi’s golden rule, Fermi constant, Fermi theory of beta decay, fermi as aunit of length, Fermi age of neutrons, and so on (it is common to forgetsome in this list). This also shows that his fields of interest went from generalrelativity to statistical mechanics, from atomic physics to solid state, fromquantum electrodynamics to nuclear physics, from elementary particles toastrophysics: actually, there is no field of modern physics in which Fermi didnot contribute in a memorable way.This, I believe, is the reason why so many distinguished people agreed tocontribute to this Conference: everybody had, in some way, to pay a debtto an undisputed master of the 20 th century, both the organizers and thespeakers.Italy is a nice country, beloved by visitors from abroad because of monuments,museums, climate, perhaps people; arts and literature are apparentlythe most congenial activities to the population. At first, it might seem thatscience doesn’t have a central role, if any, in the Italian culture; therefore, thesudden appearance of such outstanding personalities as Galilei or Fermi (andmany others, indeed) looks like a miracle. Undoubtedly, this is a good reasonto examine how and why the “miracle” happened and to illustrate, particularlyto Italians, that it is perfectly possible at any moment to repeat theprodigy. With this in mind, some years ago the old and glorious SocietàItaliana per il Progresso delle Scienze (SIPS, of which Fermi was a member)decided to ask government financial support to invite people of the internationalphysics community in some way or other related to Fermi, to reconstructin a public occasion both the achievements of the Scientist and the circumstancesin which his activity developed.9

10Thanks to the above-mentioned far-sightedness of SIPS, the Ministero deiBeni Culturali (especially the general director, Francesco Sicilia, who wasextremely cooperative) gave us the opportunity to organize a NationalCommittee and I had the honor to chair it with the task to prepare a detailedproposal. I accepted in the second half of 1999, well knowing that it isextremely difficult to do “the best”. Now that the event is concluded, I canand want to say that I would never had reached any result without theinvaluable help of Rocco Capasso, secretary-general of SIPS, and LuisaBonolis, who had a special grant from the INFN (Istituto Nazionale di FisicaNucleare) to assist the activity of the Comitato. It was decided from the verybeginning that the Accademia Nazionale dei Lincei should have a role in theorganization of the Conference, so that the Comitato agreed in assigning apart of the program (about one third) to a special commission of theAccademia.During and after the Conference an Exhibition was open to the public containingsome documents, pictures, films and original instruments; theExhibition was installed in a theather in Rome, the “Teatro dei Dioscuri”near the Presidential residence at the Quirinale. The President of the ItalianRepublic actually was the first visitor of the Exhibition at the opening ceremony,on September 29, 2001. A large representation of the Fermi family,up to the great-granddaughter Ishbel who delighted all people present, hadbeen there since a couple of days before, because of a ceremony we had promotedin via Gaeta 19, were Enrico was born; also, many members of theCapon family were there, the family of Laura Fermi.The conference was, in my opinion, very satisfactory; all the aspects of thescientific activity of Enrico Fermi were considered and the peculiarities of hisapproach to the problems were analyzed. Here you can find the written versionof the talks that, all together, constitute an important recollection oforiginal thoughts on Fermi’s ideas, Fermi’s role, Fermi’s time. Almost all thespeakers have sent their text in due time to allow a quick preparation of theProceedings thanks to the full commitment of Diana Savelli and ENEA(Ente per le Nuove tecnologie, l’Energia e l’Ambiente) helped by RoccoCapasso of SIPS and Giovanna Dall’Ongaro (who was engaged by theComitato in the Conference Secretariat). Professor Chen Ning Yang andprofessor Leon Lederman, who were not able to join the Conference becauseof the serious difficulties with international flights after September 11, 2001,were both so kind as to mail a short written contribution to the event: we arevery grateful to them for their intention to participate in difficult moments.

A lot of open questions arise when examining Fermi’s life: why was he sucha precocious child? Which were the books he studied? Where came his interestin analytical mechanics from? How was he able to get a chair in theoreticalphysics at the age of 25 in a hostile academic surrounding?Where did he get the idea of his statistics? How did he became quicklyreknown in the international physics community and which were his relationswith English, Germans and French laboratories? What was his genuine contributionto the new-born Quantum Electrodynamics and how did this preludeto the theory of beta decay? Why did he decide to convert from atomicto nuclear physics? How did he understand slow neutrons? Why did hisgroup miss uranium fission? How was he able to realize the first nuclear reactorin such a short time? What was his contribution at Los Alamos? What washis commitment in political decisions at and after the end of WWII? Whatwere his ideas in elementary particle physics? What the problems he contributedto in astrophysics? What his suggestions for helping Italian physicsto restart after the war? How and why did he become interested in computingdevices?All these questions will find answers in the Proceedings of thisConference; this is the reason why I feel very indebted to all the speakersand want to express my gratitude to all of them and to the colleagues whochaired the sessions and conducted the discussion. I want to mention herethat on July 2, 2001, the Italian Physical Society (SIF) organized a smallmeeting at the “E. Fermi International School” in Varenna (Como Lake) on“Fermi as a teacher”; and on October 3-6 a special meeting was organizedby professor Remo Ruffini on “E. Fermi and Astrophysics” under the jointsponsorship of the Comitato Nazionale and the International Center forRelativistic Astrophysics (ICRA): both those events were quite successful andhave their own separate proceedings.Finally, besides the debt I already mentioned with Rocco Capasso andLuisa Bonolis, I want to express my great gratitude to some colleagues andfriends in the Comitato who gave me invaluable help, particularly in avoidingmistakes: Giorgio Salvini, Franco Bassani, Renato Angelo Ricci andAlessandro Pascolini; I want also to remark the friendly open-mindedness ofEdoardo Vesentini, President of the Accademia dei Lincei, in cooperatingwith the Comitato Nazionale on the common part of the program.11

Giorgio SalviniEnrico Fermi:a Guiding Light in an Anguished CenturyOur twentieth century has just ended. It contained so many hopes and humancontradictions. Let’s try to outline it with regard of physics. At the beginning ofthe century, six great physicists were born, and they led us toward a new visionand understanding of matter, light, stars and particles in our universe. The greatrevolution occurred between 1922 and 1935. The basis of their theoreticaldiscoveries were special relativity (1905), the atom’s structure (1911), the Bohrmodel (1913), the universal role of h, the Planck’s constant in thermodynamicsand electromagnetism. Among the new conquers, we recall the exclusionprinciple and the uncertainty relations. It is sad to recall that, in this splendidphase of human history, violent barbarian wars took place, in 1914-18 and1939-45. We recall the youth of Fermi, his coherence and character. Hegained immortal fame with the Fermi-Dirac statistics; with the behaviour ofneutrons in matter; with the discovery of a new type of field and forces, theweak interactions. In the United States, between 1938 and 1954, he built thefirst atomic pile (1942) and contributed to the study of nuclear energy for civiland military use. In 1946 he tried unsuccessfully to stop the preparation of thehydrogen bomb. In his last years of life, Enrico Fermi studied the different natureof muons and pions, and the best ways to study elementary particles. He was agreat experimentalist and a great theoretician. His successes and his surprises infront of unexpected phenomena in nature make us realize to be very far fromhaving fully understood our Universe and its general laws. Therefore we shallcontinue and boldly prepare the instruments which are necessary to progressand to satisfy our curiosity.13

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEEnrico Fermi:una guida in un secolo tormentatoÈ da poco terminato il XX secolo, pieno di tante speranze e tante umanecontraddizioni. Tracciamone un brevissimo profilo scientifico.Proprio all’inizio del secolo, tra il 1900 ed il 1902, nacquero sei grandi fisici,che ci portarono verso una nuova visione e comprensione della materia cheforma la nostra Terra, e della luce, delle stelle, d’ogni radiazione in tutto il nostroUniverso. La grande rivoluzione della quale sto parlando avvenne tra il 1922 edil 1935. Alla base delle loro scoperte teoriche vi fu la relatività (1905), lastruttura dell’atomo (1911), il modello di Bohr (1913), il ruolo universale di h, lacostante di Planck in termodinamica ed elettromagnetismo. Tra le nuoveconquiste possiamo citare il principio di esclusione e le relazioni diindeterminazione. È triste ricordare però che in questo fecondo periodo dellastoria dell’uomo il mondo fu scosso da guerre barbariche e violente nel 1914-18e nel 1939-45. Parleremo della giovinezza di Fermi, della sua coerenza e dellasua personalità. Egli si guadagnò fama immortale con la teoria statistica Fermi-Dirac, con il comportamento dei neutroni nella materia e con la scoperta di unnuovo tipo di campo e di forze, le interazioni deboli. Fermi realizzò negli StatiUniti, dove soggiornò dal 1938 al 1954, la prima pila atomica (1942) econtribuì allo studio dell’energia nucleare per scopi civili e militari. Nel 1946cercò, senza riuscirvi, di fermare la creazione della bomba ad idrogeno. Negliultimi giorni della sua vita Enrico Fermi studiò la diversa natura dei muoni epioni, ed il modo migliore per comprendere le particelle elementari. Egli fugrande sperimentatore e grande teorico. La sua incessante curiosità e il suorinnovato stupore per tutti i fenomeni naturali ci incoraggiano a proseguire lericerche sull’Universo e le leggi che lo governano, forgiando gli strumentinecessari al progresso della scienza.14

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYPhysics in the early 20 th centuryThe 20 th century, which held so many human hopes and contradictions,has just ended. Let’s try to outline its achievements in physics.After the Franco-German war of 1870-71, Europe enjoyed 45 years withoutmajor wars. There was suffering, society was plagued by huge differencesin culture and wealth, atrocious social conflicts were in store and eventuallyexploded in the First World War. But the frontiers and hopes for a betterfuture were open, and many educated people believed humankind wouldsoon have in hand the main keys to understanding the nature of our planetand our universe.Six great physicists were born at the very beginning of the century,between 1900 and 1902. Heirs to the achievements of Maxwell, Planck,Einstein, de Broglie and Bohr, they brought a new understanding of thematter of which our Earth is made, of light, stars, and the particles in ouruniverse. The people I am talking about were:• Werner Karl HEISENBERG, 1901-1976• Wolfgang PAULI, 1900-1958• Paul Adrien Maurice DIRAC, 1902-1984• Ernest Pascual JORDAN, 1902-1980• Enrico FERMI, 1901-1954• Eugene WIGNER, 1902-1995.The great scientific revolution of which they were among the protagonistsoccurred between 1922 and 1935.Let me proceed with order to justify these statements. I shall limit myselfto physics, although I know revolutions also occurred in chemistry, biologyand society as a whole.From 1890 to 1905 there were good reasons for people to be happy. Thenew sciences of electricity, magnetism, optics and thermodynamics seemed tohave revealed the fundamental secrets of our world and how they could beused for human benefit. Freedom from manual labor – first with thermodynamicmachines and a few years later with generators and electric motors –the understanding of light as an electromagnetic wave and, soon after, thelarge vision of electromagnetic waves and radio, which could spread informationinstantly around the world and promote brotherhood among its peoples,were among the greatest achievements.Based on this new knowledge and these successes, some eminent physicistsof that day thought their science had come close to a final explanation of theinorganic world. They did not know it was just on the brink of a series of fun-15

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEdamental theoretical and experimental discoveries: the revolution producedby the six scientists I’ve named.From 1900 to 1915, physics progressed along two lines, originally nearlyindependent but eventually largely joined in a coherent representation.One was the analysis of space, time and light, which led in 1905 to the theoryof special relativity, essentially due to Albert Einstein, and definitivelystated the relationship between mass (m) and total energy (E) for any particleof matter in the equation E = mc 2 , where c stands for the speed of lightin a vacuum [1].The other was the understanding of the microscopic structure of matter. Thefamous experiments of Rutherford and others (1911) clarified the commonstructure of atoms: a central nucleus with a diameter of ten thousand billionthpart of a centimeter, surrounded by a cloud of electrons [2]. The n. of electronswas found to range from one in hydrogen to 92 in the heaviest atom thenknown, uranium. The dimensions of this tiny solar system, with the nucleus atits center, were between 10 -7 and 10 -8 centimeters. The atom was seen as essentiallyempty, with a nucleus of enormous relative density at its center.In 1913-14, when the six men I named were still teenagers, a new modelof the atom was proposed by Bohr, followed by Sommerfeld. It incorporatedthe new progress in classical and relativistic mechanics and Planck’s andEinstein’s recent discoveries of the existence of a fundamental quantum ofaction, a quantity that has the dimensions of an action (energy × time) andhas been indicated since then by the letter h [2].The coincidence with experimentalfacts was astonishing.Another success was de Broglie’s revolutionary and still absolutely trueproposal (1923) that every elementary particle is also a wave: it propagateswith a characteristic wavelike motion and has a wavelength equal to h/p,where p stands for the particle’s momentum (mass × velocity) [2].Physicists were thus confronted with very important results, but they didnot yet have a coherent and consistent theoretical basis. They were askingthemselves: “What are these things, anyway – these electrons, photons, protons– are they waves or particles?”.A new representation of the worldThese elements – very sound but conceptually inadequate – were the startingpoint for the renewal of ideas I referred to, which led in 1925-35 to anew vision of the physical world. At first this renewal might have looked like16

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYexcessive critical research – useless twists and turns of ever-unsatisfied humancuriosity – but when the cracks were laid bare and the real underlying rocksof knowledge came to light, it was seen as an enormous and irreversiblehuman step forward.Now hang on to your hats, because the flight to a new world was such thateven some great scientists, young and old, had trouble understanding it.We are now going beyond 1913-15, the years of the soon outdated Bohr-Sommerfeld model, and beyond the theory of special relativity, which bythen had been generally accepted. Scientific thought was going down twonew roads, both valid but not yet merging.One was the theory of general relativity, which, through a new analysis ofgravitational forces, opens or closes and at any rate describes our universe. Iam not going to speak here of this new opening, which was due to Einstein;I shall simply mention a book that elegantly underlines the fundamentalvalue of the new ideas, Brian Greene’s The Elegant Universe [3].The other road was essentially opened by the six young physicists I namedat the start (Heisenberg, Pauli, Dirac, Jordan, Fermi and Wigner). It is onlyright to join to their names those of their elders Max Born (1992-1970) andErwin Schrödinger 1887-1961). But let me make it clear that a whole cohortof young physicists contributed to the new opening with unforgettable works.What we can take as the starting point was a paper Heisenberg publishedin 1925. Let me quote Enrico Persico’s exemplary presentation of it in histreatise on The Foundations of Atomic Mechanics [2]: “The new line wasopened by W. Heisenberg with a note published in July of 1925. The fundamentalidea expressed in it is that some of the quantities of the atomicmodel, such as the coordinates of an electron in a given instant, the durationof an orbital revolution, etc., have never been measured directly. Consideringthat the reasoning based on them leads to known difficulties, one can seriouslydoubt that these quantities have a real physical meaning and that theywill ever be measured in the future. Conversely, other quantities (emitted frequencies,intensities, etc.) can be observed and measured directly. Therefore,rather than searching for a geometric mechanical model that would allow usto find the values of the observable quantities from an unobservable structure,it is better to try to interconnect the values of the observable quantitiesdirectly, without using any model”.The “Göttingen boys” (as the very young physicists at the University ofGöttingen were dubbed) deserve credit for having shown in 1922-25 howto achieve this objective. The new relationships among observable quantities17

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEcannot be expressed using the ordinary methods of algebra; Heisenberg’sidea was to use a mathematical algorithm that was already known but had notyet been applied in physics; that is, matrix algebra. This method was largelydeveloped by Heisenberg, Born and Jordan, and they succeeded in findingnot only the results already known from the Bohr-Sommerfeld model, butalso new results that fit experimental data better.But still more happened in that prodigious period of 1925-27. Again let mequote Persico: “The ultimate reason why it is not possible to found atomicphysics on a mechanical model without a loss of logical coherence and precisionwas pointed by Heisenberg in a later paper (1927). In it he established theso-called uncertainty principle, which we can say is the key to all atomic physics,and which made it possible to show quantum mechanics in its true light”.One can come up with approximate images of this new wave-particle situation.But we must resign ourselves: we are confronted with a new representationof the microscopic world. The elementary quanta which constitutereality are no longer an ensemble of precise infinitesimal points, as if therewere a reality that our senses cannot perceive but which is as precise as theplanets and the stars of our universe. Quantum mechanics is a new vision,indeterminate in the dynamic values of each individual particle but nonethelessrigorously ordered and described in its overall structure. If we wish toexplain our reality, the existence of the solid state, the properties and originof helium, spectroscopy, and the nature of the stars, we must accept it.We are thus confronted with a physical reality that we can largely predictand calculate. But perhaps we have not yet reached a complete understandingof quantum mechanics, hence of our world’s essential structure. Thegreat physicist Richard Feynman remarked in 1965: “At this point, manyphysicists have come, with much effort, to understand general relativity. ButI think it is safe to say that nobody fully understands quantum mechanics”.I think this is still true today.Peace and war; moltingLet me pause for a moment in my account of these happenings from 1910to 1930, which changed our scientific world. I’m thinking of snakes orinsects that shed their skin. The snake sheds its old skin but remains its ownsplendid, nimble self. In the same way, during those years human knowledgeexperienced strong and perhaps unexpected evolution, a new sign of ourcapacity to progress.18

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYBut a violent, barbarous war broke out in the middle of this magnificentmolting phase; from 1914 to 1918, young people from France, Germany,England, Austria, Italy and the United States slaughtered each other. Nocomment of mine can do justice to this coincidence between a great elevationof the human spirit and an elementary tragedy, but I cannot fail to recallhere this duality of human nature. We shall return to it again when we reachthe time when so many physicists, Enrico Fermi among them, were swept upin the new tragedy of World War II. But let’s go back to our history, fromthe perspective of Fermi’s life.Enrico Fermi: the new statisticsEnrico Fermi was born in Rome in 1901. He left us too early, and still witha long program of scientific work to finish, on November 29, 1954.In his biography of Fermi, Enrico Persico – his friend since the age of 14 –says he discovered with surprise that he had a schoolmate who was not onlyvery smart, but had a mind completely different from those of all the beststudents Persico knew. He writes: “We soon discovered that we were face toface with an extraordinary genius”. I can only mention in passing the biographieswritten by other colleagues, E. Amaldi and F. Rasetti. They areincluded in Conoscere Fermi (Knowing Fermi), a book recently published forthis centenary.Fermi attended the Normal School of Pisa in 1918 and received his degreein 1922. During his university years he published his first papers on electromagnetismand relativity, two branches of physics that were fairly well cultivatedin Italy.This wide-ranging activity did not prevent Fermi from taking part in studentlife in Pisa or from taking advantage of the nearby Apuan Alps toindulge in his lifelong love of the mountains.Soon after Fermi’s graduation, the Italian physicist Orso Mario Corbino,who had a good idea of the young man’s merits, sent him with two researchgrants to Göttingen and Leiden. Göttingen had a very active school of theoreticalphysics [7] operating under Max Born’s leadership, and there Fermimet Dirac, Heisenberg, Jordan and Pauli – the people who opened up thenew quantum physics with the matrix method already known to mathematicians.For reasons that are not easy to understand, the exchange of ideas betweenFermi and the other young people at Göttingen was not very productive.19

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEConversely, his stay in Leiden was very useful. Here Fermi’s value was appreciatedby Paul Ehrenfest, a real master of statistical mechanics. The positiveresults of this visit appeared when Fermi returned in 1926 to Italy, where hefirst took up a temporary chair of Mathematical Physics at the University ofFlorence, and published the statistical theory of a gas of particles which obeyPauli’s exclusion principle – the particles now known as fermions.Going back to my metaphor of molting snakes, the process had enormousconsequences and proved irreversible in respect of the old ideas. It broughtnew discoveries, eliminated old paradoxes, and marked out new roads inphysics, astronomy, cosmogony and biology. Here are a few examples frommicrophysics:– the structure of hydrogen, deuterium, helium, atoms and molecules wasgreatly clarified by the new rules of quantum mechanics and bySchrödinger’s equation, which Fermi and Heisenberg appreciated immediately[2,5];– some aspects of the general symmetries that dominate the world of quantummechanics and are still used today to explain the microscopic andmacroscopic order of matter [2,7];– the distribution of electrons in complex atoms, particularly in the solidstate (F. BASSANI, [6]).In this ongoing analysis of experimental facts, a new principle wasannounced in 1925 by the 24-year-old Wolfgang Pauli. It could only beexplained by the new quantum mechanics, and made clear the structure andarchitecture of all atoms. This principle, known as Pauli’s exclusion principle,says that two electrons cannot occupy the same dynamic position in an atom.The complete explanation can be given only by the new quantum mechanics,but it is worth noting that Pauli formulated his principle at a time whenthe Bohr-Sommerfeld model of the atom was still the accepted one; in fact,that model sufficed for a first enunciation.Back in Florence in 1926, Fermi, with his great capacity for synthesis, seizedon the Pauli principle and published the statistical theory of a gas of particlesthat obey it. The new statistical rules he produced go by the name of Fermi-Dirac statistics; in fact, Dirac discovered the same rules a year after Fermi, buthe was the one who gave them their proper place in the new quantummechanics. The particles in question are now universally known as fermions.In 1926-27, Fermi was known in Italy to only a small group of mathematiciansand physicists, but his fame grew rapidly after his stature was recognizedby foreign physicists (F. RASETTI, Biografia di Fermi [6]).20

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYIn September of 1927, an international physics meeting was held in Comoto commemorate the centenary of Alessandro Volta’s death. All of theworld’s most eminent physicists were there, including a dozen Nobel laureatesand all the inventors of quantum physics.Arnold Sommerfeld, the great master of the Monaco School, demonstrated,together with his young collaborators, that the strange behavior of theelectrons contained in metals could be immediately interpreted by the newFermi-Dirac statistics.It was a triumph for Fermi, and many Italians were amazed that their 26-year-old compatriot was already so well known in Germany. As the Bible says,“a prophet is not without honor, save in his own country”. But it is only fairto say that in 1926, again thanks to the great Corbino’s interest in him,Fermi was appointed to the new chair of theoretical physics at RomeUniversity – the first such chair ever established in Italy.The years in Rome at the physics department;the extraordinary properties of neutronsThis was the period when Enrico Fermi’s quick mind and creative powerscame into full bloom. In 1933-34 he discovered the behavior of neutronsexperimentally and explained it by formulating the theory of beta disintegrationof radioactive nuclei, which was soon accepted as a fundamental phenomenonof our universe.Around 1931, Fermi and his group had realized that the future of atomicphysics was rather limited: theory could explain a large part of observed phenomena,and by this time the main interest lay in the inner part of the atom,the nucleus, which is the densest part and is a hundred thousand times smallerin diameter .Many properties of the nucleus were already known. It was clear that mostnuclei in nature are stable, but others are radioactive; that is, they spontaneouslyturn into atoms of different elements, usually changing the value oftheir electric charge. The radioactive process takes place by the expulsion ofan alpha particle, i.e. a helium nucleus, or an electron, i.e. the beta particle.Both phenomena are often accompanied by the emission of electromagneticradiation in the form of gamma rays.All this seemed to show that the nucleus, like the atom, is a compoundstate. It was fairly obvious in those times to think that protons and electrons– the only particles then known – were the basic constituents of nuclei. But21

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtheoretical knowledge was advanced enough to make the presence of electronsin nuclei very difficult to explain.It was at this point (in February of 1932) that Chadwick and the Joliot-Curie couple discovered the existence of a new particle in the nucleus,dubbed the neutron, with zero electric charge and the same mass as the proton.Ettore Majorana was perhaps the first to suggest that the nucleus is composedof only neutrons and protons.This solved all the difficulties related to the presence of electrons in thenucleus, but a new one arose: how can the nucleus emit electrons?Pauli timidly suggested the hypothesis that the electron might be createdin the same moment that it was emitted, together with another light, neutrallycharged particle that Fermi later called the neutrino. How this mightactually happen was a very serious problem, and Fermi was the one whosolved it [6,7,8].In fact, in the fall of 1933 Fermi presented to his group an article he hadwritten in the early morning hours of the previous days, with full mathematicaldetails. It was based on Pauli’s hypothesis of beta ray emission, but it wasa complete theory which immediately gave precise explanations of the experimentalfacts. The basic point lay in the assumption that a neutron can transformitself into a proton plus one electron plus one neutrino (today this iscalled an antineutrino): n → p +e – + ν, with a new kind of interaction.Only a few theories of modern physics have been so pregnant with results.Fermi’s theory is consistent with our present knowledge. It covers not onlythe usual processes of beta decay (the transformation of a neutron into a proton,with the creation of an electron and a neutrino), but also various othertransformations observed in those years among unstable particles 1 .The discovery of weak interactions may have been Fermi’s most importantcontribution to the progress of theoretical physics in the 20 th century. Italone would suffice to immortalize him in the history of physics. But only afew months later he made an equally important experimental discovery:radioactivity produced by bombarding nuclei with neutrons, and the particularcontribution of slow neutrons.1 In analyzing Fermi’s theory, the famous physicist and historian of science A. Pais [7, pp. 417 et seq.]notes that Fermi was the first to use the second quantization of half-spin particles. Pais also remarksthat the famous Fermi constant calculated in 1933 already had a value close to its present value, andthat Fermi’s paper pointed to the necessary existence of the heavy boson W. I agree with Pais on thispoint. I had the good fortune to collaborate with Carlo Rubbia, who rightly received the Nobel Prizefor his discovery of heavy bosons, and in those years we knew that from the very beginning the theoryof weak interaction, to be really coherent, required W and Z bosons.22

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYIrène Curie and Frédéric Joliot had succeeded in creating radioactive nuclei bybombardment with α particles. Fermi and his group thought neutrons wouldbe much more efficient, because their lack of an electric charge would allowthem to pass the electric barrier even in the case of the heaviest nuclei.Working feverishly, the “Via Panisperna boys” created and measured fortynew radioactive isotopes. But they soon observed the unexpected effects ofsome substances, like water and paraffin; their simple presence around ornear the bombarded element intensified its radioactivity.In less than a day, Fermi found the explanation of this phenomenon.Neutrons slow down when they collide with the nuclei of hydrogen containedin those substances. Slow neutrons have a larger resonating cross sectionagainst many atomic nuclei. We know that slow neutrons are a fundamentalkey for access to nuclear energy.Fermi’s group made a whole series of discoveries. In particular, they investigatedthe element uranium. Without realizing what they had done, theysplit the uranium nucleus. Fission was demonstrated only four years later, byOtto Hahn and Fritz Strassman. One may wonder whether the history of theworld would have been different had “Via Panisperna boys“ discovered fissionin 1935. Fermi was vexed by his failure to observe uranium fission. Itwas a warning that nature holds surprises and may conceal its secrets fromeven the finest minds. I shall return to this point.Fermi continued to work with neutrons until he left Italy in 1938. In1935-36, he wrote a long paper, in collaboration with Amaldi, on the diffusionof neutrons in matter and their selective absorption in various elements.An important work appeared in La Ricerca Scientifica in August 1936 [6,8].In it Fermi expounded the theory of neutron slowdown and diffusion. Thiswork was the starting point for all subsequent studies, and became the basisfor the calculations regarding moderators when the first atomic pile wasbuilt, in 1940-1942.The scientific work done at Rome University’s Physics Department inthose years was a very remarkable contribution to the development of physicsworldwide. These results earned Enrico Fermi the Nobel Prize in 1938.Fermi in the United States; nuclear energy and warAfter his first trip to the United States, in 1930, Fermi was often invited byAmerican universities to lecture at their summer sessions or to join their facultieson a permanent basis. Torn between his desire to remain in Italy and23

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEhis desire to remove his family from the distressing environment at home, hehesitated to accept these offers. But in 1938, when the Fascist governmentpassed anti-Semitic legislation that affected him personally – his wife, ourunforgettable Laura Fermi Capon, was Jewish, and no guarantee of protectionfrom the new laws could be believed – he made his decision and acceptedan offer from Columbia University.The trip to Stockholm to receive the Nobel Prize provided the occasion forthe family’s departure. They sailed straight to New York from Stockholm,and arrived on January 2, 1939 (Italy had not yet entered the war). Fermiwas then in the middle of his career, and could not have expected to beinvolved very soon in historical and scientific events of the greatest moment,events that were the direct result of those properties of uranium that had fortuitouslyescaped the Via Panisperna boys.In 1939, Otto Hahn and Fritz Strassman had discovered barium in theproducts created by the bombardment of uranium with neutrons. This wasan unexpected discovery, and one of the greatest magnitude. It was soonestablished that the uranium nucleus could be split into at least two largenuclear fragments, releasing neutrons. These neutrons could in turn freeother neutrons by splitting other uranium nuclei, triggering a chain reactionthat would affect a whole mass of uranium. A huge amount of energy wouldbe released from the uranium mass, and could be used for peaceful purposes,for instance to generate electricity by providing superheated steam for turbines.But if the process was instantaneous, it would release immensedestructive energy; that is, the atom bomb (E. AMALDI [6]).The decisive step in turning these dramatic new possibilities into reality wastaken with the famous Chicago atomic pile. The historic goal was achievedat 2:20 p.m. on December 2, 1942, when the uranium-graphite reactorbecame active, meaning that the pile went critical, the chain reaction started,and energy was released. The pile was left critical for 28 minutes, with apower of around half a watt, after which the reaction was quenched so thatthe pile would not become too radioactive and dangerous.This experiment, directed and controlled by Enrico Fermi in collaborationwith the best physicists of that time, in particular L. Szilard, can be consideredthe first fundamental step in the development of atomic energy. Abronze sculpture by Henry Moore, erected at the site, commemorates theevent (C. SALVETTI [6]).Fermi took part in all the subsequent efforts that led to the first experimentalatomic bomb, and followed, with less direct involvement, the studies24

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYfor the hydrogen bomb, a nuclear fission reaction of limitless energy triggeredby the uranium bomb [9,6].The new situation wracked the consciences of the most eminent scientistsand politicians. In a letter to the president of the University of Chicago datedSeptember, 6, 1945, Fermi outlined the possible development of the hydrogenbomb and said: “The new weapon is so destructive that in case of warbetween two powers equipped with atomic weapons, both the belligerents,even the victor, would have their cities destroyed.... The possibility of anhonest international agreement should be studied with energy and hope.Today the possibility of such an agreement is the highest hope of the menwho contributed to these developments. In their optimistic moments, theyexpress the view that perhaps the new dangers may lead to an understandingbetween nations much greater than has been thought possible until now”.In a letter written in 1949 [9], Fermi and Rabi stated that “the fact thatthe destruction power of this weapon is unlimited means that its very existenceand the knowledge of how to build it are a real danger for all mankind.It is undeniably bad from all points of view. This is why we consider it importantfor the President of the United States to declare to all the world that, onthe basis of fundamental ethical principles, we consider it a great mistake todevelop such a weapon”.Fifty years later, we know all too well how these weapons have developedand the terrible dangers they pose.Let me also report, as accurately as I can, a thought of Fermi’s which Ilearned about in conversations with Amaldi and Bernardini. In 1954, inVarenna, Italy, a few months before his death, he said that the next century– the one we are living in now – could be really decisive for human history,which teeters between a possible absolute tragedy and the beginning of apossible new epoch of serenity and peace.Return to fundamental scientific researchAfter the fall of Germany and Japan, in the summer of 1945, Fermi decidedto go back to basic research and moved to the University of Chicago,where in January of 1946 he was appointed full professor of physics. He thusreturned to his old life as a researcher. I shall recount only a few essentialmilestones in his subsequent work, dwelling in particular on his interest inItaly and on his last visit to this country, at the Varenna conference.Italy had been devastated and disoriented by the war, as I saw for myself as25

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEa soldier from 1940 to 1943, then while in hiding in the vicinity of Milanfrom 1943 to 1945. It is worth noting that even though they were in hiding,the physicists of Milan (and I with them) maintained their interest inresearch; that is, their hope for a better future. But from the standpoint ofphysics history, the most important thing was a long-term project on cosmicrays conducted by three physicists at the University of Rome, Conversi,Pancini and Piccioni. Their experiment showed that the µ mesons in cosmicradiation are not the same as the nuclear mesons (pions) that would explainnuclear forces; they were particles of a different kind, totally or almost totallylacking nuclear force [10]. The existence of pions had been predicted bythe Japanese physicist Yukawa in 1936, but the particles observed in cosmicradiation by the physicists in Rome (now called muons) belong to the familyof leptons (which also includes electrons and other charged or neutral particles),not the family of nuclear or adronic particles.In 1947, upon learning these results, Fermi and other theoreticians immediatelyrealized the importance of this new research and its significance forour understanding of the properties of nuclear forces. I take pride in thisresearch by the three Romans, though I had nothing to do with it myself,because it was born in the midst of the bombing, hidden in the cellars of alocal high school, and attests to the unstoppable curiosity of human beingsand their determination to know and understand.Fermi’s postwar years, from 1946 to 1954 – the year of his prematuredeath – were years of intense activity. His achievements in this period includethe first experimental analysis of nucleon (proton or neutron) excitement levels,an original theory of the origin of cosmic radiation, and an initial analysisof the possible complex structure of nuclear mesons [6,8]. Using theatomic pile as an intense source of neutrons, he studied the properties of slowneutrons. Among his results I recall the analysis of neutrons applied to thestudy of crystals, which marked the beginning of a new chapter in experimentalcrystallography.After the construction of the Chicago cyclotron, Fermi began to studypion-proton interactions, producing initial evidence of the proton structureand its resonances. This was a fundamental field of research that was to challengephysicists for the next fifty years.The problem of the origin of cosmic rays interested him for a few years,and in 1949 he presented his own model, based on the collision of ionizedhydrogen with the clouds of ionized matter that wander through interstellarspace. As Amaldi said, it is a great and elegant vision of our universe.26

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYFermi’s new contribution to ItalyI shall now give an account of Fermi’s contribution to Italy after the war,in the years of reconstruction. In 1949 he infused new zest into Italianphysics research with his lectures in Milan, Rome and other cities, and tookan interest in our research laboratories, which he found livelier and doingmore original work than he had expected. The year before, still in the UnitedStates, he had expressed this hope for Italy [11]. In fact, on April 27 th of1948 Fermi had written to Prime Minister De Gasperi to recommend thatthe government budget 500 million lire for scientific research. This sumwould make it possible to open new experimental laboratories and equipthem with new machines. In the end, the government came up with only halfthat sum – enough to continue research, but not to start brand new projects.I well remember our first meeting with Fermi, in Milan, in 1949. Since1945 I had been working on cosmic rays. To us, living in a largely devastatedcountry, he was a legend. His lectures in Milan, delivered in his unforgettablevoice, were of great scientific and human comfort to me.Italian researchers now wanted to move beyond cosmic rays and explore newareas. This was a phenomenon of scientific unity of which our country can stillbe proud. In this connection, I recollect the physicists Edoardo Amaldi andGilberto Bernardini in particular, and of course many others as well.In 1952, Amaldi and Bernardini managed to concentrate the funds madeavailable to Italian universities on one national-scale problem, instead of seeingthem scattered over a series of interesting but relatively minor researchprojects. This was the origin of the National Synchrotron Laboratories. Thenew facilities were to be built speedily and well at a location to be chosenthrough a competition open to the various regions of Italy. The location chosenthrough this process was the town of Frascati, just outside Rome. Studiesand preparations for the new machine began in 1953.The 1 GeV electron synchrotron went into service in 1958, with the relatedservices and laboratories already operating. The time from start to finishwas considered very short, especially since in 1953 the new site was still afield for rooted cutting, with no power lines in sight [12].But what made this speed possible was not only the inspiration provided byour greatest teachers, but also the practical advice we had from Enrico Fermi,who reviewed our projects and discussed them with us. I want to be quiteexplicit about this, both as an eye-witness and to pay a debt of gratitude [13].In August of 1954, Fermi attended a conference held at Villa Monasteroin the Italian town of Varenna (R. RICCI [6]). Our synchrotron group was27

PROCEEDINGS OF THE INTERNATIONAL CONFERENCErepresented by Enrico Persico, the young researchers Fernando Amman andCarlo Bernardini, and myself.During those unforgettable days, two lectures or scientific reports werepresented on the Frascati electron synchrotron. One was Persico’s explanationof the theory behind the injection of electrons into the “doughnut”; theother, which I myself presented, was on the overall design of the machineand its progress [13].These were the last two lectures Fermi heard. He was already sick, and wasto leave for the United States a few days later. He listened attentively andmade comments and suggestions for which we were grateful and remain everin his debt.Analyzing Persico’s report and recapitulating his figures, Fermi concludedthat for our machine to work as well as possible, it would be most importantto inject the electrons produced by the electrostatic accelerator at the maximumpossible energy. At the time we were still uncertain about what wouldbe the most suitable type of injector, and Fermi’s opinion and advice wereessential.But this was not the only advice we had from Fermi in those spell-bindingdays. After the competition among many Italian cities and the choice ofFrascati, some of the money earmarked for research was still available for newinitiatives. The provinces of Lucca and Pisa looked like the best bets. Fermiexamined the problem together with Edoardo Amaldi, Gilberto Bernardiniand Marcello Conversi, and in the end his advice – unequivocal and precise– was: “Use the money to build an electronic computer”.Conversi immediately seized on this suggestion, and it also helps explainwhy Italian nuclear physicists began to work with computers first in Pisa, andlater in Bologna and Rome. Let me recall that in those months Fermi hadjust emerged from a period of intense thinking about the functions and thefuture of electronic computers in scientific research (G. GALLAVOTTI, M. FAL-CIONI, A. VULPIANI [6]). In 1951-54 he had engaged in long discussions onthe subject with J. Pasta and S. Ulam, and, based on the results obtained, hehad reached the conclusion that it would be interesting to put computers towork on specific problems involving the long-term behavior of certain simplenonlinear physical systems.Today his idea has been fully confirmed. A whole line of research, with nolack of surprises, stemmed from that first project of Fermi’s; it opened theway to the birth of fertile new concepts related to the theory of complexityand chaos.28

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYFermi’s last daysAfter Varenna, when Fermi suddenly went back to the United States, hiscolleagues realized that his health was rapidly deteriorating. To quote whatEmilio Segrè reported in his book on Fermi [9]: “I found Enrico in the hospital,attended by his wife, Laura. He was perfectly aware of the situation andspoke of it with Socratic serenity. The impression I got from this visit, thepainful reality and the astonishing moral strength with which he was facing it,overwhelmed me, and when I left his room after a while, I almost fainted”.Fermi survived his surgery for only a few weeks. He went back home andtried to revise the notes for his last nuclear physics course. At the hospital, hehad told me that this would be his last effort, if his strength held out; in fact,his last piece of writing is a page of the book’s table of contents. He died onNovember 29, 1954, two months after his fifty-fourth birthday.Let me quote the great physicist Eugene Wigner, who was with Fermi duringthe war: “His acceptance of death was on an heroic scale” [7, p. 485].The importance of scientific research, and a warning to nationsEnrico Fermi ranks among the last century’s greatest and most devotedstudents of nature. Our world reveals its deepest character to a few geniusesand lucky people, as if to remind us of its uniqueness, takes us by surprise andoverturns all our theoretical and mathematical intuitions.Enrico Fermi, who was both a great theoretician and a great experimentalist,had direct experience of what we do not know and do not know that wedo not know, because only experimental research can lead us through theunknown and reveal the truth.I shall take three examples from Fermi’s life and try to show how they holda warning for all of us.The first was the surprising result that appeared to Fermi the experimentalistin 1933, when he was studying the unexpected behavior of neutronscolliding with nuclei. From the experimental evidence, he understood that itwas due to the neutrons slowing down in water and other hydrogenated substances,and to the increase in the low-energy cross section.The second was the splitting of uranium into two or three heavy fragments.Uranium fission, announced in 1939 by Hahn and Strassman, came as a surpriseafter all the years of measurements made in Rome and elsewhere.These two experimental “surprises” were the basis for our nuclear cultureand nuclear energy, and for all the good and bad things they have brought.29

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThe third was a surprise of high theoretical and mathematical value.Contrary to what Fermi had thought for a long time, a nonlinear system isnot always and not simply ergodic. In other words, it can retain its initialconditions for a long time, or forever. The empirical demonstration thatFermi and his collaborators gave with the help of an advanced computer plusa fundamental theorem of Kolmogorov were of the greatest importance, andopened the way to our modern concept of chaos [6, pp. 279 et seq.].I shall try to draw some conclusions from these and other examples. I thinkwe are still very far from fully understanding our universe and its generallaws. Rather, we are just at the beginning of scientific knowledge. This isborne out by the fact that in the last thirty years we have continuouslyreceived other splendid surprises from our most advanced research, forinstance the breaking of what seemed to be the most solid symmetries, thediscovery of the particles at an unexpected mass, the new superconductors,the extended black holes, the still-uncertain origin of our universe after someyears of excessive confidence.The way to understand more is to keep on doing experimental researchwith an open mind, and to accompany it with mathematical and theoreticalmeditation. A country that encourages the curiosity to learn about andexplore nature, and boldly readies the instruments necessary to satisfy it, isindeed fortunate. We are only at the beginning of knowledge.Human curiosity, in all directions, will not stop. The societies that are ableto satisfy it will progress. We must defend basic scientific research and thelaboratories in which it is done, because that is where our future lies. EnricoFermi’s whole life proves it.I take the liberty of insisting on this point, because I fear that our country’sunderstanding of the need of basic research and its willingness to supportit has waned somewhat in recent years.Of course we also need to analyze the good and the bad in the practicalapplications of our discoveries. We must work for their use in civilian developmentand fight against their use for war and abuses of power. We must figureout how they can be used to promote peace among the world’s peoples,and we must ensure that our schools educate the new generations to bealtruistic and to value knowledge.It is an immense and difficult aim, but one that it is worth living for.30

Giorgio SalviniENRICO FERMI: A GUIDING LIGHT IN AN ANGUISHED CENTURYREFERENCES01. C. MØLLER, The Theory of Relativity, Oxford: Clarendon Press, 1952: A. EINSTEIN, TheMeaning of Relativity, Princeton: Princeton University Press, 1950.02. E. PERSICO, Fondamenti della Meccanica Atomica, Bologna: Zanichelli, 1940.03. B. GREENE, The Elegant Universe. Plainly, this was new, impassioned research. It remainedlatent from the 1940s through the ‘60s but has now been taken up again, seeking a synthesisbetween gravitational forces and weak nuclear forces. This result is still far off, butthe 21 st century will surely bring brand new ideas that cannot be imagined today.04. W. HEISENBERG, Zeitschrift für Physik, 879 (1925).05. W. HEISENBERG, The Physical Principles of the Quantum Theory, Dover Publications, 1930.06. C. BERNARDINI and L. BONOLIS, Conoscere Fermi, Bologna: Editrice Compositori, 2001.Includes twenty essays by leading Italian physicists on Fermi’s scientific work.07. A. PAIS, Inward Bound, Oxford: Clarendon Press, 1986.08. E. FERMI, Collected Papers, Chicago, University of Chicago Press, 2 vols. (around 2000pages). Edited in collaboration with the Accademia Nazionale dei Lincei and annotated byFermi’s students and contemporaries.09. E. SEGRÈ, Enrico Fermi, fisico, Bologna: Zanichelli, 1987 (2 nd ed.).10. M. CONVERSI, E. PANCINI and O. PICCIONI, in Physical Review 71 (1947), p. 209.11. M. DE MARIA, Un fisico da Via Panisperna all’America, “Great Scientists” series, LeScienze II:8, 1999.12. G. SALVINI, ed., L’elettrosincrotrone ed i Laboratori di Frascati, Bologna: Zanichelli, 1962.13. Insert dedicated to the memory of Enrico Fermi, supplement to vol. 2, series 10 of NuovoCimento 1 (1955).Giorgio SalviniBorn in Milan in 1920, professor of physics at the Universities of Pisa (1952-55) and Rome (1955-95); now professor emeritus. From 1952 to 1960, hedirected the construction of the Italian Electron-Synchrotron (1100 MeV),which went into service in Frascati in 1958 and was for several years theworld’s most powerful electron synchrotron.Giorgio Salvini conducted research on extensive showers of cosmic rays andon the photoproduction of mesons, in particular eta mesons. In an internationalproject at the European Organisation for Nuclear Research (CERN) inGeneva, he established the existence of large-mass W and Z intermediatebosons (1978-83), thereby confirming definitively the validity of the electroweaktheory. At present he is engaged in research on CERN’s new LHCproton accelerator. Minister of Universities and Scientific Research in 1995-96; member and Honorary President of the Lincei National Academy.31

Carlo RubbiaFermi’s Contribution to the World Energy SupplyThe contributions of Enrico Fermi on the field of energy production will bereviewed, primarily on his early developments of the Nuclear Reactor. Theimmense consequences of such an invention will be discussed, especially forwhat concerns the present status of nuclear power and its future, in the light ofthe present concerns on emissions of conventional fossil fuels. The main problemswith an extended world-wide use of nuclear power will be discussed, includingpossible alternatives in order to alleviate them.Il contributo di Fermiall’approvvigionamento energetico mondialeVerrà preso in esame il contributo apportato da Enrico Fermi al settore dellaproduzione energetica, con particolare riferimento ai primissimi sviluppi delreattore nucleare. Si parlerà delle enormi conseguenze che tale invenzione haavuto, con particolare attenzione allo stato attuale di sviluppo dell’energianucleare e del suo futuro, alla luce dei crescenti timori riguardanti le emissionida combustibili fossili convenzionali. Verranno altresì esaminati i principaliproblemi derivanti dall’uso dell’energia nucleare a livello mondiale, così come lepossibili alternative che possono contribuire alla loro riduzione e/o risoluzione.33

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi’s work on the neutronI shall concentrate my presentation on Fermi’s work on the neutron – discoveredby Chadwick in 1932 – which he initiated here in Rome in 1934. Asit is well known, these studies have opened immense new horizons toNuclear Physics, not only through the understanding of the nucleus, but alsowith practical applications in a vast number of domains, including the one ofharnessing the immense energy asleep inside the atomic nuclei.In January of that year, Irene Curie and Frédéric Joliot had reported theartificial production of new types of radio-elements under bombardment ofα-particles. However, using helium nuclei of a few MeV of kinetic energy asprojectiles, they could not split atoms with atomic number higher than 20;therefore only a part of the light elements could be transmuted. Similarresults are obtained with hydrogen nuclei (protons).Fermi and his collaborators, using neutrons, succeeded in shattering theheavier and even the heaviest elements in the periodic system. Incidentally,for this work, he was granted the Nobel prize in 1938. The neutron has qualitiesthat make it particularly suitable as a projectile in atomic reactions. Boththe helium nucleus and the hydrogen nucleus carry electric charges. Thestrong electric forces of repulsion developed when such a charged particlecomes within reach of an atomic nucleus, deflect the projectile. The neutronbeing uncharged, continues on its course without suffering any hindranceuntil it is stopped by direct impact on the nucleus. Neutrons can thus traversevery large amounts of matter with small attenuation.Neutrons may split the light nuclei in different elements with reactions ofthe type: (n,p), (n,α) and so on. However, especially for heavier elements,there is no ejection of any material part and the surplus energy disappears inthe form of gamma radiation. As there is no variation in the charge, an isotopeof the same initial substance is obtained, in many cases unstable, causingradioactive activation.It was some six months after their first experiment with neutron irradiationthat Fermi and his co-workers came by chance on a discovery which provedto be of the greatest importance. As recalled by Chandrasekhar, in a conversationFermi described this discovery in this way:“I shall tell you how I succeeded in making the discovery which I believeis the most important of my career. We were working very hard on theinduced radioactivity and the results could not be understood. One day,upon arrival at the laboratory, I thought I would like to examine the effect34

Carlo RubbiaFERMI’S CONTRIBUTION TO THE WORLD ENERGY SUPPLYproduced by a lead block placed in the neutron path. After a great effortin machining it I felt very reluctant in placing it. I said to myself “No! I donot want this piece of lead, what I want is some paraffin” I took a block ofparaffin which I found at hand and I put it where it was supposed to gothe lead”.It was then observed that the effect of the neutron irradiation was oftenstrongly enhanced (by a factor up to 10 4 ) when the neutrons were allowedto pass through water or paraffin. Minute study of this phenomenon showedthat neutrons were slowed down on impact with hydrogen nuclei present inthese substances and that slowed down neutrons were much more powerful.Fermi quickly developed a simple theory in which the now well known 1/veffect of neutron capture was evidenced. Current concepts like the one of“lethargy” and the one of “Fermi’s age”, of the distance from creation tothermalisation in a diffusion process were developed. It was further foundthat the strongest effect was achieved at certain speed, which is different foreach substance. This phenomenon has been compared with resonance foundin optics and acustics.Practically all elements, with the exception of hydrogen and helium, couldbe activated. More than four hundred new radioactive substances have thusbeen obtained, of which about one half due to direct capture, the rest due todecay of the activated elements. The practical applicability of his discoverieswas a constant concern to Fermi, in particular the possibility of using activationisotopes as “tracers” for physical, chemical and biological processes, onwhich he took a patent.The general pattern that Fermi had found in 1934 took on special interestearly in 1935 when applied to the last element in the series of elements, viz.Uranium (Z=92). As it is well known today, fission is a prominent phenomenonin U-235 neutron capture. However, the extraordinary U activationassociated to fission fragments was wrongly interpreted – not only by Fermibut also by Joliot-Curie in Paris and Otto Hahn and Lise Meitner in Berlin– as due to formation of additional transuranic elements, for which even thenames of Ausonium (Z=93) and Hesperium (Z=94) were coined, from thenames of ancient Italian populations.The discovery of the fission processOne may argue why fission was not observed then in Rome. Amaldi recallsthat at a point they put a neutron activated Thorium and Uranium sample35

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEdirectly inside an ionisation chamber. However, in order to remove the naturalα-activity of the sample, a thin aluminium foil was added over the sample,thus “ranging out” the fission fragments, which travel only ≈ 10 µg/cm 2in matter. Had fission be discovered then, the history of nuclear energy andthe realisation of its enormous military applications would have been probablyentirely different, and probably so also the course of the second Worldwar, because of a likely much earlier realisation of nuclear weapons.It was only about four years later that Otto Hahn and Fritz Strassmann,after a very tortuous path, identified the presence of this absolutely new phenomenon,which no one had been able to predict theoretically. Theirattempts to separate chemically transuranic elements produced by neutronbombardment on U and Th indicated that one was dealing with a mixture ofβ-radioactive isotopes rather than with a single, chemically homogeneous,substance. In particular, it was found that there were amongst them also bariumradioactive isotopes, resulting from the fission of Uranium. Until nowone had observed that neutron activation produced nuclear species whichdiffered by one or two atomic units from the target material: Barium differedfrom Uranium by as many as 98 atomic units!At the beginning of 1939, the nature of the phenomenon was promptlyrecognised – within the Bohr liquid drop nuclear model – by Lise Meitnerand Otto Frisch, as due to an extreme collective deformation with break-upof the nucleus in two smaller droplets, each of them sufficiently apart as tobe affected only by the strong Coulomb repulsive force, resulting in a liberatedenergy of the order of 200 MeV. Because of the extreme similarity tothe duplication of living cells, they called the process “fission”. It is alsoworth recalling Bohr’s disappointment because “theorists” had not predictedthe process!These observations were promptly repeated in several laboratories: in particular,as early as 15th January 1939, Joliot-Curie confirmed and publishedsimilar findings in France. The existence of fission became at this point a universallyknown fact.When, soon later, it was also recognised that, together with the extraordinaryenergy of 200 MeV, also a few neutrons were liberated, the scientificcommunity understood that harnessing (awaking) the immense energyasleep in the atomic nuclei through a “chain reaction” had entered the realmof things possible.In January 1939, just after the 1938 Nobel ceremony, Fermi left definitelyfor the United States, where he became professor at Columbia University36

Carlo RubbiaFERMI’S CONTRIBUTION TO THE WORLD ENERGY SUPPLYuntil 1942, when he moved to Chicago. The news of the discovery of the fissionprocess had reached him only upon arrival in the United States. His firstAmerican paper is dated one month after his arrival and it is entitled “Thefission of Uranium”. It is followed by a paper with Herb Anderson and LeoSzilard on “Neutron production and absorption”, in which he gives relevantcross sections and shows that the number of neutrons emitted is larger thanthe number absorbed, as a necessary condition for a chain reaction.It should also be pointed out that Fermi’s interests were solicited at thistime both by the muon as a possible candidate of the Yukawa particle of thenuclear force and the measurement of its lifetime by Bruno Rossi.Progressively more difficult communications did not allow the US scientiststo fully appreciate the work carried out in Rome on the same subject, first byGilberto Bernardini and Gian Carlo Wick and later by Conversi, Pancini andPiccioni.War timesDuring war times, any process capable to weaken or defeat the enemy takesprecedence over all possible benign uses. It has been so also in this case whenthe possibility of a “nuclear” bomb came to the limelight. At this point intime, Einstein wrote the famous letter to President Roosevelt, in which themilitary implications of the discovery are fully spelled out.This letter marked the end of free scientific information and beginning ofthe military involvement. The subsequent history has indeed been madepublicly known only afterwards.In March 1940, another impulse to the reactor concept was given at theBerkeley Radiation Laboratory with the discovery of Plutonium. This element,not existing in nature, is produced by the U-238 capturing a neutron,as decay of the Np-239. Pu-239, just like U-235, being an odd isotope, wasexpected to be promptly fissionable.During the years 1940 and 1941 Fermi and his colleagues performed atColumbia a number of important investigations, precursory to the demonstrationin Chicago of the “chain reaction” in December 1942. At the sametime, similar activities had been taking place elsewhere, and in particular inGermany, under the impulse of von Weizsäcker and Werner Heisenberg.However, the solution of the problem was not simple and in order to reachsuccess it took all of the experience Fermi had acquired in many years ofinvestigations. Two crucial, subtle problems had to be solved:37

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1) the thermalisation of neutrons in the “pile” is generally a very fast process,of the order of hundreds of microseconds. To control criticality, anymechanical device would be too slow to cope with the build-up mechanism.Fortunately, the existence of “delayed neutrons”, due to neutronemission of the short lived fission fragments, amounting to about 0.7% inthe case of Uranium, allows enough time for an effective control action;2) it was known that the fission process for thermal neutrons was due to theU-235 component of natural uranium, amounting to 0.71%. Enrichmentwas at that time considered too difficult and expensive. However, thedominant U-238 has very strong resonances of neutron capture, leadingto Np-239 and later to Pu-239. Therefore in a Uranium medium, the isolethargicslowdown mechanism implies neutron captures at a rate far toolarge to ensure criticality. Indeed all attempts by Heisenberg in Germanyto achieve criticality with a homogeneous mixture of Uranium and graphitefailed. The smart idea developed by Fermi and Szilard was to work with adiscrete structure made of small, insulated elements of Uranium in aGraphite matrix. The fast neutrons emitted in the Uranium fission werecompletely thermalised inside the pure graphite, “missing” the U-238resonances and re-entering the U only after full thermalisation.By summer 1942 the work on sub-critical systems was so advanced – asmany as 30 sub-critical assemblies were constructed – that it was decided toproceed with the test of a critical system. Purity of the ≈ 400 ton of graphite(40’000 bricks) was finally adequate. Uranium was also available in the formof 20000 bricks. The erection of the pile CP-1 took about one month andcriticality was achieved on December 2, 1942.Fermi and Szilard later took a patent on CP-1 in 1955, after presentationin 1944: it is a magnificent lecture on the physics of the nuclear reactor,which I recommend reading.CP-1 operated on that day for 28 minutes with a peak power of 0.5 Watt.A few months later a second experimental set-up was operated at Argonne,with a power of 110 kWatt, precursory of the power reactors built by DuPont in Hartford and destined to Plutonium production.Peaceful applications of nuclear science grew only much later, for instancewith the Conference “Atoms for Peace” in Geneva in 1958.At that day, there were no journalists, no cameras or tape recorders in orderto document the event of the “birth of the nuclear era”. Everything was “topsecret”, within the Metallurgical Laboratory, a laboratory without metallurgists.I wonder if the thirty or so people present there could grasp – within38

Carlo RubbiaFERMI’S CONTRIBUTION TO THE WORLD ENERGY SUPPLYthe exaltation of the moment – the dimension and the nature of the changesthat nuclear energy was about to bring to the world. Fermi commented in alater script:“The event was not spectacular, no fuses burned, no light flashed. But tous it meant that release of atomic energy on a large scale would be only amatter of time. The further development of atomic energy during thenext three years of the war was, of course, focused on the main objectiveof producing an effective weapon. We hoped that perhaps the building ofpower plants, production of radio-isotopes for science and medicinewould become the paramount objectives. Unfortunately, the end of thewar did not bring brotherly love among nations. Secrecy that we thoughtwas an unwelcome necessity during the war, still appears to be an unwelcomenecessity.The problems posed by this world situation are not for the scientists alonebut for all people to solve. Perhaps a time will come when all scientific andtechnical progress will be hailed for the advantages that it may bring toman, and never feared on account of its destructive power”.Production of energy at an acceptable costToday, sixty years after the first criticality experiment, one may try to lookbeyond these events to their consequences in a broader historical perspective.In this time span, the significance of science in all its aspects – not only innuclear physics but also in biology and so on – has profoundly changed frombeing essentially pure knowledge to a determinant factor in the world’s economyand policies. One may identify as demarcation point the famous letter ofEinstein to President Roosevelt. Scientists today find themselves involved bothin the economic and the political world. We must learn – also from the mistakesof the past – how to deal with this new dimension of scientific research.The persisting and now dominant goal of nuclear science is the productionof energy at an acceptable cost. In the cost one has to include not only theprice of fuels and technology, but also the indirect costs to the populationand the environment. So far, we have been unable to substitute conventionalenergy sources, which have a limited duration, with some other more permanentones.From the point of view of the growing energy demand, beyond the fossilera only two known energy sources are in principle capable to supply what isneeded, namely nuclear energy and solar energy. In my view they must bothbe pursued with vigour on a planetary level. But energy from nuclei does not39

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEmean necessarily the present nuclear reactors and this for several fundamentalreasons, which are as follows:• there is no more U-235 than oil or natural gas, even at the present level ofexploitation, which is about 6% of the world energy supply;• the problem of safety, now at a probabilistic level, must be furtherimproved. The level of an acceptable risk as perceived today by society ismuch lower that what it was for instance at the times of the “Cold War”;• the problem of the disposal of nuclear waste, which has already nowreached large proportions and causes serious concern, at least for the componentwhich is supposed to last millions of years. Even if we shall not bethere to be made accountable, we cannot leave to future generations suchan inheritance of our passage on this planet.There are apriori three possible and well known new nuclear processeswhich could provide energy for many hundreds of centuries at the presentlevel of the world’s consumption. On such a time-scale, the distinctionbetween renewable and not renewable energy is unimportant. All of them arebased on breeding reactions, namely a process in which the burning (fuel)nucleus is locally generated from a natural element. These were all known atthe time of Fermi’s discoveries, which I have just mentioned.One of them is fusion, and stems directly from the idea of producingnuclear reactions with charged particles. In the process, natural Lithium istransformed with the help of a neutron in the hydrogen isotope Tritium,which in turn reacts with deuterium to produce energy and the neutron.The other two are based on transforming, again with the help of a neutron,– whose unique features have been already pointed out – either U-238(99.3% of natural Uranium) or natural Thorium (Th-232) into Pu-239 or U-233 respectively, ensuring the “breeding” neutron from fission. Fermi sawvery clearly the importance of breeding for the future of nuclear energy :”The country which first develops a breeding reactor will have a great competitiveadvantage in atomic energy” (Argonne, 1945). Today, almost sixtyyears later, I would fully subscribe his statement, however removing the word“reactor”. The main problem – and I am sure Fermi understood it very well– is the one of the neutron inventory, or attaining k = 1, for which he struggledfor three years from 1940 till 1942 and on which for instanceHeisenberg and others had failed.Indeed, in order to secure both breeding and fission, two neutrons are neededfor each Fermi cycle, rather than one. Criticality (k = 1) becomes muchharder to attain. This is why only fast neutron reactors with Plutonium and40

Carlo RubbiaFERMI’S CONTRIBUTION TO THE WORLD ENERGY SUPPLYmolten Sodium (Super-Phoenix) – in spite of the tremendous safety problemsassociated – have only a marginal chance for a realistic breeding. NaturalUranium and Thorium with thermal neutrons (whose advantage had beenamply demonstrated by Fermi’s work) are excluded, since they cannot meetdurably the requirement of criticality (k = 1) in a U-235 less configuration(see point 1 above).Extra neutrons must come from an external source. As clearly pointed outby Lawrence already sixty years ago, a high energy accelerator is the mostpromising complement to nuclear fission. Since the times of Fermi, acceleratortechnology has made enormous progress, at CERN and elsewhere, andtoday a sub-critical (k < 1), accelerator driven fission energy source hasbecome a realistic alternative. The spallation reaction – initiated for instanceby 1 GeV proton – produces as many as ≈ 50 neutrons/proton, correspondingto an energetic cost of 20 MeV/neutron, compared to the 200 MeVproduced by a neutron initiated fission. Accelerator driven sub-critical systems(ADS) have also the added advantage that they can incinerate as wellthe long lived transuranic elements of ordinary reactor’s waste and transmutetheir long-lived fission fragments (viz. Tc-99) into stable elements, thus solvingthe problem of the long lived waste.For these new developments, and as it has happened for the critical reactor,the physics community should first lay down the underlying phenomenologywith the help of specific experiments, before engineering and industrymay take over. Likewise, a vast political support is necessary, in additionto scientists’ enthusiasm and dedication.Time has come to conclude. Coming back to Fermi, I would like to recallthe words of Edoardo Amaldi at the commemoration of the Accademia deiLincei in 1955, as a testimony of someone who had the good fortune ofknowing him:“His scientific work is so powerful and so ingenious, the practical consequencesof his work so important and relevant that those who did nothave the chance of meeting him may be brought to a wrongful image ofhim. His close relatives and his friends, and those who have known himdirectly, know that it was very difficult to separate in Enrico Fermi the variousfacets of scientist, researcher, teacher and human being, since theywere all so intimately together. His simplicity and his manner of being, hisserenity in front of the problems of life, his absence of any disdain andstrangeness of behaviour, were human qualities even more remarkable inview of the contrast with his exceptional qualities as a scientist”.41

PROCEEDINGS OF THE INTERNATIONAL CONFERENCECarlo RubbiaCarlo Rubbia was born in Gorizia, Italy, on 31st March 1934. He graduatedat Scuola Normale in Pisa, where he completed his University educationwith a thesis on Cosmic Ray Experiments. He has been working at CERNsince 1961. In 1976, he suggested adapting CERN’s Super Proton Synchrotron(SPS) to collide protons and antiprotons in the same ring and the world’s firstantiproton factory was built. The collider started running in 1981 and, inearly 1983, an international team of more than 100 physicists headed byRubbia and known as the UA1 Collaboration, detected the intermediate vectorbosons. In 1984 he was awarded the Nobel Prize for Physics.Carlo Rubbia served as Director-General of CERN from 1 January 1989 tillDecember 1993.From 1970 to December 1988 Rubbia spent one semester per year atHarvard University in Cambridge, Massachusetts, where he was HigginsProfessor of Physics.Since 1999 he is the President of ENEA. Carlo Rubbia is Full Professor ofPhysics at Pavia University, in Italy.42

Alice CatonEnrico Fermi and his FamilyAlice Caton, M.A., Enrico Fermi’s oldest living descendent, tells humourousfamily stories about her grandfather. She discusses in a personal way thedilemmas she, her family and all of our descendants must resolve in order tomake full use of Enrico Fermi’s scientific legacy.Enrico Fermi e la sua famigliaAlice Caton, la più anziana discendente di Fermi ancora in vita, ci raccontadivertenti aneddoti familiari sul nonno. Con un approccio del tutto personaleaffronta le problematiche che lei stessa e la sua famiglia devono risolvere persfruttare appieno il patrimonio scientifico ereditato da Enrico Fermi.43

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEEnrico Fermi died in 1954. Two years later, his daughter Nella marriedand I was born in 1957. Although I never met my grandfather, he hada great impact on my life. His brilliance, the force of his personality, and theimpact his work has on the world affect me both as his granddaughter and asa member of society.Sometimes it’s quite delightful to be related to Enrico. Recently I was talkingwith an acquaintance. When I learned he was a retired theoretical physicist,I told him who my grandfather was. If he had been an artist, it wouldn’thave occurred to me to mention my relationship to Enrico. The physicist’sreaction was predictable. He got very excited. “That’s huge!!,” heexclaimed. “Do you realize how huge that is?” Then he started telling mehow important Enrico was. You know, the stuff I already knew.My brother Paul is a math professor. When Paul was a student, he andsome friends went on a long driving trip. They played a guessing game called20 Questions. One round stands out in my brother’s memory, because thattime Enrico Fermi was the answer. “But,” Paul said, “when I told them hewas my grandfather, they didn’t believe me!”Most of the time Paul doesn’t mention his relationship to Enrico. Then whenhis friends and colleagues find out about it, they get mad at him for not tellingthem. It must be hard for Paul to know what to do. When he tells them, theydon’t believe him and when he doesn’t tell them, he gets in trouble.Laura and Enrico’s CourtshipMany of the stories I will share with you come from my grandmother’sbook Atoms in the Family about her life with Enrico. In it she tells of hercourtship with my grandfather – logarithm style.Laura and Enrico met one spring day while among a group of friends. Itwas 1924. She was 16 and he 22. Her friends were impressed because he wasalready a professor of theoretical physics in Roma. She only thought thisexplained why he looked rather strange.They spent the afternoon playing soccer outside of Roma near the spotwhere the Tevere River splits and forms the Aniene. Enrico was the captainof Laura’s team. My grandmother was not athletic and had never played soccerbefore. Enrico put her in goal, saying that was the easiest job.At the height of the game, the sole of Enrico’s shoe came off and was danglingfrom the heel, making it hard for him to run. Then he tripped. As hefell to the ground, the ball went to my grandmother. She was startled, but44

Alice CatonENRICO FERMI AND HIS FAMILYstill managed to block the shot and won the game for their team. Laura saysit is the only time she did better than Enrico, but I am not so sure.By the time Enrico and Laura met again, two years had gone by and shehad almost forgotten who he was. During summer holidays, they were at anItalian resort where many families knew each other. The children of thesefamilies, who ranged in age from very young up to young adults, went onmany hikes with Enrico as their leader. When the littlest ones and the girlstired, Enrico carried their extra clothing in his pack. He was very competitiveand always first to the top, despite having the largest and heaviest load.Part of Enrico’s gift as a scientist was his ability to classify scientific data andtheorems so that he would have them easily at hand for his work. His needto classify did not stop at the laboratory door.For fun, he sometimes classified people – for example by height, weight,looks or sex appeal. That particular summer he sorted people by intellectualprowess.“People can be grouped into four classes,” my grandfather declared. Hewent on to explain that only those with exceptional intelligence made it intoclass four. Laura teased him, “You mean to say that, in class four there is onlyone person, Enrico Fermi”.“You are being mean to me, Miss Capon. You know very well that I placemany people in class four,” Enrico paused and then added, “I couldn’t placemyself in class three. It wouldn’t be fair”.After further teasing from my grandmother, Enrico protested, “Class fouris not so exclusive as you make it. You also belong to it”.But Laura wouldn’t let it rest. “If I am in class four, then there must be aclass five to which you and you alone belong”. That time my grandmotherhad the final word and all their friends, except Enrico, accepted her classificationsystem.After that, Laura enjoyed many social occasions with Enrico and his friends.She coerced her sister Anna to join them – coerced because Anna was an artistand did not find pleasure in the antics of scientific intellectuals. Anna remarked,“They are all so uninspiring. They’re just logarithms”. This nickname stuck.And so my grandparent’s courtship proceeded among the logarithms. At somepoint in 1927, Enrico declared he was going to do something out of theordinary. Something extravagant – he would either buy a car or get married.In September 1927, he bought a car. When Laura heard of his choice, shewas disappointed. She already knew that she did not meet Enrico’s definitionof the ideal wife: tall, blonde and athletic from country stock, with all four45

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEgrandparents still alive. Laura was short, brunette, good at falling off of skisand her ancestry bordered on aristocratic. None of her grandparents werealive. That he had chosen car over wife was just further proof Enrico wouldremain a friend. My grandmother immediately resolved to become a careerwoman instead of marrying.Soon, however, the pair were driving around Roma attracting attention inEnrico’s bright yellow Bébé Peugeot. About nine months later, in the summerof 1928, they wed in a civil ceremony. The wedding went smoothly,except the groom was late. After the rest of his family had left for the ceremony,Enrico, who was only 165 cm. tall, discovered the sleeves on his newstore-bought shirt were much too long. He got out a sewing needle, shortenedthe sleeves and went to his wedding.Family lifeIn the next few days you will hear about Enrico Fermi’s genius in bothapplied and theoretical physics. Of course, this is what he is famous for. Heis not, on the other hand, known for his domestic achievements.After my grandparents were married, Enrico told Laura she could pick thefurniture as long as it had straight legs. There was a dining room table andchairs, a desk, and so on – all with straight legs. There was a straight-legcouch with no back. The back cushions simply leaned against the wall forsupport. The couch tended to slip away from the wall and my grandmotherasked Enrico to fix it. He nailed two boards on the floor by the legs to holdit in place. Laura was horrified.Much later, I inherited some of the straight-leg furniture and brought itfrom Chicago to my home in Vancouver, Canada. I found a simpler solutionto the slippage problem, which is to put the front legs on a big rug.Enrico was fiercely independent and besides that there was no one to teachhim. He learned physics and mathematics on his own. In the early days of hisprofessorship at the University in Roma, he was the one who grasped quantumtheory. My grandfather tried to show his fellow researchers how both matterand energy consist of waves. They couldn’t follow the line of reasoning and hadto take it on faith from Enrico. And so he came to be known as the Pope.But even the Pope can’t change the weather. After my grandparents weremarried, there was a record breaking winter in Roma. Their apartment wasso cold they couldn’t get the temperature to rise above 8 degrees (C), evenwith the furnace going full blast. Enrico got out his slide rule and calculated46

Alice CatonENRICO FERMI AND HIS FAMILYthe potential benefit of blocking the drafts in the windows. He concludedstorm windows wouldn’t make much difference, so, no storm windows.They froze. Months later, after the cold snap had long ended, Enrico revisitedhis calculations and discovered he had misplaced a decimal point.While it was too late to buy storm windows, at least my grandmother’s egowas soothed by the discovery her husband was objectively fallible.Another time in the early days of their marriage, Enrico and Laura were onthe way to her aunt’s villa outside Firenze. The Bébé Peugeot broke downon the highway. Enrico replaced a torn fan belt with the belt from around hiswaist and they actually completed their journey on schedule.Laura was helping Enrico to write a textbook for high school (liceo) students.My grandmother took notes which she later transcribed. He dictated,“It is evident that in a nonuniformly accelerated motion, the ratio of thespeed to the time is not constant”.“It is not evident,” my grandmother stated, without raising her eyes fromher notes.Enrico retorted, “It is to anybody with a thinking mind”.“Not to me”.“Because you refuse to use your brains,” he snapped.Exasperated, Laura suggested they consult her sister Paola. Enrico agreed.Now Paola was the perfect one to adjudicate since she had just passed herhigh school (liceo) exams, and had even received a decent mark in physics, asubject she did not adore. Paola was baffled by Enrico’s obvious. From thenon, she was the arbiter of my grandparents’ understandability squabbles.When he accepted his first teaching engagement in the US, in 1930, Enricotaught himself English in two easy steps. Step one. He read 10 adventurenovels in English. He only allowed himself to use a dictionary for the first 10pages of each book. Step two. Enrico arrived at the University of Michigan.He arranged with friends to give him corrections at the end of each lecture.According to my grandmother, he never repeated a grammatical error oncecorrected.Enrico turned down many offers of work from US universities during the30’s. With the rise of Nazism and fascism, things changed. Laura was Jewishand by 1938 the risk of staying in Europe outweighed my grandparentsdesire to stay here in Italy. Enrico won the Nobel Prize that year and it waspresented in Stockholm, Sweden. My grandparents used this opportunity toleave for the United States with my mother Nella and her little brotherGiulio – of course, the straight-leg furniture went along too.47

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFrom Emilio Segrè’s biography of my grandfather, one learns Enrico’smother was a teacher and very intelligent. Besides being a good cook, shebuilt her own pressure cooker. Is genius learned or passed on? I don’t imagineEnrico would have had much trouble building a pressure cooker. Butwhen it came to using the kitchen that was another story.I think the family was living in New Jersey. Laura and the maid did thecooking, but one time they were both sick. So Enrico and my mother tookover. Neither of them knew how to cook anything. Enrico asked my grandmotherwhat would be easiest. “Boiled potatoes, with butter and salt,” shetold them. There was nothing to it. Or so she thought. The potatoes were adisaster. They tasted awful and were almost inedible. Enrico and Nella testedthem so many times, the potatoes never had a chance to cook properly.Once Enrico learned he was no good at housekeeping, his innovative mindwent to work. At Los Alamos, there was a labour shortage, so Enrico devised aplan. Chimpanzees and gorillas would be trained to do housework for the scientists’wives. The housing office could create an Agency of Primate Distributionwhich would both care for and train the monkeys to scrub, vacuum,dust, greet visitors and wait tables. My grandmother complained that he neverpresented the idea to the housing office and so the labour shortage went on.My mother said she had a pretty much impossible time buying gifts for herdad. However, one Christmas, she succeeded in giving him something hehad never seen. It was a toy bird made of glass. Its round body was partiallyfilled with a clear liquid and its head covered with red fuzzy stuff. If you puta glass of water in front of it, it seemed to drink perpetually and rhythmicallylike a pendulum, dunking it’s long red beak for one drink after another.Enrico was delighted. As usual, he determined the most straight-forwardand efficient experiments to find out why the bird kept drinking. First hesubstituted alcohol for water. The bird sped up. Next he cut off its air supplyby inverting a large glass jar over bird and water. The bird slowed downand soon stopped moving altogether.“It must be alive”, said Enrico laughing, “for it gets drunk on alcohol andsmothers without air”. Later the physicist Edward Teller came to visit. He toowas intrigued by the bird which became the center of conversation. “Whatwould you say if it took a step forward?” my grandfather asked Teller. “Why, Iwould set it back and see if it did it again”, answered Teller without hesitation.During the war, my grandfather was asked by a U.S. government agency toevaluate a particular substance and suggest applications for war work. Enricobrought the substance home and showed it to my mom and my uncle Giulio.48

Alice CatonENRICO FERMI AND HIS FAMILYThe stuff was soft like chewing gum and if pulled slowly could be stretchedinto a long thin string. But as soon as you jerked it, it cracked. You couldshape it or scratch designs on it, but leave it alone and it melted into a blob.A blow with a hammer shattered it like glass and sent it flying in all directions– Enrico demonstrated carefully so that none of the material would be lost.Nella says she asked a lot of questions and got a physics lesson from herfather. The stuff actually was a liquid, like glass. Given sufficient time, eitherwould melt into a blob – but for glass it took years instead of minutes.Enrico was puzzling about possible applications and asked his kids for suggestions.In spite of the fun the three of them had, no one realized the obvious– it was a great toy. Today the stuff is marketed as Silly Putty and probablymade the toymaker millions.Enrico’s legacy and our familyAt 185 cm my brother Paul is by far the tallest in our family – 20 cm tallerthan Enrico was. Paul became a vegetarian when he was in grade school. Hewouldn’t even wear leather shoes. So our grandmother gave Paul an old pairof Enrico’s tennis shoes. And they fit. Paul’s friend said: “See you can fill yourgrandfather’s shoes!”. My brother wore the sneakers until they disintegrated.I think everyone in my family grapples with Enrico’s legacy in some way 1 . Inthe early 1960’s when I was about five years old – well before I could understandwhat Enrico had achieved – I remember proudly announcing at schoolto whomever would listen, “My grandfather invented the atom bomb!”At the same time I was feeling so proud of who I was, I also learned aboutthe dangers of nuclear energy. My father taught me about radioactive falloutfrom above-ground nuclear testing – and I felt uneasy. He said it hadchanged the earth and its atmosphere for the worse. Soon the unease includ-1 My grandmother and my first cousin Rachel Fermi, Enrico’s son’s daughter have left a record whichencouraged me to continue to explore my grandfather’s legacy. In 1995, Rachel published a book ofphotographs of the Manhattan project called Picturing the Bomb. On the facing page to the book’s forward,she quotes our grandmother – filling the page with large black capital letters: “But, above all,there were the moral questions. I knew scientists had hoped that the bomb would not be possible, butthere it was and it had already killed and destroyed so much. Was war or science to be blamed? Shouldthe scientists have stopped the work once they realized that a bomb was feasible? Would there alwaysbe war in the future? To these kinds of questions there is no simple answer”. – Laura Fermi, inReminiscences of Los Alamos, edited by Lawrence Badash.Rachel’s Foreword begins: “My grandmother asked these questions twenty-five years after the firstatomic bombs were used. This book has grown out of the complexities underlying her questions, andfrom my own need to understand more fully the grandfather I never knew: a physicist whose work radicallyaltered the world he was born into and helped create the world in which I now live”.49

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEed guilt and shame as I felt so associated with the negative outcomes of therelease of nuclear energy.During that same period, I was at my grandmother’s apartment in Chicago.I was still able to walk under her dining room table from Italy with the straightlegs. From my child’s view, the table seemed very long and forbidding.My grandmother and a group of ladies were at the table folding flyers forthe Air Pollution Control Committee. It was a lobbying group my grandmotherstarted with some of her friends. They were pioneers in the environmentalmovement. They tested smoke stack emissions in Chicago. Throughtheir lobbying efforts, local government passed air quality emission standardsfor the city. This led to a significant reduction in air pollution in Chicago.On that particular day, I was allowed to help fold flyers. I got my first tasteof social action and the pride which comes from making a contribution.My childhood experience of pride and unease is not unique to me – noreven to my family. Much of what we grapple with also applies to our humanfamily. When the first atomic bomb was detonated in a test near Los Alamos,NM, there was elation and pride in a great achievement. Soon after, the scientistsalso felt uneasy as they understood the destructive potential of thisnew technology at a deeper level.Similarly, when World War II ended, after the dropping of atomic bombson Hiroshima and Nagasaki, there was great pride and celebration in thetotal lives saved and the ending of the War. People began to learn about thepositive potential uses of nuclear energy. The general public was also confrontedwith the dangers of nuclear power and its potential for devastation.This past May, I was in Chicago at the memorial service of a student of mygrandfather’s and a friend of our family Dr. Ugo Fano. One of the mostentertaining speakers was a 90 year-old professor. I was fortunate enough tofind him at the reception. He shared the following anecdote with me aboutmy grandfather:It was after the War, but before the hydrogen bomb was developed. I wastalking with Fermi over lunch at the University of Chicago. I asked Fermi,“Did you ever have any qualms about your contribution to the developmentof the atom bomb, leaving aside the necessity of winning the war?”He looked at me with a face of incredulity and said something like this:“You and I are scientists. Our purpose is to explore nature. What is donewith our work, is the responsibility of society”.The reply seemed in character with all that I had ever heard about mygrandfather.50

Alice CatonENRICO FERMI AND HIS FAMILYHere was a man who felt supremely confident in the sphere of physics, butknew his limitations in other spheres. He directed his scientific inquiry andthat of his teams so as to yield fundamental results – results which have deepenedour understanding of the physics of the universe. As a teacher and mentor,Enrico fostered continuing scientific inquiry and progress. In addition toall of that, he devoted some of his time to public service in the area of internationalpolicy development on nuclear energy, including taking a strongstance against the development of the hydrogen bomb.We, Enrico’s descendants, inherited the Fermi Italian straight-leg furniture.I have the living room chairs and the backless couch that still slips away fromthe wall. All of us alive today, and all who will come after us, are heirs toEnrico Fermi’s scientific legacy. We all have a stake in it. Since the end ofWorld War II, humanity has had knowledge of nuclear energy and its incrediblepotential for benefit as well as harm.Enrico Fermi gave us a lot. And there is more to be done. Enrico Fermi’swork, and the work of other scientists, exists in a world full of people who,in a certain way, are like Enrico. Remember Enrico couldn’t boil potatoesnor figure out his home needed storm windows in cold weather. He, like allof us, was both brilliant and fallible.We have a collective, developmental task. We must learn to integrate ourscientific knowledge and our human experience to find the answers to thenuclear dilemma, and to the many other dilemmas facing us today.My mother Nella eventually learned to boil potatoes that tasted good. Ourworld has yet to find the right nuclear recipe – how to harness nuclear powerfor the benefit of all living things.We will need all of our human gifts to survive and flourish on this planet.From here, it looks to me like Enrico contributed all of his gifts. Now it’s upto us to contribute ours. We can look back to Enrico for inspiration, if welook to ourselves for the future.ACKNOWLEDGMENTSI wish to thank the following family members, friends and colleagues who assistedme in various ways in writing this speech – for their humor, encouragement, andthoughtful and provocative suggestions: Joan Balmer, Tad Dick, Rachel Fermi, PieroP. Foà, M.D.*, Robert W. Fuller, Carol Layton, Debbie Mayotte, Terry Neiman,Peter Rastall, Ph.D., Hannah Salia, David Unterman, Kathy Weiner, Dr. PaulWeiner*, Elisabeth Zoffman.51

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEREFERENCESARGONNE NATIONAL LABORATORY (producer). (n.d.). To Fermi with love: Commemorative tworecordalbum on the life and times of Enrico Fermi. Argonne, IL: Argonne National Laboratory.*FERMI L. (1955). Atoms in the family: My life with Enrico Fermi. London, England: GeorgeAllen & Unwin Ltd.FERMI R., SAMRA E. (1995). Picturing the bomb: Photographs from the secret world of theManhattan Project. New York: Harry N. Abrams, Inc.HOLTON G. (1998). The scientific imagination. Cambridge, MA: Harvard University Press.MASON K.R. (1995). Children of Los Alamos: An oral history of the town where the atomic agebegan. New York: Twayne Publishers.MCEVOY J.P. (n.d.). Heroes and villains: Enrico Fermi. Unpublished manuscript.MOODY S., (1992, December 27). 50 years ago, man released power of the atom. SarasotaHerald-Tribune, pp. 1F, 6F.*SEGRÈ E. (1970). Enrico Fermi: Physicist. Chicago: University of Chicago Press.TELEGDI V.L. (n.d.). Enrico Fermi at the University of Chicago. Unpublished manuscript.*WEINER N.F. (1995). A daughter’s memoir of Enrico Fermi. Unpublished manuscript.WILBUR K. (2000). A theory of everything: An integral vision for business, politics, science, andspirituality. Boston: Shambhala.*Denotes source of anecdote(s).Alice CatonAlice Caton, daughter of Nella Fermi Weiner, is the oldest of Enrico Fermi’sliving descendants (of four grandchildren and three great-grandchildren). Ms.Caton grew up in Chicago, Illinois with her brother Paul Weiner. She haslived in Vancouver, BC, Canada for almost 20 years. Ms. Alice coachesindividuals and facilitates and trains groups in strategic planning, leadershipdevelopment, interest-based decision-making, communication and conflictresolution skills, cross-functional teams, business process improvement andrelated areas of organizational development.Before becoming an organizational development consultant, she ran her owncomputer training company for 7 years, offering her services to business andgovernment. Ms. Caton combines her project management experience on softwareimplementation projects with a warm and insightful approach to workingwith clients.Ms. Caton has a Bachelor of Arts in Theater from Oberlin College, Oberlin,OH (1979) and a Master of Arts in Applied Behavioral Science from theLeadership Institute of Seattle, Bastyr University, Seattle, WA (1999). She holdsa Certificate in Conflict Resolution from the Justice Institute of B.C.52

Gerald HoltonThe Birth and Early Days ofthe Fermi Group in RomeThe presentation concentrates on the formation of the group and its early years(to 1934 inclusive), with special attention to Enrico Fermi’s ability to combine hismastery of theoretical and experimental physics serendipitously with the historicsituation in which he found himself with regard to the state of science and cultureat the time.La nascita ed il periodo inizialedel gruppo di Fermi a RomaLa presentazione si sofferma sulla nascita del gruppo ed i suoi primi anni diattività (1934 compreso), con particolare riferimento alla capacità di EnricoFermi di coniugare la sua padronanza della fisica teorica e sperimentale con lasituazione storica nella quale si trovò a vivere e lavorare, ed allo stato dellascienza e della cultura in quegli anni.53

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIfeel honored to have been asked to speak on the beginning and early daysof Enrico Fermi’s group in Rome. My main sources for this lecture are ofcourse first of all Fermi’s own Collected Papers, the splendid books and essaysby Laura Fermi, Edoardo Amaldi, and Emilio Segrè, also the laboratorynotebooks of Fermi’s group that are kept at the Domus Galilaeana in Pisa,which I had occasion to visit when I spent a sabbatical leave at the Universityof Rome some years ago. I also had the great pleasure of meeting EnricoFermi when – just about a year before his tragic death – he visited our PhysicsDepartment at Harvard for two weeks, giving brilliant lectures on topicsranging from the Origin of Cosmic Radiation to High Energy NuclearCollisions.Some years later, I felt that there should be a filmed biography of a greatscientist for use in schools and colleges. Enrico Fermi was the most obviousand appealing choice. I initiated and acted as production supervisor of sucha film, called “The World of Enrico Fermi”. That allowed us to conductinterviews specially arranged with Professors Amaldi, Segrè and Rasetti, withLaura Fermi, whom I had come to know well, and with many other colleaguesand former students of Fermi in his days in the United States, suchas Agnew, Anderson, Chamberlain, Chew, Goudsmit, Morrison,Oppenheimer, Rabi, Weil, Yang and others. And that in turn caused me toresearch and publish on the role of Fermi’s group in the recapture of Italy’splace in physics. But let me add that one of the important consequences ofthis and other conferences on Fermi and his work during this Centenary isthat they will furnish much more information for historians of science. Intruth, compared to some other 20 th century scientists of the same high caliber,more needs to be done on this pivotal figure in modern science.An unexpected discoveryFor there is something quite special about the place of Fermi in history. Weall know that in the turbulent flow of time there have arisen, on rare occasions,events that did not fit any previously made plan, but which neverthelesspowerfully shaped all subsequent history. Among the most spectacularexamples is of course the discovery by a captain, born in Genoa, who set sailtoward Asia, but encountered instead the land that came to be called theNew World. From that moment, the clock for the modern period was set.Another instance of a similar sort of serendipity was when a professor ofmathematics at the University of Padua, having used his homemade spyglass54

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEfor terrestrial explorations, raised it to scan the heavens, and was the first tosee there the evidence, in the appearance of the Moon, Jupiter, and Venus,that the existing worldview had to be replaced again by a new one. That iswhen the clock for modern science suddenly came alive. And a third examplewas a seemingly unplanned event that took place right here in Rome,two-thirds of a century ago, also with transforming consequences, for largesections of physics, chemistry, engineering, medical research, and ultimatelyfor politics and warfare.I refer of course to the unexpected discovery, on a certain day in October1934, by Fermi and members of his group, of what was later called the moderatoreffect, the way to turn fast neutrons into slow ones, and the startlingnew phenomena those neutrons could induce. Over four years later, in apaper by Otto Hahn and Fritz Strassmann – in which Lise Meitner and OttoFrisch immediately recognized the evidence for nuclear fission – Hahn andStrassmann referred to the key role in their work of “slowed-down neutrons”.They did not happen to mention the Italians who had found how tomake those slow neutrons. Nevertheless, it can be said that on that day inRome, in October 1934, the clock began to tick which ever since has markedthe nuclear age in world affairs.Despite their diversities, these three examples, and others of this sortthroughout history, have in common not only the initial unintention on thepart of the discoverers, and the extraordinary transformations they eventuallycaused. They also are of the special, rare sort of research findings which donot correspond to the more usual ones. They are not merely discoveries ofnew facts, or verifications of predictions, or answers to old questions, or supportsfor an unstable theory. They are not just the addition of even anotherlarge brick to the ever-unfinished Temple of Isis. Rather, a good analogy forthe sort of discoveries I have described is that suddenly and unexpectedlythey open access to a blank area on the map of established knowledge, allowingan exploration of a new continent of fruitful ignorance. For what is mostprized in science, and is most profound, is the discovery of vast ignorance, ofa range of hitherto undiscovered truths, owing to the breakdown of a standardmodel.Superficially, those three examples of profound discoveries might tend tosupport the old illusion that the course of history itself is decided by theworks of great men, to use the title of Wilhelm Ostwald’s famous book. Thatview is contrary to the other old illusion that it is history that shapes the ideasand acts of even the greats. But I call each of these two opinions by itself illu-55

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEsory, because any study of the actual cases soon shows that both mechanismstogether are constantly at work. As the psychologist Erik Erikson put it, “anindividual life is the accidental coincidences of but one life cycle with but onesegment of history”. Even the most unexpected, fateful chance observationhas its own prehistory; and conversely, even the most turbulent event inworld affairs has never been proved to have been caused by some overarchingZeitgeist.From childhood to the UniversityWith this preamble, my ground is cleared for the task assigned to me.Properly speaking, the birth of Fermi’s group starts with the birth of Fermihimself. From childhood on and into his early student years, young Enricowas recognized by his teachers, acquaintances, and friends to be a prodigy.Relying largely on self-study – a mode typical of great scientists, from Keplerto Faraday to Einstein – Fermi soon became fully at home with modernphysics, enjoying equally the experimental and the theoretical sides. EmilioSegrè tells us that even as a very young man Fermi turned to quantum theory,probably the first to do so in Italy, where that subject was considered asort of no-man’s land between physics and mathematics, rather than a promisingresearch site. That part of physics was not taught in universities there,and a dissertation in theoretical physics as such would have been shocking.(Incidentally, Edwin C. Kemble, arguably the first to do quantum physicsresearch in the United States, had found the same to be true a few years earlier,as a student at Harvard University).At any rate, at age 21, Fermi finished his dissertation at the University of Pisa,on images obtained with monochromatic x-rays by means of a curved crystal.As elsewhere, the experimental equipment available there was largely for spectroscopy.To build a suitable source of x-rays, Fermi organized his fellow students,Franco Rasetti and Nello Carrara, to help him. It was an early indicationof his leadership quality. And again, typical of his later years, Fermi was not satisfiedwith publishing the experimental thesis (his seventh paper, dated 1923),but before that had put into print a separate, lengthy theoretical paper on theproperties and theory of x-rays. There he showed that he commanded thewhole literature – including von Laue, Bragg, Moseley, Barkla, Sommerfeld,Maurice de Broglie, Debye, Scherrer, etc. – in all the many languages.As in later years, already then he was keeping physics almost constantly inhis thoughts. There is a famous story, perhaps apocryphal but believable, that56

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEone of Fermi’s friends once found him pacing up and down in a room, witha preoccupied look. Concerned, his friend asked if Fermi was troubled bysomething. “No”, Fermi replied. “I am just estimating by how much I amdepressing the wooden floor as I walk along it”.Experimental x-ray studies, and even quantum physics, were by no meansthe only subjects then enchanting the young physicist. It is very significant,and became important for his subsequent career, that starting at age 19,Fermi’s first five published papers were all on relativity theory. Most of themshowed his mastery of the methods of general relativity, the theory justrecently and spectacularly confirmed by Eddington’s experiment. To be sure,almost all the older generation of physicists in Italy was skeptical and hostileto that theory. But like Wolfgang Pauli and Werner Heisenberg, at about thesame time and at the same young age, Fermi had evidently been captivatedby Herman Weyl’s new book, Raum, Zeit, Materie, for which Einstein himselfhad written an enthusiastic review in 1918. Fermi contributed to relativitya theorem of permanent value (later called Fermi coordinates), and soonit was incorporated into textbooks on General Relativity. Luckily, Italy had atthat time several master mathematicians working in general relativity, such asTullio Levi-Civita and Gregorio Ricci-Curbastro. They, and other mathematiciansof first rank, including Guido Castelnuovo, Federico Enriques, andVito Volterra, began to notice Fermi’s papers and support his rise.Yet, Fermi properly realized soon that this was not the field in which tobuild his own career. From 1921 to 1925, he had no less than thirty-onepublications, as reproduced in his Collected Papers, varying from relativity tostatistics to nuclear physics; some were in experimental spectroscopy, butmost in theoretical physics – even though he knew that in fact there was nota single University chair available for it in all of Italy. His persistent, widerangingand enthusiastic interests, his optimism and his sheer productivitywere astonishing.Since the theme assigned to me is not the brilliance of Fermi’s various contributions,but the formation of his group, I can point out that we have herealready met the first of the team that would soon be formed, namely theenormously talented experimental physicist and Fermi’s schoolmate, FrancoRasetti. And it is also time to introduce a remarkable figure in the eventualrise of Fermi and his group, namely Orso Mario Corbino. Twenty-five yearsolder than Fermi, he was widely known for his early work in magneto-optics,for which he had been admired by Augusto Righi of Bologna, considered theprevious generation’s leading physicist in Italy.57

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEAfter Corbino had been called to the University of Rome, his talent as anadministrator and unselfish connoisseur of talent quickly led to his becomingSenator of the Kingdom (1920), Minister of Public Instruction (1921) andMinister of National Economics (appointed in 1923, by Mussolini, althoughnever being a member of the Fascist Party). Corbino’s keen scientific mind,combined with his hope to put Italy again on the map as a center of greatphysics research, led him to mourn the sorry state of physics there, symbolizedfor him by Righi’s death in 1920. He saw clearly that Italy was thenunable to take advantage of the world-wide rise of opportunities in the newphysics of the day. Without knowing it clearly, by 1920 Corbino was readyto discover a Fermi – just as Enrico Fermi, for his part, knowing Corbino,must have realized that without such a man there might never be a Fermigroup. And yet, within a few years Corbino was able to help in the appointment,to new professorships, of two brilliant young theoretical physicists –Fermi and his childhood friend, Enrico Persico.After Fermi’s graduation from University, he returned to Rome in 1921 atage 20, living with his parents and his older sister, as he was to do for severalmore years, a member of a closely knit family. At the moment, he had neithera job nor prospects for one. But he made his first visit to Corbino. Thetwo men immediately took to each other. With Corbino’s help, Fermiobtained fellowships, spending unhappy months at Göttingen, and happyones in Leyden under Paul Ehrenfest; then a couple of years in temporaryposts at Florence, working with Rasetti. At last, in 1926, Fermi was appointedto the new Chair of Theoretical Physics at the University of Rome, engineeredby Corbino, who was officially the director of the University’sPhysical Institute at Via Panisperna 89a, the building in which the top floorwas in fact the flat of the family of Corbino himself.The Roman SchoolAnd now Fermi could begin to put his and Corbino’s dream into reality.But that was not going to be easy. So far, Fermi had admirers, but no followers.The outlook for building a school of bright young physicists was verydark. There was not even an Italian text on atomic physics for advanced universitystudents; and of those students there were only a handful, because theexpectation for eventual university employment was extremely poor. Seriousaction was called for. First, Fermi, in 1927, wrote and published that missingtextbook. Also, Corbino used his influence to bring Rasetti from Florence to58

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMERome, eventually settling him into a professorship for spectroscopy createdfor that purpose. (Oh, how we all would have liked to have had a Corbinoon our side. He seems to me the ideal candidate as patron saint for brightyoung scientists). And now Fermi and Rasetti began to recruit promisinguniversity science students for their Istituto.Emilio Segrè reports that as a youth he met Rasetti first in the spring of1927 through a mutual friend, the son of the mathematician FedericoEnriques, while they were mountain climbing. Soon after, he met Fermi,who was only four years older, with the usual result that Segrè knew instantlythat here was an extraordinary teacher, scientist and human being. Thatautumn, with Corbino again smoothing the administrative problems, Segrètransferred his studies from the engineering section to physics, therebybecoming Fermi’s first pupil. And so, in his words, “The Roman School hadstarted”. Segrè in turn persuaded his friend Ettore Majorana to join thegroup, at least informally.Here, an important aside is called for. These last three sentences containseveral clues to the vitality and unique characteristics of the formation of theRoman School. First, Corbino was ever ready to help, in any way. Second, allof Corbino’s boys, as they came to be called later, were within a few years ofthe same age. Third, among them there was a camaraderie in which the onlytrace of hierarchy was the acknowledged centrality of Fermi’s brilliance.Finally, almost all members of the group were part of one social network.They typically even spent parts of their vacations together at the seaside or inthe mountains. For example, in the summer of 1925, Fermi was in themountains with the families of Levi-Civita, Castelnuovo, and Ugo Amaldi.Amaldi’s 17 year-old son, Edoardo, was fascinated by the scientific talk, andended up accompanying Fermi on a bicycle tour of the Dolomites. A bondinghad begun there which, together with Corbino recruiting him from theengineering class, resulted two years later in Edoardo becoming part ofFermi’s physics group at the Institute. If all this sounds too much like theinteractions within a stereotypical Italian family, let us remember that thiswas not the way things then generally arranged themselves in physics laboratoriesin, say, Göttingen, or, for that matter, in Cambridge, Massachusetts.At any rate, we see that a critical mass was being formed at the Institute inRome. The group’s younger students became more and more competent,partly through participating in experiments with Rasetti, but above allthrough Fermi’s constant care and his informal theoretical seminars. ForFermi was an ideal teacher, so enthusiastic that – as John Marshall later59

PROCEEDINGS OF THE INTERNATIONAL CONFERENCErecalled – he sometimes saw to it that he was the only person near the blackboardwho had the chalk. Marshall added: “It was very difficult to argue withthe only person who had the chalk”.Fermi’s typical mode of teaching was to keep it clear and seemingly improvised,distrusting abstract theories such as the quasi-philosophicalCopenhagen versions of quantum mechanics, favoring instead the visualizableapproach of Schrödinger. Hans Bethe referred admiringly to Fermi’sway as “enlightened simplicity”. It also helped his students that Fermi at thattime read omnivorously in new physics publications, interested in the wholespectrum of new ideas. Bruno Pontecorvo, in his book on Fermi, called himsimply “Scienziato universale”. And despite his extraordinary command andexpertise, Fermi showed no trace of vanity, but rather won immediate respectthrough his unselfconscious charisma.Last but not least, one must mention the famous, perhaps unique, wayFermi thought and taught about physical phenomena: Just as his experimentalequipment functioned well despite being often assembled out of cannibalizedpieces and put together in the least complex manner, so also didFermi consider Nature herself put together in the most parsimonious way.That is to say, he recognized again and again the same scenario to be at workin completely different contexts. Thus he applied the same idea of scatteringlength in explaining the pressure shift of spectral lines (Document 95 inFermi’s Collected Papers) and in artificial radioactivity produced by neutronbombardment (Document 107) – even using the same diagrams. Or again,applying the same statistical theme to atoms on the one hand, and to neutronson the other. Fermi’s great paper on beta decay at its core treats theemission of electrons and neutrinos in nuclear events as analogous to theemission of photons from atoms in excited states (Document 80b). AsFermi’s colleague at the University of Chicago (and co-author on twopapers), the great astrophysicist Subrahmanyan Chandrasekhar put it (FERMI,Collected Papers, v. II, p. 923): “Fermi was instantly able to bring to bear, onany physical problem with which he was confronted, his profound and deepfeeling for physical laws: the result invariably was that the problem was illuminatedand clarified. Thus, the motions of interstellar clouds with magneticlines of force threading through them reminded him of the vibrations of acrystal lattice; and the gravitational instability of a spiral arm of a galaxy suggestedto him the instability of a plasma and led him to consider its stabilizationby an axial magnetic field”.One can recognize here the way a thematic undercurrent guides some sci-60

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEentists’ understanding of how Nature works at the fundamental level. ForEinstein, the basic assumption was again and again that entirely differentphenomena are aspects of one grand unity. Niels Bohr, often quoting a sayingof Friedrich Schiller, thought that truths may be found “in the abyss”between contrary theories. Fermi thought of a phenomenon as exhibitingone of only a relatively small number of different basic scenarios of whichNature availed herself; of these, Fermi kept a catalogue throughout his life.The physics of the futureTo learn new skills, members of Fermi’s group, already international in outlook,traveled to laboratories abroad: Rasetti to Millikan in Pasadena and laterto Lise Meitner in Berlin. Segrè went to Pieter Zeemann in Amsterdam andOtto Stern in Hamburg. By transfer from other universities, more studentschose to join the Rome group, including Eugenio Fubini, Ugo Fano, andBruno Pontecorvo. By the early 1930s, they were attracted by Fermi’s work,for example on the quantum theory of radiation, on statistics, above all on thetheory of beta decay, the paper first published in 1933, after having been rejectedby the editor of the journal Nature as “containing abstract speculations tooremote from physical reality”. Also, a good number of young physicists camefrom abroad, to visit and sometimes to stay for longer periods and collaborate.They included Hans Bethe, George Placzek, Felix Bloch, Rudolf Peierls, FritzLondon, Edward Teller, Eugene Feenberg. And before that, there were collaborationwith and visits from colleagues at other Italian universities, such asRenato Einaudi from Turin, at Persico’s recommendation, but perhaps mostfrequently from the newly flourishing physics group in Florence under AntonioGarbasso, including Bruno Rossi, Gilberto Bernardini, Giuseppe Occhialini,Enrico Persico, Giulio Racah, and Sergio De Benedetti.But where was the freshly hatched young Roman group itself heading inphysics? Up to 1929, the largest part of their teamwork was still in spectroscopy.Starting then, it became more and more rapidly clear that remarkablechanges in physics abroad signalled that the search for a promised landon which to strike gold for Italian physics would have to be reorganized. Thehistorical development of physics itself revealed to the Fermi team what itwas that these young men had been preparing themselves for in all thoseyears of wide-ranging study and perfection of various skills. The quantummechanics of Bohr, Heisenberg, Pauli, Dirac, Schrödinger was taking centerstage in the field of theory; and on the experimental side, nuclear physics was61

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEbeing transformed in exciting ways, by the findings of Chadwick, Urey,Davisson and Germer, Carl Anderson, Neddermeyer and Street. The protonneutronmodel of the nucleus was becoming plausible. The neutrino hypothesisof Pauli was tantalizing; and E.O. Lawrence’s cyclotron was a muchenvied sensation.In a speech in September 1929, Corbino showed he had already smelledout that nuclear physics was, in his words, “the true field for physics of thefuture”. So now, the core members of the team which had patiently andoften at great personal cost stuck together for years, began to re-educatethemselves in a systematic study from late 1931. Amaldi led a special seminaron radioactivity, and the group learned how to build neutron sources,construct a cloud chamber, make Geiger counters. Some additional researchfunds became available from the Italian National Research Council (CNR).And all this without the group realizing in the least precisely what and whenan opportunity would come along for using that new knowledge, to achievethe ultimate desire of the team: to make, at long last, a world-class discovery.It was a curious moment in the history of science: Here was arguably the firstmodern research team in physics, waiting for the signal exactly how to be putto use for a high purpose.The first fruitsThat did happen, and remarkably soon. It was helped, as so often, by anaccidental discovery, published in mid-January 1934, by Irène Curie Joliotand her husband, Frédéric Joliot. They had used alpha particles from polonium,sent into a cloud chamber to bombard aluminium, thereby causing theemission of positrons from the target. Amaldi wrote, “The discovery of artificialradioactivity was due to an accidental observation by Joliot. One day, inJanuary 1934, Joliot noticed that the emission of positrons persisted whenthe polonium source was taken away”. One might add here that earlier, anon-discovery of artificial radioactivity took place in E. O. Lawrence’scyclotron laboratory in Berkeley. As Lawrence confessed in his Nobel Prizespeech (for 1939, but given in 1951), “Looking back, it is remarkable thatwe [at Berkeley] managed to avoid the discovery”, by neglecting the fact thatthe Geiger counters kept up their chatter after the 27-inch cyclotron hadbeen turned off.At any rate, with the finding by the Joliot-Curies, a huge window was suddenlyopened on a new landscape of exciting ignorance. Immediately the62

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMErush was on to explore this territory, using of course alpha particle sources.But Fermi at once had the crucial intuition that unlike all others, he and histeam should use a beam of neutrons instead of alpha particles to produceartificial radioactivity. It seemed to him reasonable to expect that in a neutronbeam the lack of charge on such projectiles, much of them emerging athigh energies from the radon-beryllium sources now available, would have agreat effect on the targets, despite the admittedly still relatively weak sources.On March 25, 1934, Fermi was able to publish the first results, in the journalof the National Research Council, the Ricerca Scientifica. It was the firstof ten such papers, sometimes one appearing per week. From the third to thetenth of these publications, the list of authors was always given as follows: E.Amaldi, O[scar] D’Agostino (a young chemist who happened to come backto Rome on a vacation from a fellowship in Paris, but happily was pressedinto service), E. Fermi, F. Rasetti, E. Segrè. Note that all core members ofthe “family” were listed in alphabetical order, and that, perhaps for the firsttime in the whole physics literature, there were as many as five authors.As to results, Fermi typically had decided to test all available chemical elementsfor artificial radioactivity, going methodically up the periodic table.The team divided the labor – getting the targets, monitoring the electric circuitryof the Geiger counters, the chemical analysis, etc. – in a cooperativeway. One should note that Fermi’s group, from the beginning, generallytended to work together on one project – unlike the operation at, say,Rutherford’s Cavendish Laboratory, where different small groups worked ondifferent projects, whose commonality was chiefly that they represented differentparts of Rutherford’s wide-ranging interests.The work in Rome was now quite frantic and tedious for some months,and a few mistakes were made. None was later more regretted than the presumedidentification of transuranium radioactive products, produced by irradiatingthorium and uranium with neutrons. It was the same mistake madeby others at the same time, including Hahn and Meitner, and the Joliot-Curies. Altogether, apart from thorium and uranium, sixty elements wereirradiated with the fast neutrons by the Roman team, thirty-five provided atleast one new radioactive product, and the total of new ones identified, withtheir respective half lives, came to forty-four.Here was truly excellent work, the unexpected first fruits after the long waitand preparation. The Fermi group was now widely noted. Since at the timesuch publications had to be first in the Italian language, I.I. Rabi at ColumbiaUniversity is said to have advised, “Well, now we all have to learn Italian”.63

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThe “miracolous effect” of slow neutronsBut nobody realized the best part: that the team was now standing at thethreshold of their truly startling discovery, with its long resonance into scienceand world history. In fact, at that point, the whole Roman group tooka break for the lengthy summer vacation, getting away from hot Rome, likeall sensible Romans.They reassembled at the Istituto in the fall of 1934, now joined by a closefamily friend of Rasetti, Bruno Pontecorvo. But by mid-October thingsbegan to go wrong. Their whole experimental activity was upset by a strangeinconsistency in the results of irradiation of targets during an attempt to calibratethe degrees of induced radioactivity. The inconsistency in the readingsthey now obtained turned out to depend on the tables used as support of theequipment. Thus, one table, made of wood, had once been the bearer ofthose spectroscopes of earlier day; the other, not far away, was a shelf madeof stone. When an experiment on inducing radioactivity in a target made ofsilver was placed on the first of these tables, a markedly greater activity resultedthan if the same experiment was tried on the marble support. The groupfamously christened it the “miracle of the two tables”.To get to the bottom of it, Fermi initiated a systematic observation, startingOctober 18, 1934. He reasoned that perhaps the lead housing aroundthe target affected the neutrons reaching the target in those two cases, andhe observed that the interposition of a block of lead changed the activationsomewhat. Thus, Fermi decided to insert a lead filter, a wedge of varyingthickness, into the neutron beam. As Segrè put it later, on that day, October22, “Persico and Bruno Rossi [were] there on a visit, kibitzing”. The astonishingaccount of the events on the morning of that crucial day was later toldby Fermi to Subrahmanyan Chandrasekhar, who published his report (FERMI,Collected Papers, v. II, p. 927). The essential last paragraph was repeated verbatimby others close to Fermi, such as Edoardo Amaldi and Emilio Segrè 1 .Although some here may remember the account well, allow me to quote it,because it needs more analysis.“I will tell you how I came to make the discovery which I suppose is themost important one I have made. We were working very hard on the neutron-inducedradioactivity and the results we were obtaining made no sense.One day, as I came to the laboratory, it occurred to me that I should exam-1 A detailed version of the events was given by Laura Fermi in her book, Atoms in the Family (1954, p.98). It differs in some details, but comes to the same conclusion.64

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEine the effect of placing a piece of lead before the incident neutrons. Andinstead of my usual custom, I took great pains to have the piece of lead preciselymachined. I was clearly dissatisfied with something: I tried every‘excuse’ to postpone putting the piece of lead in its place. When finally, withsome reluctance, I was going to put it in its place, I said to myself: ‘No! I donot want this piece of lead here; what I want is a piece of paraffin.’ It was justlike that: with no advanced warning, no conscious, prior, reasoning. I immediatelytook some odd piece of paraffin I could put my hands on and placedit where the piece of lead was to have been”.The result was immediately obvious: a great increase in the radioactivityinduced in the target, even if the target and the paraffin filter were placed onthe marble shelf. As Segrè recalled, at about noon “everybody was summonedto watch the miraculous effect of the filtration by paraffin”. And in a“still extremely puzzled” state, “we went home for lunch and our usual siesta”.“When we came back at about three in the afternoon, Fermi had foundthe explanation of the strange behavior of filtered neutrons. He hypothesizedthat neutrons could be slowed down by elastic collisions, and in this waybecome more effective – an idea that was contrary to our expectation” (inSEGRÈ, Enrico Fermi, Physicist, p. 80).As Amaldi reported, it was only later that the so-called 1/v law was determined,i.e., that the capture cross-section (σ c ) was inversely proportional tothe speed of the neutrons at low velocities. But on that day Fermi realized thatthe hydrogen nuclei in the wooden table had greatly slowed some of the incidentneutrons, being of about the same mass, and then had scattered them tothe target, whereas the heavy nuclei in the marble in the other table could dothis only very poorly. Repeating the experiment quickly by using water insteadof paraffin helped prove Fermi’s initial hypothesis. Moreover, the enhancedradioactivity was also observed for copper, iodine, and aluminium.That evening, in Amaldi’s home, they all met to prepare a short report oftheir work for the Ricerca Scientifica, with Fermi dictating, Segrè writing,Rasetti, Amaldi and Pontecorvo excitedly adding their comments. Amaldi’swife Ginestra, who was working with that journal, saw to it that the articlewould be published within two weeks, with preprints – another novelty –becoming available within days, and sent out to some forty of the mostprominent researchers in the field. Soon the whole profession knew that theRoman group had reached a new frontier. It was a climactic moment forFermi’s team in Rome, and – as it turned out – for the world on its path intothe uncertain future.65

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntuitive intelligenceBut in that story, there is a haunting puzzle. Fermi was the most rationalof scientists; yet, not by accident or chance but by determined action, he hadplaced the crucial piece of paraffin in front of the neutron source, “with noadvanced warning, no conscious, prior reasoning”. Why did he, the leastimpulsive physicist, do this? 2 Part of the answer, it seems to me, is that thatthere exists a kind of intuitive intelligence which sometimes secretly guidescertain brilliant minds in the early phases of their research. That concept isnow rarely mentioned, least of all by scientists themselves, who tend to shyaway from such a difficult-to-defend idea. But it had figured prominently inthe writings of philosophers such as Baruch Spinoza, Immanuel Kant, andHenri Bergson. Arthur Schopenhauer, widely read at the time, even held thatintuition is the hallmark of genius.Einstein referred to it as “Fingerspitzengefühl”, a sense or a feeling at thetips of one’s fingers, and specifically referred to intuition as necessary, e.g., inhis essay, Motive des Forschens (1918): “There is no logical path to the elementarylaws, but only intuition, resting on empathy gained by experience”.Henri Poincaré, in Science and Method, Book II, Chapter 2) noted that it isby logic that we prove, but by intuition that we discover. The scientist andphilosopher Michael Polanyi wrote at length about what he called the scientist’s“tacit knowledge”, largely resulting from one’s lengthy immersion or“in-dwelling” in the subject of research. He summarized the result in the simplesentence: “We know more than we can tell”. Much earlier, Hans ChristianOersted provided for this rare gift the happy term “anticipatory consonancewith nature”. And a chemist and great writer, Primo Levi, wrote, “I knowwith my hands and my nose, with my senses” (in The Voice of Memory, p. 8).So one might well understand that when Fermi’s hand was reaching for the“odd piece of paraffin” instead of the lead wedge, he was guided by a speculationbelow the level of consciousness at that moment, but a result of anintimate knowledge of neutron physics, one built up during years of intensestudy, discussions and experimentation with neutronics. As Dr. Alberto De2 One historian of science was so astonished by the report of an action so uncharacteristic of Fermi thathe even doubted the account reported by Chandrasekhar. But that idea must surely be dismissed.Chandrasekhar, who was one of the most distinguished and precision-minded scientists, even felt it necessaryto start his report with a footnote: “His [Fermi’s] account made so great an impression on methat though this is written from memory, I believe that it is very nearly a true verbatim account”.Moreover, he published it (in 1965) when those who had “kibbitzed” that morning, on October 22,1934 – Rossi and Persico – were still alive; and as mentioned, Fermi’s co-workers, Segrè and Amaldi,endorsed Chandrasekhar’s account as given above, quoting it in full.66

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEGregorio 3 has shown, Fermi may well have read publications in 1932-33 inwhich slow neutrons and effects of hydrogenous substances on neutronswere discussed, and he also had participated in the 1933 Solvay Conferencewhich included discussions of these topics. But it is significant that nobodyother than Fermi and his group entered into the crash program producingartificial radioactivity, first with fast neutrons, and then with slow ones, startingthat morning when Fermi was able to draw on resources that had by thenslipped below the conscious level.In fact, Chandrasekhar’s account, given above, is part of a longer piece ofhis, which reveals that the whole discussion with Fermi had begun preciselywith a consideration of the role of “subconscious” ideas in creative work inscience: Chandrasekhar wrote (p. 926, Fermi Papers): “I described to Fermi[Jacques] Hadamard’s thesis regarding the psychology of invention in mathematics,namely, how one must distinguish four different stages: a period ofconscious effort, a period of ‘incubation’ when various combinations aremade in the subconscious mind, the moment of ‘revelation’ when the ‘rightcombination’ (made in the subconscious) emerges into the conscious, andfinally the stage of further conscious effort. I then asked Fermi if the processof discovery in physics had any similarity. Fermi volunteered and said [therefollowed his account, as given above]”.There are also other accounts of Fermi’s ability to dredge up, from hiddenresources, answers to questions facing him. Thus, Herbert Anderson recalledthat at a crucial moment during the difficult early work in 1939 at ColumbiaUniversity on the possibility of a chain reaction, “Fermi asked to be left alonefor 20 minutes”, and emerged with a rough estimate of the effect of resonanceabsorption by uranium. Anderson reported that the estimate, whichproved to be correct, “was largely intuitive. Fermi was never far wrong insuch things...”, and, what is important for the purpose of the topic of myessay, one can imagine the positive effect such talent had on Fermi’s group.Elsewhere Fermi was even credited with helping reactor engineers to obtaina rough estimate of data not yet measured, such as nuclear cross-section.They did it reportedly by watching Fermi closely for an “involuntary twinklein his eyes” while reciting to him possible cross-section values.Science historians have struggled to understand the mechanism behind suchexamples of “anticipatory consonance with nature”. It seems to me another caseof finding ourselves cast upon the shores of a large island of fruitful ignorance.3 In a personal communication of an unpublished manuscript, for which I am grateful.67

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi and the Fascist disasterI am relieved that it is not part of my assignment to report on the rapidlyensuing disintegration and near destruction of the Roman group, to useEdoardo Amaldi’s phrase, as well as those in Florence and elsewhere in Italyat that time. To be sure, in the early days of Fermi’s ascent, some scientistshad been at least indirectly helped – in hastening appointments and in theavailability of some funds – by the cult of the Fascist government to revivethe myth of national regeneration, on the model of ancient Rome as a centerof Western civilization. Among the sixteen institutions founded afterMussolini’s assumption of dictatorship in 1925, two were the new RoyalAcademy of Italy and the National Council of Research (CNR). Fermi’swork had obtained financial support from both, although he himself was bynature and design apolitical, and felt repugnance from the regime’s ideology.In turn, the government expressed annoyance with Fermi for his refusingthe prestigious chair in physics left by Schrödinger in Zurich, where Fermi,acting as a proxy for Italy’s science, would have been highly visible throughoutthe European continent.From the mid 1930s on, a whole slew of institutions founded by the Fascistgovernment withered, part of a general growing bleakness and collapse ofcivilized life. The physicists at Via Panisperna submerged themselves in hardwork, hoping to use “physics as soma”, on the model of Aldous Huxley’s victimsin his novel Brave New World. All this is movingly described in severalessays in Edoardo Amaldi’s volume of his selected historical writings – fromthe effect of the state’s lurching toward the Ethiopian Campaign that startedin October 1935, to the growing economic and political dependence onNazi Germany, including the formation of the Rome-Berlin Axis, to Italy’sparticipation in the Civil War in Spain, and to the institution of racist laws inItaly in July 1938, roughly along the German model. There followed theemigration of most of the group’s members and, during World War II, thearrest, deportation and death of persons close to the Roman group, such asLaura Fermi’s father, Augusto Capon. Among the many other such victimswere several relatives of Segrè.There had been so few years between launching upon the recovery ofItaly’s place in world-class physics in the mid-20s, and seeing it descend againby the end of the 30s for many years in horror and flames. That whole arc ofthe brave rise of Fermi and his group, their extraordinary achievements, andthen the ghastly dissolution forced on them, is a symbol of the best and theworst of that tragic twentieth century.68

Gerald HoltonTHE BIRTH AND EARLY DAYSOFTHEFERMI GROUP IN ROMEREFERENCESAMALDI E., 20 th -Century Physics. Essays and Recollections: A Selection of Historical Writings byEdoardo Amaldi (Singapore: World Scientific, 1998).BUCK B., Italian Physicists and Their Institutions, 1861-1911 (PhD dissertation, HarvardUniversity, 1980; Supervisor, G. Holton).FERMI E., Collected Papers, v. I (Chicago and London: University of Chicago Press, 1962).FERMI E., Collected Papers, v. II (Chicago and London: University of Chicago Press, 1965).FERMI L., Atoms in the Family (New York: American Institute of Physics, 1987).HOLTON G., The Scientific Imagination, rev. ed. (Cambridge, MA: Harvard University Press),1998. See Ch. 5, “Fermi’s Group and the Recapture of Italy’s Place in Physics”. Translated asL’Immaginazione Scientifica (Torino, Italy: Giulio Einaudi Editore, 1983), “Il gruppo diFermi e la riconquista da parte dell’Italia del suo posto nella fisica moderna”, pp. 351-402.HOLTON G., ET AL., The World of Enrico Fermi, film.PONTECORVO B., Fermi e la fisica moderna (Rome: Editori Riuniti, 1972).SEGRÈ E., A Mind Always in Motion: The Autobiography of Emilio Segrè (Berkeley, CA:University of California Press, 1993). Translated as Autobiografia di un fisico (Bologna: IlMulino, 1995).SEGRÈ E., Enrico Fermi, Physicist (Chicago and London: University of Chicago Press, 1970).WEINER C., ed., Storia della fisica del XX secolo. Rendiconti della Scuola Internazionale diFisica “Enrico Fermi”, Varenna, (New York: Academic Press, 1977), especially the essay by E.Amaldi.Gerald HoltonHolton is Mallinckrodt Professor of Physics at Harvard University. Among hisbooks (several of which have been issued in Italian translations), are ThematicOrigins of Scientific Thought: Kepler to Einstein; Science and Anti-Science;The Advancement of Science and its Burdens; Einstein, History and OtherPassions; and Project Physics. As part of his historical research on the workof Enrico Fermi, he co-produced a biographical film, “The World of EnricoFermi”. He is on the Editorial Committee of the Collected Papers of AlbertEinstein and of learned journals, including Physis and Nuncius. Among thehonors he has received are the George Sarton Medal, the R. A. Millikan andH. C. Oersted Medals, and election to such offices as President of the Historyof Science Society, Vice President of the Academie Internationale d’Histoiredes Sciences, and to other Academies in Europe and the United States.69

Fabio Sebastiani, Francesco CordellaFermi toward Quantum Statistics (1923-1925)There are some uncertainties about the influences that might have led Fermi to theformulation of quantum statistics. Like already remarked by F. Rasetti, little isknown about the circumstances that led the great Italian physicist to one of hismost important theoretical contributions. It can be said that the “preparatory role”of two works by Fermi (the one about Stern’s method for the calculation of theentropy constant of a perfect gas and the other on the quantization of systemscontaining identical particles) is unanimously recognized. Based on a recenthistorical reconstruction, it will be shown how some circumstances pushed Fermito tackle these problems. It seems that Göttingen’s environment had a stronginfluence on his work. We will also try to specify the time of the quantumstatistics formulation.Fermi verso la statistica quantica (1923-1925)Sussistono alcune incertezze circa le influenze che possono aver indirizzato ilpercorso di Fermi verso la formulazione della statistica quantica. Come giàsottolineato da F. Rasetti, poco è noto delle circostanze che hanno condottoFermi a uno dei suoi più importanti contributi teorici. È comunque unanimementericonosciuto il ruolo preparatorio di due lavori del giovane fisico romano,riguardanti il metodo di Stern per il calcolo della costante dell'entropia di un gasperfetto e la quantizzazione di sistemi contenenti particelle identiche. In base aduna recente ricostruzione storica, saranno mostrate le circostanze che spinseroFermi ad affontare questi problemi. L’ambiente scientifico di Gottinga sembraaver avuto una forte influenza sui due suoi lavori preparatori. Si cerca inoltre diprecisare la collocazione temporale della formulazione della statistica quantica.71

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThe anomalous case of Enrico Fermi, in comparison with the internationalscientific context of the early twenties, is evident since his firstworks. The young scientist Fermi behaved as an outsider fairly proud of hisindependence, mainly because of his strong personality. The Italian scientificenvironment too forced him to a self-teaching method and a cut offposition. Nevertheless, it must be said that Fermi never much complainedabout it.In particular, the genesis of his eponymous quantum statistics gives aninteresting trail to outline, at the same time, his personality and the way, generallynot well known, he followed to reach a result that put a final seal onhis fame at an international level. The high level of the about thirty worksfrom 1921 to 1926 shows a precocious technical talent. Moreover, the existenceof a defined scientific style and a tendency to concentrate himself onpersonal research programs was already clear. Furthermore, the young Fermihad great competence in various fields of physics and an uncommon interestfor both the theoretical and experimental aspects.The theoretician Fermi, although confident in old quantum physics, was notvery interested in the formulation of new principles. He was rather in searchof applications that descended from those principles. That explained his pragmaticuse of mathematics of which, nevertheless, he had a total mastery.The roots of this “modus operandi” should also be searched in the pre-universityyears, when all the main features of his scientific personality werealready emerging. 1 Anyway, it was only after his two stays in Germany(Göttingen) and the Netherlands (Leyden) that Fermi started to becomeaware of his value and what kind of physics was produced in the ‘sacred’places. These two stays abroad were useful to Fermi also for the many prestigiouspeople he met there (Born, Ehrenfest, Goudsmit, Heisenberg,Kronig, Uhlenbeck, etc.). Moreover, unlike what asserted up to now (mainlyby Segrè), this work will point out the scientific importance of the influenceof the German stay on Fermi.Always devoted to a major clarification and simplification of subjects, heshuns any possible technical virtuosity and not strictly necessary hypotheses.This is evident especially in the formulation of his quantum statistics.The key point of Fermi’s discovery (typical of his way of proceeding) liesin the bold application of Pauli’s principle to the quantization of the perfectgas, that was at the time a fairly distant problem. Fermi’s approach, here1 Cmp. SASSI, SEBASTIANI (1999).72

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)defined as ‘analogy method’, is present also in other significant theoreticalcontributions. These results are due to Fermi’s great ability to profitably putin relation concepts that differ greatly.However, Fermi’s article didn’t provoke any reaction, at least until Diraccame to the same results. The silence from the scientific community wasmainly justified by Dirac’s larger fame and powerful use of the new quantumconcepts, that allowed in-depth explanations of the subject studied. 2 In hisarticle on the new quantum statistics, Fermi also introduces an harmonicpotential to contain atoms of the gas. That could be considered as an unnecessarycomplication, but there are also some interesting motivations for thisunusual choice. In any case, later on, the harmonic potential was abandonedeven by Fermi.The years before Fermi’s quantum statisticsThe beginning of the twenties, as it is known, was a crucial period forphysics. S. Goudsmit humorously described the physics community of thetime: “The concept of the ‘good old days’ does not apply […] In the 1920’s,by comparison, we lived in a small village with its little feuds, a Peyton Placewithout sex”. 3The “Peyton Place without sex” it’s a nice metaphor to illustrate the anxietyof those managing quantum physics, that were getting few gratificationsand many disappointments. The few that, like Fermi in Italy, were devotingthemselves to the new physics, were considered to all intents and purposeslike “sinners”. 4From January to August 1923, he stayed eight months in Germany, atGöttingen, with Max Born, without much advantage, according to Segrè. 5Later, from September to December 1924, Fermi spent four months inHolland, at Leyden, with Paul Ehrenfest. This shorter period of study was,as for human relations, much more satisfactory. The two stays abroad had a2 “[…] playing with symmetrical and anti-symmetrical functions, Dirac derived both quantum statisticsin one stroke. […] Fermi had in fact derived ‘only’ his statistics”, cmp. BELLONI (1994), p. 107.3 Cmp. GOUDSMIT (1976).4 Actually, Fermi was almost the sole ‘sinner’. Rasetti reports that: “By 1920 or even ‘22, quantum theoryin Italy was essentially confined in Fermi’s mind and there was very little outside. For instance, Ifirst heard of the quantum theory and Planck’s constant from Fermi”, cmp. A.H.Q.P. transcript of atape recorded interview by T. S. Kuhn with F. Rasetti and E. Persico, 8 April 1963, p. 8.5 Cmp. F.N.M., p. XXVI-XXVII.73

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEgreat influence on Fermi. They can be considered as his first direct encounterwith “modern” physicists and with two places extremely favourable to thescientific activity. 6It was also Fermi’s first opportunity to get to know the culture, politics andsocial organisation of two countries very different from Italy’s at the time:“[...] he said that he found everything so superior to what he was used to inItaly in every respect. The country is so well organised. They like good functioningin everything”. 7As it emerges from his correspondence, Fermi never expressed his opinionon matters that did not strictly concerned physics; it was an unpleasant peculiarityof Fermi. Certainly it was a period in which events of some considerationdid not lack both in Italy and in Germany! 8During approximately the three years from the end of university and the formulationof his statistics theory, Fermi’s work can be divided into four phases.Göttingen (January 1923-August 1923)In these eight months, Fermi went to Göttingen on a scholarship assignedhim on 4 November 1922 by the Ministry of Education.The Weimar Republic was undergoing a very bad crisis and although Fermipersonally witnessed its economical disaster, still greatly admired the country’sorganising ability (cmp. the quoted recollections of Rasetti). 9 However,there is no trace of these events in Fermi’s letters from Germany. Even moresurprising, there isn’t any comment on Göttingen’s scientific environment,except for the quite generic statement: “The professors, especially Born, arenice people and they don’t give it as if it were the Keys of the Kingdom”. 10Heisenberg, in an interview with T. S. Kuhn of 1963, remembered then thathe had met Fermi at that time and that he hadn’t much liked him:06 Until then he was, to all intents and purposes, an autodidact; cmp. SASSI, SEBASTIANI (1999).07 Cmp. A.H.Q.P. transcript of a tape recorded interview by T. S. Kuhn with F. Rasetti and E. Persico, 8April 1963, p. 12.08 Fermi had this attitude all his life.09 For instance, in November 1923, one dollar was worth some milliards of marks and the exchange ratewith Italian money was especially favourable, so that Fermi was able to buy a brand new bicycle, cmp.L. FERMI (1954). The political situation was also tragical and in January 1923, when Fermi arrived atGöttingen, there was the Franco-Belgian occupation of the near Ruhr zone (about 100 km west ofGöttingen) as pledge for the German war debts.10 “I professori, specialmente Born, sono persone simpatiche e non la fanno cader troppo dall’alto”, cmp.stamped postcard to Persico of 30.1.1923; a photostat is in the AMAL. ARCH. (1E bis /n.c.).74

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)“I had some discussions with Fermi, but it must have been that Fermi wasnot – I would say – in a good period of his young life. He may have hadpersonal problems; I don’t know what the matter was. He had alwaysbeen a bit shy and kept by himself, and it was not too easy to get reallyclose to him. Still, I liked him as a rather different type of physicist. […]in Göttingen we never had a real conversation; we met in the seminar, andoccasionally on the streets, but not in that way that we really got intouch”. 11The lack of agreement with the German scientific environment is testifiedalso by other sources. 12 Furthermore, at Göttingen Fermi could be sufferingfrom the so-called ‘swot syndrome’. Fermi, accustomed to be outstandingand considered a very talented youth in Italy, when suddenly in an ‘interpares’ environment, could have had psychological problems. Anyhow, in thisperiod Born was holding a seminar for a few people, among whom therewere Fermi and Heisenberg. 13 Born seemed to Heisenberg: “as an extremelygood mathematician who […] had not so much feeling about how thethings in atomic physics were”. But Fermi, “disliked these mathematical subtleties,proof of convergence and such […] I mean, Fermi felt, ‘That’s notphysics’. [...] Fermi was not so pleased with [this seminar of Born]”. 14Göttingen’s interest for the new physics was partly due to the great mathematicianDavid Hilbert who in 1912, as Tagliaferri relates, 15 decided that‘physics was too difficult for physicists’. So he asked Sommerfeld to send himsome youths of great merit. Among them there were Heisenberg and Pauli.In a letter to Einstein dated April 7 1923, about three months after Fermi’s11 Cmp. A.H.Q.P. transcript of a tape recorded interview by T. S. Kuhn with W. Heisenberg, 15 February1963, p. 14 (We are grateful to D. Cassidy for this information).12 “According to Samuel Allison, many years later Fermi remembered that period with some bitterness:the professors of Göttingen considered themselves, in Fermi’s opinion, as omniscients and they didn’tat all care to encourage him”, “Secondo Samuel Allison, molti anni dopo Fermi ricordava quel periodocon una certa amarezza: i professori di Gottinga si consideravano, secondo Fermi, onniscienti e nonsi preoccupavano certo di incoraggiarlo”, cmp. PONTECORVO (1993), pp. 26-27. When Fermi cameback to Italy and met G. Uhlenbeck in the fall of 1923, his disappointment was even more evident:“[Uhlenbeck] found he’d just come back from Germany, completely discouraged. He’d been toGöttingen for a term and had been given the works - on the lines of ‘This guy can’t know anything,he’s small fry, he’s never studied any place where it’s worth studying.’ The man was so thoroughlydejected that he was planning to give up physics. Uhlenbeck advised: ‘Don’t do that before you’ve hada talk with Ehrenfest. Go and see him’.”, cmp. GOUDSMIT (1972). However, the idea of a Fermi intentionedto give up physics is surely exaggerated.13Those present at the seminar were: Heisenberg, Jordan, Fermi, probably Hund, and at most anothercouple of persons.14Cmp. the mentioned interview with Heisenberg, p. 6.15Cmp. TAGLIAFERRI (1985), note 92, p. 336.75

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEarrival at Göttingen, Born wrote about Heisenberg’qualities and their regretfor the state of quantum physics, 16 also mentioned in several previousHeisenberg’s letters to Pauli. 17If these were Born and Heisenberg’s worries, the following assertion bySegrè, concerning the beginning of 1923 at Göttingen, sounds quite unlikely:“[…] an extremely important incubation period preluding the floweringof the new quantum mechanics that just in Göttingen had in this period oneof the most important centre”. 18 The impression is, instead, of a widespreaddisappointment and, as Tagliaferri objects: “[...] this is an unjustified inference:in 1923 the new mechanics could be a desire but it wasn’t known –either in Göttingen or elsewhere – which way to follow to achieve it”. 19Fermi was not discouraged and worked hard, also not to disappoint friends’expectations in his sojourn in Göttingen. 20In February 1923, only one month after his arrival, Fermi prepared a work16 “[…] I worked a lot and kept a good number of pupils busy. However, the problems faced ar small: inspite of all efforts, I’m not able to penetrate the big quantum enigmas”, “[…] ho lavorato parecchioe ho fatto anche lavorare un buon numero di allievi. Ma i problemi affrontati sono soltanto piccoliproblemi: nonostante ogni sforzo, non riesco a penetrare i grandi enigmi dei quanti”, cmp. Born(1973 2 ), p. 89. When Fermi arrived at Göttingen, the two most renowned Born’s collaborators weretaking turns. In fact Pauli, Born’s assistant until the spring of 1922, went to Copenhagen as Bohr’sassistant from October 1922 to September 1923, and Heisenberg was to replace him, cmp. for exampleTAGLIAFERRI (1985), p. 316.17 As a matter of fact, on 19 February 1923 writing to Pauli about the work conducted with Born,Heisenberg asserts: “[...] to summarise it all: ‘it’s a torture’”, “[...] um alles kurz zusammenzufassen:‘es ist ein Jammer’”, cmp. PAULI (1979), p. 80. Two days after, always writing to Pauli, Heisenbergironically states : “[…] a theory can always still be wrong, if it produces something right, but can neverbe right if it produces something wrong”, “Eine Theorie kann immer noch falsch sein, wenn sie etwasrichtiges ergibt, aber sie kann nie richtig sein, wenn sie etwas falsches ergibt”, cmp. PAULI (1979), p.82. And, on 26 March of the same year, Heisenberg closed a letter to Pauli saying: “[...] we[Heisenberg and Born] don’t want to get uselessly tired. Basically we are convinced that all heliummodels proposed until now are false as the whole atomic physics. We hope that this wonderful spring[...] would change all, but really all”, “Aber wir wollen uns nicht unnötig streiten. Im Grunde sind wirbeide der Überzeugung, daß alle bisherigen He-Modelle ebenso falsch sind, wie die ganzeAtomphysik. Hoffen wir, daß der jetzige prachtvolle Frühling [...] alles, alles wendet”, cmp. PAULI(1979), p. 86.18 “[…] un periodo estremamente importante di incubazione preludente allo sboccio della nuova meccanicaquantistica, che appunto in Göttingen aveva in quegli anni uno dei centri maggiori”, cmp.F.N.M., p. XXVI.19 “[…] quest’illazione è ingiustificata: nel 1923 la nuova meccanica poteva essere un’aspirazione, ma nonsi sapeva – né a Gottinga né altrove – che strada prendere per realizzarla”, cmp. TAGLIAFERRI (1985),p. 351, note 4.20 Persico, besides waiting for scientific news from what he calls “quantum land” (“paese dei quanti”,cmp. AMAL. ARCH. (1E bis /n.c)), when Fermi is about to return in Italy, writes to him: “And we hopethat you’ll bring us some Göttingen’s air bottles to renew our scientific environment and guide us ona serious and organised work”, “E speriamo che ci porterai alcune bombole di aria gottinghese, perrinnovare i nostri ambienti scientifici e guidarci ad un lavoro organizzato e serio”, cmp. copy of the23.06.1923 stamped postcard, ibid.76

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)that would be later published on the Nuovo Cimento: The adiabatic principleand systems that don’t admit angular coordinates 21 (F.N.M.12).After nearly two months, namely in April 1923, Fermi completed a secondwork that he considered important. Following the rules he had given to himself,22 he published it on the Physikalische Zeitschrift: Proof that a normalmechanical system is usually quasi-ergodish 23 (F.N.M.11a).As Segrè stated in the F.N.M. introduction: “[...] Prof. Ehrenfest, who haddelved deeply into the foundations of statistical mechanics, was impressed bythe paper. He gave to Uhlenbeck, who was going to Rome for a while, a letterfor Fermi with a number of questions and in this way Uhlenbeck metFermi for the first time in the fall of 1924 [sic]”. Actually things went differently,as the meeting between the two physicists took place one yearbefore, namely in the autumn of 1923. 24 It’s worth noting that Ehrenfestwas struck by this article which he later quoted in an analytic mechanics articlearrived at the Zeitschrift für Physik on 2 October 1923. 25The third work published by Fermi at Göttingen is: Some theorems of analyticalmechanics that are important for quantum theory 26 (F.N.M.13) anddates back to April 1923. The same date of the previous article. 27On 16 April 1923 Fermi wrote to Persico: “I’m working hard on a borderwork among celestial mechanics, statistical mechanics and quantum theory.But I can’t foresee where I’ll be driven at”. 28 In addition, on the 21 st of April21 Il principio delle adiabatiche ed i sistemi che non ammettono coordinate angolari, Nuovo Cimento, 25(1923), 171-175.22 Fermi, well aware of the Italian scientific isolation, published his most important works on foreignreviews, cmp. SEGRÈ (1970), p. 35.23 Beweis, dass ein mechanisches normalsystem im allgemeinen quasi-ergodisch ist, Physikalische Zeitschrift,24 (1923), 261-265.24 The spreading of the error, that involved Segrè and others, presumably originated with the book byFermi’s wife; cmp. L. Fermi (1954). In the fall of 1924 Fermi was in Leyden, Holland. After all,Uhlenbeck refers that: “[...] in 1923 I also met and became good friends with Enrico Fermi”, cmp.UHLENBECK (1976), p. 45.25 Cmp. EHRENFEST (1923). It seems that Ehrenfest used with Uhlenbeck the following expression: “[...]‘I’ve seen an article by a young fellow and it looks pretty good; you should look him up”, cmp.GOUDSMIT (1972), p. 83.26 Alcuni teoremi di meccanica analitica importanti per la teoria dei quanti, Nuovo Cimento, 25 (1923),271-285.27 There arose the issue of the time order of the works, cleared up in the fifth note: “[…] the writer hasrecently demonstrated that normal mechanical systems are generally quasi ergodish”, “[...] chi scriveha recentemente dimostrato che i sistemi meccanici normali sono in generale quasi-ergodici”, cmp.F.N.M., p. 93.28 “Io sto molto lavorando ad un lavoro di confine fra la meccanica celeste, la meccanica statistica e la teoriaquantistica. Ma non posso ancora prevedere dove andrò a sbattere”, cmp. stamped postcard toPersico of 16.04.1923. A photostat is conserved by AMAL. ARCH. (1E bis /n.c.).77

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEhe specified to his friend: “[…] I have three rather important publicationsready […]”. 29Rome (September 1923-August 1924)In September 1923 Fermi came back home from Germany. On his arrivalhe found a country grieved by fascist violence. It was more then ever necessaryfor Fermi to find a job. With Corbino’s help, he was assigned with teachingmathematics to chemistry students for the academical year 1923-24 inRome. 30In the autumn of 1923 Fermi met Uhlenbeck and, as already mentioned,the latter was deeply impressed by Fermi’s disappointment about his stay inGöttingen. 31 On 29 October 1923 the board of examiners assigned the fellowshipto Fermi for the second consecutive year. 32 However, since Fermihad already taken advantage of one fellowship: “[…] it would not be possible,as laid down in article 157 of the current university regulations, to assignit to him a second time”. 33 In spite of this the board of examiners, onaccount of “[…] the exceptional value of dr. Fermi” 34 in a departure fromregulations, expressed itself favourably on a second fellowship assignment. Asa matter of fact, Fermi remained in Italy until September 1924, when hewent to Leyden on a fellowship grant by the Rockefeller foundation.29 Cmp. SEGRÈ (1970), p. 204. Probably the work Fermi refers to in the letter of the 16 th it’s inclusiveof those mentioned in the letter of the 21 st of April.30 Cmp. SEGRÈ (1970), p. 34.31 Perhaps it’s worth noting that Uhlenbeck’s recollections could have been distorted, and perhaps ‘projected’on Fermi, by the identity crisis the Dutch physicist was going through. In fact, when in Rome,he was devoting himself to a career of professional historian: “[...] still, even his [Fermi’s] influence didnot turn my back to physics. I suppose I went through what nowadays is called an identity crisis.Anyway, when I came back in June 1925, I thought that my real interest was in the study of culturalhistory, and that perhaps I should forget about physics”, cmp. UHLENBECK (1976), p. 45.32 As in the previous year, Fermi in 1923-24, competed both for a scholarship abroad and for an internalone. The board of examiners stated: “Mighty and fertile is the activity of this young candidate ofabsolutely exceptional value and the Committee expresses the vow that to him will be given the possibilityto widen the field of his knowledge in the interest of the Italian science. […] The Committeetherefore, declares Fermi Enrico winner of the scholarship abroad”, “Poderosa e feconda è l’attività diquesto giovane concorrente di valore assolutamente eccezionale e la Commissione formula il voto chea lui sia dato modo di allargare sempre più il campo delle sue conoscenze nell’interesse della scienzaitaliana. […] La Commissione pertanto dichiara vincitore dell’assegno di perfezionamento all’estero ildott. Fermi Enrico”, cmp. “Bollettino Ufficiale, Atti di Amministrazione”, Ministero della PubblicaIstruzione, 27 March (1924), year 51, no.13, pp. 714-719.33“[…] non sarà possibile, a norma dell’articolo 157 del vigente regolamento generale universitario,assegnargliela una seconda volta”34 “[…] valore eccezionale del dott. Fermi”.78

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)Fermi’s didactical activity did not affect his scientific production. In fact, inDecember 1923 - January 1924 he prepared three very important works(F.N.M.16, F.N.M. 19 and F.N.M.17a). Two (F.N.M. 16 e 19) are fundamentalto understand the evolution towards the new quantum statistics andwill be considered later. The third can be defined his first article on quantum 35and was presented on 16 December 1923 by Corbino at the Lincei, as a shortessay titled: On the probability of quantum states. 36 In this work Fermi dealsoriginally with a delicate quantum problem that later attracted major attention.37 The work, that Fermi considered quite important, appeared also in aGerman version on the Zeitschrift für Physik (F.N.M.17b) 38 and was quotedby Planck in June 1924. 39 The German version has a ‘post quem’ limit,defined in February 1924; 40 in this version Fermi thanks Born for his adviceconcerning an imprecision in the previous Italian version. This is indirect evidenceof a corrispondence between Born and Fermi, immediately after hisreturn from Germany. In the Amaldi archive is kept the typewritten versionthat Fermi sent to the editor of the Zeitschrift für Physik. Above the title anote says: “Corrections to Mr. Prof. Dr. M. Born, Göttingen, Planckstrasse21”. 41 A few months later Fermi made use 42 of the results obtained to dealwith some astrophysical topics that M. N. Saha had proposed in 1921.In the summer of 1924 the political situation in Italy was very similar tothat of summer 1922. The Matteotti murder on 10 June 1924 shaked thefascist regime, saved by the indifference of the Italian democratic forces.Thanks to an unpublished letter 43 it’s possible to infer that Fermi, alreadybefore the summer vacations of 1924 he spent at Moena on the Dolomites,started to draw up what was later called the ‘virtual quantum method’. 44 This35 The work on Richardson’s statistical theory still constituted after all a classical attempt to study thephotoelectric effect. That was a problem more simply and effectively tackled with the introduction oflight quanta as Einstein did in 1905, even if the scientific community refused such an innovativeapproach.36 Sulla probabilità degli stati quantici, Rendiconti Lincei, 32 (1923), 493-495.37 In BRILLOUIN (1930), find an in-depth comparison of different treatments on the subject.38 Über die Wahrscheinlichkeit der Quantenzustände, Zeitschrift für Physik, 26 (1924), 54-56.39Cmp. PLANCK (1924).40 That’s a consequence of the fact that in F.N.M.20 (of February 1924), Fermi still uses the results hefound in F.N.M.17a and not those, slightly different, he reached in F.N.M.17b.41 “Korrektur an Hrrn. Prof. Dr. M. Born, Göttingen, Planckstrasse 21”, cmp. AMAL. ARCH. (446/n.c.).That is a proof of Born’s direct interest in Fermi. Note the odd coincidence of street names!42 Cmp. Nuovo Cimento, 1 (1924), 153-158.43Letter to Persico dated Varese 19.VIII.’24, cmp. AMAL. ARCH. (1E bis /n.c.).44 It’s important to note that there are many other denominations for the virtual quantum method: collisiontheory, impact theory, equivalent photon method, Weizsäcker-Williams’ method.79

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEarticle appeared on the Zeitschrift für Physik as: On the collision theorybetween atoms and electrical charged particles 45 (F.N.M.23b). This work canbe considered as one of the most significant Fermi’s contributions before thediscovery of quantum statistics. It is based on a simple, efficient idea that usesanalogy as a scientific method: utilize consolidated results in a specific area ofphysics to solve an apparently distant problem. 46Leyden (September 1924-December 1924)From September to December 1924, Fermi stayed at Leyden on anotherfellowship grant by the International Education Board, founded by J. D.Rockefeller. V. Volterra, with the precious help of H. A. Lorentz and W. Rose(President of the Foundation), did his best for Fermi’s stay in Holland. Intwo letters, Rose showed his interest for Fermi’s case. 47From the correspondence with Persico it’s possible to reconstruct Fermi’sjourney, 48 arriving at Leyden, by sea, on 12 September 1924. This secondperiod of study abroad was, as for human relations, much more congenial toFermi. This is evident from a letter dated 27 October 1924 to his sisterMaria. 49 In Leyden Fermi made acquaintance, besides Ehrenfest, Einstein,Keesom, Lorentz, with some young physicists as G. Dicke, S. Goudsmit, R. deL. Kronig, J. Tinbergen.45 Über die Theorie des Stosses zwischen Atomen und elektrisch geladenen Teilchen, Zeitschrift für Physik, 29(1924), 315-327. An Italian version appeared also on the Nuovo Cimento (F.N.M.23a): Sulla teoriadell’urto tra atomi e corpuscoli elettrici, Nuovo Cimento, 2 (1925), 143-158.46 The application of this method, here called ‘analogy method’, will be the keystone for the formulationof Fermi’s quantum statistic.47 Cmp. VOLT. ARCH. (20/518). It results that Fermi was given a $350 check for a period of threemonths at Leyden. Initially Fermi should stay six months (this reduction of period was a rule exceptfor the foundation). We are grateful to M. De Maria for this information.48 Cmp. SEGRÈ (1970), pp. 205, 206. The correspondence recently emerged shows how Fermi, on 26August 1924, was still in Moena on the Dolomites. Persico sent him the passport he needed for theNetherlands.49 “Leyden 27.10.1924.[…] I always feel good and, amongst big and small, I make a discovery everytwenty days on the average […] everybody holds me in deep respect […] Einstein left the past weekmaking me enthusiastic sympathy declarations […] Among my new acquaintances: prof. Ehrenfest is avery nice person, even though he wouldn’t look too bad in a second-hand clothing shop in the ghetto;he takes very good care of the school and his pupils, and he has a special quality to get hold of thosefrom whom one can expect good results for the future. I then met naturally many youngs […]”,“Leyden 27.10.1924.[…] mi trovo sempre bene e, tra grandi e piccole, faccio in media una scopertaogni venti giorni […] tutti hanno un profondo rispetto di me […]. Einstein è partito la settimana scorsa,facendomi entusiastiche dichiarazioni di simpatia […] Tra i miei nuovi conoscenti: il prof. Ehrenfestè una persona molto simpatica, benché non sfigurerebbe affatto in un negozio di abiti usati in ghetto;si occupa moltissimo della scuola e dei suoi studenti, ed ha una speciale abilità nel saper pescare fin daiprimi anni quelli dai quali si possono sperare dei buoni risultati per l’avvenire. Ho conosciuto poi naturalmentemolti giovani […]”, cmp. E. VINASSA DE REGNY (1992).80

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)Ehrenfest, together with Lorentz, was the most important person inLeyden and much of his time was devoted to teaching and forming his youngpupils (he was really a talent-scout). 50In Leyden Fermi became part of an ‘horizontal’ vision of the teacher-studentrelation. On the contrary, Göttingen’s was structured more ‘vertically’.During the Dutch period (unlike the German), Fermi made many new“discoveries” without yet completing one single article. There were manytopics to write about, but writing an article would have needed a time thatFermi, at Leyden, preferred to employ otherwise.In conclusion it can be said that the major advantage obtained by Fermiduring the three months spent at Leyden, wasn’t just the widening of histechnical knowledge, but mainly the opportunity to collaborate with otherphysicists. Ehrenfest in fact, as good a teacher as he was, understood verywell the psychological frustration of a pupil facing too hazy physical issues. 51On the contrary Born, at Göttingen, did not worry over such issues. AsDavid Cassidy states, he had a totally different attitude: “[...] the shy andretiring theorist, plagued by hypochondria [...] the bashful Born seemedoverwhelmed by the numbers of students flocking to Göttingen”. 52 In a letterto Einstein dated 30 April 1922, Born writes: “[…] it’s just about to startthe wretched semester, true ‘perturbation’ of meditative work”. 53Ehrenfest was instead very happy to work with students. He was a greatteacher, thanks to his great knowledge of physics and his extremely collaborativeand open attitude. Such a milieu was ideal for Fermi, very pleased towork with people more akin to his scientific style, less mathematical andmore physical, like Ehrenfest. Naturally Ehrenfest soon noticed Fermi’s tal-50 Some hand-written drafts of Ehrenfest, dating spring 1926 or 1927 following the visit of an English-American group of students, read (note Fermi’s name among the “leading students”): “[...] for notbeing a Dutchman I can freely express my great admiration for Dutch science and Dutch scientists [...]you get the chance of > 1/Million to get the Nobel-Prize in your life-time if you only arrange to beborn as a Dutchman (Density for Leiden !) [...] Leading students (Fermi, Breit, Kronig, Gibbson) [...]small numbers, atmosphere of play (Einstein !!!) [...] not hasty, steadiness, perseverance, enormousquiet, pressing energy, big reserves of times for exigency [...] an organism not a machinery, just as sciencein Holland”, cmp. A.H.Q.P. (60/...).51 In a beautiful letter of January 1924, Ehrenfest talked about the young Americans he had met inAmerica: “[...] The young [here in America] is terribly sound – hygiene, sport, school education as easyas winking until 23 years old, so that not even a soul is tickled by the devil”, “[...] Die Jugend istbeängstigend gesund - Hygiene, Sport, strand-einfacher Schuldrill bis 23 sorgt, dass keine Seele vomTeufel gekitzelt wird”, cmp. A.H.Q.P. (60/2).52Cmp. CASSIDY (1992), p. 138. Quotation reported as in BELLONI (1994), notes 39-40.53 “[...] sta per ricominciare il benedetto semestre, vera ‘perturbazione’ del lavoro contemplativo”, cmp.BORN (1973 2 ), p. 83.81

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEent and there is evidence that they analyzed together Frenkel’s work on electroconductionin metals. 54 Moreover, it would be interesting to verify ifFermi found out about the Bose-Einstein statistics through Ehrenfest or, atany rate, during his stay in Holland. 55Florence (January 1925-December 1925)In December 1924 Fermi, just back from Leyden, went to Florence as lecturerof theoretical mechanics and electromagnetism with an annual appointment.56 Conscientiously, he had started to prepare the lectures and thecourse two months before in Leyden. The Florence Physics Institute waslocated in Arcetri, and was directed by the physicist and Senator A. Garbasso,also Florence’s mayor. Rasetti had also been there since November 1922. 57In December 1924, in Florence, Fermi completed two works. One had beenstarted at Leyden in the previous October. However, it can be said that boththese works and some others that followed, were carried out mostly to increasethe number of his publications for university teaching qualifications (obtainedon 2 March 1925). Among them we remember an experimental work conductedtogether with his friend Rasetti, from January 1925 to May 1925.Thanks to Rasetti, in fact, Fermi got to know some works by Wood, Ellet,and Hanle 58 concerning the weak effects of magnetic fields on the polarisationof mercury resonance radiation. From Fermi-Kronig’s correspondencein the A.H.Q.P., it’s possible to reconstruct the evolution of Fermi’s interest(initially a bit different). The influence of a work by Bohr on the same subjectis also evident. 59 It’s important to observe that this work representedFermi’s second attempt in experimental physics after several years of theo-54Cmp. EHRENFEST-JOFFÉ (1990), letter no. 77 on 24 November 1924: “Here when we inspectedFrenkel’s work on metals electroconduction [Zeitschrift für Physik, 24 (1924), 214-240] I convincedmyself, even more than before, that in this work there are many ingenious ideas but also an enormousconfusion. There are not only heavenly ways but also earthly ones. Perhaps me and E. Fermi (Professorin Florence, now here), that appraised the sharpness of this work, we’ll find the right way and put astop to the enormous confusion”. We are grateful to R. Pisegna and to T. Jakobson for the translationfrom Russian.55The second paragraph of EHRENFEST’S (1925) contains his first note on the Bose-Einstein statistics.56 Cmp. SEGRÈ (1970), p. 37.57Rasetti remembers that, in this period: “[...] we were very close. We practically lived together”, cmp.A.H.Q.P. transcript of a tape recorded interview by T.S. Kuhn with F. Rasetti and E. Persico, 8 April1963, p. 12.58Cmp. F.N.M. for bibliographical indications.59Fermi-Kronig’s correspondence is contained in A.H.Q.P. (16/4).82

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)retical work. The first experimental contribution dated back to 1922 and wasa part of the thesis on Image formation with Röntgen rays. The idea to use aradiofrequency field to conduct experimental research on atomic spectra wasforerunner of a number of subsequent applications. It is probably for thisidea that this contribution is to be appreciated.The physicists Fermi came into contact with at Leyden exerted a positiveinfluence on him. He kept in touch with the Dutch scientific environmentalso after his return to Italy, and Kronig can be considered to all intents andpurposes as the link, during 1925, between Fermi and the other Europeanphysicists.Kronig and Fermi met at Leyden and after Fermi’s return to Italy there wasa considerable exchange of letters between the two young physicists, less frequentafter 1926. Travelling a lot and meeting many people, Kronig updatedFermi on what was going on in Berlin, Copenhagen, Göttingen, Leydenand Munich. Furthermore, Kronig spent with Fermi the August 1925 summervacations in S. Vito di Cadore 60 . Probably that was the occasion forFermi to discuss for the first time the new-born quantum mechanics. It’simportant to observe that Heisenberg, on 5 June 1925 (about two monthsbefore his famous article), wrote Kronig a letter where the non-commutativemultiplication rule first appeared. 61 Also Pauli, in that period, kept in closetouch with Kronig.Fermi’s quantum statisticsAs it is known, Fermi or Fermi-Dirac statistics is the second quantum statisticsproposed shortly after Bose-Einstein’s in 1924-1925. Dirac recalls: “Iworked out the basic relations for this new statistics, and I published thiswork. Soon after publication I got a letter from Fermi pointing out that thisstatistics was not really a new one; he had proposed it some time earlier [...]When I looked through Fermi’s paper, I remembered that I had seen it previously,but I had completely forgotten it [...] At the time that I read Fermi’spaper, I did not see how it could be important for any of the basic problemsof quantum theory; it was so much a detached piece of work. It had com-60Amaldi witnessed the meeting with Kronig: “Fermi was very young; he was 23 or 24 years old. A friendof his had come to the same place. That was R. de L. Kronig. [...] Kronig was a great friend of Fermi.They met when Fermi had been in the Netherlands to work with Ehrenfest. [...]”, cmp. A.H.Q.P. transcriptof a tape recorded interview by C. Weiner with E. Amaldi, 9 and 10 April 1969, p. 1.61 Cmp. VAN DER WAERDEN (1967) and CASSIDY (1992).83

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEpletely slipped out of my mind, and when I wrote up my work on the antisymmetricalwave functions, I had no recollection of it at all”. 62The two physicists arrived independently to the formulation of their quantumstatistics, following very different approaches that, although both basedon classical physics, differed greatly from 63 the drastic positions of Göttingenand Copenhagen schools. Dirac’s work 64 was presented to the Royal Societyon 26 August 1926. That was more than six months after the Italian versionby Fermi (F.N.M.30) 65 and more than three months after the more detailedGerman version (F.N.M.31). 66In Fermi’s case, two other previous contributions anticipated the conclusivearticle of 1926. The first one is a memoir presented to the Lincei inDecember 1923: On Stern’s theory of absolute entropy constant of a perfectmonatomic gas (F.N.M.16). 67 The second significant contribution is an articleFermi wrote in January 1924, later published on the Nuovo Cimento:Considerations on the quantization of systems containing identical elements(F.N.M.19). 68Therefore, both the mentioned precursory works (on thermodynamical-62 Cmp. DIRAC (1977), p. 133. The short Fermi’s letter, somewhat angry, to which Dirac refers is datedRome 25 October 1926 and is fully reported here: “Mr. P.A.M. Dirac, St. John’s College, Cambridge.Dear Sir! In your interesting [sic] paper “On the theory of Quantum Mechanics” (Proc. Roy. Soc. 112,661, 1926) you have put forward a theory of the Ideal Gas based on Pauli’s exclusion Principle. Now atheory of the ideal gas that is practically identical to yours was published by me at the beginning of 1926(Zs. f. Phys, 36, p. 902; Lincei Rend. February 1926). Since I suppose that you have not seen my paper,I beg to attract your attention on it. I am, Sir, Yours Truly Enrico Fermi”, cmp. A.H.Q.P. (59/2).63 About Dirac: “he struggled to construct the new QM as a generalization of (and not as a break with)classical physics, through a systematic utilisation of the classical Hamiltonian formalism”, cmp. DEMARIA, LA TEANA (1983), p. 596. In a letter to Persico of 23 September 1925, he says of Fermi: “Myimpression is that during the past few months there has not been much progress, in spite of the formalresults on the zoology of spectroscopic terms achieved by Heisenberg. For my taste, they havebegun to exaggerate their tendency to give up understanding things”, cmp. SEGRÈ (1970), p. 209.Dirac remembers his own impressions of the period: “I was so impressed then with the Hamiltonianformalism as the basis of atomic physics, that I thought anything not connected with it would not bemuch good. I thought there was not much in it [Heisenberg’s paper] and I put it aside for a week orso”, reported by MEHRA in SALAM, WIGNER (1972), p. 31.64 Cmp. DIRAC (1926). Previously Dirac, in an article that was not published, showed interest for the newdevelopments of the Bose-Einstein new quantum statistics, cmp. MEHRA, RECHENBERG (1982), p. 109.65 This first formulation was presented (as a memoir) by Garbasso to Lincei on 7 February 1926: On thequantization of the monatomic perfect gas, (F.N.M.30), cmp. Rend. Lincei, 3 (1926), 145-149.66 This version, larger than the previous, appeared on 11 May 1926 on the Zeitschrift für Physik(F.N.M.31), cmp. Zeitschrift für Physik, 36 (1926), 902-912. Later on, unless different indications,one will always refer to this work.67Sopra la teoria di Stern della costante assoluta dell’entropia di un gas perfetto monoatomico, RendicontiLincei, 32 (II) (1923), 395-398.68 Considerazioni sulla quantizzazione dei sistemi che contengono degli elementi identici, Nuovo Cimento,1 (1924), 145-152.84

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)statistical topics), can be set in the Italian ‘intermezzo’ of Fermi, between theGerman and Dutch period.The ‘Leitmotiv’ that ideally links these three works (F.N.M.16, 19, 31) isthe Sackur and Tetrode formula for the entropy absolute constant of an idealmonatomic gas:5⎡2 mS0 = R+Rln⎛ π⎢ ⎞22 ⎢⎝h ⎠⎣This result, obtained thanks to many scientists’ efforts at the beginning ofthe century 69 , represented for Fermi a guide on the way towards the discoveryof his quantum statistics. 70In his article of 1923 (F.N.M.16), Fermi seems to be already favourablyimpressed by Stern’s derivation 71 of the entropy constant. This interest continuedalso afterwards. 72 It is natural to wonder how Fermi became interestedin Stern’s method and, more generally, in entropy constant.One possible hypothesis is tightly connected with the Göttingen stay. InAugust 1923 Born published a very long article (nearly 250 pages) on theproperties of solids: Atomic theory of the solid state (dynamics of the crystal lattices).73 In chapter 35, Born defined Stern’s method. He followed almost52k52⎤⎥⎥⎦69 For an excellent storiographical reconstruction, cmp. DESALVO (1992).70 Actually, Dirac’s approach was based solely on the study of symmetry properties of a wave function ina system of many particles in the new ondulatory mechanics. It can be said, in fact, that Fermi’s workis the last important thermodynamical statistical work written in the language of old quantum physics,whereas Dirac’s is the first important statistical result obtained by new quantum mechanics.71 Cmp. STERN (1913) and Stern (1919). Although Stern arrived at the same formula of Sackur andTetrode, he adopted a very different method. In 1913 he had the brilliant idea to carry out the calculustwice to find the equilibrium pressure of vapour, between solid and vapour phases. The calculus wascarried out by Stern first thermodynamically and then with a kinetic model. With the thermodynamicalcalculus, extrapolating the high temperature limit, Stern obtained an expression containing theentropy constant S 0 for the pressure of vapour. As for kinetic calculus, it was valid only at high temperatures,and vapour pressure was obtainable without undeterminated constants. Comparing the twoexpressions, Stern was then able to determinate the value of S 0 , reaching exactly the formula Sackurand Tetrode had found the previous year. In 1919 Stern returned on the subject, accepting part ofTETRODE’s method (1915).72 In fact a rich paragraph of his 1934 book Molecole e Cristalli, is dedicated to this subject, cmp. FERMI(1966) a , par. 8-2. He dealt with this subject also in the 1951-52 Notes on Thermodynamics andStatistics, cmp. FERMI (1966) b , par. 49.73Cmp. BORN (1923), pp. 701-709. For more information see CORDELLA, SEBASTIANI (1999) d ,(2000) a,b . For what concerns Sackur and Tetrode’s works, in his article Born writes (almost exactly asStern did in 1919) rather pessimistically: “[..] In this derivation there is a lot of arbitrariety, especiallyfor the introduction of atoms number N”, “[...] Bei dieser Ableitung bleibt vieles willkürlich, vor allemdie Einführung der Atomzahl N”. Born is much more enthusiastic of Stern’s method: “[...] Through85

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEexactly Stern’s 1919 second formulation. Significantly, Born completed thiswork just when Fermi was in Göttingen. 74 Born used to have his own workchecked by collaborators who liked finding mistakes or making suggestions.In 1921 E. Brody 75 was especially concerned with entropy constant. He wasof great help to Born in preparing the review on solids. 76 As showed in theprevious paragraph, in Germany Fermi was busy with analytical dynamicsuntil April 1923. From this time on, there is no trace of Fermi’s scientificinterest. However, in F.N.M.19 Fermi made a clear reference to Brody’swork of 1921. Moreover, in Göttingen in the same period, Enskog andNordheim were working at the additivity entropy problem. 77 So it is quitelikely that Fermi found, in the last four months in Göttingen, the right environmentto deal with this subject.F.N.M.16 was presented by Corbino to the Lincei on 2 December 1923.It is a short work of 3 pages and as many paragraphs. In the first two, Fermirefers briefly to the works of SACKUR (1913) TETRODE (1912) and STERN(1913), (1919). Fermi shows appreciation for Stern’s method and assertsthat the necessity to quantize the phase space of gas, as stated by Sackur andTetrode, appeared to him unnecessary. 78Stern’s deduction, on the basis of Nernst’s theorem, it is possible to define the only value of the chemicalconstant, that is the entropy constant of the gas, referred to the condensed phase at the absolutezero”, “[...] Bei der sicherlich einwandfreien Ableitung von Stern kommt auch dem Einzelwerte derchemischen Konstanten auf Grund des Nernstschen Theorems ein Sinn zu, nämlich als dieEntropiekonstante des Gases, bezogen auf das Kondensat beim absolutem Nullpunkt”.74 From Born’s letters to Einstein, reported in BORN (1973 2 ), one can understand the effort that Borndevoted to this work.75 Brody was an Hungarian physicists facing serious economic difficulties. The main reason is that, forthose living on a fixed salary, as Brody, the inflation of the paper-mark was extremely heavy. Moreover,at that time it was not easy to carve out a career for an Hungarian Jewish in Germany. Cmp. BORN(1973 2 ), p. 81.76 In the introduction Born writes: “[…] The more valuable help was given to me by prof. E. Brody; notonly he contributed to gather the literature and elaborating some parts, but also provided, mainlythrough his sharp remarks, to clarify many relations and developing new methods. I’d like to thank himbefore everybody. Also some of my students helped me with the elaboration of texts and with corrections,especially Mr. P. Jordan, whom I thank for his many valuable comments, and Mr. K. Hermann,G. Heckmann and H. Kornfeld”, “[…] Die wertvollste Hilfe bei der Arbeit fand ich durch Herrn Prof.E. Brody; er hat nicht nur zur Sammlung der Literatur beigetragen und manche Abschnitte ausgearbeitet,sondern vor allem durch scharf sinnige Bemerkungen die Klärung vieler Zusammenhänge herbeigeführtund neue Methoden entwickelt. Ihm gebührt an erster Stelle mein Dank. Auch einige meinerSchüler haben mir bei der Ausarbeitung des Textes und dem Lesen der Korrekturen in freundlicherWeise geholfen, vor allem Herr P. Jordan, dem ich viele wertvolle winke verdanke, und die HerrenK. Hermann, G. Heckmann und H. Kornfeld”, cmp. BORN (1923), pp. V and VI.77 Cmp. DESALVO (1992), p. 512.78 “[...] That, despite the experimental testing[of Sackur-Tetrode’s formula], this method seemed to beunsatisfactory, it’s demonstrated by the many theoretical works produced, aiming at finding a betterdemonstration. Of all these attempts, Stern’s is the best […] His method has the advantage of making86

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)Fermi then devoted himself to eliminate the null point energy hypothesisfrom previous treatments, as Born in 1923 and Stern did in 1919: “in thiswork I intend to demonstrate that this unnatural hypothesis is by no meansnecessary […]”. 79As stated above, in 1921 Brody was concerned with the entropy constant.Since his approach was carefully studied by Fermi, the next paragraph willoutline the main features of Brody’s article.Brody’s article of 1921Brody’s article of 1921: On the theoretical determination of the chemicalconstant of a monatomic gas, 80 was very important for its influence on Fermiand its concise and elegant solution to the problem of the entropy constant.As stated by Desalvo: “Brody’s treatment became a standard, at least formost of the people accepting the quantization of translational motion. It representsthe closest approach to the correct results in terms of the old quantumtheory”. 81 The work is divided into two sections: a first quantistic half(Quantentheoretischer Teil) and a second statistics half (Statistischer Teil).In the quantistic part, Brody takes into consideration a punctiform particleof mass m in a cubic box of side l with perfect reflecting walls. He refers toa system of Cartesian coordinates parallel to the sides of the box. The particleis free, supposing the gas perfect, so that its velocity components have aconstant modulus. The quantum conditions for the particle periodic motionsinside the box are:∫∫pdx = mvdx = 2mv dx = 2mv l= nh ( i=x, y, z).i i i i i i0l∫iinone of the arbitrary hypotheses on the gas that other authors need, such as gas quantization of whichthe reason is not clear”, “[…] Che nonostante la verifica sperimentale [della formula di Sackur-Tetrode] questo modo di dedurla non sia apparso a molti soddisfacente, è dimostrato dal gran numerodi lavori teorici, che furono fatti in seguito, con lo scopo di trovarne una dimostrazione migliore. Ditutti questi tentativi, quello che senza dubbio ha meglio raggiunto il suo scopo è quello di Stern [...]Il suo metodo ha il vantaggio di non fare sopra il gas perfetto nessuna di quelle poco legittime ipotesi,che sono necessarie agli altri Autori, come per esempio quella di una quantizzazione del gas stesso,della quale non si vede chiaramente la ragione”, excerpts from F.N.M.16.79 “[...] in questo lavoro mi propongo di dimostrare che questa ipotesi innaturale non è affatto necessaria[…]”.80 Cmp. BRODY (1921). In note eight of this article, Brody refers that this work appeared in Hungarianas a degree thesis in 1917. The purpose of the work was to eliminate a discrepancy in a previous workof Scherrer dated 1916.81 Cmp. DESALVO (1992), p. 506.87

PROCEEDINGS OF THE INTERNATIONAL CONFERENCETherefore, the kinetic energy of the particle is:21 2 2 2 h 2 2 2E= m( vx + vy + vz) = ( nx + ny + n2z)2 8mlthat agrees with the value that would be obtained by the solution ofSchrödinger’s equation for a particle in an infinite potential well.In the statistics part, Brody suggests a substantially new reasoning. First ofall he defines energy and volume as physical quantities describing the macroscopicstate of the system. For the microscopic state (and that’s the mainassumption) instead of the coordinates and moments of the N particles, hetakes into consideration the quantum numbers n ji (where j = 1, ..., N and i= x, y, z). In order to calculate the thermodynamic probability W, to beinserted in the Boltzmann’s formula S = k⋅lnW, one has to determine in howmany different ways it’s possible to choose the n ji microscopic states correspondingto a given macroscopic system determined by E and l = V 1/3 .Since energy can only take discontinuous values, there can be several otherpossible systems of values for n ji . That is:2h 2 2 2 2 2 2E ≤ ( nx+ ny+ nz+ + nNx + nNy + nNz≤ E+dE2 1 1 1... ) .8mlThe search for numbers of n ji satisfying this inequality is conducted byBrody assuming the 3N values of nji as the Cartesian coordinates of a pointin a 3N-dimensional space. To calculate W, Brody introduces, without manyjustifications, a further division by N! so as not to consider the two microscopicstates different, but distinguished only by a permutation of atoms. 82Finally Brody obtains, as macroscopic state probability:W =1 dVNN!dE3N2 3where dV 3N denotes the 3N-dimensional spherical shell whose radius are limitedby the energy constraint. As Fermi stated in the article of January 1924(F.N.M.19), to obtain W, Brody: “[…] is forced to put [...] dE = 1, being E82This procedure, needed to justify the entropy additivity and avoid Gibbs’ paradox, caused an animateddiscussion among Planck, Ehrenfest and Schrödinger. In particular Ehrenfest and Trkal, in theirwell-known article of 1920, stated: “In the majority of calculations of the chemical constant, a specialobscurity remains as to the way in which the “thermodynamic probability” of a gas depends on thenumber of molecules”, cmp. EHRENFEST and TRKAL (1920). The German version of the articleappeared in 1921.88

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)an energy, so that the probability is substantially defined as the number of gasquantum states […] reducing to an energy between E and E+1. In this wayhis probability has the dimensions, instead that of a number, of the inverseof an energy”. 83 This remark significantly shows how Fermi had carefullystudied this work.Searching for a lacking principleAs already mentioned, in January 1924 Fermi wrote another thermodynamical-statisticalarticle, later published on the Nuovo Cimento(F.N.M.19). A little more than a month after the memoir on his improvementof Stern’s method.In the introduction, Fermi recalls that Sommerfeld’s quantization ruleseffectively described the hydrogen atom. On the other hand, they wereunsuitable for the description of atoms with many electrons. To justify theneed of modifying the quantum rules, for a system containing identical elements,Fermi suggested a simple example. He considered a ring with threeelectrons placed at the vertex of an equilateral triangle. 84Subsequently Fermi considered the perfect gas as a separate system of variablesand intended to apply the quantization rules: “[…] making varioushypotheses on the way to quantize it (to obtain a finite value for the entropyof an ideal gas it’s necessary to quantize it one way or another, since the classicaltreatment would always lead us to an infinite value)”. 85So let’s consider, following Fermi, a perfect gas formed by N punctiformmolecules contained in a vessel of volume V. It’s possible to divide the volumeV in many parallelepipedal rectangular cells, each one of sides a, b, c, and vol-83 “[...] è però costretto a porre [...] dE = 1, essendo E una energia, con che la probabilità viene in sostanzaa essere da lui definita come il numero degli stati quantici del gas [...] che conducono ad una energiacompresa tra E ed E + 1, di modo che la sua probabilità viene ad avere le dimensioni, anziché diun numero, dell’inverso di un’energia”84 Considering the electrons as distinguishable, it’s clear that one has to rotate the ring by a 2π angle tore-obtain the initial situation. If the electrons were instead indistinguishable it would be necessary torotate the ring only by 2π/3. Therefore, denoting with p the angular momentum of the ring, in thefirst case Sommerfeld’s quantization rules give (2π)p = nh, while in the second case (2π)p =3nh. Thiskind of argumentations on the indistinguishability concept were inspired to Fermi by two works ofCompton and Breit, both quoted in F.N.M.19, cmp. A.H. COMPTON (1923) and G. BREIT (1923).85 “[...] facendo diverse ipotesi sopra il modo di quantizzarlo (per ottenere un valore finito dell’entropiadi un gas perfetto è necessario quantizzarlo in un modo o nell’altro, poiché la trattazione classica cicondurrebbe sempre ad un valore infinito)” It’s therefore evident that Fermi changed opinion. InF.N.M.16 he still considered an unsuitable hypothesis: “[...] that of a quantization of the gas of whichthe reason is not clear”.89

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEume V C = a⋅b⋅c. Fermi assumed that inside every cell there would be the samenumber of molecules. Therefore, there were many possibilities, because we canimagine the volume V as constituted by: N equal cells with 1 molecule, N/2equal cells with 2 molecules, ...,1 cell with N molecules. Hence, one has N/xcells with x = N⋅V C /V molecules in every cell. Assuming, as Brody did, theCartesian coordinates parallel to the sides of the cell, the system is clearly a separatevariables system. In this way, referring to Brody’s results, one arrives tothe following expression for the total entropy of the N molecules (we havegeneralised Fermi’s procedure):3 5⎡2 2m k eS = kN⎧5⎨ lnT − lnP + ⎢ 2ln ( π )⎩2⎢3h⎣⎢where V is supposed to be divided in N/x equal cells, each containing x molecules.So far, Fermi’s considerations are quite similar to Brody’s. But now,following the latter, it would be necessary to consider a single cell that containsN molecules, that is x = N. Then, introducing the very arguable divisionby N! from the previous expression, it’s easy to find exactly the Sackur-Tetrode formula. Yet Fermi doesn’t follow this procedure and suggests anew, more subtle reasoning. As a matter of fact, the previous formula wasderived assuming a particular distribution of molecules into the cells. Let P rbe the probability of this choice, Fermi asserts that the real entropy of the gasS r is obtainable taking into consideration a further addend –k⋅ln P r . Thisassumption, that Fermi doesn’t try to justify thoroughly, has actually theimportance of a new thermodynamic definition of probability, namely S =k⋅ln(W/P r ). In so doing, one would obtain:3 5⎡2 2m k eSr= kN⎧5⎨ lnT − lnP + ln⎢( 2π)⎩2⎢3h⎣⎢⎤⎥ + ln(!)x⎥⎦⎥Therefore, it’s evident that the agreement with the Sackur-Tetrode’s formulais reached only with x = 1. In conclusion, following Fermi’s reasoning,the experimental testing of the Sackur-Tetrode formula requires the following.The vessel must be divided into equal N cells of volume V/N, each containingonly one molecule, as it was supposed by Sackur in 1913. Of course,the ‘ad hoc’ character of this hypothesis is evident, but all other ways are tobe excluded in the light of experimental facts. In his 1926 article on quantumstatistics (where F.N.M.19 is quoted) Fermi would assert: “[…] you5252⎤x⋅ ⎥e ⎥⎦⎥1x90

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)obtain a degeneracy of an expected order of magnitude only if you pick a vesselof so small dimensions that it generally contains only one molecule”. 86Further on in the 1924 article, Fermi points out that the discrepanciesbetween S and S r , arise precisely from the identity of two or more moleculescontained in a single cell. In the case of missing identity (for example if manyparticles in a single cell are of different species), Fermi shows how S wouldprovide, in this case, a correct result for the entropy.Pursuing this line of thought, Pauli’s exclusion principle can be reached ina roundabout way. Applying Fermi’s analogy method, we can identify, forexample, the helium atom with a cell into which two electrons are disposed.In that case, the previous topics suggest that there must be lack of a principleaffirming that it’s impossible to find both the electrons with the same quantumnumbers. 87 This “organizing” principle is obviously Pauli’s exclusionprinciple, but not in Pauli’s originally formulation. In fact, following Fermi,thanks to what we called here the analogy method, this result can be extendedto a lot of situations (collection of quantum harmonic oscillators, etc.).Rasetti recalls that: “[Fermi] told much later to Segrè that the division ofphase space into finite cells had occupied him very much and that had notPauli discovered the exclusion principle he might have arrived at it in aroundabout way from the entropy constant”. 88“Ante/post-quem” limits of Fermi’s statisticsFermi’s article on new quantum statistics 89 was presented by Garbasso tothe Lincei, in a condensed form, on 7 February 1926 (F.N.M.30), a littlemore than two years after F.N.M.19. On 26 March 1926, the Zeitschrift fürPhysik received a more detailed version of the article, then published on theGerman review on 11 May 1926 (F.N.M.31). 90The ‘ante quem’ limit of Fermi’s quantum statistics may therefore be set atthe beginning of February 1926.86“[…] si ottiene una degenerazione di un atteso ordine di grandezza solo se si sceglie il recipiente didimensioni così piccole che esso in media contenga soltanto una molecola”.87“Helium was only understood after quantum mechanical methods could be brought to bear, includingimportant applications of spin and of the exclusion principle”, cmp. PAIS (1986), p. 215.88 Cmp. Rasetti’s introduction to F.N.M.30 and 31.89For more information, cmp. CORDELLA, SEBASTIANI (1999) f e (2000) c .90Cmp. Rasetti’s introduction to F.N.M.30 and 31. Otherwise AMALDI (1983), p. 253. From an immediateanalysis of the Italian version of the article it’s evident that Fermi had already reached all theimportant results of his new statistics.91

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi was very busy finding a post as a teacher (in February 1926 he participatedunsuccessfully to an examination for a mathematical physics teachingpost in Cagliari) 91 . Fermi’s letter to Uhlenbeck and Goudsmit, dated 25February 1926, stood between the two versions of the article:“Since I came away from Holland, I was unfortunately always very busy sothat I couldn’t work very much and I was forced to be satisfied with thereadings of reviews. Recently I have prepared two works, one on the quantizationof an ideal gas, the other on the apparition of the forbidden transitionsin a magnetic field; I’ll send you the abstracts as soon as I get them.” 92As for the more important ‘post quem’ limit, Segrè states that Fermi, a fewweeks after reading Pauli’s work on the exclusion principle, was able to presentat the Lincei, through Corbino, 93 an Italian version of the article. 94However that may be, it is still in doubt when Fermi was acquainted withPauli’s article. This one appeared in the February-April 1925 number of theZeitschrift für Physik, 95 so that Fermi could have known it at least since thespring of 1925. However, as showed in the previous chapter, during thespring of 1925 Fermi was busy carrying out experimental work with Rasetti.In July, Fermi was engaged with state examinations in Florence. Fermi spentthe summer with Kronig and others in S. Vito di Cadore. That may beimportant because, as asserted by A. Pais, Kronig had been aware of theexclusion principle at least since January 1925. 96 Therefore a likely hypothesisis that Kronig talked to Fermi about it during the summer vacations inS.Vito. Anyway, in the various sources regarding Fermi before F.N.M.30,there is no trace of Pauli’s principle, while Fermi was puzzled by the articlesof Heisenberg, Born and Jordan on the new quantum mechanics. 9791 Cmp. F.N.M., p. XXVII and SEGRÈ (1970), p. 40.92 Cmp. A.H.Q.P. (60/6). “In der ganzen Zeit seit Ich von Holland weg kam, war ich leider immer sehrbeschäftig, so dass ich habe sehr wenig Arbeiten können und habe mich hauptsächlich mit dem Lesender Zeitschriften begnügen müssen. Ich habe neulich zwei Arbeiten gemacht, die eine über dieQuantelung idealer Gase die andere über das auftreten verbotene Übergänge in einem Magnetsfelde;ich werde Euch die Separata schicken, sobald ich sie bekomme” The second work to which Fermi refersis F.N.M.32: Sopra l’intensità delle righe proibite nei campi magnetici intensi, Rendiconti Lincei, 3 (1926),478-483. In the letter Fermi congratulates them for the discovery of the spin.93 In the Rend. Acc. Lincei, Garbasso is mentioned as the member who presented Fermi’s article.94 Cmp. SEGRÈ (1970), p. 42.95 Cmp. PAULI (1925).96 Cmp. PAIS (1986), p. 280.97 The T. S. Kuhn’s interview to Persico and Rasetti reads: “[...] TSK: Did Fermi say anything that youremember about the matrix mechanics papers? R: Oh, Fermi tried to read them, but he could notunderstand them. He said, ‘I cannot do any. I don’t see how I can use it, how I can do any calculationwith these. I don’t understand what’s behind it.’ Oh, he read them and he was very much puzzled by92

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)Rasetti remembers an event (also recalled by Laura Fermi) occurred whenFermi was making his gas statistics: “We were practically together frommorning till evening, from discussing physics to hunting for certain geckos,a sort of lizard […]. That was precisely when he was making the gas statistics.He was probably thinking while lying down and catching the geckoswith the noose”. 98 In Central Italy, at the end of September geckos usuallyhibernate. 99Therefore, the ‘post quem’ limit of Fermi’s statistics, less precisely of the‘ante quem’ limit, is roughly set in mid- September 1925.ABBREVIATIONSA.H.Q.P. (x/y) = “Archive for History of Quantum Physics”, microfilm x, section y.AMAL. ARCH. (x/y) = “Amaldi Archive”, Department of Physics, University “La Sapienza”,Rome, box x, folder y.PERS. ARCH. (x/y) = “Persico Archive”, Department of Physics, University “La Sapienza”,Rome, box x, folder y.VOLT. ARCH. (x/y) = “Volterra Archive”, Accademia Nazionale dei Lincei, Rome, box x, folder y.F.N.M.k = FERMI (1962-1965), vol. I., the kth work.REFERENCESE. AMALDI (1983), The Fermi-Dirac statistics and the statistics of nuclei, in Symmetries inPhysics (1600-1980), by M.G. DONCEL, A. HERMANN, L. MICHEL, A. PAIS, Universitatautònoma de Barcelona, Seminari d’historia de les ciències.L. BELLONI (1994), On Fermi’s route to Fermi-Dirac statistics, European Journal of Physics,15, 102-109.M. BORN (1923), Atomtheorie des festen Zustandes (Dynamik der Kristallgitter), in Encykl. d.math. Wiss., vol. V, Leipzig: Teubner.M. BORN (1973 2 ), Scienza e vita, Lettere 1916-1955, Torino: Einaudi (Italian edition).M. BORN (1978), My Life, London: Taylor and Francis.G. BREIT, (1923), Note on the Width of Spectral Lines Due to Collisions and Quantum Theory,Proceedings Natural Academy of Sciences, vol. 9, no.11, 244-245.them. P: I don’t remember that I ever discussed them with Fermi. R: I know that he showed me thesepapers and said, ‘Now I’m trying to read them and see what Heisenberg is trying to say, but so far Idon’t understand it.’”, cmp. A.H.Q.P. transcript of a tape recorded interview by T. S. Kuhn (TSK)with F. Rasetti (R) and E. Persico (P), 8 April 1963, p. 16.98Cmp. A.H.Q.P. transcript of a tape recorded interview by T. S. Kuhn with F. Rasetti and E. Persico, 8April 1963, p. 13.99 M. Di Domenico, collaborator of the Zoology Department of the Istituto dell’Enciclopedia Italiana,private communication.93

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEL. BRILLOUIN (1930), Les statistiques quantiques, Paris: Les Presses Universitaires de France.E. BRODY (1921), Zur theoretischen Bestimmung der chemischen Konstante einatomiger Gase,Zeitschrift für Physik, 6, 79-83.D.C. CASSIDY (1992), Uncertainity. The Life and Science of Werner Heisenberg, New York:Freeman.A.H. COMPTON (1923), The Quantum Integral and Diffraction by a Crystal, Proceedings ofthe Natural Academy of Sciences, vol. 9, no. 11, 359-362.F. CORDELLA, F. SEBASTIANI (1999) a , Il debutto di Enrico Fermi come fisico teorico: i primilavori sulla relatività (1921-1922/23), Quaderno di Storia della Fisica del Giornale di Fisica,5, 69-88.F. CORDELLA, F. SEBASTIANI (1999) b , Fermi a Gottinga e a Leida: gli anni che precedono la statisticaquantica (1922-1925), Dipartimento di fisica, Università degli Studi di Roma “LaSapienza”, Internal note, no.1104; Quaderno di Storia della Fisica del Giornale di Fisica, 6(2000), 17-45.F. CORDELLA, F. SEBASTIANI (1999) c , La corrispondenza Persico-Fermi (1922-1926), Giornaledi Fisica, 40, 143-164.F. CORDELLA, F. SEBASTIANI (1999) d , La genesi della statistica di Fermi, Dipartimento diFisica, Università degli Studi di Roma “La Sapienza”, Internal note, no. 1106.F. CORDELLA, F. SEBASTIANI (1999) e , La corrispondenza inedita Fermi-Persico (1917-1938),Dipartimento di Fisica, Università degli Studi di Roma “La Sapienza”, Internal note, no.1107.F. CORDELLA, F. SEBASTIANI (1999) f , La statistica di Fermi, Dipartimento di Fisica, Universitàdegli Studi di Roma “La Sapienza”, Internal note, no. 1110.F. CORDELLA, F. SEBASTIANI (2000) a , I due lavori di Fermi che preludono alla statistica quantica,Giornale di Fisica, 41, 83-101.F. CORDELLA, F. SEBASTIANI (2000) b , Sul percorso di Fermi verso la statistica quantica, IlNuovo saggiatore, 16, no. 1-2, 11-22.F. CORDELLA, F. SEBASTIANI (2000) c , La statistica di Fermi, Giornale di Fisica 41 (2000), 131-156.M. DE MARIA, F. LA TEANA (1983), Dirac’s ‘Unorthodox’ Contribution to Orthodox QuantumMechanics (1925-1927), Scientia, 77, vol. 118, 595-611.M. DE MARIA (1999), Fermi: un fisico da via Panisperna all’America, I grandi della Scienza,no. 8.A. DESALVO (1992), From the chemical constant to quantum statistics: a thermodynamic routeto quantum mechanics, Physis, 29, 465-537.P.A.M. DIRAC (1926), On the Theory of Quantum Mechanics, Proceedings of the RoyalSociety, A112, 661-667.P.A.M. DIRAC (1977), Recollections of an Exciting Era, in History of Twentieth Century Physics(Proceedings of the Internal School of Physics “Enrico Fermi”, course LVII, Varenna 31 July-12 August 1972) by C. WEINER, New York: Academic Press, 109-146.P. EHRENFEST, V. TRKAL (1920), Deduction of the Dissociation-Equilibrium from the Theory ofQuanta and a Calculation of the Chemical Constant Based on this, Proceedings Amsterdam,23, 162-183.94

Fabio Sebastiani, Francesco Cordella FERMI TOWARD QUANTUM STATISTICS (1923-1925)P. EHRENFEST (1923), Kann die Bewegung eines Systems von s Freiheitsgraden mehr als (2s-1)-fach-periodisch sein?, Zeitschrift für Physik, 19, 242-245.P. EHRENFEST (1925), Energieschwankungen im Strahlungsfeld oder Kristallgitter beiSuperposition quantisierter Eigenschwingungen, Zeitschrift für Physik, 34, 362-373.EHRENFEST-JOFFÉ (1990), Nauchnaia perepiska, 1907-1933, by N. MOSKOVCHENKO, V. FRENKEL,Leningrad: Nauka.E. FERMI (1962-1965), Note e Memorie (Collected Papers), by E. AMALDI et al., 2 voll., Roma:Accademia Nazionale dei Lincei, Chicago: University of Chicago Press.E. FERMI (1966)a, Molecules, Crystals, and Quantum Statistics, New York: W.A. Benjamin(English version).E. FERMI (1966)b, Notes on Thermodynamics and Statistics, Chicago: University of ChicagoPress.L. FERMI (1954), Atoms in the Family, Chicago: University of Chicago Press.S.A. GOUDSMIT (1972), Guess Work: The Discovery of the Electron Spin, Delta, summer, 77-91.S.A. GOUDSMIT (1976), It might as well be spin, Physics Today, June, 40-43.H.S. KRAGH (1990), Dirac: a scientific biography, Cambridge: Cambridge University Press.J. MEHRA, H. RECHENBERG (1982), The Historical Development of Quantum Theory, vol. 4,New York: Springer.A. PAIS (1986), Inward Bound, New York: Oxford University Press.W. PAULI (1925), Über den Zusammenhang des Abschlusses der Elektronengruppen im Atom mitder Komplexstruktur der Spektren, Zeitschrift für Physik, 31, 765-783.W. PAULI (1979), Wissenschaftlicher Briefwechsel mit Bohr, Einstein, Heisenberg, u. a. 1919-1929, by A. HERMANN, K. V. MEYENN, V.F. WEISSKOPF, New York: Springer.M. PLANCK (1924), Zur Quantenstatistik des Bohrschen Atommodells, Annalen der Physik, 75,673-684.B. PONTECORVO (1993), Enrico Fermi. Ricordi di allievi e amici, Pordenone: Studio Tesi(Italian edition).O. SACKUR (1913), Die Universelle Bedeutung des sogenannten elementaren Wirkungsquantums,Annalen der Physik, 40, 67-86.A. SALAM, E.P. WIGNER (by) (1972), Aspects of quantum theory, Cambridge: CambridgeUniversity Press.C. SASSI, F. SEBASTIANI (1999), La formazione scientifica di Enrico Fermi, Giornale di Fisica,2, vol. XL, 89-113.E. SEGRÈ (1970), Enrico Fermi Physicist, Chicago: University of Chicago Press.O. STERN (1913), Zur kinetischen Theorie des Dampfdrucks einatomiger fester Stoffe und überdie Entropiekonstante einatomiger Gase, Physikalische Zeitschrift, 14, 629-632.O. STERN (1919), Zusammenfassender Bericht über die Molekulartheorie des Dampfdruckes festerStoffe und ihre Bedeutung für die Berechnung chemischer Konstanten, Zeitschrift fürElektrochemie, 25, 66-80.G. TAGLIAFERRI (1985), Storia della fisica quantistica. Dalle origini alla meccanica ondulatoria,Milano: Franco Angeli.95

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEH. TETRODE (1912)a, Die chemische Konstante der Gase und das elementare Wirkungsquantum,Annalen der Physik, 38, 434-442.H. TETRODE (1912)b , Berichtigung, Annalen der Physik, 39, 255-256.H. TETRODE (1915), Theoretical Determination of the Entropy Constant of Gases and Liquids,Proceedings Amsterdam, 15, 1167-1183.G.E. UHLENBECK (1976), Personal reminiscences, Physics Today, June, 43-48.B.L. VAN DER WAERDEN (1967), Sources of Quantum Mechanics, Amsterdam: North-HollandPublishing Company.E. VINASSA DE REGNY (by) (1992), Una scoperta ogni venti giorni..., Linea d’Ombra, 76, 38-39.Fabio SebastianiFabio Sebastiani is Professor of History of Physics and Director of the Museumof Physics at the University “La Sapienza” of Rome. Within the programs ofthe National Institute for Nuclear Physics, he carried out activities in experimentalphysics of elementary particles at the National Laboratories of Frascatiand the CERN of Geneva. Subsequently he dedicated himself to historicalresearches on the genesis and development of heat theories in the 1700’sand 1800’s. He has carried out historical researches on the Italian period ofEnrico Fermi for several years.Francesco CordellaFrancesco Cordella is a history of physics graduate (with Fabio Sebastiani).His degree thesis “The first theoretical researches of Enrico Fermi (1921-1926)” was awarded with the 1998 prize of the National Academy ofSciences (known as that of the XL). Now he’s working as Analyst Programmerwith a software house of Rome.96

Jan Philip SolovejThe Evolution of Fermi’s Statistical Theory of AtomsIn this talk I shall give a historical review of Fermi’s statistical theory of atomswith emphasis on rigorous work. The theory has had a great impact on physicsand chemistry, but has long been considered far too simplistic to be of anypractical interest. From a rigourous theoretical point of view however the theoryhas had some very important applications. I will discuss these briefly, but alsoargue that even from a practical point of view it may not be quite fair to deemthe theory as “too simplistic”.L’evoluzione della teoria statistica degli atomi di FermiDelineerò un profilo storico della teoria statistica degli atomi di Fermi conparticolare attenzione all’approccio rigoroso.Tale teoria ha avuto considerevoli ripercussioni sulla fisica e la chimica, ma èstata a lungo considerata troppo semplicistica per farne discendere un qualcheinteresse pratico. Tuttavia, da un punto di vista strettamente teorico, ha avutoalcune importanti applicazioni. Prenderò sinteticamente in esame alcune diqueste, ribadendo però che, da un punto di vista strettamente pratico, ladefinizione di “teoria semplicistica” non le rende giustizia.97

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIt is a great honor to be able to give a presentation at this meeting celebratingthe centennial of the Birth of Enrico Fermi. My talk is about thestatistical model for atoms. Versions of this model were published independentlyby Fermi and Thomas in the two papers [5,22]. The model is thereforeoften referred to as the Thomas-Fermi model.I will not talk about the early history of this model, but rather discuss someof the more recent developments.It may be surprising to find a mathematician talking about the statisticaltheory of atoms, but the Thomas-Fermi theory has, in fact, been a greatsource of inspiration to mathematicians since the early 70s.The virtue of the Thomas-Fermi theory is its great simplicity in comparisonto the full many-body quantum mechanical description of atoms or molecules.In fact, the model is so simple that Fermi was able to numerically calculatethe atomic solution to the model on the crude hand calculators available inthe late 1920s. The model can also be applied to molecules, but in that caseit is more dificult to calculate solutions.Today the theory is however often considered to be too crude to be of anyreal computational interest in Chemistry or Physics. With the advent of bigcomputers one can today do calculations on much more refined models.It should be pointed out however that one of the methods used with greatsuccess today in computational quantum chemistry is what is called densityfunctional theory. The Thomas-Fermi theory is in fact the simplest imaginabledensity functional theory. The use of more elaborate such theories goesback to the works of Kohn and Hohenberg in the early 60s and for whichKohn received the Nobel prize in 1998 [9].It is however not always the case that one can use computers to get usefulanswers. There are cases where the problem is simply too complicated to calculateeven with a computer and there are cases where one would like a more qualitativeunderstanding than what one gets from a long computer calculation.An example of a problem which is too complicated for a computer is thebinding energy of a macroscopic piece of material consisting of more than10 23 particles. As I shall explain it turns out that the Thomas-Fermi theoryis very useful here. In fact it was discovered in 1976 by Lieb and Thirring[14] that one can explain the stability of ordinary matter using the theory ofThomas and Fermi. Stability here refers to the fact that matter does not collapsein an implosion caused by electrostatic forces.In fact it was realized already in 1930 by Chandrasekhar [1] that a modelsimilar to the Thomas-Fermi model could explain why certain cold stars98

Jan Philip SolovejTHE EVOLUTION OF FERMI’S STATISTICAL THEORY OF ATOMSknown as white dwarfs did not collapse under the influence of gravity. Anexample where one would like a qualitative understanding is the question ofthe size of heavy atoms. The fact that atoms have the particular size that theydo and in particular the fact that the radii of atoms varies at most by a factor3-4 over the periodic table is the result of a delicate balance between the electrostaticforces and Fermi pressure. The size of everything around usdepends on this delicate balance. It is therefore important to be able to givea simple qualitative explanation of this balance. As we shall see it can be providedby the Thomas-Fermi model.The Thomas-Fermi modelThe Thomas-Fermi model gives a description of the atomic density ρ. Onthe one hand, knowing the atomic density of an atom with nuclear charge Zallows one to calculate the mean field potentialϕ( x) = Zex − 1− eρ( y)x−y dy . (1)On the other hand the mean field potential allows one to calculate the densityof the corresponding Fermi gas below some Fermi level µwhere γ = (3π 2 )2/3 h -2 (2m) -1 . Here [t]+ = max{t,0}. The two equations (1)and (2) define in a self-consistent way the density in the statistical model.For a molecule with K atoms of nuclear charges Z 1 , … Z K , the mean fieldpotential is insteadAlternatively the statistical model may be formulated from a variationalprinciple. The equations (1) and (2) are the Euler-Lagrange equations forthe Thomas-Fermi energy minimization (µ is the Lagrange multiplier for theconstraint ∫ ρ = N):E TF ( N) = inf {ε ( ρ): ∫ ρ = N,ρ ≥ 0, }(3)where−3−ρ( x) = 22 ( πh) d p = γ eφ ( x)−µK∑∫ϕ( x) = Z e x − R − d yeρ( y) x − y .k −11φ ( ) µm p 2− x

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEHereK2ZejVxx R U ZZei j( ) = ∑ , = ∑−R − Rj = 1j 1≤≤ i j≤Kij. (5)The nuclear repulsion U has been added to get the correct energy.Mathematical results and Stability of MatterThe first to study the Thomas-Fermi theory from a mathematical point ofview was E. Hille [6,7] more than 40 years after the original papers. A completeanalysis establishing existence and uniqueness of the solution also in themolecular case was first given by Lieb and Simon in [13].One of the most important facts realized about the Thomas-Fermi modelis that the energy defined in (3) (with small modifications, which I shallexplain below) gives a lower value (more negative) than the true quantumenergy.This is a consequence of a kinetic energy bound proved by Lieb andThirring in [14] and a bound on the indirect Coulomb energy proved in[10] and improved in [12]. These two estimates imply that if H N;K is theHamiltonian for N electrons and K nuclei and ψ is a fermionic wave functionfor N electrons with corresponding density ρ ψ then the energy expectationin the state ψ, i.e., (ψ, H N,K ψ) satisfies the bound( ψH NK ,ψ) ≥ε γ( ρψ) −168 .2 ∫ ρ4 3~ψ(6)Here ε _ γrefers to the energy defined as in (4), but with a different value forthe constant γ. This is what one has been able to prove, but, in fact, it wasconjectured in [15] that one does not have to change γ, i.e., that (6) holdswith ε defined exactly as in (4). Establishing this fact is from a mathematicalpoint of view one of the most challenging questions concerning the Thomas-Fermi theory and there is extensive literature on the subject.A correction to the Thomas-Fermi theory corresponding to the last termin (6) was suggested by Dirac in [2] and is known as the Dirac exchange correction.Another very important fact about the Thomas-Fermi theory is Teller’sNo-binding Theorem. It states that in the Thomas-Fermi theory atoms donot bind to form molecules. Or more precisely the Thomas-Fermi energy ofa molecule is greater than the sum of the Thomas-Fermi energies of the individualatoms.100

Jan Philip SolovejTHE EVOLUTION OF FERMI’S STATISTICAL THEORY OF ATOMSThis fact was originally realized by Teller [21] and proved rigorously byLieb and Simon [13].Lieb and Thirring [14] used the No-binding Theorem together with (6)[or rather a somewhat similar result, since (6) was only proved subsequently]to give a very simple and extremely elegant proof of the result known asStability of Matter. This result originally due to Dyson and Lenard [3] statesthat the binding energy per particle has to remain bounded even as the numberof particles become arbitrarily large (e.g. of order 10 23 ).Validity of the Thomas-Fermi model as an approximationOne may ask how well the Thomas-Fermi energy E TF (N = Z), which infact scales like C TF Z 7/3 , approximates the real ground state energy E Q =E Q (N = Z) of a neutral atom of nuclear charge Z.The answer is that the real ground state energy satisfies an asymptoticexpansion of the formEQ473 meC Z Z2=TF+ + CDirac Schwinger Z5 3+2o Z5 3/( )2has Z→∞.That the Thomas-Fermi model gives the leading term of order Z 7/3 wasestablished by Lieb and Simon [13]. The next to leading term of order Z 2was predicted by Scott [17] and proved mathematically by Hughes [8] andSiedentop-Weikard [18]. One contribution to the order Z 5/3 comes from theDirac exchange term mentioned above. That there was another contributionto the same order was realized by Schwinger [16]. The mathematical proofwas given by Fefferman and Seco [4].The energy asymptotics can be traced to different regions in a heavy atom.In an atom with large nuclear charge Z the bulk of the electrons live a distancefrom the nucleus that scales like Z -1/3 , i.e., for atoms with larger andlarger Z the bulk of the electrons live closer and closer to the nucleus.These electrons contribute to the leading term Z 7/3 to the energy. TheScott term Z 2 comes from the innermost electrons living on a scale Z -1 . InFigure 1 we show the order of the density on the different scales of the atom.It is however the outermost electrons that are of importance to chemistry.From the point of view of an approximation to the total binding energy theThomas-Fermi theory is too crude to say anything about energies on thechemical scale.101

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEO(z 3 )ρ(x)W ↓O(z 2 )Chemical RadiusFigure 1A picture of a heavyatomz –1 z –1/3 1O(1)lxlIn [20] a mathematical result was proved that indicates that the Thomas-Fermi model is in fact not such a bad approximation to the density even atthe chemical radius. The precise statement is beyond the scope of this presentation.To stress the point I shall instead show what I find to be a convincingcomparison of the Thomas-Fermi theory with experimental data.The radius of an atom is not a clearly defined quantity and is certainly notdirectly measurable. In the paper [19] Slater pointed out, however, that one250TF-RADIUS R, GROUP 1200R/pm150100Figure 2Comparison ofThomas-Fermi radius Rwith the Slater atomicradii in group 1500 10 20 30 40 50Z102

Jan Philip SolovejTHE EVOLUTION OF FERMI’S STATISTICAL THEORY OF ATOMSmay assign to most atoms a radius such that the bond length between anytwo of these atoms as found in crystals is to very high accuracy equal to thesum of their radii.In the Thomas-Fermi theory it is also not clear how to define a radius. Forthe elements in the first group in the periodic table (H, Li, Na, K, Rb, Cs,and Fr) one possibility is to say that the radius is where we find the last(valence) electron. Mathematically this amounts to defining the radius Rsuch that ∫ |x|>R d 3 xρ(x) = 1. Figure 2 shows the comparison of R defined asabove calculated in the Thomas-Fermi theory (the solid curve) comparedwith the data given by Slater (the circled points).REFERENCES01. CHANDRASEKHAR S., Phil. Mag. 11, 592 (1931); Astrphys. J. 74, 81 (1931); MonthlyNotices Roy. Astron. Soc. 91, 456 (1931).02. DIRAC P.A.M., Note on exchange phenomena in the Thomas-Fermi atom, Proc. CambridgePhilos. Soc. 26, 376{385 (1930).03. DYSON F.J., LENARD A., Stability of Matter I and II, J. Math. Phys. 8, 423-434 (1967);ibid 9, 698-711 (1968).04. FEFFERMAN C., SECO L.A., On the Dirac and Schwinger corrections to the ground-state energyof an atom, Adv. Math. 107 No. 1, 1-185 (1994).05. FERMI E., Un metodo statistico per la determinazione di alcune proprietà dell’atomo, Rend.Accad. Naz. Lincei 6, 602{607 (1927).06. HILLE E., On the Thomas-Fermi equation, Proc. Natl. Acad. Sci. USA 62, 7-10 (1969).07. HILLE E., Some aspects of the Thomas-Fermi equation, J. Anal. Math. 23, 147{170 (1970).08. HUGHES W., An atomic energy lower bound that gives Scott’s correction, Adv. Math. 79,213-270 (1990).09. KOHN W., Nobel Lecture: Electronic structure of matter-wave functions and density functionals,Rev. Mod. Phys. 71 No. 5, 1253-1266 (1999).10. LIEB E.H., A lower bound for Coulomb energies, Phys. Lett. A 70, 444-446 (1979).11. LIEB E.H., Thomas-Fermi and related theories, Rev. Mod. Physics 53 No. 4, 603-642(1981).12. LIEB E.H., OXFORD S., An improved lower bound on the indirect Coulomb energy, Int. Jour.Quantum Chem. 19, 429-439 (1981).13. LIEB E.H., SIMON B., The Thomas-Fermi theory of atoms, molecules and solids, Adv. Math.23, No. 1, 22-116 (1977).14. LIEB E.H., THIRRING W., Bound for the kinetic energy of fermions which prove the stabilityof matter, Phys. Rev. Lett. 35, 687-689 (1975); Errata 35, 1116 (1975).15. LIEB E.H., THIRRING W., A bound for the moments of the eigenvalues of the SchrödingerHamiltonian and their relation to Sobolev inequalities, in Studies in Mathematical Physics:Essays in honor of Valentine Bargmann, edited by E.H. Lieb, B. Simon, and A.S.Wightman (Princeton University Press, Princeton), 269-303 (1976).103

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE16. SCHWINGER J., Thomas-Fermi model: The second correction, Phys rev A 24, 2353-2361(1981).17. SCOTT J.M.C., The binding energy of the Thomas-Fermi atom, Philos. Mag. series 43, 859-867 (1952).18. SIEDENTOP H., WEIKARD R., On the leading energy correction for the statistical model of theatom: interacting case, Comm. Math. Phys. 112 No. 3, 471-490 (1987); “Upper boundon the ground state energy of atoms that proves Scott’s conjecture”, Phys. Lett. A 120No. 7, 341-342 (1987).19. SLATER J.C., Atomic radii in crystals, Jour. Chem. Phys. 41 No. 10, 3199-3204 (1964).20. SOLOVEJ J.P., Proof of the ionization conjecture in a reduced Hartree-Fock model,Inventiones Math. 104, 291-311 (1991); The ionization conjecture in Hartree-Fock theory,Preprint 2001.21. TELLER E., On the Stability of molecules in the Thomas-Fermi theory, Rev. Mod. Phys. 34,627-631 (1962).22. THOMAS L.H., The calculation of atomic fields, Proc. Camb. Phil. Soc. 23, 542-548(1927).Jan Philip SolovejBorn: June 14, 1961, Copenhagen, Denmark; Education: Cand. Scient.(Masters), University of Copenhagen, 1985; Ph.D., Princeton University,1989. Employment:1989-90: Visiting Assistant Professor, Dept. of Math.,University of Michigan; 1990 (Fall): Post-doctoral fellow, Dept. of Math.,University of Toronto; 1991 (Spring): Member, School of Math., Institute forAdvanced Study; 1991-1995: Assistant Professor, Dept. of Math., PrincetonUniversity; 1995-1997: Research Professor (Forskningsprofessor), Dept. ofMath., Aarhus University; 1997-present: Professor, Dept. of Math., Universityof Copenhagen.104

Jeff HughesNuclear Physics at the Cavendish Laboratoryin the ThirtiesErnest Rutherford became Professor of Experimental Physics at the CavendishLaboratory, Cambridge, in 1919. He brought with him a programme ofresearch into radioactivity and the nature of the atom. Contrary to the “sealingwax and string” stories which surround the Cavendish, Rutherford worked withmany colleagues and students using sophisticated instrumentation and theories inhis quest to map the structure of the nucleus. However his programme faceduncertainty inside the lab and controversy from without. This paper exploressome of the hidden history of nuclear physics at the Cavendish and its relationswith other laboratories.La fisica nucleare nel Laboratorio Cavendishnegli anni TrentaErnest Rutherford divenne Professore di fisica sperimentale del LaboratorioCavendish a Cambridge nel 1919. Portò con lui un programma di ricerca sullaradioattività e la natura dell’atomo. Contrario alle storie “stringhe e ceralacca”che circondano il Laboratorio Cavendish, Rutherford collaborò con diversicolleghi e studenti al mappaggio della struttura del nucleo con l’ausilio distrumentazioni e teorie sofisticate. Tuttavia il suo programma dovette affrontareincertezze all’interno del Laboratorio e controversie all’esterno. Il mio interventoverterà su alcuni eventi sconosciuti della storia della fisica nucleare nelLaboratorio Cavendish e dei suoi rapporti con altri laboratori.105

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntroductionIn April 1934, Ernest Rutherford wrote to Enrico Fermi to thank him fora preprint of a paper on artificial radioactivity produced by nuclear bombardment.Having commented on the interest of the the Rome group’sresults, he added with characteristically wry humour: 1I congratulate you on your escape from the sphere of theoretical phyiscs!You seem to have struck a good line to start with. You may be interestedto hear that Professor Dirac is also doing some experiments. This seemsto be a good augury for the future of theoretical physics!Rutherford wrote as the director of the world’s leading centre for experimentalnuclear physics research: the Cavendish Laboratory, Cambridge. Oneof the pioneers both of radioactivity and of investigations into the nature ofthe atomic nucleus, Rutherford was a towering authority in the emergentfield of nuclear physics in the early 1930s. Renowned too for his attitudetowards speculators and theoreticians, one can only imagine the effect of hisletter on Fermi and his colleagues!Rutherford had trained at the Cavendish under J.J. Thomson in the 1890s,and had returned to succeed his teacher as Professor and director of the laboratoryin 1919 after twelve years at Manchester University, where he hadboth discovered and then disintegrated the nucleus. At Cambridge, hedevoted his research to mapping the structure of the nucleus. With a seriesof gifted collaborators and co-workers using a variety of techniques – includingoptical scintillation counters, cloud chambers and the mass-spectrograph– the Cavendish of the 1920s and 1930s charted a path towards an understandingof the nucleus. Dominating the field of nuclear disintegration in the1920s, the Cavendish was the ‘Mecca’ for nuclear studies. A series of spectaculardiscoveries in experimental nuclear physics in Cambridge and elsewherein the early 1930s transformed the field, and after 1932 the Cavendishincreasingly interacted with other laboratories and institutes in an atmosphereof competitive internationalism.By the mid-1930s the Cavendish in nuclear physics was facing serious challengesto its authority, not just from the growth of nuclear physics in Europeand the United States but also within Britain itself. Key members ofRutherford’s staff left for other universities where they, too, would establishnuclear physics in competition with Cambridge. More broadly, nuclear1Rutherford to Fermi, 23 April 1934, quoted in E. SEGRÈ, Enrico Fermi: Physicist (Chicago: Universityof Chicago, 1970) 74-75 on 75.106

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESphysics – which was increasingly machine physics – came under criticismwithin the British physics community as being irrelevant to national economicconcerns and the social responsibility of science. The Cavendish founditself on the defensive. In this paper, I aim to explore some of these aspectsof nuclear physics at Cambridge in the 1930s, both in the national contextof British physics and in the international context of the development ofnuclear physics as a discipline. In so doing, I hope to illuminate some ofwider context in which the work of Fermi and his group took shape.The Cavendish Laboratory in the 1920sLet me begin by outlining some of the 1920s background to the developmentof nuclear physics. When Rutherford arrived at the Cavendish in 1919,he brought with him his new programme of experimental and theoreticalresearch devoted to the elucidation of the structure of the nucleus. In a 1920lecture to the Royal Society Rutherford presented his latest findings, inwhich he pictured the nuclei of a number of the lighter elements as consistingof various arrangements of protons and electrons. He also outlined hismanifesto for future nuclear research, in which systematic nuclear disintegrationexperiments would be used in conjunction with information from F.W.Aston’s mass-spectrograph, C.T.R. Wilson’s cloud chamber and other instrumentsto piece together an understanding of the structure of the nucleus.The key technique in the disintegration experiments was the optical scintillationmethod, in which sub-atomic fragments resulting from the disintegrationof a nucleus strike a zinc sulphide screen causing minute flashes oflight or scintillations. When the experiment was carried out in a darkenedroom, these scintillations could be counted through a microscope, yieldinginformation about what had happened during the experiment. These experimentswere very difficult to carry out, however, being laborious, time-consuming,hard on the eyes of the counters and always susceptible to corruptionby radioactive contamination, lack of skill or loss of concentration by thecounter, or any number of other reasons.Very particular protocols were therefore required to ensure the integrity ofthese experiments and of the information which flowed from them. By strictdisciplining of the experimental process, James Chadwick, Rutherford’sdeputy at the Cavendish, was able to achieve a certain degree of confidencein the results of the scintillation counting experiments and the conclusionsbased on them.107

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEWith resources in short supply in the immediate aftermath of the GreatWar, it had been difficult for laboratories elsewhere to take part in the excitingnew programme of nuclear research. From 1923, however, Rutherfordand his group became involved in an increasingly bitter dispute over theresults of their nuclear disintegration experiments. Hans Pettersson andGerhard Kirsch, two young researchers at the Institut für Radiumforschungin Vienna, began using the scintillation method to repeat the Cambridge disintegrationexperiments. They found that they could effect nuclear disintegrationfar more easily than could researchers in Cambridge. Sharp exchangesin print in Nature, Naturwissenschaften, the Philosophical Magazine, theProceedings of the Physical Society, the Zeitschrift für Physik and elsewhere –nearly 40 papers between 1923 and 1928 – were supplemented by flurries ofprivate correspondence between the two laboratories, in which each sideattempted to point out the shortcomings in the other’s practices and conclusions.All to no avail: by 1927, the controversy had reached an unpleasantstalemate, with each side claiming the legitimacy and superiority of its ownpractices and results. 2A parallel controversy between Charles Ellis of the Cavendish and LiseMeitner in Berlin over the nature of the β-ray spectrum also cast the experimentalfoundations of nuclear science in doubt. 3 Though Ellis and Meitnerultimately came to agree about the facts and their interpretation, movementin the Cambridge-Vienna controversy only came in December 1927 whenChadwick himself visited the Institut für Radiumforschung where he wasable to show that when Cambridge conditions were imposed, the Cambridgeresults held. Ironically, though, one of the consequences of the Cambridge-Vienna controversy – and a third controversy with workers at ColumbiaUniversity, again concerning scintillation counting – was to cast doubt on thereliability of the scintillation method, foundation of much of the previous fifteenyears’ work in nuclear research. Incidentally, it was the Columbia controversywhich led to the introduction of nuclear physics there by GeorgePegram in the early 1930s, and thereby the research school to which Fermiwould migrate in 1938-39. 42 R.H. STUEWER, “Artificial Disintegration and the Cambridge-Vienna Controversy”, in P. ACHINSTEINand O. HANNAWAY (eds.), Observation, Experiment and Hypothesis in Modern Physical Science(Cambridge, Mass. and London: M.I.T. Press, 1985), 239-307.3C. JENSEN, Controversy and Consensus: Nuclear Beta Decay 1911-1934 (Basel: Birkhäuser Verlag, 2000).4 J. HUGHES, “The Radioactivists. Community, Controversy and the Rise of Nuclear Physics”, unpublishedPh.D dissertation, University of Cambridge, 1993, 170-204.108

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESTransforming a discipline: making technology countThe Cavendish emerged from the controversies of the 1920s with itsauthority more or less intact, and encoded in the 1930 volume Radiationsfrom Radioactive Substances by the Cambridge troika of Rutherford,Chadwick and Ellis (this was the book studied by the Rome group as theysought to enter the emerging field of nuclear physics). During the course ofthe Cambridge-Vienna controversy, it had become increasingly clear that anindependent method of carrying out the disintegration experiments wouldbe necessary to escape the regress in which the Cambridge and Vienna workersfound themselves. Two key technical strategies took shape in light of thisrealisation. First, a number of workers in European laboratories – notablyHans Geiger and his students – invested considerable effort in the developmentof electrical counting methods, at least partly to provide a direct alternativeto the disputed scintillation method. Aided by the development ofreliable valves and sophisticated electronic circuits in connection with theburgeoning radio industry, electrical counting methods like the Geiger-Müller counter were quickly accepted in nuclear research. Though the newtechnique had problems of its own at first, it allowed experimenters to countmany more particles than the slow, unreliable scintillation method, openingup new possibilities for experimental work. Used in conjunction with a camera,a cloud chamber and a strong magnetic field, for example, electricalcounters made possible the development of detectors which could photographthe behaviour of cosmic ray particles automatically.Second, experimentalists began to consider new ways of providing the projectilesfor the disintegration experiments. During the 1920s, attempts toexplore the atomic nucleus had been constrained by the kinds of probeswhich could be used: the alpha-particles emitted at fixed energies by naturally-occurringradioactive substances. In the late 1920s, aided by its excellentconnections with the electrical industry (John Cockcroft had come tothe Cavendish from the Manchester electrical engineering firmMetropolitan-Vickers, and retained strong links with them), the CavendishLaboratory led the world in the development of machines to accelerate subatomicparticles for use in atom-smashing experiments. Informed by thefresh insights into the behaviour of radiation and matter provided by the newwave mechanics of Schrödinger, Heisenberg and others, physicists began tosee the nucleus not simply as a conglomeration of particles but as a complexquantum phenomenon. As quantum mechanics acquired a new legitimacy inthe eyes of the experimentalists, the kinds of experiments which could be per-109

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEformed and the ways in which physicists thought about the nucleus bothchanged significantly in the late 1920s.By about 1930, then, these transformations of technique in nuclearresearch were leading to the establishment of a new way of doing physicsbased on big machines, electrical and photographic detectors and wavemechanics. More than that, the new technologies of research were based onwidely distributed skills – the same skills used by thousands of radio hams toconstruct and modify wireless circuits could be used in the physics laboratoryto construct circuitry for an electrical particle counter, for example. Thismeant that many more researchers could enter the field of nuclear research,so that by 1930 not just Cambridge and Vienna but groups in Berlin, Paris,Halle, Rome, Washington, Berkeley and elsewhere were beginning to getinvolved in nuclear work. Though some labs were naturally better equippedthan others, this expansion of the disciplinary field produced a large increasein the amount of research being done, and threw up sometimes surprisingnew results which could act as a focus for further investigations. Out of thiscombination of social and material factors would come the events of 1932and a new disciplinary label: nuclear physics. And it was a conference organisedby the Fermi group in Rome in 1931 – followed by one in London in1934 – which set the seal on this new disciplinary identity.From crisis to coherence: the emergence of nuclear physics 1930-1935One surprising result thrown up in 1930 was the observation by WaltherBothe in Berlin that beryllium, when bombarded with alpha particles frompolonium, produced not the expected disintegration protons but an intenseform of gamma radiation. This observation was followed up by a number ofthe other researchers who had entered the emergent field of nuclear physics,among them Irène and Frédéric Joliot-Curie in Paris. Numerous attempts tomake sense of Bothe’s observation followed, but it was James Chadwick atCambridge who made systematic experiments on the puzzling new radiationusing a cloud chamber and the new electrical counters. In February 1932 heproposed that the radiation in fact consisted of uncharged particles, which hecalled ‘neutrons.’ His suggestion was quickly taken up, not least because somany laboratories now had the equipment to repeat Chadwick’s results.Within days of Chadwick’s suggestion, neutrons were being produced andmanipulated in several laboratories. Yet there was disagreement about whatexactly the neutron was: experimentalists disagreed about its mass, while the-110

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESoreticians debated whether it was a proton-electron combination (asChadwick believed) or a new elementary particle (as subsequent workseemed to show). Crucially, it was the new, widely shared material culture ofnuclear physics which both revealed and sustained the neutron; and converselyit was the neutron which cemented together the new community ofnuclear physicists by providing them with the shared, unifying focus of attentionrequired for a coherent discipline.The new technologies also raised difficulties for physicists, however. Wherethe 1920s had begun with small-scale, table-top experiments, the 1930s sawthe development of ever-larger, ever-more powerful atom-smashing machines.Though Cockcroft and Walton were the first to succeed in using high-speedelectrically accelerated particles to break an atomic nucleus apart, however,engineers and physicists elsewhere – at Berkeley, MIT and Caltech – were alsoworking hard to produce particle accelerators of different designs, sometimeswith the goal of exploring the constitution of the atomic nucleus but sometimesjust for the pleasure of working with cutting-edge, large-scale electricaltechnology. In the early 1930s, these various groups, with their own favoureddesigns, were competing hard with each other to make their machines stableat the very high energies required for nuclear research. They were also competingto reach higher and higher energies, with the prize of enormous scientificcredit likely awarded to the first to succeed.In this context Cavendish physicists very quickly learned the art of ‘spin doctoring’– of working with the media to present the laboratory and its work inthe most favourable light possible. Their chosen vehicle was James Crowther,science correspondent of the Manchester Guardian (and forty years later theofficial centenary historian of the Cavendish). An admirer of the Soviet Union,Crowther was a close friend of the Kapitzas and of left-leaning Cavendishphysicists. Favoured with inside information on the discovery of the neutronfor his press reports in February 1932, Crowther was called in again withinweeks to help propagate the Cavendish line on Cockcroft and Walton’s workon the disintegration of nuclei using artificially accelerated protons. He gleefullytold his editor “I now find I am becoming as if I were the press-agent ofthe Cavendish Laboratory” and sought his advice on “how I can best exploitthis situation”. 5 Crowther’s help came at an opportune time for Cavendishphysicists, for it helped them both to promote themselves and the laboratoryand to stave off criticisms about the arcane and possibly irrelevant nature of5 J.G. Crowther to W.P. Crozier, 9 May 1932, Box 127, J.G. Crowther papers, University of Sussex.111

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtheir work. It also allowed them to control press comment very effectively:Rutherford must have sympathised with Fermi when the latter wrote in 1934that “We have been forced to publish [the] results of a research which is actuallynot yet finished by the fact that the newspapers have published so manyphantastic statements about our work that we found it necessary to state clearlyour point of view”. 6 That, at least, was not a problem in Cambridge.Research at the Cavendish in the 1930sIn the atmosphere of competitive internationalism I have tried to describe,discoveries like that of the neutron, the positron and the deuteron offerednew explanatory and exploratory tools to both experimental physicists andthe burgeoning number of mathematical theorists. Work done in one laboratorywas quickly replicated and pushed forward in others in this new internationalnetwork, and the Cavendish now found itself as one laboratoryamong many, often struggling to keep up with the various lines of development.Nevertheless with its concentration of resources and experience itretained its prestige and its authority. One research student in the early 1930s– Harold Miller – was almost overwhelmed by the thought of having to leavethis charmed scientific life: 7There is no doubt that my time of close connection with nuclear physicshas been the most thrilling since the century began – Recently the newresults come out with galloping speed – The Curie-Joliot inducedradioactivity and their chemical separation of radio-nitrogen is scarcely oldnews yet and now the Cockcroft-Walton and Oliphant firms are producingresults of astounding interest daily. Cockcroft produces radio-nitrogen.Oliphant finds deutons bombarding deutons give an enormous yieldof particles and now today Shire has separated the Lithium isotopes andOliphant in one day has targets of Li 6 and Li 7 under bombardment byprotons and deutons – What a life.The research and postdoctoral students of course played a major role in thelife and work of the laboratory, and felt perhaps more keenly than their seniorsthe constant quest for priority and credit in the spirit of competitiveinternationalism. Miller could also note in his diary in February 1934 that:“Today Haxel sends results on aluminium which duplicate ours and a paper6 Fermi to Rutherford, 15 June 1934, Rutherford papers.7H. Miller diary, 1 March 1934, H. Miller papers, Sheffield University Library.112

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESappears on magnesium with many energy changes recorded. So I felt sad anddecided to have a weekend at home ...”. 8 Similarly, Miller recorded the tensionswithin the laboratory when a senior member of staff took over an investigationfrom two Ph.D. students: “[Alan Nunn] May and Eric [Duncanson]are in throes of despair now waiting for emanation. They’ve tried the newJolio [sic] radioactivity, got an effect from Aluminium and handed over theinvestigation to Ellis, who has taken all the juice, that’s hard luck”. 9 The situationmay not be entirely unfamiliar today.Whatever its internal tensions, the Cavendish remained a significant nodein the international nuclear physics network. A constant flow of visitors andresearchers helped disseminate techniques and ideas between the various laboratories,and the Cavendish maintained its reputation as an internationalspace. According to Miller again: 10Occhialini worked for a few days in our room last week. He’s a funnyman. He carried on discussions with Chadwick walking up and down theroom at a furious rate, eager to talk all the time, Chadwick occasionallytrying to pull his leg but getting his own way quietly. He had a companionwho also seemed rather whimsical – who talked in a high pitched voiceand seemed to be full of boyish enthusiasm whom I found out wasGamov.Out of the mouths of babes, sucklings and Ph.D. students!Underpinning this cosmopolitanism, of course, lay Rutherford’s enormousauthority. President of the Royal Society from 1925 to 1930 and ennobledas Lord Rutherford of Nelson in 1931, he occupied a commanding positionnot just in nuclear physics but in British science. It was entirely appropriate,then, that when the Fermi group sought to publish in English the results oftheir work on nuclear transformations by neutrons, Segrè and Amaldi wentto Cambridge in the summer of 1934 to present the manuscript toRutherford, who in turn communicated it to the Royal Society. When Segrèasked whether speedy publication might be possible (competitive internationalismagain?), Rutherford replied “What do you think I was the Presidentof the Royal Society for?” and laughed “with great glee”! 11Rutherford used his authority most effectively to support the Cavendish.08H. Miller diary, 5 February 1934, Miller papers.09 H. Miller diary, 29 January 1934, Miller papers.10H. Miller diary, 14 January 1934, Miller papers.11 SEGRÈ, Enrico Fermi: Physicist (Chicago: University of Chicago Press, 1970), 77.113

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFor example, he had marshalled a bequest to the Royal Society to fund alarge new laboratory for Kapitza, which was on a markedly new scale. Onevisitor remarked that: “at Professor Kapitza’s laboratory, you [have] to ringto be admitted by a ‘flunkey’ and [are confronted not with men working intheir shirt sleeves, but with Prof. Kapitza seated at a table, like the arch criminalin a detective story, only having to press a button to do a gigantic experiment”.12 Now, in 1934, as it became clear (at least to some) that theCavendish would need to acquire particle accelerators if it was to keepabreast of the field which it had so long dominated, Rutherford again intervened.He initiated an appeal to raise funds for the construction of acceleratorscomparable to those being built in the United States. Wealthy “friendsof science and of Cambridge”, particularly industrialists, would be invited togive generously in support of the work of the Cavendish to enable it to keepup with developments elsewhere. In a stroke of genius, Rutherford askedArthur Eddington, Plumian Professor of Astronomy at CambridgeUniversity, a distinguished Fellow of the Royal Society and author of therecent best-seller The Expanding Universe, to write a brief account of theCavendish and the work being done there. 13Eddington made a special tour of the laboratory in October 1934, and produceda 17-page booklet for circulation to potential benefactors. In it, heinvoked the heritage of the Cavendish, the discoveries of J.J. Thomson andRutherford in the world of the atom, and asked: “As little can we foresee newworlds of thought, what new control of natural forces will be opened to usby those who in years to come carry on the Cavendish tradition in a new andampler home?”. 14 He also re-wrote history: 15A period of about twelve months in 1932-1933 was an annus mirabilisfor experimental physics. For some years previously the centre of advancehad been in theoretical physics while experimental physics ploddedpatiently on. Then in rapid succession came a series of experimentalachievements, not only startling in themselves but presenting immensepossibilities for further advance. The laboratories of the world are nowpressing forward in an orgy of experiment which has left the theoreticalphysicist gasping – though not entirely mute.12 Cavendish Laboratory archives, Cambridge University Library.13 On the Cavendish Appeal, see J. Hughes, “1932: the annus mirabilis of nuclear physics?” PhysicsWorld, 13 (7), July 2000, 43-48.14 A. EDDINGTON, The Cavendish Laboratory (Cambridge: Cambridge University Press, 1934), 3.15A. EDDINGTON, The Cavendish Laboratory, 11.114

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESHere is Eddington inventing what will subsequently become one of thecentral ornaments of the historiography of nuclear physics – the annusmirabilis of 1932. Yet he did it because the Cavendish “calls for support, thatit may continue in the front rank of scientific institutions, enlarging the frontiersof Man’s knowledge, leading his mind into new worlds of thought, andextending his mastery over the forces of nature”. 16Drift at the Cavendish?: the later 1930sAs it turned out, the Cavendish Appeal was successful, resulting in the1936 donation of £250,000 from the motor manufacturer Sir HerbertAustin. This allowed the Cavendish physicists to acquire large electrostaticgenerators, a cyclotron and a new building to house them. Rutherford leftthe planning of the new buildings and machines to younger members of stafflike John Cockcroft and Mark Oliphant. In 1936 Chadwick wrote toRutherford to congratulate him on the Austin coup, archly observing that“begging, like swindling, is only respectable on a big scale”. 17 The award ofthe 1935 Nobel Physics Prize to Chadwick for his neutron work had beengratifying to all in the Cavendish, but already by the time of the awardChadwick had left Cambridge for his own Chair at Liverpool University. Hisdeparture was emblematic of significant change at the Cavendish, for he wasone of a number of senior researchers to leave the laboratory at this time. In1933 the cloud chamber maestro Blackett had left for Birkbeck, London(and went from there to Manchester in 1937); in 1935 Wynn-Williams, theelectronics wizard, went to George Thomson’s department at ImperialCollege, London; in 1936 Ellis left for King’s College, London, andOliphant – by this time Rutherford’s lieutenant and in many ways his surrogateson and heir – left for a Chair at Birmingham University.This efflux of talent – and, more importantly, perhaps, experience – fromthe laboratory had important consequences for the Cavendish. These men ofcourse went on to establish nuclear physics elsewhere in Britain, challengingthe Cavendish’s national domination of the field. At the same time, therewere challenges to the Cavendish from other directions. The growth of newsub-fields in physics – for example solid state physics at Bristol, x-ray crystallographyat Manchester and Leeds, and electron diffraction in London –seemed to offer less esoteric and more industrially relevant lines of research.16 EDDINGTON, The Cavendish Laboratory, 17.17 Chadwick to Rutherford, 4 May 1936, Rutherford papers.115

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIndeed, in the economic context of the mid-1930s Rutherford came underheavy criticism for allowing nuclear physics to dominate at the Cavendish:returning from one high-level meeting of scientific administrators inLondon, he told Oliphant that “they have been at me again, implying that Iam misusing gifted young men in the Cavendish to transform them into scientistschasing useless knowledge”. 18In some ways the charge was unfair, for other kinds of research were beingcarried out at the Cavendish. Rutherford supported the development of a largegroup under Jack Ratcliffe working on wireless and the properties of the ionosphere.Following Kapitza’s detention in the Soviet Union during his summervisit there in 1934 the work of the Mond Laboratory continued underCockcroft, Shoenberg and others. Elsewhere in the Cavendish, Charles Wilsoncontinued his work on thunderstorms, taking him back to the meteorologicalinterests which had originally inspired his invention of the cloud chamber.Geoffrey Taylor continued his researches on fluid dynamics, many of themlinked to the government’s Aeronautical Research Committee and its militaryconcerns. Some of the research students used their wireless skills to help developcommunication systems for the military, and it is telling that in the mid-1930s many Cavendish graduates – even nuclear physics Ph.D.s – were hiredby large electronics companies like EMI and Marconi for their specialist skills.Nevertheless, as the Austin wing took shape and large sums of money weredevoted to what many saw as abstruse technology far removed from the practicalneeds of the nation, the Cavendish was on the defensive. Rutherford himselfseems to have had little appetite for the futuristic new developments: hecommented, perhaps with a tinge of regret, that “At Cambridge, a great hallcontains massive and elaborate machines rising tier on tier”, reminiscent of “aphotograph in the film of H.G. Wells’ ‘The Shape of Things to Come’”. 19 Butas we know, these machines were exactly the shape of things to come.ConclusionIn October 1937, just as the Cavendish was beginning to adapt to therequirements of high-tech “atom-smashing”, Rutherford died unexpectedlyafter a short illness. Announcing the news at an international conference inItaly in celebration of the two hundredth anniversary of the birth of Luigi18 Quoted in M. Oliphant, Rutherford: Recollections of the Cambridge Days (Amsterdam: Elsevier, 1972),146.19Quoted in A. Wood, The Cavendish Laboratory (Cambridge: Cambridge University Press, 1946), 48.116

Jeff HughesNUCLEAR PHYSICS AT THE CAVENDISH LABORATORY IN THE THIRTIESGalvani, Niels Bohr was in tears. British physics, and international nuclearphysics, had lost an intellectual leader and a powerful spokesman. The lead atthe Cavendish passed to the talents of a new generation. In Cambridge, speculationfocused on who would succeed Rutherford. Though C.V. Raman privatelyexpressed an interest to one of the electors, Chadwick was widelyexpected to step into his master’s shoes. Yet, perhaps sensitive to criticismsabout the dominance of nuclear physics, the electors chose not a nuclearphysicist but the x-ray crystallographer Lawrence Bragg to become the fifthProfessor of Experimental Physics and Director of the Cavendish Laboratory.The journal Nature approved the appointment, noting that the Cavendishwas now “so large that no one man can control it all closely”, and adding that“Bragg’s tact and gift of leadership form the best possible assurance of thehappy co-operation of its many groups of research workers”. 20 Nevertheless,the place of nuclear physics at Cambridge no longer seemed assured.By this time, in any case, the threat of war was impacting on the Cavendishand other laboratories. In the spring and summer of 1939 many of theCavendish physicists were mobilised to work in the defensive radar chain takingshape around the eastern and southern coasts of Britain. Early that year,the laboratories at Liverpool, Birmingham and Oxford were in many waysbetter placed than the Cavendish to work on aspects of the most recent discoveryanimating nuclear physicists: nuclear fission.ACKNOWLEDGMENTSI am grateful to the Syndics of Cambridge University Library for permission to quotefrom the Rutherford papers and the Cambridge University Archives; to the Universityof Sussex for permission to quote from the Crowther papers; and to the UniversityLibrarian, University of Sheffield, for permission to quote from the Miller papers.Jeff HughesStudied Chemistry at the University of Oxford and History of Science at theUniversity of Cambridge. A former Research Fellow at Cambridge, he hasbeen Lecturer in History of Science and Technology at the University ofManchester since 1993. His research interests are in the social and culturalhistory of radioactivity and nuclear physics. He is currently completing bookson the discovery of isotopes and on the history of nuclear physics 1918-1940. He was Secretary of the British Society for the History of Science1995-2000, and also has interests in history of science and the public understandingof science.20 “Prof. W.L. Bragg, O.B.E., F.R.S.”, Nature, 141 (1938), 403.117

Michel PinaultCooperation and Competition among Nuclear PhysicsLaboratories during the Thirties: the Role of Frédéric JoliotMy contribution will reach two essential aspects of cooperation and competitionamong nuclear physics laboratories during the Thirties, a period marked by astrong change of scale in research equipments and by the fast development ofAmerican science: on the one hand I will deal with the building by FrédéricJoliot of his first accelerators, when he feared that French physics might beovertaken because of a lack of effective laboratory instruments, and on the otherhand I will come back on the beginning of the race to achieve a chain reaction,in 1939-1940, when Joliot, being first reluctant to accept a secret agreementbetween scientists from western countries, then became strongly involved in thescientists military mobilization. Enrico Fermi and Joliot were then in constantcompetition and Fermi eventually won, being the first to realise a nuclear pile inChicago.Cooperazione e competizione tra i laboratori di fisica nuclearenegli anni Trenta: il ruolo di Frédéric JoliotIl mio intervento verterà su due aspetti essenziali della cooperazione e dellacompetizione tra i Laboratori di Fisica nucleare negli anni Trenta, periodo chevide una considerevole evoluzione della strumentazione scientifica,accompagnato da un veloce sviluppo della scienza negli Stati Uniti. Tratteròdella creazione da parte di Frédéric Joliot dei primi acceleratori e del suo timoreche la fisica francese potesse rimanere in secondo piano a causa dellamancanza di strumentazione valida, ed anche di come ebbe inizio, nel 1939-1940, la competizione per arrivare alla reazione a catena, quando Joliot,inizialmente riluttante a stipulare un accordo segreto con scienziati occidentali,fu progressivamente e intensamente coinvolto nella mobilitazione militare degliscienziati. La competizione senza fine tra Enrico Fermi e Frédéric Joliot vide allafine la vittoria di Fermi, il primo a realizzare, a Chicago, la pila nucleare.119

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIam going to evoke two aspects of the relations of cooperation and competitionbetween laboratories of nuclear physics in the Thirties, at amoment when the European scientists were confronted simultaneously withthe change of scale in the equipments demanded by their researches and withthe fast development of the American science. This paper concerns on theone hand the construction of the first accelerators, a phase during whichFrédéric Joliot tried to avoid that French physics would lag behind for lackof successful laboratory equipments, and on the other hand about the startof a run toward the chain reaction, in 1939-1940: Joliot, at first reluctant atthe idea of a secret agreement among the scientists of western countries, wasthen involved determinedly in the war mobilization of the scientists. I’d liketo add that Enrico Fermi and Joliot were then in constant competition andthat Fermi triumphed by realizing, in Chicago, in 1942, the first nuclear pile.In 1935, the year of the Nobel prize, Frédéric Joliot, 35-years-old, hadbeen leading for several years an intense activity to acquire new and moresophisticated equipments. As France again distinguished itself in the sector ofradioactivity, Joliot did not want to appear as the mere heir of a “Curie tradition”whose limits he knew 1 . He was conscious that physics moved fast andthat the English and American science were to take the lead because of thetheir discoveries and the means they possessed. Actually the French, who hadacquired a scientific advance in the field of radioactivity thanks to the sourcesaccumulated in Marie Curie’s laboratory, lagged behind the Anglo-Saxon scientists.From his part, Enrico Fermi still worked with traditional means,moreover less powerful than Joliot’s, who understood that his success wouldbe strongly conditioned by the quality of help and cooperation he wouldobtain. Engineer himself, he turned to manufacturers, who were not able offulfilling his requests, and then to his colleagues abroad. A new scientificcommunity was indeed being born at the beginning of the 30s, with ErnestLawrence and James Chadwick, of course, but also Merle Tuve and GregoryBreit, Charles Lauristen, Robert de Graaff, John Cockcroft and ErnestWalton, Arno Brasch and Fritz Lange, Wolfgang Gentner, Manne Siegbahnand many others. These builders of laboratories and inventors of equipments,engineers as well as researchers, these engineers-physicists, were going tobecome “research workers of a rare quality” 2 . They planned to build their1 See MICHEL PINAULT, Frédéric Joliot-Curie, Odile jacob, Paris, 2000, 712 p.2See J.L. HEILBRON and R.W. SEIDEL, Lawrence and his laboratory, University California Press, 1989, t.1,and JEFFREY HUGHES, “Interactions and comparisons between France and Britain: Joliot, Chadwick and120

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIESlaboratories around the instrument. They were going to transform them intoworkshops, supply them with more and more sophisticated installations,populate them with technicians and workers and set scientific research as anew profession, based on team work. Joliot identified himself with these“technicians-instrumentalists”, of whom Aimé Cotton, before him, was oneof the first representatives in France.In June 1932 Joliot, already set forward in this direction, had entered intocorrespondence with Lawrence. This one had answered in detail his questionson the functioning of its invention, the circular accelerator of particles, thankinghim at the same time for sending his recent notes on the neutron. He toldhim of an electromagnet in Bordeaux that had belonged to a broadcasting stationbuilt by American engineers during the First World War. Joliot did notobtain the license to use this installation 3 . In 1933, Joliot had attended withWolfgang Gentner, who was then a researcher in the Curie Laboratoire, themeeting Paul Scherrer had organised for European experimenters at thePolytechnicum, in Zürich. Gentner and Joliot took advantage of the occasionto visit the Oerlikon company, which made electromagnets. There was therea tradition, an industrial know-how, associated to technical and scientificresearch, that many experimenters physicists knew. Joliot, having boughtthere the equipments for his Wilson’s cloud chambers, would soon order theelectromagnet for his cyclotron, as also Gentner and Scherrer did 4 .In 1933 the Joliot-Curie left the Solvay Council fearing that Lawrence,thanks to his first cyclotron, or Cockcroft with his electrostatic accelerator,would seize their ideas and make important discoveries before they did.Their discovery of artificial radioactivity, some months later, made themaware of the urgency to have these new devices at their disposal 5 . Theyunderlined it, in their note of March 20, 1934, adding that, following theirBlackett”, in M. BORDRY and P. RADVANYI (ed.), Œuvre et engagement de Frédéric Joliot-Curie, EDP-Sciences, Paris, 2001, p. 153-162.3 Letter from E. Lawrence to F. Joliot, August 20, 1932, Archive Curie et Joliot-Curie. Letter from theengineer of the PTT to F. Joliot, January 4, 1933, ACJC - F 28. See F. JOLIOT, in M. NAHMIAS, Thecyclotron, Editions de la Revue d’Optique théorique et instrumentale, Paris, 1945.4 Interview of Charles Weiner with Wolfgang Gentner, November 15, 1971, p. 42, Archives of theAmerican Institute for Physics. See J.L. HEILBRON, “The First European Cyclotrons”, Rivista di Storiadella Scienza, 1986, 3-1.5 IRENE CURIE and FRÉDÉRIC JOLIOT, “Un nouveau type de radioactivité”, January 15, 1934, Comptesrendus des sessions de l’Académie des Sciences, 1934, t.198, p. 254, “Séparation chimique des nouveauxradioéléments émetteurs d’électrons positifs”, January 29, 1934, Comptes rendus des sessions del’Académie des Sciences, 1934, t.198, p. 559, “I – Production artificielle d’éléments radioactifs, II –Preuve chimique de la transmutation des éléments”, March 20, 1934, Journal de Physique et LeRadium, 1934, t. 5, p. 153, in I. and F. JOLIOT-CURIE, Œuvres scientifiques complètes, PUF, Paris, 1961.121

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEdiscovery, Cockcroft, Gilbert and Walton had already begun working with anaccelerating tube of protons. From their part, Crane, Lauristen andLawrence’s team announced the discovery, thanks to the use of acceleratingtubes, of a dozen new radioelements 6 .Frédéric Joliot then proceded at the same time in two parallel directions.On the one hand he set, in a vast available premises near Paris, a Van de Graaffhigh tension electrostatic generator, producing a tension of about 1.2 millionvolts, coupled with a Lauristen accelerating tube. On the other hand, havingdiscovered an industrial laboratory provided with a high tension apparatus,equipped with a generator of impulses able to reach 3 million volts, heobtained the support of the dean of the Faculty of Science to set there severalions or electrons accelerating tubes. The correspondence, based on thenumerous visits made by researchers and foreign technicians, keeps the tracksof the difficulties encountered in setting this installation. In it, Joliotenounced several practical suggestions on the vacuum technique or the choiceof materials for electrodes, quite revealing of his doubts 7 . The relations amongJoliot and Gentner who, associated to Walter Bothe, had built a Van de Graaffand defended a project of cyclotron in Germany, were then particularly closeand without competitiveness. They kept mutually informed about theirundertakings. Joliot wrote, in May 1937:“I am really very satisfied to see you pursuing splendidly your researchesin Heidelberg. It is certain that at present the best production in the fieldof radioactivity and nuclear physics comes from your laboratory” 8 .Later, when Gentner was in charge, as officer of the German army of occupation,of Joliot’s laboratory, at the Collège de France, they maintained a relationbased on confidence and scientific cooperation.But let us return to 1935. Joliot’s aim was, as for the installations he triedto set up, to waste no time and try and stay on the run. To carry out his otherprojects, he should obtain consistent financing. Now, the funds he wouldhave needed exceeded the subsidies of the CNRS itself. Joliot tried to avoidthe obstacle by asking the Rockefeller Foundation two million francs, but hedid not obtain them 9 . So, in the eventuality of winning the Nobel price6 CRANE and LAURISTEN, Physical Review, 45, 1934, p. 431 and 49. MCHENDERSON, LIVINGSTON andLAWRENCE, Physical Review, 45,1934, p. 428.7 ACJC - F 28.8Letter from F. Joliot to W. Gentner, May 3, 1937, AC.JC.9 F. JOLIOT, “Project of creation of a laboratory specialized in the production of new radioelements andtheir biologic and physico-chemical applications”, ACJC.122

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIESwhich would gain him the good graces of the University, in the summer of1935 he presented to the vice-chancellor of the Academy of Paris its projectof the Laboratoire de Synthèse des radioéléments artificiels. And actually,three days after the announcement of the Nobel, the vice-chancellor let himknow “that the present moment (was) particularly favourable for the realizationof the project” 10 .Another action in favour of Joliot was then taken at the Collège de France.Paul Langevin, holder of the chair of Experimental Physics, explained that itwas desirable to promote without delay, as it was the vocation of the Collègede France, “the new science in which France had just become famous” 11 .And so, on June 13, 1936, after the victory of the Popular Front, Joliot’sappointment as head of a nuclear chemistry laboratory was announced. Theplan to equip it with a cyclotron was carried out without delay, thanks to thepolitical weight of the scientists close to the Président du Conseil, LéonBlum. Also, the setting up of the Laboratoire de Synthèse Atomique, whichJoliot provided with different high-tension accelerators, was largely financedby the Blum ministry in which his wife, Irene Curie, was in charge of thequite new sub-ministry of the Scientific Research 12 .Fermi who, according to Michelangelo De Maria, had decided since 1935to obtain accelerators of particles, asked in 1937, as Joliot had two years earlier,for a 2 million francs subsidy. It amounted to twenty times the annualsubsidy of the Consiglio nazionale della ricerca (CNR) of which he receivedthe twentieth. “One notices, he wrote, that all big countries develop artificialsources”. He added:“It is illusory to envisage an effective competition with the foreigners ifone does not find in Italy the means to organize adequate researches”.Fermi had to found a way to be financed by the Istituto superiore di Sanità,connected to the Home Office, and wait for Mussolini to be personally interestedin the matter for reasons of nationalist prestige, to be able to carry outhis projects 13 . Unlike Fermi, or Bothe and Gentner, who did not succeded10 Charles Maurain's letter to F. Joliot, November 18, 1935, ACJC.11 Assembly of professors, January 26, 1936, Archives of the Collège de France.12 Irene Joliot-Curie's letter, as Undersecretary of State of Scientific Research, to Frédéric Joliot,September 17, 1936, AC.JC. See M. PINAULT, “The Joliot-Curie: Science, Politics, Networks”, Historyand Technology, 1997, vol. 13, p. 307-324.13 MICHELANGELO DE MARIA, “Fermi, A physicist in the storm”, Pour la science, February-May, 2001, p.48, and IVANA GAMBARO, “Acceleratori di particelle e laboratori per le alte energie: Roma e Parigi neglianni trenta”, in Rivista di Storia della Scienza, 2 a serie, giugno, 1993, p. 105-154.123

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEin getting funds for financing their respective projects of cyclotrons by themussolinian and nazi powers, Joliot thus benefited from a very favourablepolitical situation.While elaborating his cyclotron project, Joliot got much closer toLawrence. His personality and Joliot’s could certainly favour such sympathy.Lawrence embodied a “boss’style” breaking up with the dusty and stiff affectationof relations based on titles, age and hierarchy, and membership in the“establishment”, of the time. The nonconformism and the enterprising mindof the Americans, well embodied by Lawrence, thus appeared to Joliot as amodel he was going to confront with more or less consciously. At the sametime, and partially thanks to his friendship with Lawrence, Joliot obtained astrong support from the Rockefeller Foundation. So he was allowed torecruit a biologist to work on the radioactive tracers, and financed a stay atthe Collège de France for Hugh Paxton, a specialist of the cyclotron,researcher at Lawrence’s laboratory, as well as a one year stay in Berkeley forJoliot’s assistant, Nahmias. At the same time, Hans von Halban left forCopenhagen, to go to Niels Bohr’s laboratory, where the project of acyclotron was being developed by the the same Foundation with the collaboration– there as well – of one of Lawrence’s assistants. A notebook of somepages reports the first trials of Joliot’s cyclotron, between June andSeptember 1938, before Paxton’s departure for Columbia University. Joliothoped then, as he wrote to George Pegram, president of Columbia, “to finishthe trials” and “to arrive at a result before M. Paxton’s departure”. Sincethere still were lots of difficulties, Paxton, from Columbia, proposed somesolutions inspired by the cyclotron, just beginning to run. Joliot tried to followhis suggestions but the beam, while allowing to produce radioelements,remained very unstable 14 . The starting on, in January 1939, of research onthe chain reaction, made suddenly secondary, for Joliot, the setting up of thecyclotron.Much has already been said on Leo Szilard’s vain attempts, at the beginningof the research on the nuclear chain reaction, to convince his colleaguesto establish not a general moratorium on these researches but an agreement14 “Cyclotron trials”, Notebook of laboratory, from June 24, 1938, till September 7, 1938, IPN-Orsay.G.B. Pegram’s letter to F. Joliot, from Columbia University, in June 23, 1938, ACJC - F28. HughPaxton's letter to F. Joliot, from New York, November 14, 1938. On April 30, 1940, F. Joliot wroteto Irene, that “the cyclotron worked and very well and (that) it prepared easily rather big quantities ofiodine 8 days” (AC.JC). See SHIZUE HINOKAWA, “Frédéric Joliot-Curie and Cyclotron Development”in The Journal of Humanities and Sciences, n° 4, October, 2000, Takushoku University, p. 229-254.124

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIESof secrecy of cooperation among the researchers of three or four countries. Iwould like to add some remarks about the strong evolutions which underwentin the ways of cooperation and competition between laboratories.From the discovery of the artificial radioactivity, Joliot had worried aboutthe predictable moment when “the researchers, he had declared, will knowhow to carry out explosive transmutations, real chemical chain reactions”.He had then asserted that “a discovery is neither moral nor immoral, it is itsemployment in fact that it is necessary to judge”. In 1936 he declared however that“if society should continue to live according to the current rules, it would be preferablethat the men of science do not reveal any more of their discoveries. They willannounce them when the world will be better” 15 .Such was his state of mind. From his part, true precursor, Szilard, thenemigrated in London, who had gotten interested very early at the idea ofreleasing nuclear energy, had deposited, on March 12, 1934, a patent to keepa right over his works in case of possible military applications of which he wasafraid. At the same time, he hoped to limit to some researchers the informationabout the discoveries to come, until the risk to discover a new explosivedisappeared 16 .But this idea went against the principles, then admitted, of the universalityof science and free communication of its results. The international communityof radioactivists was a small world of some dozens members. These communicatedregularly, exchanging their pupils, observing and commentingeach other continuously, and occasionally engaging in a running contestbefore assembling to confront their views 17 . The spirit of the time of Pierreand Marie Curie had profoundly affected the researchers of the Institut duRadium. They had written:“We published, without any reserve, all the results of our researches, aswell as the processes of preparation of the radium. We gave, furthermore,to the interested all the information which they asked for” 18 .15 Conference Nobel (December 12, 1935), in F. and I. JOLIOT-CURIE, Œuvres scientifiques complètes, op.cit., p. 549-552, and Joliot’s conference at the Cercle Peuple et Culture, Grenoble, March 4, 1936,ACJC. See M. PINAULT, “Frédéric Joliot-Curie, chercheur tourmenté”, La Recherche, n° 335, October,2000, p. 56-61.16 SPENCER WEART, “Scientists with a secret”, Physics today, February, 1976, 29-2. Leo Szilard's letter toprofessor Lindemann, at the Clarendon Laboratory of Oxford, June 3, 1935, in S. WEART and G.WEISS, Leo Szilard, His version of the facts, PUT Press, on 1980, p. 41.17See DOMINIQUE PESTRE, Physique et physiciens en France (1918-1940), Archives contemporaines, Paris1984, and DANIEL J. KEVLES, The physicists, History of a profession which changed the world, op. cit.18 MARIE CURIE, Pierre Curie, Denoël, Paris 1955, p. 71.125

PROCEEDINGS OF THE INTERNATIONAL CONFERENCESzilard’s propositions of secrecy were formulated against this spirit and itwas natural to accept them. Many researchers, oddly in the French progressivecircles, got shaked by the disastrous and lasting divisions of the scientificcommunity, during and after the First World war, and were afraid of itspossible renewal.The issue got moving again in January 1939. Following the discovery ofthe fission, certain researchers, particularly at the Collège de France, withJoliot, and at Columbia University, with Fermi, started studying the possibilitiesof activating a chain fission. While being engaged in a relentless competition,they had to face the responsibility they were taking by opening this“Pandora’s box”. It is well known that, from February 2 1939, Szilard, bythen at Columbia, wrote a letter to Joliot suggesting to stop publishing onthis subject 19 . But Fermi wrote as well to Joliot, the same day, without mentioningthe question. He indicated that he “was engaged as, I think, all thelaboratories of Nuclear physics, in trying to understand what takes place inthe catastrophale destruction of uranium”. At the end of January, Frenchphysicists, among whom Fernand Holweck, visited Columbia’s cyclotron,not of having any message for Joliot 20 . In several letters Paxton, who had justspent one year in Joliot’s laboratory before joining Columbia, did not suggestany particular attitude: on February 12, he explained “the first job thatthe cyclotroneers here find themselves involved in is the Uranium split businesswith which half the world seems to be occupied. It seems that Fermiturned Dunning toward this just as soon as the cyclotron gave a beam –which was almost a month ago” 21 . Nothing which could have alerted Joliotand his team aside from an inevitable rivalry with Fermi’s group.When, after the invasion of Czechoslovakia by the Nazi troops, a telegramfrom Victor Weisskopf indicated that several publications were from then onsuspended by their authors, Joliot’s answer was quite full of nuances:“I certainly do agree with the principle of an agreement, he wrote, but forit to be effective, it would be necessary to spread it among all the labora-19 Letter from L. Szilard to F. Joliot, New York, February 2, 1939, ACJC. Szilard became attached tothe hypothesis of the chain reaction from 1933 and from this time he dreamed of “the small but realpossibility of building an explosive a thousand times more powerful than the common bombs”. (S.WEART, art. cit.).20 Let us add that a team of physicists led by Joliot to set up experiments in the Exhibition was then inNew York. In their mails, they evoked their visits to the team of Columbia's cyclotron (ACJC - F30).21 Letter from Hugh Paxton to Ignace Zlotowski, New York, January 29, 1939. Letter from H. Paxtonto Maurice Nahmias, from New York, February 12, 1939, ACJC F28.126

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIEStories equipped to handle the matter. I would be grateful to you forannouncing these considerations to the American colleagues, whom youcan get in touch with” 22 .To Joliot, Szilard and Weisskopf’s idea, although not coming from theleaders of the American nuclear physics, seemed to create more problemsthan it could solve. Therefore, the secret risked to be aired at once if textsshould circulate between both banks of the Atlantic Ocean. Rather than asecret shared between some countries, Joliot seemed to prefer a conspiracyof all the physicists from all countries, decided to hide the secret from all thegovernments. Now, Szilard and Fermi had already decided to alert theAmerican government and so was also going to do Cockcroft in England.It would take several months for Joliot to get there.During the spring and summer of 1939, the teams continued to publish.However, Joliot decided to apply for patents, on behalf of the CNRS, ofwhich one, “Perfection in explosive charges”, remained secret 23 . After thedeclaration of war, the experiments were called to remain secret. Joliot evendecided “to transfer the research project to the War Office” 24 . A French militaryatomic program, the first one in the world, had been already defined.The issue of secrecy then became a State affair, involving the army and thespecial services, and the relations with foreign scientists entered this new scenario:on one side the British were allies, with whom closer contacts weretaken, on the other the Germans were enemies towards whom effective precautionarymeasures were taken.Informed about the German projects of purchasing Norwegian heavywater, Joliot suggested to prevent these deliveries and followed closely theGerman researchers: “It would be interesting – he wrote – to obtain informationon the current activity of these scientists and, in particular, to knowif some of them have recently left their laboratories so as to form a teamworking in a single place under a unique management. Such a group, if con-22 Letter from F. Joliot to L. Szilard, April 19, 1939, A. AIP, Kowarski, 2-14.23 “Mise en évidence d’une réaction nucléaire en chaîne au sein d’une masse uranifère”, handwritten correctionsby Joliot and Kowarski, ACJC - C 8, Journal de Physique et Le Radium, October, 1939. A “plicacheté” was deposited, October 30, 1939, at the Académie des Sciences (published in the CR,November 7, 1949).24Kowarski’s manuscript (ACJC), “Novembre 1939”. The official version, signed by the three researchers,sent to Raoul Dautry, accompanied with Joliot's letter, is dated February 13, 1940 (Archives of theCEA (Atomic Energy Commission in France) - DRI - F4 / 22-78).127

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEfirmed, would constitute a very clear indication of a German effort towardsthe solution of the problem which interests us” 25 .At the same time, closer contacts were taken with the British researchers.Joliot met Cockcroft several times, as a member of the service of scientificresearch, in the Ministry of Supply. In December 1939, the latter wrote him:“I was amazed by what you and the French nuclear physicists are doing.I suggested (…) that contacts should be organized as quickly as possibleamong the British and French physicists” 26 .A “confidential mission” arrived in London, on April 10, 1940, just whenthe scientific committee for the study of the questions of the uranium, theMAUD committee, was to meet for the first time 27 . There, a note probablydrafted by Joliot, was read, saying that “the results of the current researches (inFrance) are held secret” and that “the same should be asked of all otherresearchers, who, in the allied Countries, are working on the same question” 28 .Meanwhile, after more than a year, Szilard wrote to Joliot, bringing upagain the problem of the publications:“I have not discussed this matter with anyone else in America since Aprillast year, he strangely wrote, and I don’t know what view others wouldtake if the question was to be raised again. If, however, I should hear fromyou that in the meantime you have adopted some new policy of delayingpublications, I could then perhaps talk to others here and find out whatthe general feeling is on this subject” 29 .Obviously Szilard seemed to write without having succeeded in obtaininganything, and he also seemed very isolated. Given that for more than sixmonths French scientists had not publish because of the war, this matter didnot concern them any more, but only scientists in the United States.Nevertheless, Szilard had few chances to receive an answer. Joliot had bythe time several contacts with the most important American physicists. He25Typed note and draft from J. Allier’s hand, Archives Graf-Allier.26 Letters from F. Joliot to J.D. Cockcroft, Ministry of Supply, January 17, 1940, and from J.D.Cockcroft to F. Joliot, January 24 and February 18, 1940, ACJC-C 7. J.D. Cockcroft's letter to F.Joliot, December 7, 1939, ACJC - C 7.27 In a letter to Paul Montel, responsible for the scientific mission of the Ministry of the Armament, inLondon, H.J. Gough, director of the British service of the Scientific research, wrote, April 11, 1940:“It was fortunate that Mr Allier arrived one the day which has special meeting was being held to considerthe same problem. We have taken of all the questions raised by Mr Allier, and will take the necessaryactions”. (A. Graf-Allier).28 “Confidential Note”, not signed, undated: “Note handed?? in London”, id.29 Letter from L. Szilard to F. Joliot, April 12, 1940, ACJC - K4b.128

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIESindeed put a lot, as vice-president of the Haut comité de coordination desrecherches scientifiques (HCCRS), into a now forgotten large-scale action:the organization of an International Congress of Pure and applied Sciences,in September 1940, in New York. Joliot was the inspirer of this project,which financing was assured, in France, by the Ministère de l’Armement.Only the defeat in 1940 prevented him from succeeding. The aim was toorganize, in occasion of the International Exhibition of New York in 1940,a congress which would be the continuation of the “Congrès du Palais de laDécouverte”, organized under the presidency of Jean Perrin and Joliot, duringthe International Exhibition of Paris in 1937 30 . The leaders of the Frenchscientific community had not then hidden their wish to make their colleaguesaware of France’s lag in research, particularly for certain new branches. In1940, Joliot clearly defined identical objectives, at least about the industrialand military applications 31 .The foreign scientists, eager to know more about this surprising project inthis restless period, contacted Joliot. Niels Bohr wrote him a fascinating andmoving letter, which reveals the actual terms of the scientists’ cooperation:“Of course, wrote Bohr, it would be wonderful if it was really possible inthese critical days to meet and discuss scientific questions of actual interestand the many problems with which scientists are at the moment confronted.But, he added, I felt it difficult to promise my participationbefore I had more detailed information about the organization of thecongress and the character and formulation of the invitation. In fact, I amafraid that an invitation, especially from a permanent committee which atthe moment cannot be quite international – thus M. Thomarkin (theagent in charge of the organization of the congress) told me that it is theirintentionto exclude the countries at war with France or not representedat the New York exhibition (as far as I remember it is not so, however, ashe thinks, that Russia is not represented at the exposition) – will involveserious dangers if the whole matter is not handled with the greatest caution.(…) I believe that it is quite essential, not least in order to defendthe moral cause of the free nations against mischievous propaganda, thatfrom the very outset all precautions are taken against any possible misunderstandingsand that this is made absolutely clear in the formulation ofthe invitation. I know you understand that I am just as interested as your-30 Letter from Jean Perrin to Grover Wahlen, general commissioner of the Exposition of New York,November 30, 1939, ACJC - F 30.31 Letter from L. W. Tomarkin, agent in charge of the organization of the congress, to F. Joliot, January15, 1940, idem.129

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEself to support the upholding of international scientific relations in thesecritical days and as little prepared to submit to the pressure to destroyintellectual and scientific freedom. I am only afraid of any step likely toincrease the difficulties of reorganizing scientific relations when onceagain peace is established. Indeed I hope taht such relations – contrary towhat happened afler the last war – will this time prove to be a main sourceof that revivement of the common human spirit, which is the very aim ofthe present struggle for humanity and freedom. I shall therefore be verythankful if you would write to me quite openly what you and your colleaguesin France are thinking of the whole matter” 32 .These issues had already been tackled in Paris. As for the participation ofthe scientists from non-allied countries, Joliot affirmed that “the Americansshould decide on it” 33 . The American committee, chaired by Urey, included70 leading Americans scientists, among whom the staff of ColumbiaUniversity – Fermi and his team included – as well as most of the membersof the advisory committee of nuclear physicists, just created in June 1940,under Urey’s authority. At the request of the State department wishingAmerican neutrality be respected, this committee invited two German scientists,Domagk and Ku, knowing already they would not come, and OttoWarburg, a “non-Aryan”, according to the expression of Tomarkin, whoaccepted the invitation. Of the Russian side, Stern, Vavilov, Frenkel and Iofféwere invited: if Vavilov answered that he wished the success of the congress,the decision to participate lay in the hands of the Academy of Sciences of theUSSR. As for Fermi’s participation, the Italian ambassador indicated that he“was representing Italian Science in the United States”. Three other Italians– Bottazzi, Amaldi and Rondoni – answered affirmatively, and “of their owninitiative” included in their delegation Vallauri, Quagliarello and Bergami.Bohr said he could not attend the congress but Hevesy and Madsen wouldcome. Of Switzerland, Pauli and Ruzicka answered affirmatively.Consequently, delegations from the United Kingdom and Scandinaviancountries were expected. The congress was going to be really representative,particularly as regarded nuclear physics.Finally, in the summer of 1940, Frédéric Joliot was appointed responsible,for France, of the scientific war mobilization through the CNRS-A (AppliedNational Centre for Scientific Research). He had organized several actions32Niels Bohr's letter to F. Joliot, February 16, 1940, 3 p, ACJC.33Project of report of the “First session of the permanent desk of the congress of pure and applied sciences”,February 16, 1940, ACJC - F 30.130

Michel PinaultCOOPERATION AND COMPETITION AMONG NUCLEAR PHYSICS LABORATORIES DURING THE THIRTIESaiming at organizing, at the Allies level, the coordination of the scientificcommunities, first of France and United Kingdom, while waiting for the bigforum in New York, in the autumn of 1940. As a physicist, he implementeda strategic program of nuclear researches, which his contacts with the Britishcould accelerate. The meeting of New York, where all the researchers concerned,particularly those in the United States, United Kingdom and France,would be reunited, could even spurr him on to reach another stage in thecoordination of the researches. But Joliot did not lose sight of the competitionand, until the last hours of the Bataille de France, remained set on theobjective to activate the first divergent chain reaction in oxide of uraniumand heavy water. If such a success had been obtained before the congress ofNew York, the ceremony of “Celebration of the fifth anniversary of the discoveryof the artificial radioactivity”, during which the American committeehad planned to hand to Irene and Frédéric Joliot-Curie the Barnard goldenmedal, awarded by the Academy of the Sciences, would then have acquiredmuch greater significance 34 .Michel PinaultMichel Pinault is an historian, now working on the scientific research and scientists’milieu in European societies during the XXth century. He disputed, inApril 1999, his thesis, at University Paris I-Panthéon Sorbonne, on “FrédéricJoliot, la science et la société - Un itinéraire de la physique nucléaire à la politiquenucléaire, 1900-1958”. From this thesis a book has been published,Frédéric Joliot-Curie (Paris, Odile Jacob, 2000, 712 pages). He took part inthe organisation of a conference on “L'Actualité de Frédéric Joliot-Curie”, atthe Collège de France, in Paris. The proceedings have been published:Oeuvre et engagement de Frédéric Joliot-Curie, Paris, EDP-Sciences, 2001,209 pages.Michel Pinault is a member of the editorial staff of the journal Histoire etSociétés - Revue européenne d’histoire sociale (20 rue Alexandre Dumas,Paris, 75011). He is permanent professor of history and is currently teachingin a secondary school in France.34 L.W. TOMARKIN, “Memorandum, March 19 - April 12, 1940”, id.131

Ruth Lewin SimeFrom Fermi to Fission:Meitner, Hahn and Strassmann in BerlinAfter 1934, when Fermi suggested that the first transuranium elements had beenproduced, the investigation was pursued most intensively by Lise Meitner, aphysicist, and the chemists Otto Hahn and Fritz Strassmann in Berlin. Theirdiscovery of nuclear fission in 1938 was a complete surprise, and all theapparent transuranium elements were proved false. My paper focuses on theinterdisciplinary nature of the work in Berlin, in particular the prevailing conceptsfrom nuclear physics and chemistry that misguided the investigation for four yearsbut which, in the end, made the fission discovery possible.Da Fermi alla fissione:Meitner, Hahn e Strassmann a BerlinoDopo il 1934, quando Fermi ipotizzò che fossero stati prodotti i primi elementitransuranici, la ricerca fu condotta in maniera intensiva a Berlino da LiseMeitner, fisica, e dai chimici Otto Hahn e Fritz Strassmann. La scoperta dellafissione nucleare nel 1938 fu una grande sorpresa e tutti gli apparenti elementitransuranici furono provati falsi. Il mio intervento riguarderà la naturainterdisciplinare del lavoro condotto a Berlino ed in particolare i concettipreponderanti che avevano fuorviato la ricerca per quattro anni ma che, allafine, resero possibile la scoperta della fissione.133

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEUranium nuclei were split in a laboratory for the first time in 1934, herein Rome by Fermi and his group on the Via Panisperna. 1 At the time,no one understood this. Instead, Fermi and scientists everywhere believedthey were creating new elements beyond uranium, and for several years thelist of these new elements kept growing. When fission was discovered, in1938, it was a surprise and a shock. It shattered assumptions about nuclearbehavior and showed that all the transuranium elements were false: all werefission fragments. We can see the surprise in the events following Fermi’sNobel Prize in December 1938. The prize was awarded to Fermi for his workwith neutrons, including the creation of the first transuranium elements. Ayear before, the Nobel physics committee had considered Fermi, but theywere unsure about the transuranics; in 1938 they went ahead. 2 Fermi himselfwas confident. In his Nobel lecture he even referred to elements 93 and94 by name: ausonium and hesperium. But at that moment, fission wasabout to be discovered in Berlin. Barium was identified just beforeChristmas, and the fission process was understood by New Year’s Eve. Thetransuranium elements were gone. When Fermi sent his Nobel lecture to theprinter he added a footnote to that effect, but by then ausonium and hesperiumwere themselves footnotes in the history of science. 3For four years, the world’s leading nuclear physicists and radiochemists hadbeen mis-guided by assumptions about nuclear behavior and the chemistryof heavy elements that turned out not to be true. Today I will focus on thescience: I want to emphasize the interdisciplinary nature of the research,which involved nuclear physics and chemistry at every stage, difficult experimentsand theory that was new. The social context also played a role, ofcourse. For one thing, the work attracted the most prominent scientists inthe field: Fermi and his group; then Lise Meitner, Otto Hahn, and FritzStrassmann in Berlin; and Irène Curie and her coworkers in Paris, amongothers. Their expertise was essential, but their prominence also seems to havebeen an inhibiting factor, in that their conclusions were not challenged byyounger people, even those with more data and better equipment. Therewere psychological factors too: each new element was a prize, people want-1 EMILIO SEGRÈ, Enrico Fermi: Physicist, The University of Chicago Press, Chicago (1970).2 ELISABETH CRAWFORD, pers. comm., 30 July 2001; ROBERT MARC FRIEDMAN, The Politics of Excellence:Behind the Nobel Prize in Science, Henry Holt & Co., New York (2001), p. 248.3 SEGRÈ, Enrico Fermi, pp. 98-99, 214-221; Enrico Fermi: Collected Papers/Note e Memorie, vol. 1, TheUniversity of Chicago Press, Chicago/Accademia Nazionale dei Lincei, Roma (1962), pp. 1037-1043.134

Ruth Lewin SimeFROM FERMI TO FISSION: MEITNER, HAHN AND STRASSMANN IN BERLINed them to be real. And there was a political edge: the Berlin group hopedthat the international spotlight would protect them somehow in NaziGermany. Altogether, these external factors seem to have narrowed the focusto the search for transuranium elements only, keeping people from beingalert to the entire range of phenomena before them. This surely delayed thediscovery, but still it did not prevent it. In the end, the nuclear physics andchemistry that misled scientists to the false transuranium elements did, finally,also lead them to recognize nuclear fission.The work began with Fermi in the spring of 1934. He and his group werefairly new to experimental nuclear physics. In 1931 and again in 1932,Franco Rasetti had visited Lise Meitner’s lab at the Kaiser Wilhelm Institutefor Chemistry to learn nuclear techniques. He was there soon after the discoveryof the neutron, wrote some papers, and returned to Rome with experiencewith neutron sources, counters, cloud chambers, and radioactive substances.In 1934, after Irène and Frédéric Joliot-Curie reported the discoveryof artificial radioactivity, Fermi put this together and began systematicallybombarding elements with neutrons in an effort to produce artificialradioactive species and new nuclear reactions. We know that Lise Meitnerreceived their preprints from Ricerca Scientifica, repeated their experiments,and verified their results. Her interest was intense, and that was true ofnuclear physicists everywhere. 4When Fermi and his group reached uranium and found several new activities,he cautiously proposed that the uranium nucleus had captured a neutronand begun a sequence of beta decays, producing element 93 and 94 –the first artificial elements. This was sensational news. One Italian newspaperhailed it as an example of Italy’s restored scientific grandeur under theFascists, another wrote that Fermi presented a vial of element 93 to theQueen of Italy. 5 Such stories ranged from dubious to completely untrue. Butscientists were also fascinated.At this point, in the summer of 1934, Meitner asked Otto Hahn to join herfor their first collaboration in many years; she realized that “one could not getahead…with physics alone; an outstanding chemist like Otto was needed toget results”. Hahn joined Meitner late in 1934. They made a formidable4 RUTH LEWIN SIME, Lise Meitner: A Life in Physics, University of California Press, Berkeley (1996), p.161-163; SEGRÈ, Enrico Fermi, pp. 68, 73; Rasetti to Meitner, 18 March 1933.5 LAURA FERMI, Atoms in the Family: My Life with Enrico Fermi, The University of Chicago Press,Chicago (1954), p. 91.135

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEteam, which got stronger when Strassmann, a young analytical chemist, joinedthem in 1935. 6 The uranium investigation had shifted from Rome to Berlin.The search for the transuranium elements was framed from the start by twoguiding assumptions, from physics and from chemistry. Physicists had alwaysobserved that nuclei were quite stable: when nuclear reactions did occur, thechanges were small. Fermi’s neutron results were consistent with this. Withlight elements, he found that a neutron might knock out a proton or analpha particle, but nothing bigger. With heavier elements, the reaction wasalways neutron capture, followed by beta decay to the next higher element.So it was reasonable to assume that the new beta activities from uraniumwould be elements beyond uranium.And there was theoretical support for the idea of small nuclear changes. In1928 George Gamow formulated a successful theory of alpha decay, in whichthe nucleus is quantized and only small particles – protons or alpha particles– had a finite probability of escaping. That year Gamow proposed also anothertheory, in which subnuclear particles are bound together like molecules ina drop of water. The liquid-drop theory accounted for nuclear stability andthe known nuclear mass defects. In the mid-1930s Niels Bohr and FritzKalckar developed the theory of the compound nucleus, also based on a liquiddrop, which was useful for nuclear reactions. 7 No theory predicted, andno physicist imagined, anything as disruptive as nuclear fission.The chemists also contributed a false assumption in predicting the expectedchemical behavior of the transuranium elements. We now know that theactinides, including uranium, are homologous to the rare-earth elements,but in the 1920s and 1930s, uranium was considered a transition element(figure 1) 8 and so the elements beyond uranium were also expected to betransition elements. Like the physics assumption, the chemistry predictionwas inductive: the known elements up to U are chemically very similar to thetransition elements above them so it was assumed that the elements beyondU would have the chemistry of Re, Os, Ir, Pt, etc.It is interesting to note that at the time there were some questions aboutthe placement of these elements. In the early 1920’s, Bohr had establishedthe relationship between chemical behavior, periodicity, and electronic struc-6 SIME, Lise Meitner, chapter 7.7 ROGER H. STUEWER, The Origin of the Liquid-Drop Model and the Interpretation of Nuclear Fission,Perspectives on Science, 2 (1994), pp. 76-129.8 J. W. VAN SPRONSEN, The Periodic System of Chemical Elements: A History of the First Hundred YearsElsevier, Amsterdam (1969), p. 160.136

Ruth Lewin SimeFROM FERMI TO FISSION: MEITNER, HAHN AND STRASSMANN IN BERLINFigure 1Periodic system of von Antropoff, 1920s and 1930s. The lanthanides, or rare-earth elements, weregrouped separately, but Th, Pa, and U were ciassifíed as transition elementsSource: Spronsen, Periodic System (note 9).ture. One of his great successes was his proposal of a 4f sublevel, which incorporatedand correctly placed the rare earths into the periodic table. Bohr alsopredicted the existence of a second rare-earth series in a 5f sublevel, but hecould not predict where the 5f would begin. In his table (figure 2) 9 the boxwith the dotted lines places the second group of rare-earths somewherebeyond uranium. Bohr did this because the spectroscopic data were inconclusiveand the chemical evidence for uranium as a transition element wasvery strong.Nevertheless, the start of the 5f series was still an open question. 10 But thechemists who were searching for transuranium elements simply regardeduranium as a transition element and extrapolated from there. Hahn and09 SPRONSEN, p. 156.10 SPRONSEN, pp. 317-320.137

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFigure 2Bohr's periodicsystem, 1922. Bohrpredicted that thesecond rare-earthgroup (dotted lines)would beginsomewhere afteruraniumSource: Spronsen, Periodic System (note 9).Meitner may have been especially inclined to do so because their discoveryof protactinium in 1918 was based on its chemical similarity to tantalum. 11Uranium was doubly deceiving: it behaves like a transition elementalthough it isn’t one, and its nucleus appears to be stable even though it ison the verge of disintegrating explosively. This was bad luck, the more sobecause the false assumptions from nuclear physics dovetailed with thosefrom chemistry. The only public challenge came from Ida Noddack in 1934.Noddack was an inorganic chemist and the co-discoverer of rhenium. Shequestioned Fermi’s chemical separations and noted that no one had excludedthe possibility of the uranium nucleus breaking into large pieces. 12 Much11 For protactinium, see SIME, Lise Meitner, chapter 3.12 IDA NODDACK, “Über das Element 93”, Zeitschrift für Angewandte Chemie, 47 (1934), pp. 653-655.138

Ruth Lewin SimeFROM FERMI TO FISSION: MEITNER, HAHN AND STRASSMANN IN BERLINlater Edoardo Amaldi speculated on why her suggestion was not looked into,but he had little explanation. 13 According to Emilio Segrè, Fermi laterremembered that the mass defect data was misleading, 14 but the curve from1935 (figure 3), 15 has the familiar minimum, suggesting that it is energeticallyfeasible for large nuclei like uranium to split in two. No one saw theimplications of it. It seems that physicists regarded the nucleus as a stableunit and that was that. 16For much of the investigation, the experimental approach was constrainedby the limits of the radiochemistry. The neutron sources were weak, and sothe new beta activities were not much stronger than the natural radioactivityfrom uranium and its decay products. Fermi chemically separated the newactivities from uranium by precipitating them with transition metal compounds,which supported the notion that these were transuranium elements.This approach also structured the investigation in Berlin. In early 1935,Hahn, Meitner, and Strassmann improved Fermi’s separation and began disentanglingthe activities in the precipitate. For the next three years, with few020E40N + Z60801000 50 100 150 200N + ZSource: Stuewer, “Origin of the Liquid-Drop Model”, p. 96 (note 8).Figure 3Mass defect curve,1935. The dotsrepresent Aston’s massspectrographic data.The semi-empiricalcurve calculated byCarl Friedrich vonWeizsäcker is basedon Gamow’s liquiddroptheory13E. AMALDI, “From the discovery of the neutron to the discovery of nuclear fission”, p. 277 in PhysicsReports, 111, pp. 1-332. Amaldi noted that the Fermi group was scientifically conservative and thusreluctant to consider something entirely new, and he noted that Noddack herself did not pursue it. Seealso SIME, Lise Meitner, pp. 271-273.14 SEGRÈ, Enrico Fermi, p. 76.15 STUEWER, p. 92, 96.16 SPENCER R. WEART, “The Discovery of Fission and a Nuclear Physics Paradigm”, pp. 103-104 inWILLIAM R. SHEA, ed., Otto Hahn and the Rise of Nuclear Physics, D. Reidel Publishing Co., Dordrecht(1983), pp. 91-133. “One still imagined the nucleus as a unit…Theory served best when it simply suggestedthat the experiments were getting into something unexplained.”139

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1. U + n [fast/thermal] → 92 U (10′′) → 93 EkaRe (2.2′) → 94 EkaOs (59′) →95EkaIr (66h) → 96 EkaPt (2.5h) → 97 EkaAu?2. U + n [fast/thermal] → 92 U (40′′) → 93 EkaRe (16′) → 94 EkaOs (5.7h) → 95 EkaIr?3. U + n [slow] → 92 U (23′) → 93 EkaRe?Figure 4The “transuranium” elements, 1937. In 1937 Meitner, Hahn, and Strassmann assigned theradioactive species they found to three different reaction processes. In processes 1 and 2, thesequence of beta decays was assigned to elements 93, 94, etc., ali with mass 239 (Half-lives arein parentheses; EkaRe denotes the expected position of element 93 below Re, etc.). Later it wasrecognized that processes 1 and 2 are in fact fission processes, but process 3 was correctlyinterpreted at the time as a typical resonance capture of slow (25 ev) neutrons to form 239 U, whichin 1940 was shown to produce element 93 ( 239 Np)Source: Meitner, Hahn, and Strassmann, “Umwandlungsreihen” (note 17)exceptions, they worked on the precipitate and ignored the filtrate, whichcontained uranium, its decay products, and quite a lot more.We remember that fission involves a long sequence of beta decays; parallelsequences of isotopes; and elements from all groups in the periodic table,including transition elements. By 1937, the Berlin group had assembled theirfindings into three processes (figure 4): 17• in process 1, it appeared that U-238 captured fast or thermal neutrons, followedby a sequence of beta emitters, which they assigned to elements 93,94, etc.• process 2 is parallel to process 1, the same elements but different half-lives.• process 3 is clearly different. Here, U-238 captures only slow neutrons,and there are no further beta decays.Later, after the discovery of fission, it became clear that only process 3 waswhat it appeared to be. Processes 1 and 2 result from fission. From all the possiblefission products, the scientists were selecting out just those with thechemistry of transition elements, the ones they thought they were looking for.This diagram represents the combined efforts of radiochemistry and physics.The chemists were very confident. Hahn repeatedly wrote that there could be“no doubt” that these were transuranium elements: the genetic sequences (93decaying to 94 and so on) fit the expected chemistry of EkaRe, EkaOs, etc.,17 L. MEITNER, O. HAHN, and F. STRASSMANN, “Über die Umwandlungsreihen des Urans, die durchNeutronenbestrahlung erzeugt werden”, Zeitschrift für Physik, 106 (1937), pp. 249-270.140

Ruth Lewin SimeFROM FERMI TO FISSION: MEITNER, HAHN AND STRASSMANN IN BERLINso well it seemed it just had to be true. Meitner measured reaction cross-sections,neutron energies, and irradiation conditions; as the physicist she wasresponsible for interpreting all the results. And here there were problems.How could just one isotope, U-238, be the starting point for three differentprocesses? Why did the capture of just one neutron create such great instabilitythat it took many beta decays to alleviate it? How to explain triple isomerismand worse, the inherited isomerism of processes 1 and 2?Meitner knew that process 3 was the most normal: a resonance capture ofslow neutrons to form U-239, which was chemically identified as uraniumand which necessarily decays to element 93. If the Berlin team had detectedthis “93” and determined its chemical properties, they would have knownthat the “93” in processes 1 and 2 were not right. But they didn’t do it.Their neutron sources were too weak and, as Hahn later wrote, they werenot very interested: 18 after all, they already had found several transuraniumelements and that, of course, was what they were looking for.At the time no one contested this, although everyone was aware of theproblems. 19 Irène Curie and her co-workers in Paris were the Berlin team’schief competitors, and they verified it. Some physicists tried to find reactionmechanisms physically but they covered their ionization chambers to screenout the natural decay of uranium and never detected the large ionizationbursts from fission fragments. In Berkeley, Philip Abelson used thecyclotron as a neutron source – it was orders of magnitude more intensethan the ones in Europe and gave far more activities, but he too verified theBerlin results. Later he attributed it to the “high reputation and prestige”of the Fermi group. 20 Glenn Seaborg, also at Berkeley, regarded Hahn’s1933 book on Applied Radiochemistry as his bible; he avidly followed theBerlin publications and accepted the results. 21 And in 1938 Lawrence Quilldiscussed the difficulties in a 70-page article in Chemical Reviews, but he didnot question processes 1 and 2. Instead, he agreed that the elements up to97 were transition elements, and that the 5f sublevel would not beginbefore element 98. 22 14118 OTTO HAHN, A Scientific Autobiography, Willy Ley, transl. and ed., MacGibbon & Kee, London(1967), p. 175.19 For overview, see SIME, Lise Meitner, chapter 6.20 PHILIP H. ABELSON, “Discovery of Neptunium”, pp. 51-53 in L. R. MORSS and J. FUGER, eds., TransuraniumElements: A Half Century, American Chemical Society, Washington, D.C. (1992), pp. 50-55.21 GLENN T. SEABORG, Nuclear Milestones, W. H. Freeman and Company, San Francisco (1972), p. 5;SEABORG in HAHN, Autobiography, p. ix.22 LAWRENCE L. QUILL, “The Transuranium Elements”, Chemical Reviews, 23 (1938), pp. 87-155.

PROCEEDINGS OF THE INTERNATIONAL CONFERENCELater, after the fission discovery, Hahn would say that physics had misledthe investigation by insisting on small nuclear changes; he never acknowledgedthe mistaken assumptions of chemistry. 23 I have shown elsewhere thatHahn had political motives for separating himself from Lise Meitner andclaiming fission for chemistry. And one can argue that the limiting factor inBerlin was the radiochemistry: they separated out the precipitate with thesupposed transuranics, and almost never looked at the filtrate.In an interview in 1963, Meitner said: “I really think our misfortune wasthat we didn’t search the filtrate... The chemists absolutely didn’t want to. Ipestered them to do it while I was there because I was so disturbed by it”. 24The breakthrough came from Paris, where Irène Curie had devised amethod for measuring the uranium activities without separation. Early in1938, she and Pavel Savitch reported a strong new activity with uncertainchemistry. By the time Hahn and Strassmann looked into it, it was October1938. Meitner, who was of Jewish origin, had escaped from Germany a fewmonths before and had gone to Stockholm, but she and Hahn correspondedconstantly. Hahn and Strassmann separated the Curie activity and decidedit was an isotope of radium because it followed a barium carrier (figure 1).The reaction conditions were the same as in Processes 1 and 2, and againthere were several isomers.It is at this point that nuclear physics and radiochemistry were able to solvethe problem. It happened because chemists were now in familiar territory,working with elements whose chemistry and radiochemistry were known.When their findings conflicted with the physicists’ assumption of smallchanges, the discrepancy was obvious and could be resolved.We know from Meitner’s letters that she was doubtful about the radiumresult. From theoretical considerations she and other physicists were convincedthat slow neutrons could not make uranium eject even one alpha particle– and certainly not two. In November 1938 Meitner met Hahn inCopenhagen and, according to Strassmann, she “urgently requested” thatthey scrutinize the radium very intensively one more time. 25 In Berlin, Hahnand Strassmann began new experiments that led directly to the finding ofbarium a few weeks later.23 SIME, Lise Meitner, chapters 10, 11, 12.24 Lise Meitner interview by Thomas Kuhn, 12 May 1963: American Institute of Physics Oral HistoryProject, Tape 65a, transcript pp. 19-20.25 FRITZ KRAFFT, Im Schatten der Sensation: Leben und Wirken von Fritz Strassmann, Verlag Chemie,Weinheim (1981), pp. 208, 210.142

Ruth Lewin SimeFROM FERMI TO FISSION: MEITNER, HAHN AND STRASSMANN IN BERLINTo verify the radium, Hahn and Strassmann used Marie Curie’s method offractional crystallization, a classic radiochemical procedure, to separate theradium from its barium carrier. When there was no separation, they knewthat their “radium” was barium. Hahn informed Meitner about the barium,but he was mystified and asked her “for some sort of fantastic explanation”.Meitner responded instantly: “A major breakup seems very difficult tome...but one cannot unconditionally say: it is impossible”. 26 Within a weekshe and her nephew Otto Frisch, also a physicist, devised the first theoreticalinterpretation of the fission process, calculated the energy released, understoodthat the transuranium elements were fission fragments, and realizedthat only process 3 led to element 93.The barium was reported by the chemists, 27 and the theory by the physicists28 – separately, in different journals, in different languages. I have arguedthat this separation was artificial and unjust, the result of Meitner’s forcedemigration and the politics of the time. The separation did not reflect the science:it excluded physics from the discovery of barium. This artificial separationwas reinforced when Hahn later denied the role of physics and of LiseMeitner, and it was reinforced further by a Nobel Prize – a badly mistakenNobel prize – in chemistry that went to Hahn, alone. 29As a postscript, let me note that once fission was discovered, the interdependenceof nuclear physicists and chemists was essentially over. Thechemists were left with nothing but fission fragments – the false transuranicsthat had inspired such confidence turned out to be a messy mixture of lightelements from all over the periodic table. 30 Actually the chemists were leftwith less than nothing, since they still expected transuranium elements to betransition elements, and this prevented them from detecting the real element93 for more than a year. 31 In 1940 McMillan and Abelson found this 9326 SIME, Lise Meitner, pp. 233, 235.27 O. HAHN and F. STRASSMANN, “Über den Nachweis und das Verhalten der bei der Bestrahlung desUrans mittels Neutronen entstehenden Erdalkalimetalle”, Naturwissenschaften, 27 (1939), pp. 11-15.28 L. MEITNER and O. R. FRISCH, “Disintegration of Uranium by Neutrons: A New Type of NuclearReaction”, Nature, 143 (1939) pp. 239-240.29 ELISABETH CRAWFORD, RUTH LEWIN SIME, MARK WALKER, “A Nobel Tale of Wartime Injustice”,Nature, 143 (1996), pp. 393-396; “A Nobel Tale of Postwar Injustice”, Physics Today, 50:9(September 1997), pp. 26-33; Friedman, Politics of Excellence, pp. 232-250.30H. MENKE and G. HERRMANN, “Was waren die ‘Transurane’ der dreißiger Jahre in Wirklichkeit?”,Radiochimica Acta, 16 (1971), pp. 119-123.31 EMILIO SEGRÈ, A Mind Always in Motion: The Autobiography of Emilio Segrè, University of CaliforniaPress, Berkeley (1993), pp. 152-153.143

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE(neptunium) and showed that its chemistry was more like uranium than rhenium,the first evidence of the 5f series. 32Fission belonged to nuclear physics, and it took off rapidly, with remarkabledevelopments in experiment and theory. In contrast to the chemistry,the physics data of the previous years was entirely valid. For example, NielsBohr immediately used the reaction cross-sections that Meitner had measuredin 1937 to deduce that the fissile isotope of uranium was U-235 andnot U-238. Fermi, at Columbia, was instantly involved as well, all his experiencewith neutrons coming into play. Now we have returned to Fermi andI will end my talk, since I know this next period in Fermi’s work will be coveredby other speakers.Ruth Lewin SimeA native of New York City who taught undergraduate chemistry at SacramentoCity College for many years, she has been concerned with attractingwomen and minorities to the physical sciences. Sime’s interest in history of sciencebegan when she taught a women science course and discovered thatsurprisingly little was known of Lise Meitner’s life and work. Her biography“Lise Meitner: A Life in Physics” appeared in 1996 and has been translatedinto several languages. Recently Sime retired from teaching to work on astudy of Meitner’s colleagues Otto Hahn and Max von Laue during theNational Socialist years and the postwar period.32 GLENN T. SEABORG and WALTER T. LOVELAND, The Elements Beyond Uranium, John Wiley & Sons,New York (1990), pp. 8-11, 65ff.; Abelson, “Neptunium”, pp. 53-55.144

Ugo AmaldiSlow Neutrons at Via Panisperna:the Discovery, the Production of Isotopesand the Birth of Nuclear MedicineThe paper sent to La Ricerca Scientifica in March 1934 by Enrico Fermi titled“Radioattività indotta dal bombardamento di neutroni - I” was the first of along series published on the same subject with his collaborators E. Amaldi,O. D’Agostino, B. Pontecorvo, F. Rasetti and G. Segrè. These papersdescribe the production of about fifty new artificial radioactive isotopes andcontain four major discoveries. The first part of this contribution describes thefirst two of them: the initial observation by Fermi and the discovery in October1934 of the very large effects produced by slow neutrons. The second partaddresses a non-scientific question: why that day Fermi suddenly decided toplace, between the neutron source and the material to be bombarded withneutrons, a piece of paraffin instead of the lead block he was machining?With the help of a recent paper by Alberto De Gregorio, one can guess theunconscious thoughts that may have induced Fermi to make the move thatbrought to the second discovery. The third part discusses the actions that wenton in Rome from 1935 to 1938 to secure the production of radioactiveisotopes to be used in medicine. In these developments – together with Fermi,Rasetti and Amaldi – two figures are most important: Giulio Cesare Trabacchiand Domenico Marotta, the leaders of the physics and chemistry laboratory ofthe Istituto di Sanità Pubblica. The presentation is focused on the proposalmade by Marotta, with the support of Fermi, of the construction of the 1 MeVCockcroft-Walton electrostatic accelerator and the discovery, made in Palermoin 1937 by Segrè and Perrier of technetium, the element that is used in 90%of all modern nuclear medicine examinations.145

PROCEEDINGS OF THE INTERNATIONAL CONFERENCENeutroni lenti a via Panisperna:la scoperta e la produzione degli isotopie la nascita della medicina nucleareLa relazione inviata da Enrico Fermi alla Ricerca Scientifica nel marzodel 1934, intitolata “La radioattività indotta dal bombardamento dineutroni”, fu la prima di una lunga serie di pubblicazioni sulle stessetematiche, realizzate con la collaborazione di E. Amaldi, O. D’Agostino,B. Pontecorvo, F. Rasetti e G. Segrè.Queste pubblicazioni descrivono la creazione di circa cinquantanuovi isotopi radioattivi artificiali e contengono quattro importantissimescoperte. La prima parte della relazione riguarda le prime due, e riporta leosservazioni iniziali fatte da Enrico Fermi e la scoperta, nell’ottobre 1934,degli imponenti effetti provocati dai neutroni lenti, mentre la secondaaffronta un importante quesito scientifico, ovvero cosa spinse Enrico Fermiad apporre, tra la sorgente neutronica ed il materiale da bombardare, unpezzo di paraffina anziché il blocco di piombo al quale stava lavorando.Una recente pubblicazione di Alberto De Gregorio può essere d’ausilio allacomprensione dei processi inconsci che potrebbero aver condotto Fermialla seconda scoperta. La terza parte prende in esame l’arco di tempo cheva dal 1935 al 1938, nel quale il gruppo romano concentrò la sua ricercasulla produzione di isotopi radioattivi a scopi medici. Due nomi risaltanoparticolarmente, assieme a quelli di Fermi, Rasetti ed Amaldi: quelli diGiulio Cesare Trabacchi e Domenico Marotta, direttori dei laboratori difisica e di chimica dell’Istituto di Sanità Pubblica. Questo contributo discutela proposta, fatta da Marotta e sostenuta da Fermi, della costruzionedell’acceleratore elettrostatico Cockcroft-Walton da 1 MeV e sulla scopertafatta a Palermo nel 1937, da Segrè e Perrier, del technetium, l’elementoimpiegato nel 90% delle moderne diagnostiche mediche.146

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAArtificial radioactivity produced by neutronsThe long stream of experiments initiated by the first paper on neutronradioactivity, published by Enrico Fermi in March 1934, led to four majordiscoveries:(i) the radioactivity induced by neutrons,(ii) the radioactivity induced by neutrons slowed down by collisions withlight nuclei, in particular hydrogen,(iii) the law of the inverse of the velocity, with which slow neutrons areabsorbed in nuclei with the emission of gamma rays,(iv) the existence of strong selective absorption bands and the effect of chemicalbonds on the phenomenon.In the first part of this contribution I will discuss only the first two discoveries,so as to devote the second part to the much less known parallel engagementof Fermi and collaborators in trying to secure the abundant productionof new isotopes for medical and industrial applications.The first two papers on the discovery of the radioactivity induced by neu-Figure 1Enrico Fermi with hisdaughter Nella in 1931147

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtrons are signed by Fermi [1]. Already in the second, one he acknowledgesthe contribution of Amaldi and Segrè in carrying out the experiment. Howthis happened is described by Edoardo Amaldi in a Physics Report publishedin 1984, exactly fifty years after the events [2]. In a Section that bears the title‘Fermi’s discovery’ he writes [3]:“After the papers of Joliot and Curie were read in Rome, Fermi, at thebeginning of March 1934, suggested to Rasetti that they should try toobserve similar effects with neutrons by using the Po a + Be source preparedby Rasetti. About two weeks later several elements were irradiated and testedfor activity by means of a thin-walled Geiger-Müller counter but theresults were negative due to lack of intensity”.“Then Rasetti left for Morocco for a vacation while Fermi continued theexperiments. The idea then occurred to Fermi that in order to observe aneutron induced activity it was not necessary to use a Po α + Be source. Amuch stronger Rn α + Be source could be employed, since its beta andgamma radiations (absent in Po α + Be sources) were no objection to theobservation of a delayed effect.Radon sources were familiar toFermi since they had been suppliedpreviously by Professor G.C.Trabacchi (of the LaboratorioFisico dell’Istituto di SanitàPubblica) for use with the gammarayspectrometer”.“All one had to do was to preparea similar source consisting of aglass bulb filled with berylliumpowder and radon. When Fermihad his stronger neutron source(about 30 millicurie of Rn) he systematicallybombarded the elementsin order of increasing atomicnumber, starting from hydrogenand following with lithium, beryllium,boron, carbon, nitrogen andoxygen, all with negative results.Finally, he was successful inFigure 2One of the Roman Geiger counters, made byEdoardo Amaldi from an aluminium pill boxobtaining a few counts on hisGeiger-Müller counter when hebombarded fluorine and alumini-148

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAum. These results and their interpretation in terms of (n,(γ) reaction wereannounced in a letter to Ricerca Scientifica on March 25, 1934. The title:Radioattività indotta da bombardamento di neutroni – I indicated hisintention to start a systematic study of the phenomenon which wouldhave brought to the publication of a series of similar papers”.“Fermi wanted to proceed with the work as quick as possible and thereforeasked Segrè and me to help him with the experiments, as it appearsalso from the acknowledgement at the end of his second Letter to theEditor of the Ricerca Scientifica where he reported preliminary resultsobtained in a number of other elements (Si, P, Cl, Fe, V, Cu, As, Ag, Te,Cr, Ba)”.“A cable was sent to Rasetti asking him to come back from his vacation.The work immediately was organised in a very efficient way. Fermi, helpeda few days later by Rasetti, did a good part of the measurements and calculations,Segrè secured the substances to be irradiated and the necessaryequipment and later was involvedin most of the chemical work. Itook care in the construction ofthe Geiger-Müller counters and ofwhat we now call electronics. Thedivision of the activities, however,was not rigid at all and each of usparticipated in all phases of thework. We immediately realisedthat we needed the help of a professionalchemist. Fortunately wesucceeded almost immediately inconvincing Oscar D’Agostino,[…] (who) had held a fellowshipin Paris in the laboratory ofMadame Curie. […] The resultsobtained during the first twoweeks were summarised by Fermiin a letter to Nature”.Since then, the Rome groupworked actively together and by summer1934 about fifty new radioactiveisotopes had been found and threearticles had been published in LaRicerca Scientifica [4], where at theFigure 3From the left, Edoardo Amaldi, Franco Rasettiand Emilio Segrè during a walk in thesurroundings of Rome149

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtime Ginestra Giovene – who was an astronomer before becoming in 1933Edoardo’s wife – worked as assistent editor. Through her, the reprints weremade available within days, so that they could be sent by mail to a selected listof prominent physicists: the Rome group was the first to use ‘preprints’ tospread its results rapidly.Because of the organisation of the work and the use of preprints the Romegroup, as discussed by Gerald Holton [5], was the first team of physicists actingas it has become customary after the Second World War.In summer 1934, a manuscript summarising the work done in Rome wasbrought by Amaldi and Segrè to Lord Rutherford in Cambridge [6]. At thefirst encounter, Segrè asked whether it would be possible to obtain promptpublication in the Proceedings of the Royal Society. Many years later hewrote: “I imprudently recommended prompt publication, whereupon heanswered, whether in jest or annoyance I could not tell ‘What do you thinkI am the President of the Royal Society for?’” [7]. Amaldi adds:“Unfortunately our understanding of Rutherford English at the time wasimperfect and we could not follow most of his remarks, many of which musthave been humorous because he laughed from time to time and only thentook the pipe out of his mouth” [8].The effect of slow neutronsThe way to the second discovery was opened when, on October 18 th ,1934, Edoardo Amaldi started a systematic investigation to clarify the miraculousproperties of some wooden tables, on which the induced radioactivitywas larger than the one measured with the same apparatus mounted on amarble table.The Physics Report contains many more interesting, and by now wellknown, details [9]:“In the paper published by Fermi’s group in the Proceedings of the RoyalSociety the activity of the various artificial bodies had been classified onlyqualitatively. […] Therefore, around the middle of September 1934, wedecided to try to establish a quantitative scale of activities which for themoment could be in arbitrary units. This work was assigned to me and B.Pontecorvo (b. 1913), one of our best students, who had taken thedegree (laurea) in July 1934 and after the summer vacations had joinedthe group. We started by studying the conditions of irradiation most convenientfor obtaining well reproducible results. For this type of work weused the activity of 2.3 min half-life of silver”.150

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNA“We immediately found, however, some difficulty because it becameapparent that the activation depended on the conditions of irradiation. Inparticular in the dark room, where usually we carried out the neutron irradiation,there were certain wooden tables near a spectroscope that hadmiraculous properties. As Pontecorvo noticed accidentally silver irradiaedon those tables gained more activity than when it was irradiated on theusual marble table in the same room”.“These results, daily reported to Fermi and the others, were friendly, butat the same time strongly, criticised by Rasetti who, in a teasing mood,insinuated that I and Pontecorvo were unable to perform ‘clean andreproducible measurements’”.“In order to clarify the situation I started a systematic investigation. In thenote book B1, where the data of that period are recorded, these measurementswere started on October 18, 1934. Page 3 [contains] the summaryof a typical series of measurements made inside and outside a leadhousing (‘castelletto’), the walls of which were 5 cm thick. […]”“On the morning of October 22 most of us were busy doing examinationsand Fermi decided to proceed in making the measurements. BrunoRossi from the University of Padua and Enrico Persico from theUniversity of Turin were around in the Istituto di Via Panisperna andFigure 4Ginestra Giovene Amaldi had adegree in astronomy and, afterworking at “La Ricerca Scientifica”, in1936 wrote with Laura Capon Fermi“Alchimia del nostro tempo” (Alchemyof our time), the first Italian book onmodern physics for the layman. Afterthe war she wrote alone many otherpopular science books, of which thebest known has been translated in fourlanguages151

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEPersico was, I believe, the only eyewitness of what happened. At themoment of using the lead Fermi decided suddenly to try it with a wedgeof some light element and paraffin was used first. The results of thesemeasurements are recorded on pages 8 and 9 of the same note book B1.They are written by Fermi at the beginning and towards the end byPersico. Towards noon we were all summoned to watch the extraordinaryeffect of the filtration by paraffin: the activity was increased by an appreciablefactor”.On the same day other well-known episodes took place. Starting with themeasurements – performed in the water of a fountain – and ending with theexcitement of the authors of the letter written to La Ricerca Scientifica in theapartment of the Amaldi’s. Emilio Segrè described the scene as follows:“Fermi dictated while I wrote. He stood by me; Rasetti, Amaldi andPontecorvo paced the room excitedly, all making comments at the sametime. The din was such that when we left, Amaldi’s maid discreetly askedwhether the evening guests were tipsy. Ginestra Amaldi handed the paper toher boss at La Ricerca Scientifica the following morning” [7].Why paraffin?The paper published by La Ricerca Scientifica was the first step along a trailwhich brought to the discovery of other new radioactive species, to the confirmationof the 1/v law for the reaction cross section, to the experimental definitionof the various neutron ‘groups’, to the discovery of chemical effects andto the experimental evidence of the presence of neutron resonances.Leaving aside these very important scientific consequences of the initial discovery,I shall concentrate in this Section on a non-scientific question: whydid Enrico Fermi suddenly decide to choose a block of paraffin?Many years later Fermi himself described what happened to SubrahmanyanChandraseckhar who reported the episode with the following words [10]:“Others with greater competence have written about Fermi’s fundamentalcontributions to physics. But his own account of the critical momentwhen the effect of the slowing down of neutrons on their ability to inducenuclear transformations was discovered is perhaps worth recording. Idescribed to Fermi Hadamard’s thesis regarding the psychology of inventionin mathematics, namely, how one must distinguish four differentstages: a period of conscious effort, a period of ‘incubation’ when variouscombinations are made in the subconscious mind, the moment of ‘reve-152

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAlation’ when the ‘right combination’ (made in the subconscious) emergesinto the conscious, and finally the stage of further conscious effort. I thenasked Fermi if the process of discovery in physics had any similarity. Fermivolunteered and said (his account made so great an impression on me thatthough this is written from memory, I believe that it is very nearly a trulyverbatim account): ‘I will tell you how I came to make the discoverywhich I suppose is the most important one I have made. We were workingvery hard on the neutron-induced radioactivity and the results wewere obtaining made no sense. One day, as I came to the laboratory, itoccurred to me that I should examine the effect of placing a piece of leadbefore the incident neutrons. Instead of my usual custom, I took greatpains to have the piece of lead precisely machined. I was clearly dissatisfiedwith something: I tried every excuse to postpone putting the piece oflead in its place. I said to myself: ‘No, I do not want the piece of lead here;what I want is a piece of paraffin’. It was just like that with no advancewarning, no conscious prior reasoning. I immediately took some oddpiece of paraffin and placed it where the piece of lead was to have been’”.Figure 5The Institute of Via Panisperna in Rome. On the top floor lived the Corbino family153

PROCEEDINGS OF THE INTERNATIONAL CONFERENCETo complete the picture, in his book on Fermi Bruno Pontecorvodescribed what happened immediately after the first observation [11]:“The results were most surprising: the silver activity was hundreds oftimes greater than the one previously measured. Fermi stopped the confusionand agitation of his collaborators pronouncing a famous sentencethat, they say, he repeated eight years later at the start-up of the firstnuclear reactor: ‘Let us go for lunch’. … [In the discovery of the effect ofslow neutrons] some accidental circumstances and the depth and intuitionof a great mind, both played a crucial role. When we asked Fermi why hehad used paraffin instead of lead, he smiled and teasingly said ‘C.I.F.’, thatin Italian can be read ‘Con Intuito Formidabile’ (with formidable intuition).If the reader would conclude that Fermi was immodest he wouldbe grossly wrong. He was direct, very simple and modest, but he was wellconscious of his qualities. To this point I can add that, after lunch whenhe came back to the Institute and explained very clearly the effect of theparaffin block - thus introducing the concept of the slowing down of neutrons- with total sincerity he told us: ‘What a stupidity to have discoveredthis effect by chance without having being capable of predicting it’”.Figure 6Senator Orso Mario CorbinoC.I.F. was an expression invented andused in the Rome group, as reported byEmilio Segrè in his autobiography:“C.I.F. (Con Intuito Formidabile)[was] a joking acronym we used forstatements by Fermi that were true, butthat he could not prove” [12].Immediately after the discoveryFermi proposed the correct explanationof the phenomenon by combiningthree arguments. Firstly, the neutronsslow down through elastic collisionswith the hydrogen nuclei of paraffin orwater. Secondly, the reaction cross sectionon nuclei decreases with the velocityof the neutron, so that slow neutronsare more effective than fast neutronsin producing radioactive substances.Thirdly, the reaction cross sectionfor all the processes in which the154

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAneutron is absorbed is much smaller than the neutron-proton elastic cross section,so that the slowing down phenomenon can take place.At that time, the terms “slow neutrons” and “fast neutrons” were used bysome physicists and many thought that the elastic cross section against protonwas decreasing with an increase of the neutron velocity. Instead, everybodywas expecting that the reaction cross section of the neutrons wouldincrease, and not decrease, with their velocity since intuitively larger energies inan inelastic collision produce more and not less damage. Fermi guessed thatthe opposite was true and this indeed was the fully unexpected physics resultof that momentous day.However any reasoning built up a posteriori does not account for the mentaljump by which Fermi told himself “what I want is a piece of paraffin”.Recently Alberto De Gregorio has carefully examined the experimental factsthat were surely known to Fermi at that moment and could shed light on thesudden decision to use paraffin and not something else [13]. In the first partof his paper he traces the experiments that in the years 1932 and 1933 hadconvinced the physicists working with neutrons that these particles are morescattered and absorbed by paraffin than by lead. For this it is enough toquote here the Joliot-Curies who wrote [14]: “The radiation emitted by a Po+ Li source is much more absorbed, for the same mass per square centimeter,by paraffin rather than by lead, at variance with what happens to thegamma rays emitted by polonium”.In connection with the knowledge that Fermi had of these results, DeGregorio points out the importance of the detailed discussions that tookplace at the Solvay Conference on Structure et propriétés des noyaux atomiques.This Conference was held in Bruxells from October 22 to October 29,1933 – exactly one year before the discovery [15]. There J. Chadwick discussedthe available knowledge on the collisions between neutrons and atomicnuclei by specifying [16]: “It seems that, in general, slow neutrons aremore easily scattered than fast neutrons. […] I found that the collision radiusof hydrogen varies with the velocity of the neutrons. […] Some experimentswith slow neutrons seem to indicate that the collision radius [i.e. the elasticcross section] continues to increases when the neutron velocity decreases”.He even went so far as to derive – from the fact that slow neutrons behaveas waves and their wavelength is much larger than the nuclear radius – a formulain which the elastic cross-section is inversely proportional to the squareof the velocity. This formula, reproduced in the proceedings, had been publishedby him previously.155

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEAt the same Conference the Joliot-Curies presented a paper titledRayonnement pénétrant des atomes sous l’action des rayons alfa, where theresults discussed above were presented. As underlined by De Gregorio, thediscussion following this presentation is very illuminating due to the qualityand the number of the interventions: Meitner, Chadwick, Perrin, Heisenberg,Fermi, de Broglie, Bothe, Lawrence, Gamow, Rutherford, Peierls,Bohr, Pauli… . Heisenberg expressed doubts about the inverse square lawand Fermi, after recalling the hypotheses needed for deriving Chadwick’s formula,said “the experimental cross sections are many times smaller than whatis predicted by the formula”.De Gregorio concludes his paper by writing: “Fermi’s intervention inBruxells proves the interest of the Roman physicist for the behaviour of neutrons.We can definitely state that, already at the end of 1933, he was awareboth of the increase of the [neutron-proton] scattering cross section whenthe energy decreases and of the larger efficiency of paraffin with respect tolead in the slowing down and in the absorption of neutrons. […] The suddendecision of October 1934 would thus have been the result of a subconsciouselaboration of what was already known to the Italian physicist. Such areconstruction would, among other things, confirm Hadamard’s thesis onthe psychology of inventions in mathematics. [… The hypothesis of a previousunconscious elaboration of known information] is supported by the veryfact that Fermi [in answering to Chandrasekhar] thought to his ‘sudden’decision to use paraffin as an example that could confirm the hypothesis ofthe great French mathematician”.Of course this chain of arguments does not reduce Fermi’s merits for both1. the experimental discovery of an unexpected phenomenon, that followedsix months of concentrated work performed with his collaborators, and2. the prompt interpretation of the observations, which required the newhypothesis of an increasing reaction cross section when the neutron velocitydecreases.The patentLeaving the main course of the Roman discoveries, I now wish to discussthe activity that went on in Rome to secure the production of radioactive isotopesfor medical and industrial applications. The beginnings of this developmentcan be traced back to Orso Mario Corbino, the Director of theInstitute and Fermi’s mentor. As described by Laura Fermi in Atoms in thefamily, the first scene went as follows [17]:156

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNA“One morning, a couple of days after [the discovery], Corbino came tothe laboratory; although he did not actively participated in research, hekept informed and often gave good advice. He had followed the youngermen’s work step by step, and on that morning also he asked to be toldwhat they were at. They were preparing to write a more extensive reporton their experiments, they answered. Corbino became incensed. ‘What?Do you want to publish more than you have already?’ he asked in a swiftrush of words, helping the oral expression with brisk gestures, as allSicilians do. ‘Are you crazy? Can’t you see that your discovery may haveindustrial applications? You should take a patent before you give out moredetails on how to make artificial radioactive substances!’”.The boys of Via Panisperna had not thought about this possibility and at thebeginning they considered it completely at variance with what respectable scientistsdo of their discoveries. But Corbino was a very practical man connectedwith many industries and had a lot of influence on the people around him.Thus on October 26, only four days after the discovery, Amaldi, D’Agostino,Fermi, Pontecorvo, Rasetti, Segrè, and Trabacchi – the ‘Divine Providence’who had provided the radon for the neutron sources – jointly applied to obtaina patent for their process to produce artificial radioactivity with slow neutrons.The Italian patent n. 324 458 was later extended to other countries. Its historyis very interesting, but there is no space for it in this contribution.Figure 7From the left, Oscar D’Agostino and Giulio Cesare Trabacchi,the “Divine Providence”As often said by Edoardo Amaldi, the patent was a really unexpected outcomeof their research. In the 1984 Physics Report he wrote [18]: “We wereextremely pleased and amused, not so much because a patent could result,sometime in the future, in a financial benefit for the ‘inventors’, but ratherbecause a work, carried out with great energy and dedication, only for its157

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEintrinsic merits, had, unexpectedly, brought us to applications, which, inaddition, would be mainly of a scientific and medical nature”.The medical applications were of immediate interest for Giulio CesareTrabacchi (the ‘Divine Providence’), who was the leader of the small but relativelyrich Laboratorio Fisico della Sanità Pubblica. This Laboratory was createdby Corbino, who in the years 1921-1922 had been Minister ofEducation in the last democratic government before Mussolini took power.Since then the Laboratory was occupying four offices of the building of ViaPanisperna. The radon for the neutron sources, used by Fermi and collaborators,was extracted from the radium belonging to the public health serviceand kept in the basement of the same building.The first Italian acceleratorAfter the patent was deposited, it must have been very natural for Trabacchito get interested in the medical utilisation of the new isotopes the person whowas his colleague as leader of the Laboratorio Chimico della Sanità Pubblica:Domenico Marotta (1886-1964) [19]. Marotta was a chemist and a great sciencemanager. He had been for a few years one of the main promoters of thecreation of the Istituto di Sanità Pubblica, whose building was funded in 1929by the Rockfeller Foundation and inaugurated by Mussolini on April 21 st ,1934. The Physics Laboratory, led by Trabacchi, and the ChemistryLaboratory, led by Marotta, became two of the five laboratories forming thenew Institute. At the beginning of 1935 Domenico Marotta was nominatedDirector of the Health Institute and Trabacchi and his small group movedfrom Via Panisperna to the new building on Viale Regina Margherita [20,21].Marotta had very clear ideas about the importance of fundamental researchin the life of the new Institute, and greatly valued the collaboration of Fermiwho was known worldwide and could also have political influence since hewas the youngest member of the Accademia d’Italia created by Mussolini.After many discussions with Trabacchi and Fermi, on October 21, 1935,exactly one year after the discovery of slow neutrons, Domenico Marottawrote to Fermi to obtain a written statement on the possible practical uses ofthe new radioactive substances. The reply, dated October 23, 1935 containsthe following statement [22]:“I believe that it is reasonable to predict that, in a near future, it will bepossible to currently produce artificial radioactive bodies having activitiesequal or greater than the ones of the radioactive sources now used in ther-158

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAFigure 8Domenico Marotta during the visit at the Istituto Superiore di Sanità of her Highness Maria Josè,Princess of Piedmontapy. Thus the artificial sources will be at least equivalent, and probably lesscostly, than radium. Given the variety of elements in which, with the newmethods, artificial radioactivity can be produced, there is also the possibility– which can only be checked with extensive dedicated studies – thatsome elements will be found that are particularly convenient as far as theirchemical and physiological properties are concerned”.Since it was obvious that more intense neutron sources were needed forboth fundamental research and new medical applications, during the year1936 the subject was widely discussed in Rome between Fermi, Marotta,Trabacchi and Amaldi. At that time the other junior members of the groupwere far away: Rasetti was for one year at Columbia University, Segrè hadbeen appointed professor in Palermo and Pontecorvo, after devoting himselffor some time to theoretical physics with G.C. Wick, went to Paris to workwith the Joliots. Since one of the main subjects of discussion was the choicebetween an electrostatic accelerator and a cyclotron, it was decided that159

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEdirect information should be collected on the matter. Thus in summer 1936Edoardo Amaldi left for the United States, sharing his time betweenColumbia University and the Carnegie Institute of Washington, where MerleTuve and collaborators had constructed a new type of Van de Graf electrostaticaccelerator. Before going to the States Amaldi reported about the workdone in Rome at the international “Probleme der Atomkernphysik” held inCopenhagen from June 14 to June 20, 1936. In listening to the other presentationshe got even more convinced of the fact that, in order to be scientificallycompetitive, more intense neutron sources were mandatory.In the following months, Trabacchi requested for his laboratory a one millionvolt electrostatic accelerator with a current of 10 milliampere, most probablybecause he was convinced that a cyclotron was too expensive. On October 16,1936, Marotta wrote again to Fermi indicating his decision to engage hisInstitute in the production of radioactive isotopes [23]. The phrasing of the letterindicates that he considered the electrostatic accelerator requested byTrabacchi insufficient and that he was pushing in the direction of a much morepowerful cyclotron. Marotta wanted also to be sure that Fermi was ready to collaborate,in case the needed funds would have been found.Fermi’s reply was reproduced by Marotta in the document sent onDecember 20, 1936, to the Cabinet of the Minister [24]. In this memorandumthe idea of the cyclotron is not even mentioned, one – and not ten –milliaperes are quoted and the following excerpts of the reply by Fermi arereproduced.“Having an apparatus of up to one million volt, the best method to produceneutrons consist in bombarding with nuclei of heavy hydrogen a targetof either beryllium or lithium. With a beryllium target and one millionvolt, the yield is 1.5 10 11 neutrons for a current of one milliampereof deuterium ions. […] With a current of one milliampere one can produceartificial radioactive substances having an activity of up to twoCuries. […] With short irradiations one could use iodine (with a lifetimeof 25 minutes), for intermediate irradiations manganese (lifetime: 2.5hours), arsenic for long irradiations (26 hours) or other substances, ascobalt and iridium, that have months long lifetimes. On top of the applicationsto cancer therapy, sizeable quantities of artificial radioactive substancescould be used as tracers in chemistry and biochemistry research”.For the one million volt accelerator Marotta requested 300,000 lire as investmentmoney and 100,000 lire per year as running budget. Being a very capablescience manager Marotta added also the following economic argument:160

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNA“The apparatus could produce eight curie-hour per day that, at the presentmarket prices, have a commercial value of 2,500 lire. Thus the runningcosts would be covered with only 40 irradiation days per year. Giventhe large demand of radioactive substances this minimum will certainly bepassed and not only the facility will be profitable, but also the cost of theproducts could be reduced, so that their use will be extended with benefitsfor humankind”.As underlined by G. Battimelli [25], the arguments put forward were medicalbut certainly another reason, not written in the memorandum to theHealth Minister, was very clear to him and to all the physicists working inRome. An accelerator would have allowed the group to compete in nuclearfundamental research with foreign laboratories, that already had accelerators.They knew very well that to this end a cyclotron would have been better thana Cockcroft-Walton, but the cost would have been much larger. The fear toloose everything by asking too much is probably at the basis of Marotta’schoice to single out the electrostaticaccelerator for the request to theMinistry.Waiting for the funds, a prototype200 keV Cockcroft-Walton was constructed;it accelerated particles inJune 1937, as reported in a papersigned by Amaldi, Fermi and Rasetti[26]. Shortly afterwards Amaldi wasappointed to the chair of Corbino,who had prematurely died. Thefunds for the accelerator were availableand the construction had juststarted when, at the end of 1938,Fermi left for the States directly afterreceiving in Stockholm the Nobelprize for the discovery of theradioactivity induced by neutrons.With this momentous event, theRome group ceased to exist. In thefollowing year Amaldi andTrabacchi completed – with the newjunior members of the laboratoryFigure 9The Cockcroft-Walton was built on the top floorof the Istituto Superiore di Sanità161

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEMario Ageno and Daria Bocciarelli – the 1.1 MeV Cockcroft-Walton of theHealth Institute [27]. The first Italian accelerator was at the level of the onesrunning at that time at the National Bureau of Standards, the NationalPhysical Laboratory, the Physikalische Technische Reichsanstalt and theHôpital St. Antoine. Shortly after, Francis Aston [of the CavendishLaboratory] and Otto Hahn [the discoverer of fission] visited the physicslaboratory of the Health Institute and the accelerator and declared that “thiswas the most beautiful laboratory they had ever seen” [28].The accelerator was still running when, twenty years later, I entered as ajunior fellow the Physics Laboratory of the Istituto Superiore di Sanità (ISS).The birth of nuclear medicineOn April 29, 1938, six months before receiving the Nobel prize, in thecrowded auditorium of the Istituto di Sanità Pubblica Fermi addressed thestaff on ‘Prospects of application of artificial radioactivity’ [29]. After a presentationon the history of artificial radioactivity – illustrated with a simpleexperiment that used a Geiger counter and a piece of rhodium – he showeda picture of a cyclotron and a drawing of the Cockcroft-Walton, which wasFigure 10This picture was taken at the Istituto Superiore di Sanità after Fermi’s speech.From left to right: G.C. Trabacchi, E. Fermi and D. Marotta162

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAat that time under construction on the sixth floor of the same building. Toquantify the advantage of this costly apparatus he said that the acceleratorwould produce the same neutron flux as a radon-beryllium source based onsome kilograms of radio, one thousands times more than the one gram theyhad been using in Rome.In the concluding part he shortly mentioned the therapeutic uses of thenew isotopes and added:“Independently of these possibilities, the use of sizeable quantities of artificialradioactive substances will open the way, I hope, to many interestingstudies in biology and chemistry in which the radioelements will be usedas ‘tracers’. […] By mixing radioactive phosphor with the phosphor containedin the aliments one can follow the behaviour of this element in aliving being, as has been already proved in the beautiful experiments startedby Hevesy in Copenhagen and continued by Segrè and Camillo Artomin Palermo”.In 1938 the use of radioactive isotopes in medicine for diagnostic purposeswas in its infancy. In 1923 Georg von Hevesy had for the first time used anatural radioisotope of lead to study the metabolism in plants. In 1925Hermann Blumgart and Soma Weiss had studied with radioisotopes thevelocity of circulating blood. In 1936 the cyclotron, built by ErnestLawrence in Berkeley, had been used by John Lawrence to produce phosphorus-32for medical treatments. As mentioned by Fermi, the same isotopewas employed in 1936 for metabolic studies of the mouse by Segrè andArtom, who was professor of physiology in Palermo. In 1937 in BerkeleyJoseph Hamilton had used radioactive sodium to study the human metabolismof food.The scarcity of applications fully justify the ‘I hope’ in the sentence ‘it willopen the way to many interesting studies’ pronounced by Fermi, who wasalways very careful before making strong statements. His care was furtherjustified by the fact that the few artificial radioisotopes utilised at that timehad been produced with reactions initiated by the high energy particles acceleratedby the Lawrence cyclotron and not by slow neutrons.Of course Fermi could not know that at the time of his public lecture theradioactive element that is now used in more than 90% of all nuclear medicinediagnostics tests had already been produced and discovered by no lessthan his collaborator Emilio Segrè. Let us read how Segrè himself describesin his autobiography the discovery of ‘technetium’ [30]:163

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE“In February 1937 I received a letter from Lawrence containing moreradioactive stuff. In particular, it contained a molybdenum foil that hadbeen part of the cyclotron deflector. I suspected at once that it might containelement 43. […] For this investigation I enlisted the cooperation ofCarlo Perrier, who had more experience in chemistry than I. First we separatedthe activity we were studying from all known elements. […] Nextwe established several of the chemical properties of element 43. […] Wehad two radioactive isotopes: technetium 95, with a period of 61 days,and technetium 97, with a period of 90 days. […] In this work we haddiscovered the first chemical element created by man”.Figure 11The cover of the autobiography of Emilio Segrè,published in 1993 by the University of CaliforniaPress, OxfordThis was no little achievementsince previously many had prematurelyclaimed the discovery of theelement having 43 electrons, thatwas given in turn the followingnames: ilmenium, davyum, lucium,nipponium and masurium [31].Due to this long story of failuresSegrè and Perrier decided not toname the new element till everybodywould have agreed on thesolid foundations of their claim.The name technetium, justified bythe fact that this was the first artificialelement ever produced, wasproposed by them only ten yearslater [32].The masurium story is related tothe missed discovery of fission and ashort detour is fully justified.Going back to 1934, it is wellknown that in Rome many newactivities were found when bombardingthorium and uranium. In a first letter, published in May, it is written[33]: “Using chemical operations, an attempt was made to determinewhether the element, which [is formed in an uranium target and] disintegrateswith a period of 13 min, is an isotope of one of the heavy elements.[…] This complex of conclusions, which we are trying to corroborate bymeans of further experiments, give rise to the spontaneous hypothesis that164

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNAthe active substance of uranium might have atomic number 93 (homologouswith rhenium)”.The interpretation of the Rome group was discussed by von Grosse andAgruss [34] and by Ida Noddack [35]. In the paper of the first two authorsthe hypothesis of the creation of different transuranic elements was supportedwith chemical data, while the second contained the much-quoted sentence:“One can think that by bombardment of heavy elements with neutrons,these nuclei break in many large pieces, which are isotopes of knownelements, but not neighbouring of those irradiated”.After the discovery of the effect of paraffin in October 1934, the Romegroup irradiated with slow neutrons uranium and thorium finding many newactivities that were sensitive to the presence of a light material capable of slowingdown the neutrons and seemed to confirm the previous interpretationbased on transuranic elements. This was supported also by two papers writtenby O. Hahn and L. Meitner [36]. Why the Rome group did not consider theproposal by Ida Noddack? About this very puzzling question Amaldi wrote thefollowing [37]:“The work by Ida Noddack was not taken seriously by any one of the peopleworking in the field. She sent her paper to Fermi and both, she andher husband, communicated repeatedly their point of view to O. Hahnduring the years 1934-1935 and 1936. [I seem] to remember some discussionsamong the members of our group, including Fermi, in which theideas of Noddack were hastily set aside because they involved a completelynew type of reaction: fission. Enrico Fermi, and all of us grown at hisschool followed him [and] were always very reluctant to invoke new phenomenaas soon as something new was observed: New phenomena haveto be proved! As later developments showed, a much more fruitful attitudewould have been to try to test Noddack’s suggestion and eventuallydisproving it. But Fermi and all of us were, in this occasion, too conservative:an explanation of the ‘uranium case’ in terms of what we had foundfor all lower values of Z was much simpler and therefore preferable”.“Two reasons or, maybe, two late excuses, why I. Noddack’s suggestionwas not taken more seriously neither in Rome nor in Berlin or Paris, arethe following. Her suggestion of what has turned to be the correct explanation,appeared as a speculation aiming more to point out a lack of rigorin the argument for the formation of element 93, than as a serious explanationof the observations. This remark seems to be supported by the factthat she never tried, alone or with her husband, to do experiments on irradiateduranium as certainly they could have done. Furthermore in thoseyears the Noddacks had failed in some discredit because of their claim tohave discovered element Z = 43 that they called ‘masurium’”.165

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThus element 43 enters twice in the subject treated in this paper. Its falsediscovery induced the best experimenters of the time not to pay the dueattention to Noddack’s proposal and its true discovery opened the way to themodern diagnostic procedures in nuclear medicine.Going back to nuclear medicine, there is a final twist to the link made amongthe work on slow neutrons done in Rome in 1934-1935, the talk given in1938 by Fermi at the Istituto di Sanità and the use of isotopes in medicine.As already stressed, most examinations of current nuclear medicine (asbone imaging, the study of renal functions and the control of myocardial perfusion)use the metastable isotope Technetium 99m, that has a convenientlifetime of 6 hours, so that it could not be found by Segrè in his molybdenumfoil. The utilisation of this isotope became practical when, in the late1950’s, a new method for producing it was developed at BrookhavenNational Laboratory. In this ‘generator system’ a long-lived radioactive parentis packaged, from which the short-lived daughter isotope is separated.Thus 99m Tc is separated in any nuclear medicine department from molybdenum99, that is contained in an easily shipped generator. In the frameworkof this presentation, the interesting aspect is that 99 Mo is at present producedin nuclear reactors by slow neutrons absorbed by the stable nuclide 98 Mo andnot by cyclotrons.Since the reactors used are ageing and no new one is being built, variousplans exist in the world to resort to high current sector cyclotrons for thefuture medical needs. But instead of using the reactions induced by nucleiaccelerated at a few MeV, that created in Berkeley the first technetium isotopes,these cyclotrons would give technetium 99m by neutron capture. Theneeded large neutron fluxes could be created in a fission target bombardedby protons, as proposed by Carlo Rubbia with the Energy Amplifier.This development would thus close the barely visible line that connects thediscoveries in nuclear physics that took place in Rome, Berkeley and Palermoin the 30’s with nowadays medical physics.I am very grateful to Alberto De Gregorio for comments and suggestionsof improvements.REFERENCES01. E. FERMI., Ric. Scient. 5(1), 283 (1934). Ibid. 5(1), 330 (1934).02. E. AMALDI, From the discovery of the neutron to the discovery of nuclear fission, PhysicsReport 111 (1-4) (1984) 1 – 331.03. Ref. 2, p. 124.166

Ugo AmaldiSLOW NEUTRONS AT VIA PANISPERNA04. E. AMALDI, O. D’AGOSTINO, E. FERMI, F. RASETTI, and E. SEGRÈ, Ric. Scient. 5(1), 452(1934). Ibid. 5(1), 652 (1934). Ibid. 5(2), 21 (1934).05. G. HOLTON, Fermi’s Group and the Recapture of Italy’s Place in Physics, in The ScientificImagination, Case Studies, Cambridge: Cambridge University Press, Part 2, Section 5, 1978.06. E. AMALDI, O. D’AGOSTINO, E. FERMI,. F. RASETTI, and E. SEGRÈ, Proc. Roy. Soc. A146,483 (1934).07. E. SEGRÈ, Enrico Fermi Physicist, Chicago: The University of Chicago Press, 1970, p. 92.08. Ref. 2, p. 132.09. Ref. 2, p. 151.10. Enrico Fermi Collected Papers, E. Amaldi et al. eds., Accademia dei Lincei and Universityof Chicago Press, Rome-Chicago, 1965, Vol II, p. 926-927.11. B. PONTECORVO, Enrico Fermi, Edizioni Studio Tesi, Pordenone, 1993, p. 82.12. E. SEGRÈ, A mind always in motion, University of California Press, Berkeley - Los Angeles- Oxford, 1993, p. 15113. A. DE GREGORIO, Caso e necessità nella scoperta da parte di Fermi delle proprietà dei neutronilenti, Il Giornale di Fisica, 2002.14. I. CURIE and F. JOLIOT, Journal de Phys. 4, 21 (1933).15. Structure et propriétés des noyaux atomiques, Rapports et discussion du 7 me Conseil dePhysique tenu à Bruxelles du 22 au 29 octobre 1933, Gauthiers-Villars, Paris, 1934.16. J. CHADWICK, Ref. 15, p. 106.17. L. FERMI, Atoms in the Family, University of Chicago Press, Chicago, 1954, p. 100.18. Ref. 2, p. 156.19. Domenico Marotta nel 25° anniversario della morte, Rend. Acc. Naz. Scienze, 23, 77-247(2000).20. L. CERRUTI, Domenico Marotta. Dai Laboratori di Sanità pubblica alla fondazionedell’Istituto, Ref. 19, p. 112-114.21. G. BATTIMELLI, Le origini del laboratorio di fisica, Ref. 19, p. 149-160.22. Letter by Fermi to Marotta, 23 October 1935, files ‘Laboratorio di Fisica - IstitutoSuperiore di Sanità’, Central Archives of the State, Rome.23. Letter by Marotta to Fermi, 16 October 1936, files ‘Laboratorio di Fisica - IstitutoSuperiore di Sanità’, Central Archives of the State, Rome.24. Memorandum by Marotta to the Cabinet, 20 December 1937, files ‘Laboratorio di Fisica- Istituto Superiore di Sanità’, Central Archives of the State, Rome.25. G. BATTIMELLI, Le origini del laboratorio di fisica, Ref. 19, p. 157.26. E. AMALDI, E. FERMI, and F. RASETTI, Ric. Scient. 8(2), 40 (1937).27. M. AGENO, E. AMALDI, D. BOCCIARELLI, and G.C. TRABACCHI, Rend. Ist. Sup. Sanità 3,201 (1940).28. G. BATTIMELLI, Le origini del laboratorio di fisica, Ref. 19, p. 1589.29. The text of the address, that has the Italian title Prospettive di applicazioni della radioattivitàartificiale, appears in the first volume of the Rendiconti of the Institute, 421-432(1938).167

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE30. E. SEGRÈ, Ref. 12, p. 115-116.31. E. SEGRÈ, Ref. 12, p. 308.32. C. PERRIER and E. SEGRÈ, Nature 159, 24 (1947).33. E. AMALDI, O. D’AGOSTINO, E. FERMI, F. RASETTI and G. SEGRÈ, Ric. Scient. 5(1), 677(1934).34. A. V. GROSSE and M. ANGRUSS, Phys. Rev. 46, 241 (1934).35. I. NODDACK, “Über das element 93”, Angewandte Chemie, 47 and 391 (1934).36. O. HAHN and L. MEITNER, Naturwiss., 23, 37 and 230 (1935).37. Ref. 2, p. 277-278.Ugo AmaldiHe initially worked for the Italian National Health Institute’s Physics Laboratoryon nuclear and radiation physics. In the 1970s, Ugo Amaldi served asSenior Scientist at the European Organisation for Nuclear Research (CERN)in Geneva, where he conducted many experiments in particle physics. Atpresent he teachs Medical Physics at the University of Milano Bicocca.Among other activities, he headed for 15 years the DELPHI project, whichbuilt and managed a large-scale detector that collected data on the LEP electron-positroncollider from 1989 to 2000.He has over 400 scientific publications to his credit, including a score ofhigh-school physics textbooks, the earliest of which he co-authored withEdoardo Amaldi. He holds honourary doctorates from the Universities ofHelsinki, Lyon, Uppsala and Valencia. As president of the TERA Foundation,he is now working to introduce adron therapy techniques in Europe for thetreatment of deep, radio-resistant tumors.168

Giovanni BattimelliFunds and Failures:the Political Economy of Fermi’s GroupPolitical protection and academic patronage, offered by Corbino and Marconi,were not enough to secure the experimental researches on nuclear physics doneby Fermi and his younger collaborators in the early thirties; although it wascertainly not yet the “big science” of the afterwar years, and has been depictedby Segrè as “string and sealing wax physics”, still that kind of work requiredalso adequate funding and financial support. The institutions who weresupposed to provide that money (mainly the newly reconstituted ConsiglioNazionale delle Ricerche, where the Physics Committee was firmly controlled bysupporters of the “new physics” and had Fermi as secretary) were actuallyunable to do that adequately. Fermi’s work was in fact made possible by meansprovided through the direct intervention of the Istituto di Sanità Pubblica, aninstitution which had in principle nothing to share with fundamental nuclearresearch, but was deeply linked, through its Physics Laboratory, to Corbino andthe Physics Institute of via Panisperna. Tracing the details of that side of the“political economy” of the Fermi group allows to get a clearer picture of thesupport given to fundamental physics in Italy in that period, and of its limitations,and ultimately makes it possible to understand why Fermi’s design to create inItaly a national laboratory for research in fundamental physics, endowed withthe best equipment available in the mid-thirties (a cyclotron) to keep it competitivewith the great research centers abroad, eventually failed.169

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFinanziamenti e fallimenti:l’economia politica del gruppo FermiLa protezione politica ed accademica offerta da Corbino e Marconi nonerano sufficienti ad assicurare la prosecuzione della ricerca sperimentalecondotta da Fermi ed i suoi più giovani collaboratori nei primi anni trenta.Sebbene non si trattasse ancora della “big science” del dopoguerra, e siastata descritta da Segrè come fisica “spago e ceralacca”, essa necessitavaciononostante di congrui sostegni e finanziamenti adeguati.Le istituzioni a ciò preposte (nella fattispecie l’allora appena ricostituitoConsiglio Nazionale delle Ricerche, il cui Comitato per la Fisica erasaldamente controllato dai sostenitori della “nuova fisica” e avevaFermi come segretario), non furono in grado di adempiereadeguatamente a tale funzione.Il lavoro di Fermi fu difatti reso possibile dall’intervento diretto dell’Istitutodi Sanità Pubblica, un’istituzione che in linea di principio non aveva nullaa che fare con la ricerca nucleare fondamentale, ma che era strettamentelegata, attraverso il suo Laboratorio di Fisica, a Corbino ed all’Istituto diFisica di via Panisperna.La ricostruzione dettagliata di questo lato dell’“economia politica” delgruppo di Fermi ci permette di avere una visione più chiara del sostegnodato alla fisica fondamentale in quegli anni in Italia e dei suoi limiti,nonché delle ragioni del fallimento del progetto di Fermi di creare unlaboratorio nazionale di ricerca per la fisica fondamentale, dotato dellemigliori strumentazioni esistenti all’epoca (un ciclotrone), al fine di poterlorendere competitivo con i maggiori centri di ricerca stranieri.170

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPFunds: “a fabulous wealth”The Nobel prize for physics awarded to Enrico Fermi in 1938 came as themost visible recognition of a long string of brilliant achievements in boththeoretical and experimental research. These, in turn, were the outcome notonly of the outstanding intellectual abilities and professional skills of theItalian physicist, but of a planned and organized effort to raise the standardsof fundamental physical research in Italy that turned out to be highly successful,eventually leading to what has been defined “the recapture of Italy’splace in physics”. 1 The fundamental role played in this context by OrsoMario Corbino’s scientific vision, for the development of the scheme, and ofhis patronage, both in academic circles and outside, to turn it into a successfulenterprise, has been widely recognized, by the actors of the story and bylater historians as well. 2 It has equally been stressed the importance of theelection of Fermi, as the only physicist, among the members of the newlyfounded Accademia d’Italia in 1929; through the Accademia and the connectedcircles came to Fermi not only prestige but also support for his andhis team’s work, in the form of grants for travels abroad and financial meansto organize scientific events (the 1931 nuclear physics conference in Rome,the first international gathering in the field, was held under the aegis of theAccademia and lavishly sponsored by the Fondazione Volta, an institutionwhere Corbino had an influential voice).Less attention has been generally paid, on the contrary, to the problem ofthe sources and amount of direct financial support to the researches ofFermi’s “boys” in via Panisperna. There is little or no talk of money, in therecollections of the golden days of the thirties provided by the members ofthe team, or in subsequent historical investigations. The general consensusseems to be that the matter wasn’t a really serious one, the limited supportavailable being more than sufficient for what was, after all, as Emilio Segrèput it in a way that has become part of the image and legend of the viaPanisperna saga, “a string and sealing wax physics”. 3 Segrè recalls that when,after Fermi’s initial success with fluorine, it was decided to “irradiate all the1 G. HOLTON, “Fermi’s group and the recapture of Italy’s place in physics”, in G. HOLTON (ed.), The scientificimagination. Case studies, Cambridge 1978, pp. 155-198.2 Among the several accounts of the activities of Fermi’s group in via Panisperna, particular attention isdevoted to discuss and elucidate the personality and the influence of Corbino by C. Tarsitani,“Tradizione e innovazione nella fisica italiana tra le due guerre: il caso del gruppo Fermi”, Critica marxista6 (1981), pp. 79-120.3“You see, it was a different type of physics. It was done on a few tables with string and sealing wax. Itwas extremely simple. It cost very little”; quoted in G. HOLTON, Fermi’s group… , p. 194.171

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEsubstances we could lay our hands on”, for which “we needed a littlemoney”, this was provided by “a phone call by Fermi to the NationalResearch Council (that) got us about $1000 with no strings attached”. 4 Inlater writings he reported the same amount of money (converted into20,000 lire) as having been granted and spent for the acquisition of chemicalsubstances for the 1934 experiments, stressing “the extremely small costof this research”. 5 Segrè also gives a figure of about 50,000 lire, granted bythe National Research Council (Consiglio Nazionale delle Ricerche, CNR), asthe sum spent for researches at the via Panisperna institute by Fermi’s groupin the two previous years, commenting on it as being “a considerable amountof money for that time”. 6 Further information is provided by Franco Rasetti:referring to the work done up to the end of 1933, he states that “these developmentswere made possible by a grant from the Consiglio Nazionale delleRicerche, which had raised the research budget of the department to anamount of the order of $2000 to $3000 per year; a fabulous wealth whenone considers that the average for physics departments in Italian universitieswas about one-tenth of that amount”. 7 In a speech delivered in 1937, thesame Rasetti gave an estimate of the total expenditure for the researches innuclear physics under Fermi’s direction in the four previous years as being“less than 150,000 lire”. 8These rough estimates fit quite well together, and the overall pictureemerging from the different comments is a consistent one: a few tens ofthousands lire per year are indeed small money if compared with what will bethe typical investment needed for experimental research in nuclear physics inlater years, while constituting at the same time “a fabulous wealth” if comparisonis made with the general situation of financial support to physics inItaly at the time, when the annual budget of a physics institute oscillated4 E. SEGRÈ, “Fermi and Neutron Physics”, Reviews of Modern Physics 27, 3 (1955), pp. 257-263, quot.p. 259.5 E. SEGRÈ, preface to papers 84a to 110, in E. FERMI, Note e memorie (Collected Papers), vol. I,Accademia Nazionale dei Lincei , Roma, and The University of Chicago Press, 1962, p.640; E. SEGRÈ,Nota biografica, ibid. p. XXXV; E. SEGRÈ, Enrico Fermi, Physicist, The University of Chicago Press,1970, p. 78 of the Italian edition (Zanichelli, Bologna 1971). The conversion rate of dollars into liregrew from about 12 lire per dollar in the early thirties to about 20 lire per dollar at the end of thedecade.6 E. SEGRÈ, Enrico Fermi, Physicist, The University of Chicago Press, 1970, p. 75-76 of the Italian edition(Zanichelli, Bologna 1971).7 F. RASETTI, preface to paper 78, in E. FERMI, Note e memorie (Collected Papers), vol. I, AccademiaNazionale dei Lincei , Roma, and The University of Chicago Press, 1962, p. 548.8 F. RASETTI, Progressi recenti della fisica nucleare, SIPS – Scienza e tecnica, supplemento agli Atti dellaSocietà Italiana per il Progresso delle Scienze, 1937, 337.172

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPbetween a few thousands lire for the small universities to twenty- to thirtythousandlire in the main centers of research, such as Rome or Bologna.Support to physical research began arriving from CNR in sensible measurefollowing the 1927 reform of the Council, when firm political control over itwas finally established through the destitution of former President andfounder Vito Volterra, an outspoken antifascist, and his replacement with themore reliable Guglielmo Marconi; the reorganization of the Council thatwent along with such measures meant also that, for the first time since itsfoundation in 1923, the Council’s budget was raised to an amount that,although still hopelessly small if compared with that of analogous bodiesabroad, allowed the various Committees to actually do something for theactive support of research and scientific projects. The CNR budget, which hadstayed for years at the ridiculous 1923 level of 175,000 lire, grew to half a millionin 1927, jumped to a million and a half in 1930 and kept increasingthroughout the thirties to a peak of 25 millions lire in 1939. 9The main supporters of the “new physics” in the universities also held keypositions in the relevant CNR bodies: while Corbino was called by Marconito preside over the Committee for Scientific Radiotelegraphy, the PhysicsCommittee was headed (from 1927 to his death in 1933) by AntonioGarbasso, the director of the physics institute in Florence, and had Fermi asits secretary. They all saw in the renewed institution a privileged channelthrough which secure financial support to the more modern, promisingtrends in physical research, and actively managed to successfully steer a largepart of the available funds in that direction.The records of the CNR Directory and of the Physics Committee show thatindeed a large fraction of the annual budget of the latter, and some significantcontributions coming directly from the main central body, went to the researchgroups in Florence and Rome. Altogether, what these official records allow tocalculate as the contribution offered by CNR to support Fermi’ researches is inexcellent agreement with Rasetti’s estimate mentioned earlier. 10 17309 On CNR in general see G. PAOLONI, R. SIMILI (eds.), Per una storia del Consiglio Nazionale delleRicerche, 2 Vol., Laterza, Roma-Bari 2001; in particular, for the main lines of development in the periodconcerned, see in Vol. 1 the essays by R. SIMILI, La Presidenza Volterra (pp. 72-127) and LaPresidenza Marconi (pp. 128-172), and by G. PAOLONI, Organizzazione e risorse di un ente in formazione(pp. 201-223).10 On the CNR Physics Committee in these years see G. BATTIMELLI, M. DE MARIA, La fisica, in G.PAOLONI, R. SIMILI (eds.), Per una storia del Consiglio Nazionale delle Ricerche, quot., Vol. 1, pp. 281-311. The Committee budget was (in lire) 64,000 in 1931, 47,000 in 1932, 67,000 in 1933, 115,000in 1934, 98,000 in 1935, 167,000 in 1936.

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThese sums, though constituting “a fabulous wealth” when compared tothe average situation, should not lead to attribute to the new areas ofresearch in Italian physics at the time more weight than they actually hadmanaged to obtain. It may be interesting to notice that in 1930, on a muchmore traditional field, a special contribution of 150,000 lire was granted bythe CNR Directory to the director of the National Institute of Optics inFlorence, Vasco Ronchi, who had advanced the request for the purpose ofbuying high precision optical equipment.Applied science always was the focus of attention in CNR, and largeresearch centers such as the Istituto Nazionale di Ottica got the larger shareof the cake. Fermi was perfectly aware of this and, as a consequence, of theimportance of establishing in Italy a large national laboratory for physicsable to go beyond the intrinsic limits of a university institute. He did a firstmove in that direction soon after his election to the Accademia d’Italia,when he felt that the repeated statements by Mussolini on the need to givea strong support to science gave him a chance to push his project successfully.Fermi went to talk to Mussolini himself on January 1930, submittinghim a proposal for the transformation of the via Panisperna institute into aNational Physics Institute, with special status in the university system andcorresponding special financial support from the State (he envisaged a specificcontribution of 200,000 lire per year).The project was forwarded by Mussolini to the Minister of NationalEducation Balbino Giuliano, who sternly refused to take it into considerationon the basis of the disrupting effects that such a move would produceon the whole university system. 11 It was the first failure on the road towardsthe creation of a national laboratory for physics, a goal that figured eminentlythroughout the successive years in the CNR agenda, and that nevermaterialized.“La Divina Provvidenza”Whatever the limits and the shortcomings of CNR’s action on the largerscale, they didn’t prevent Fermi and his “boys” to secure for themselves themeans needed to do excellent physics. With a skillful combination of “frugal-11 The documentation is in Archivio Centrale dello Stato, Presidenza del Consiglio dei Ministri, Gabinetto,1928-30, folder 5-1-10527, and is reproduced in the Addenda to the second Italian edition ofE. SEGRÈ, Enrico Fermi, fisico, Zanichelli, Bologna 1987, p. 245-247.174

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPity and improvisation” (to use Holton’s words) and a good use of the CNRmoney they could build with their own hands or buy the necessary equipment.Not all of it, however. They could build by themselves the primitive butefficient Geiger-Müller counters to detect radiation, and buy the substancesto be irradiated by their neutron sources, but there was a key element of theirinstrumentation that they couldn’t build by themselves nor buy, but had to beacquired by some other channel. Radioactive sources, the only really expensivepiece of their equipment, came into their hands by lucky coincidence:“The start of the neutron experiments was facilitated by the very lucky circumstancethat Prof. G.C. Trabacchi in the “Laboratorio della SanitàPubblica”, which was located in the same premises as the Physics Institutein Via Panisperna in Rome, had on hand more than one gram of radiumand the plant with which to extract the radium emanation and prepareradon-beryllium sources. His wholehearted cooperation was invaluable…”12Trabacchi’s “invaluable” cooperation can actually be accurately evaluated.His contribution to the success of Fermi’s investigations, which came underthe form of one gram of radium, was worth about a million lire. Though thegenerosity and friendly attitude of Trabacchi towards Fermi and his team hasbeen widely and repeatedly recognized by all of them in several occasions, noone has ever bothered to translate the meaning of this generosity into crudenumbers. 13 These numbers put into a rather different perspective the roleactually played by Trabacchi in the story; they allow to better appreciate towhat extent, far from being just a benevolent old fellow, he fully deserved thenickname of “La Divina Provvidenza”. They help to explain why Trabacchi,though he didn’t take active part in the experimental work on artificialradioactivity, was included in the group of “inventors” that applied for thefirst patent on neutron bombardment in October 1934, or why he is the onlyindividual whose support Fermi explicitly and thankfully acknowledged in his1938 Nobel lecture: he was the one who had made the whole thing possible.12E. SEGRÈ, preface to papers 84a to 110, in E. FERMI, Note e memorie (Collected Papers), vol. I,Accademia Nazionale dei Lincei , Roma, and The University of Chicago Press, 1962, pp. 639-640.13The only reference to the actual value of Trabacchi’s radium can be found in Laura Fermi’s memoriesof the days in via Panisperna; she relates an episode in the Institute, when Rasetti showed her andGinestra Amaldi the laboratory and commented “In the safe behind these glass tubes there is the gramof radium of the Divine Providence. It is worth about 670,000 lire”, which is a surprisingly accuratefigure, surprisingly ignored in all later, less anecdotal accounts of the story. L. FERMI, Atoms in theFamily, The University of Chicago Press, 1954.175

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEEstablishing state control over radioactive substances and creating a specificscientific body to that effect had been a project pushed by Corbino backin 1923, in his capacity as Minister of National Economy during the firstMussolini government. An Office for Radioactive Substances had been created(usually called Ufficio del Radio), which in 1925 changed name and status,becoming the Laboratorio Fisico under the responsibility of the GeneralDirection of Public Health, at the time a branch of the Ministerodell’Interno. The Laboratory was located in the basement of the PhysicsInstitute in via Panisperna; Giulio Cesare Trabacchi, a physicist and formerassistant of Corbino in that same Institute, was named director already in1924 (he kept office until 1958). 14 The task of the Laboratory was to exercisecontrol over the radioactive material in possession of the State, to distributeit among the various medical institutions and supervise its use fortherapeutical purposes, to deal with the technical problems related to the calibrationand safe handling of such material, and more generally to performany kind of scientific research in the field of physics connected with the taskof safeguarding public health. It was a small office hosted inside a large institute,yet it disposed of means that the larger institute couldn’t even dreamof. The Direction of Public Health was not the National Education; as abranch of the Ministero dell’Interno, it could afford large expenditures, andradium was expensive. Though its price had dropped in the afterwar years tostabilize around a thousand lire per milligram, the total amount of radioactivematerial handled by Trabacchi’s laboratory was still worth “a fabulouswealth”. From the original 500 mg in 1924, the laboratory came to managein 1936 about four grams of radium; its cost was approximately four millionslire. Already in 1928 Trabacchi could sign an order to the Union Minière duHaut Katanga for the acquisition of 1041 mg of radium minerals, for anamount of slightly less than a million lire: a sum vastly superior to the totalbudget of CNR for that same year. 15In view of his institutional duties, radioactivity meant to Trabacchi sampledosimetry and calibration, radiological screens, protection from radiation,preparation of sources for therapeutical uses. For the boys upstairs, it meantbeta decay, nuclear structure, artificial nuclear processes induced by neutron14G. BATTIMELLI, Le origini del laboratorio di fisica, in Domenico Marotta nel 25° anniversario della morte(Proceedings of the Conference, Rome July 9, 1999), Vol. 117, Memorie di Scienze Fisiche e Naturali,Rendiconti della Accademia Nazionale delle Scienze detta dei XL, ser. V, vol. XXIII (1999), pp. 149-160.15 Documents from the folders “Laboratorio di Fisica”, Istituto Superiore di Sanità, Archivio Centraledello Stato, Rome.176

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPbombardment; by a “lucky circumstance” the investigation of the related fundamentalphysical properties required the use of those very sources that theycouldn’t afford to buy given the limited means at disposal, and that Trabacchihandled liberally in his laboratory in the basement, for reasons that had inprinciple nothing to do with research in fundamental physics. The link providedby Corbino made the rest; fully aware of the significance of Fermi’swork, Trabacchi compensated with his sources for the inadequate supportgiven to fundamental research by the institutions that were supposed to do so.It was a lucky circumstance indeed, that allowed the completion of the outstandingwork on nuclear structure and neutron properties that would grantFermi the Nobel Prize; it was, however, a circumstance that couldn’t indefinitelycompensate for the lack of investment in the field, as it became soonclear when a leap forward in instrumentation and scale was required by theadvancements in nuclear science and the related technological developments.Failures: the laboratory that never materializedThe cyclotron and the different types of high-voltage accelerators developedthroughout the thirties, and by the second half of the decade themachine invented and perfected by E.O. Lawrence at Berkeley had establisheditself as the best tool for producing beams of high-energy particles tobe used for research in the fast growing field of nuclear physics. Up to 1935physicists visiting Berkeley tended to give a skeptical judgment about themerits of the cyclotron; it still was seen as a not very reliable, complicatedcontraption, giving beams of feeble intensity compared with those obtainableby van de Graaff or Cockcroft-Walton HV accelerators, and having the addeddisadvantage of requiring unfamiliar electronic technology for its operation,not to mention – last but not least – the fact that it was definitely moreexpensive than HV machines. Already in 1936, however, the balance beganto shift; the 27-inch cyclotron started operating in Berkeley (and operatingin a regular way), while the following year Lawrence introduced animproved, 37-inch version. These machines were now capable of producingbeams whose intensities were not different from those given by HV accelerators,but at definitely higher energies. The growing interest in beams ofenergetic deuterons or neutrons for the production of artificial isotopes inthe “high” region of the periodic system established in a few years thecyclotron as an almost indispensable tool for any active nuclear physics laboratory.In 1939 Lawrence put into operation the 60-inch version of the177

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEmachine, and by that time cyclotrons were working, or under construction,in several american laboratories and in Cambridge, Copenhagen, Liverpool,Paris and Stockholm in Europe; towards the end of the decade, “a laboratorywithout a cyclotron could no longer compete in the interdisciplinarynuclear science invented in Berkeley”. 16The need to move from natural radioactive sources to accelerators was feltby Fermi and his team as early as 1935. Thanks to money provided by theFondazione Volta, the Rome physicists travelled to the States during the summersof 1935 and 1936 to learn about the different kinds of accelerators beingdeveloped, and make up their minds on which machine to prefer. Rasetti wentto Pasadena and Berkeley in 1935, and Amaldi visited the East Coast laboratoriesat Columbia and at the Carnegie Institution in 1936, while at the sametime Segrè was studying the cyclotron in Berkeley. 17 Rasetti’s lack of enthousiasmabout Lawrence’s cyclotron gave way the following year to Segrè’sadmiration for the performances of the 27-inch version, that had more thandoubled the beam intensity and energy. A few months later, Segrè would discoverin Palermo element 43 analyzing material irradiated by that samecyclotron, sent to him from Berkeley, and express his thanks to Lawrencereferring to the cyclotron as “a sort of hen laying golden eggs”. 18A first chance to raise the financial means needed to build an acceleratorcame through the direct intervention of the director of the Istituto di SanitàPubblica. The Istituto had been created in 1934, putting together the differentlaboratories previously attached to the Direzione Generale della Sanità,and the chemist Domenico Marotta had been appointed director in July1935. In that same year the Istituto with its laboratories moved to its newheadquarters, an imposing building erected with the financial support of theRockefeller Foundation just across the street from the site where the newCittà Universitaria was being completed. Trabacchi moved with his laboratoryto the new site; the Physics Institute would do the same less than twoyears later, leaving via Panisperna to find accomodation in its present locationat the Città Universitaria. Marotta saw a promising road for the devel-16J.L. HEILBRON, “The First European Cyclotrons”, Rivista di Storia della Scienza, 3 (1986), 1-44,quot. p. 7.17 F. RASETTI, Sorgenti artificiali di neutroni (Stati Uniti, agosto-ottobre 1935-XIII), Viaggi di studio promossidalla Fondazione Volta III, 1936, pp. 77-79; E. AMALDI, Istituti di fisica negli Stati uniti (luglioottobre1936-XIV), Viaggi di studio promossi dalla Fondazione Volta IV, 1938, pp. 7-10.18I. GAMBARO, La scoperta del tecnezio, Atti dell’VIII Congresso Nazionale di Storia della Fisica (Napoli12-17 ottobre 1987), 1987, pp. 187-200; E. SEGRÈ, A Mind always in Motion – The Autobiography ofEmilio Segrè, University of California Press, Berkeley 1993.178

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPopment of the scientific activity of his Istituto through the collaboration withFermi on the ground of artificial radioactivity. He could dispose of the meansneeded to start an ambitious program of production of radioactive substances,a program that would highly profit from being backed by the scientificauthority of Fermi, and Fermi could rely on the support of Marotta andthe means provided by the Sanità to try to achieve that leap forward ininstrumentation that university and CNR would likely not make possible. Assoon as October 1935 Marotta started to look for ways of interaction withFermi, asking “his opinion on the possibility that artificial radioactive substancesmay be of practical use to substitute Radium in medical applications,which for Public Health would be of invaluable interest”. Fermi’s positiveanswer clearly showed his interest in future joint projects on the subject. 19These exchanges and others that followed gave birth to the idea of buildingat the physics laboratory of the Sanità an accelerator for the production ofartificial radioactive substances. The proposal, formally advanced byTrabacchi but certainly discussed previously in detail between him, Marottaand Fermi, was forwarded by Marotta to the Ministero dell’Interno inDecember 1936. To justify such a request Marotta stressed the advantagesfor his Istituto, and for the country at large: the possibility of producing substancesfor therapeutic uses on a relatively large scale, the prospect of nothaving to rely on foreign sources for the acquisition of radium, the increasedsafety due to the controlled source of the radioactive materials, the addedprestige coming to Italy “in a field where our country already acquired a brilliantstanding thanks to the researches of the Academician Fermi”. 20 Nomention was made of a further benefit, which was however obviously presentto Marotta, and to Fermi as well: the new machine would have providedthe physicists with a badly needed tool to keep investigating the fundamentalproperties of the nucleus.The choice for the Sanità accelerator fell on the more conventional, highvoltagemachine. Marotta’s request was for a 1 MV Cockcroft-Walton: in hisproposal he asked for 300,000 lire for the construction of the apparatus, andaround 100,000 more lire per year for its operation. Though the estimatedcost was sensibly inferior to that of a cyclotron, it was nonetheless a sum19D. Marotta to E. Fermi, October 21, 1935; E. Fermi to D. Marotta, October 23, 1935; folders“Laboratorio di Fisica”, Istituto Superiore di Sanità, Archivio Centrale dello Stato, Rome.20D. MAROTTA, Appunto per l’on. gabinetto – Oggetto: fabbricazione di sostanze radioattive artificiali,Amaldi Archive, Dipartimento di Fisica, Università “La Sapienza”, box 21 E.179

PROCEEDINGS OF THE INTERNATIONAL CONFERENCElargely exceeding the total investment made by CNR in nuclear physics in theprevious years, and a good order of magnitude larger than the average budgetof a university physics institute at the time. A 200 kV prototype was realizedin June 1937 by Amaldi, Fermi and Rasetti in the new Physics Institute,while the final 1 MV version was completed two years later in the basementof the Istituto di Sanità; Fermi had by that time already left Italy for good. 21It was however clear to Fermi that the generous support of the Istituto diSanità and its physics laboratory could not substitute for what he perceivedas absolute priority for the development of physical research in Italy: the creationof a national laboratory for physics, independent from any single universityinstitute and endowed with the best available equipment.Remembering his ill-fated attempt of 1930 to turn the physics institute inRome into such a special laboratory, he resolved to push the project addressinghimself to CNR. The move was carefully prepared: at the end of 1936Fermi wrote to the directors of some of the more prestigious European laboratories,inquiring about size, equipment and personnel dotation, andbudget. On the basis of information received by Cockcroft, Joliot andScherrer, 22 he submitted to CNR a proposal for the creation of a nationallaboratory modeled on the most advanced research institutions abroad. 23 Inthe accompanying letter to the CNR Directory, Fermi made clear the natureof the changes affecting the field of nuclear research: if “radioactive techniquecould up to now largely use as primary sources the natural radioactivesubstances”, so that “the ordinary means of a university physics laboratorycould, with limited external support, be adequate for the development ofresearch”, this was no longer going to be true.“In the main foreign countries, beside the technique of natural sources, anew one has been developed, based on artificial sources obtained throughbombardment by accelerated ions… It is clear that these circumstances21 E. AMALDI, E. FERMI, F. RASETTI, “Un generatore artificiale di neutroni”, Ricerca Scientifica 8(2),1937, 40; E. AMALDI, D. BOCCIARELLI, F. RASETTI, G.C. TRABACCHI, “Generatore di neutroni a 1000kV”, Ricerca Scientifica 10, 1939, 623.22P. Scherrer to E. Fermi, January 16,1937; J. Cockroft to E. Fermi, January 21, 1937; F. Joliot to E.Fermi, January 25, 1937; Amaldi Archive, Dipartimento di Fisica, Università “La Sapienza”, box 1E.23 For a study of parallel developments on the matter in Rome and Paris see I. GAMBARO, Acceleratori diparticelle e laboratori per le alte energie: Roma e Parigi negli anni Trenta, Rivista di Storia della Scienza1, II ser. (1993), pp. 105-154. On Fermi’s and later Italian efforts on accelerators see G. BATTIMELLI,I. GAMBARO, Un laboratorio per le alte energie alla vigilia della seconda guerra mondiale, Atti del XIVe XV Congresso Nazionale di Storia della Fisica, Conte, Lecce 1995, pp. 475-487; G. BATTIMELLI, I.GAMBARO, Da via Panisperna a Frascati: gli acceleratori mai realizzati, Quaderni di Storia della fisica 1(1997), pp. 319-333.180

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPmake it hopeless to think of an effective competitiveness with laboratoriesabroad, unless even in Italy a way is found to organize these researches onan adequate basis, for which it seems highly unlikely that the resources ofa single university institute may be sufficient. I therefore take the libertyof suggesting the opportunity for the Consiglio Nazionale delle Ricercheto take the initiative for the creation of a National Institute forRadioactivity.” 24That the proposed laboratory was to be meant essentially for the benefit offundamental physics emerged clearly from the research targets that Fermi listedfor such an Institute: alongside with “the study of the properties of newradioactive bodies” and the “application of artificial radioactive substances asindicators for the study of chemical reactions”, first and foremost came the“innumerable unsolved problems related to nuclear structure and neutronproperties”. To the proposal Fermi appended a detailed (though a little conservative)budget estimate: 300,000 lire for equipment, and 230,000 lire peryear for ordinary administration. Though in the proposal it was not explicitlystated what kind of equipment Fermi envisaged for the laboratory, it can beconfidently assumed that he was considering a cyclotron. This, at least, wasobvious in the summer of 1937, when he went to Stanford and visitedBerkeley: in August he wrote to the director of the Physics Institute in Romeabout “the reasonable prospect of building a cheap cyclotron”. 25How “cheap” a cyclotron could be was translated in crude numbers by Rasettinot much later, in an address delivered at the annual meeting of the ItalianSociety for the Advancement of Sciences (Società Italiana per il Progresso delleScienze, SIPS). Talking on “Recent advancements of nuclear physics”, Rasettiwent on, in the last part of his speech, to discuss the new means developed fornuclear research, high tension accelerators and the cyclotron:“This last apparatus has proven itself to be the more powerful, andpresently there are, functioning or in an advanced stage of contruction,12 exemplars in the United States, one in France, two in England and onein Denmark. Why don’t we build one here at home? It will not be necessaryfor me to explain the reasons to the audience, who knows well thenot astronomical numbers of the budgets of university institutes, when Isay that the construction of a cyclotron requires about 80 tons of iron, 824 E. Fermi to CNR, January 27, 1937; Archivio Centrale dello Stato, CNR, box 105, folder “Istituto difisica dell’Università di Roma”.25 E. Fermi to A. Lo Surdo, August 5,1937; Amaldi Archive, Dipartimento di Fisica, Università “LaSapienza”, box 1E.181

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtons of copper, and the installation of a short-wave oscillator with a powercomparable to that of the most powerful broadcasting station in Italy. Orwhen I say, more synthetically, that the cost of a cyclotron today is arounda million lire”. 26Rasetti went on to say that, while Fermi’s discoveries had been made possibleeven with limited means (here he gave the figure, mentioned earlier, of150,000 lire for the total cost of these researches over a period of four years),this time was over. And, to give a more optimistic tone to the conclusions ofhis talk, he ended with an appeal to CNR and to the highest authority of thecountry:“For further progress we need the collaboration of several researchers anda powerful organisation of laboratories, such as only a special body likeCNR could develop. The interest of the Chief for science and its applications,that led to the creation of this highly effective body, gives us theright to be confident that these problems, just as endless others faced andsolved by the Regime, will find in a short time a solution worthy of imperialItaly”.Most likely, Rasetti was not all that confident in the effectiveness of CNR,or in the interest of the Chief in the matter. He had no reason to be. Pressedby more immediate concerns of application of science to the contingentproblems of autarchy and impending war, CNR did not pay any seriousattention to Fermi’s proposal for a national laboratory. In May 1937, a sumof 30,000 lire was granted to Fermi for the completion of the 200 kV prototypeaccelerator at the physics institute. The death of Guglielmo Marconiin July, following that of Orso Mario Corbino, suddenly deceased in January,deprived Fermi of most of the support he could count on in the Council. Afinal decision on Fermi’s proposal was taken only in June 1938: consideringthat “for the creation of an Institute of Radioactivity… much larger andmore conspicuous means would be required that those approximately estimatedby S.E.Fermi”, the Presidency of CNR resolved not to take into considerationthe creation of such an institute, leaving to the Directory the decisionwhether to grant Fermi an annual budget “to organize researches in thefield of radioactivity”. 2726 F. RASETTI, Progressi recenti della fisica nucleare, SIPS – Scienza e tecnica, supplemento agli Atti dellaSocietà Italiana per il Progresso delle Scienze, 1937, 337.27The relative documents are in Archivio Centrale dello Stato, CNR, box 105, folder “Istituto di fisicadell’Università di Roma”.182

Giovanni BattimelliFUNDS AND FAILURES: THE POLITICAL ECONOMY OF FERMI’S GROUPConclusionThe untimely death of Corbino in January 1937 prevented him from witnessingthe final disruption of Fermi’s group, and the emigration of severalof his members. It is not clear what his perception was of the deterioratingclimate and of the downhill slope physical research in the country had startedsliding on. According to Amaldi, he didn’t seem to worry about that issuein the last months of his life:“Around 1936 he used to say that, given the international reputationgained by Fermi and his school, it was no longer necessary for him to takecare of the further development of nuclear physics: it was in excellenthands, and its future could therefore be given for granted”. 28The usually far-sighted Corbino was on that occasion deluding himself.Nuclear physics was “in excellent hands” as far as its practitioners were bynow firmly installed in academic positions, and had made a name for themselvesthanks to the excellent work done under Fermi’s guidance. To give itsfuture for granted, however, one had to count on the fact that such excellencewould be maintained in the future thanks to adequate support. Thiswas not likely going to be the case; evidence pointed in the opposite direction.The Nobel prize awarded to Fermi for his outstanding researches onnuclear physics came shortly after the main national state agency in charge ofsupporting science had let him know that the means required to keep doingthat kind of research were not available, and will not be for time to come.There is no doubt that the promulgation of the racial laws in the second halfof 1938 was a key factor in forcing Fermi to take the decision to emigrate,but they didn’t arrive as a sudden and unexpected blow from the outsideworld to perturb what would otherwise be a rising parable of scientific production.The parable was already declining, and the racial laws were the lastelement leading to a final move that was already contemplated on the basisof strictly scientific considerations. Fermi’s failure to create a large physicallaboratory to keep the competitive status that Italian nuclear science hadacquired in previous years points to the failure of Italian scientific institutions,pressed by needs of immediate application and constrained by chronicshortage of funds, to give adequate support to fundamental science. This, inturn, reflects the failure of the Italian ruling class (or, at least, of that part of28 E. AMALDI, Corbino, Orso Mario, Dizionario Biografico degli Italiani, Vol. 28, Istituto dellaEnciclopedia Italiana, Roma 1983, pp. 760-762.183

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEthe Italian ruling class that finally emerged to power through the inner tensionsof late fascism) to fully appreciate science’s role in society, and illustratesthe impoverished and distorted way in which the relation between scienceand modernization was then perceived and pursued.Giovanni BattimelliGiovanni Battimelli is associate professor at the Physics Department of theUniversity "La Sapienza" in Rome. He has done extensive research on differentaspects of late XIXth and XXth century physics, and on the developmentof Italian scientific institutions since 1870. In collaboration with M. De Mariaand G. Paoloni, he has edited the writings by E. Amaldi on the history ofphysics; recently he has co-authored volumes on the history of CNR(Consiglio Nazionale delle Ricerche) and INFN (Istituto Nazionale di FisicaNucleare).184

Sam SchweberFermi and Quantum Electrodynamics (QED)Between 1928 and 1932 Fermi wrote several fundamental papers elucidatingin a readily vizualizable and intuitive way the physics that results from theinteraction of charged particles with the electromagnetic field when both arequantized. I will review these contributions with special emphasis on his 1932Reviews of Modern Physics article from which an entire generation of physicistslearned QED.Enrico Fermi e l’elettrodinamica dei quanti (QED)Tra il 1928 ed il 1932 Fermi scrisse diverse relazioni fondamentali in uno stilechiaro ed immediato sulla fisica risultante dall’interazione di particelle carichecon un campo elettromagnetico quando entrambi siano quantizzati.La mia relazione verterà specificatamente sul suo articolo pubblicato nel 1932sulla rivista “Reviews of Modern Physics”,dal quale una intera generazione di fisici apprese la QED.185

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntroductionIn 1926, shortly after the publication of Schrödinger’s wave mechanicspapers, papers he had carefully studied and mastered, Fermi wrote a shortarticle entitled “Arguments pro and con the hypothesis of light quanta”. Init he indicated that “at the present time the state of science is such that onecan say that we lack a theory that gives a satisfactory account of optical phenomena.”He listed the experiments that were convincingly explained bylight being assumed to be constituted of (particle-like) photons such as thephotoelectric effect and the Compton effect, and those that were readilyunderstood in terms of the wave theory, namely, interference and diffraction.The challenge, Fermi stated, was to elucidate the processes involved in theinteraction of light with matter at the atomic level and to give intuitive explanationsof optical phenomena at this microscopic level. (Fermi 1926) Fermimet the challenge. In a series of papers from 1929 to 1932 he formulated arelativistically invariant description of the interaction between charged particlesand the electromagnetic field which treated both particles and electromagneticfield quantum mechanically.He first devised a simple, readily interpretable, Hamiltonian description ofcharged particles interacting with the e.m. field, then indicated how to quantizethis formulation and thereafter showed how to exploit perturbation theoryto describe quantum electrodynamic phenomena.There were others who tackled these same problems, but none of their formulations– Heisenberg and Pauli’s papers in particular – had the simplicity,Anschaulischkeit, yet thoroughness of Fermi’s approach. What Fermi accomplishedwith his papers was the following:1) He provided a simple, vizualizable way to describe the interactionsbetween photons and charged particles. It was the formulation fromwhich an entire generation learned how to think about quantum electrodynamicaleffects in atomic phenomena, and on which Heitler based his1936 edition of The Quantum Theory of Radiation which taught physicistshow to calculate cross-sections for quantum electrodynamic processes.It was the point of departure for Feynman in 1939 when addressingquantum electrodynamics in his Lagrangian formulation, and the sourceof Weisskopf’s insight that the Lamb shift could be interpreted as theeffect of the zero point energy vacuum fluctuations of the electromagneticfield on the motion of the electron in the hydrogen atom. In addition,Fermi showed how to handle the gauge conditions in QED when theelectromagnetic field is described by vector and scalar potentials – and his186

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)treatment was the point of departure for fixing gauges in quantizedgauged theories.2) He indicated under what circumstances the intuitive picture of a photonas a massless, spin 1 particle-like entity that moves with velocity c wasappropriate. And3) in a paper with Bethe he helped secure the perturbation theoretic picturethat depicts the interaction between charged particles as stemming fromthe exchange of photons.I believe that these QED studies were important, if not necessary, preparationsfor Fermi being able to formulate in 1933 his theory ofβ-decay and that in the first of these papers he could assert that electrons donot exist as such in nuclei before β-emission occursbut that they, so to say, acquire their existence at the very moment whenthey are emitted; in the same manner as a quantum of light, emitted byan atom in a quantum jump, can in no way be considered as pre-existingin the atom prior to the emission process.In this theory, then, the total number of the electrons and of the neutrinos(like the total number of light quanta in the theory of radiation) willnot necessarily be constant, since there might be processes of creation ordestruction of these light particles. [Fermi 1934]Fermi’s paper on β-decay constitutes the birth of quantum field theory asapplied to elementary particle physics.Rendiconti della Accademia dei LinceiIn his preface to the articles on QED in Volume I of The Collected Papersof Enrico Fermi (Fermi 1962) Edoardo Amaldi indicated that Fermi startedstudying the quantum theory of radiation during the winter of 1928-29. Hemastered the two 1927 papers by Dirac that had laid the foundations of thesubject (Dirac 1927a, b). He familiarized himself with the papers of Jordanand Klein (1927)and of Jordan and Wigner (1928) in which the wavemechanicaldescription in 3N dimensional configuration space of a system ofN identical non-relativistic Bosons and Fermions was recovered by “quantizing”an appropriate Schrödinger equation considered as a field system. Andat the time he also read and was impressed by Jordan and Pauli’s 1928 paperin which they had formulated a quantization procedure for the free electromagneticfield in a relativistically invariant manner.Recall that in his first paper, Dirac (1927a) dealt with the problem of the187

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEinteraction of an atom with the radiation field and described photons as particlesof zero rest mass obeying Bose-Einstein statistics. The Hamiltonian wastaken to bewith(1)(2)where H p is the hamiltonian of the atom, and the b’s are creation and annihilationoperators for the photonswith(4)the number operator for photons of energy W r . The b operators satisfy theBose commutation rules(5)Dirac took the interaction between the photons and the atom to be of theform(6)Since this Hamiltonian conserves the number of photons it cannot describethe spontaneous emission of photons nor their absorption. However Diracassumed zero energy photons (i.e. those with r=0) to be special as they areunobservable. He characterized the vacuum as a state with an infinite numberof zero energy and zero momentum photons, and he stipulated that in anyphysical state there are an infinite number of such photons. Photon emissionwas then considered as a transition from the vacuum state to a state of a singlephoton with finite momentum and energy; photon absorption consisted of thereversed transition. 1 In fact, he imposed the limit N → 0 ∞ in such a way that(3)(7a)(7b)188

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)The interaction term thus became(7c)and the terms linear in the b s and b s * could then account for the emissionand absorption of photons, including spontaneous emission. In the last briefsection of his paper, Dirac turned to the interaction of an atom with the electromagneticfield as described “from the wave point of view.” He adoptedthe Coulomb gauge in which the radiation field is described by a transverse(divergenceless) vector potential which is considered to be a non-commutingvariable and showed the equivalence between the two approaches if inthe wave formulation the interaction is taken to be(7d)and the Fourier expansion coefficients of A are appropriately chosen.Amaldi tells us “that the method used by Dirac did not appeal to Fermi, whopreferred, as he did very often, to recast the theory in a form mathematicallymore familiar to him” (Amaldi in Fermi 1965, p. 305). It was probably not somuch the mathematical aspects of Dirac’s formulation that didn’t appeal toFermi, but the physical approach. Although in Dirac’s approach the notion ofa photon was apparent, its connection to the quantization of the radiation fieldwas not clear for his formulation did not rest upon a well defined quantizationprocedure for the electromagnetic field; nor was it obviously relativisticallyinvariant; nor could it deal with the problem of field reaction during the act ofemission of a photon – a problem that Fermi had addressed after he had readSchrödinger’s papers (Fermi 1927). Also, as initially formulated Dirac’s papersdealt only with the interaction of a single charge with the e.m. field, and it wasnot clear how retardation effects could be taken into account in the interactionbetween charges. But it is evident from the problems that Fermi addressed thathe had noted Dirac’s desiderata for any acceptable quantum electrodynamics:1) it must correctly take into account the fact that electromagnetic “forcesare propagated with the velocity of light instead of instantaneously”;2) it must describe “the production of an electromagnetic field by a movingelectron”;3) it must describe “the reaction of this field on the electron”. And4) the formulation must “satisfy all the requirements of the restricted principleof relativity.” (Dirac 1927a, p. 243-4)189

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIn his first article on “quantum electrodynamics” Fermi stressed that hewanted to formulate the equations of motion of classical electrodynamics insuch a way that “they can readily be translated into a quantum form”. Hisapproach was to describe the em field (assumed to be contained in a largecavity of volume Ω) in terms of a vector and scalar potential that satisfied:(8)These potentials were then Fourier analyzed(9)(10)(11)In these equations, α s is a unit vector in the direction of propagation of thes th wave, and β s is a phase factor.The equations of motion (8) and (9) expressed in terms of the Fouriercoefficients Q s and q s take the following form when it is assumed that thecharge and current densities’ ρ and j arise from point particles located at X iat time t and moving with velocity dX i /dt:(12)(13)Charge conservation requires that(14)which translates into the requirement that(15)190

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)where χ s is the longitudinal component of q s , i.e. the component of q s alongthe direction of propagation α s .With Eqs. (12) and (13), that is, with the translation of the description ofthe dynamics of the electromagnetic field into that of (coupled) harmonicoscillators, Fermi achieved one of his stated objectives. It allowed him toreadily formulate quantization rules for the e.m. field and to give an“anschaulisch” – intuitive and vizualizable representation of the interactionof the quantized e.m. field with quantum mechanically described electrons,atoms and molecules. Fermi’s first paper on QED concluded with writingdown the Hamiltonian that yields the equations of motion (13) and (14),and those of the charged particles (assumed to be non-relativistic):(16)where the ω s and the P s are the conjugate variables to the w s , χ s and Q s . Inwriting down (16) a decomposition of the q s along direction perpendicular(As1 and As2) and parallel to the wave s (α s ) has been made:(17)Fermi noted that Eq. (16) yields the correct equations of motion and toorder v/c reduces to the familiar Hamiltonian for interacting non-relativisticpoint charges:(18)Since the theory had now been expressed in terms of canonical variables,these could now be promoted to non-commuting operators satisfying the191

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEusual commutation rules. In configuration space these canonical momenta pare equivalent to ih ∂/∂q and thus it was clear what operations to attributeto the Hamiltonian operator in the Schrödinger equation describing the emfield-charged particle system:(19)Pauli after reading Fermi’s paper wrote Pascual Jordan that he only peruseda recent article by Landé fleetingly (“sehr flüchtig”) but that “he studiedFermi’s Rendiconti della Accademia dei Lincei (Mai 1929) electrodynamicsarticle very carefully (“genau”). It does not depend at all on Heisenberg andmy article and is methodologically interesting although it doesn’t produceany new results” (Pauli 1979, p. 523).A further methodological interesting thing that Fermi did was expoundedin his second paper on QED. There he showed explicitly that theHamiltonian does indeed yield the desired equations of motion.Furthermore, that the gauge condition (14) can be stated as follows:that its time derivative is equal to(20)(21)(corresponding to the equation div E = 4πρ) and that by virtue of the equationsof motions(22)These are classical results. When the theory is quantized, i.e. when the classicalvariables are promoted to non-commuting operators, the gauge condition(14) cannot be taken as an operator identity sincedoes not commute with the Q s and the q s . In order to circumvent this difficultyFermi made the weaker demand that Eqs. (20) and (21) restrict the192

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)possible states of the system. In fact Fermi exhibited explicitly the states Ψ ofthe system that satisfy the subsidiary conditions:(23)They areFermi then showed that Φ satisfies the following equation(24)(25)thus justifying the transverse Coulomb gauge. The Coulomb term containsa self-interaction term which is infinite since the charges are assumed to bepoint-like. Fermi excluded the terms i = j as they make an infinite constantcontribution to the Hamiltonian.Between the submission of his first QED paper and the writing of this secondpaper on QED Fermi had read Pauli and Jordan’s article on a relativisticallyinvariant formulation of the quantum theory of the charge-free electromagneticfield (Pauli 1929). In order to state his theory in a relativisticallyinvariant form Fermi described the charged particles by Dirac equations sothat the Hamiltonian in (25) now read as follows:(26)In all his QED papers from 1929 to 1932 Fermi described matter as parti-193

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEcles obeying either Schrödinger or Dirac equations rather than by quantizedfields – à la Jordan-Klein, Jordan-Wigner or Heisenberg and Pauli. Usingquantized fields to describe the electrically charged matter – an approachwith which Fermi was acquainted – would have made no difference in thenon-relativistic case, but was so fraught with difficulties in the relativistic casethat much of the Anschaulichkeit of Fermi’s approach would have been dispelled.Early in 1929 Fermi was informed of the work of Weisskopf and Wigneron the theory of line width. This was of great interest to him because veryshortly after the advent of wave mechanics he had unsuccessfully addressedthe problem of the lifetime of an excited state of an atom and that of the naturalline width of the emitted radiation (Fermi 1927). Fermi clearly masteredthat paper. In fact, as we shall see Weisskopf and Wigner’s paper was the keyfor Fermi to being to explain interference and other undulatory light phenomenafrom a microscopic viewpoint. Amaldi tells us that while Fermi wascarrying out his researcheshe taught his results to several of his pupils and friends including Amaldi,Majorana, Racah, Rasetti and Segrè. Every day when work was over hegathered the various people... around his table and started to elaboratebefore them, first the basic formulation of quantum electrodynamics andthen, one after the other, a long series of applications of the general principlesto particular physical problems. A striking feature of Fermi’smethod of working on a theoretical problem in public (so to speak) andof teaching at the same time, was the way in which he could say out loudwhat he was thinking, proceeding at a steady unhesitating pace; nevergoing extremely fast, but never failing to make progress. (Amaldi in Fermi1962, p. 305)Gulio Racah in particular, proved to be an extremely valuable assistant inthe project. Fermi gave him the problem of explaining interference phenomenaquantum electrodynamically, and in two papers submitted to theRendiconti in the spring of 1930 gave a QED treatment of Lippman fringes.(Racah 1930a, b).Fermi lectured on his findings in the course that he gave in Paris in April1929 and his lectures are summarized in the Annales de l’Institut HenriPoincaré. In them he elaborated on the physical content of his approach. Hepointed out that the description of the electromagnetic field as coupled,forced, linear harmonic oscillators allowed an intuitive (“anschaulich”) viewof electromagnetic processes. He first considered the interaction of a single194

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)charged particle with the em field. In the case that its motion is prescribed,i.e. when v = dX/dt is specified, the equation analogous to (13) correspondingto the Fourier components of A (with div A = 0) can be integrated. Itssolution will contain terms corresponding to the free motion of the oscillator– i.e. pure radiation – and a term stemming from the “force” term, thev·A term. That part of the solution corresponds to the e.m field (photons)“attached” to the charge, that travel with velocity v. For the case v = constant,these attached photons give rise to the Biot-Savart field arising fromthe charged particle’s motion. 2The principal thrust of the Paris lectures was to establish QED as a readilyusable theory. To do so Fermi indicated how perturbation theory could berecast as a technique that allowed transition amplitudes to be analyzed andcalculated in an almost algorithmic manner. Recall that until the spring of1929 no one had given a fully quantum mechanical formulation of electrodynamicprocesses. The computation of the cross-sections for the photoelectriceffect, for Compton scattering, ... all depended on either semi-classicalor correspondence principle approaches. What Fermi did was to indicatehow all these processes could be given a fully quantum mechanical treatment.He demonstrated how perturbation theory should be handled to derive thecross sections for the processes. His point of departure was the Schrödinger-Dirac perturbation theory in which the wave function for the system whichsatisfies the Schrödinger equation:is expanded in terms of solutions of the unperturbed Hamiltonianthat is,The amplitude a k (t) for finding the system in the state Φ k then satisfy(27)(28)(29)(30)How to use these equations to compute the a k for various physical processesis the subject matter of the lectures that Fermi gave at the University of195

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEMichigan Summer School in Ann Arbor during the summer of 1930. It is tothese lectures that we now turn. But before doing so it is appropriate to recallthe comments Bethe made at the Enrico Fermi memorial symposium at theWashington meeting of the APS on April 29, 1955 shortly after Fermi’sdeath:Many of you probably, like myself, have learned their first field theoryfrom Fermi’s wonderful article in the Reviews of Modern Physics of 1932.It is an example of simplicity in a difficult field which I think is unsurpassed.It came after a number of quite complicated papers and beforeanother set of quite complicated papers on the subject, and withoutFermi’s enlightening simplicity I think many of us would never have beenable to follow into the depths of field theory. I think I am one of them.(Bethe 1955)The Michigan Summer School LecturesAfter introducing his formulation of QED – as outlined in his Rendicontidella Accademia dei Lincei papers – Fermi turned to the applications andimplications of his formalism. The first problem that he addressed was thatof the line width of the radiation emitted by an atom. Weisskopf and Wignerhad indicated the solution (Weisskopf 1930) and Born had evidently communicatedto Fermi their results. The Weisskopf-Wigner solution played animportant role in the subsequent examples treated by Fermi in his lectures.Fermi’s description of the problem of the spontaneous emission of radiationis as follows: At time t=0 the atom is an excited state and there are nophotons present. After a certain time the atom makes a transition to itsground state and emits a photon 1 : To compute the amplitude that at time tthe atom is still in its exited state. We will use a more modern notation toindicate what Fermi did. The clarity of his approach will then not beobscured by the cumbersomeness of his notation. 2 We shall denote the initialstate of the system – with the atom in an excited state and no photonspresent – by Φ E0 , a time-independent eigenstate of H 0 . Similarly, Φ Gkdenotes an (unperturbed) state with the atom in its ground state and onephoton of momentum k, polarization present. The state vector in the inter-1Fermi assumed that the atom has in fact but two states.2 Fermi used the p and q variables of harmonic oscillators to operate on the wave functions describingthe state of the radiation field which made for complicated notation.196

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)action picture satisfies the equation(31)Fermi approximated the solution of the problem by assuming that the systemcan be described solely in terms of the amplitudes(32a)and that Φ(t) could be approximated by(32b)(33)Thus a(t) satisfies the equation(34)which then immediately yields(35)∆E, the level shift due the emission and reabsorption of a photon is as itstands divergent – and was omitted both by Weisskopf and Wigner and byFermi. For times long compared to atomic frequencies a(t) is thus assumedto be given by(36)197

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEWe have omitted a fair amount of nitty-gritty details. In the above one hasto account for taking the time integral from -∞ to t rather than from 0 to t.The justification given for this is that the initial condition for the atom to bein the excited state will depend on the mechanism for getting it into thatstate – and is a rather complicated matter. The solution exhibited above, i.e.the Weisskopf-Wigner approximation – is only valid for times t large comparedto all atomic frequencies after the atom has settled down to a “quasistationary”state of radiative decay. The integration from -∞ to 0 presumablysmoothes out the preparation issue and thereafter the integration to t (witht large compared to the natural frequency of the atom) t is to effect thisquasi-stationarity. 3 Fermi was of course aware of all these difficulties and thatthe Weisskopf-Wigner approximation could not be readily justified. The factthat Fermi could circumnavigate all the difficulties led Wigner to comment:Fermi disliked complicated theories and avoided them as much as possible...His article on the Quantum Theory of Radiation in the Reviews ofModern Physics (1932) is a model of many of his addresses and lectures:nobody not fully familiar with the intricacies of the theory could havewritten it, nobody could have better avoided those intricacies...(Wigner in Segrè 1970, p. 55)But once one accepts the Weisskopf-Wigner solution for a(t), the amplitudefor finding the atom in its ground state and one photon being presentis easily calculatedso that for t>>1/Γ b(t) becomes equal to(37)(38)3 See Dyson 1952, after whom the above treatment is patterned, and Low 1952.198

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)Fermi’s second example is the propagation of photons in vacuo. He consideredtwo atoms A and B. A is located at the origin and B at a distance raway from atom A. Initially A is an excited state and it is assumed that its lifetimeis very short so that the photon is emitted from A “at a very definitetime” (and at a very definite place). It is further assumed that B is in groundstate and that the mean life of the state to which B is excited by photonabsorption is very long (Again Fermi assumed that both atoms are two levelsystems). Since 1/Γ A is very short the line emitted from A is very broad andFermi considers it as part of the continuous spectrum, whereas B absorbs avery sharp line. The system is described by the amplitudes a, b, and c where(39)Φ EG0 is an eigenstate of H 0 corresponding to atom A being in an excitedstate, atom B being in ground state, and no photons being present; b GE0 (t)(40)is the amplitude for finding at time t atom A in the ground state, B in theexcited state and no photons present; and similarly,(41)is the amplitude for finding at time t both atoms in the their ground statesand one photon of momentum k polarization . Fermi approximates Φ(t) asfollows:Clearly(42)(43)199

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEso that neglecting the level shift if the initial excited state and the effect ofatom B on the lifetime of ASimilarly(44)so that for t >> 1/Γ A(45)Finally the amplitude b GE0 (t) satisfies(46)Fermi then showed that if you assume the atoms localized at the origin andat r that when r is very large compared to the wave length of the emittedradiation, c/ω S A ,and is proportional to 1/r for t > r/c. Thus the theory “correctly” attributesthe velocity c to the propagation of a photon and also gives the “correct”dependence of the intensity (which is proportional to ⎪b GE0 ⎪ 2 ) on distance,namely that it decreases as 1/r 2 . The calculation thus gave support to the pic-200

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)ture of a photon as a particle like entity traveling between emission andabsorption by widely separated atoms with velocity c. It also moderated theLandau and Peierls (1930) view that one could not give a configurationspace treatment of photons.The next problem Fermi treated in the his RPM article, the theory ofLippman fringes, depended on the analysis he had given for the two-atomproblem. He could again use atom A as a localized source for the emittedphoton, and atom B for the detector. There were several reasons for two ofthe other examples treated, namely Thomson and Compton scattering. Onthe one hand Fermi wanted to further illustrate how perturbation theoryyielded these by then familiar results, and on the other indicate how QEDrecovered the classical Thomson limit for the scattering of long wavelengthradiation off free electrons. In particular, he wanted to point to the fact thatin the non-relativistic approximation, it was the A 2 term that was responsiblefor the effect. He would come back to this observation when deriving theKlein-Nishina formula and indicate the role of the negative states in therecovering the Thomson limit. We will not discuss these matters except to saythat after Dirac had introduced his relativistic equation to describe the electron,Fermi carefully studied its properties 4 and followed all the developmentsrelating to the difficulties and novel properties associated with thenegative energy states. Thus in the his Michigan Summer School lectures andin the his RMP paper Fermi included an extensive discussion of the Diracequation. By the time of the submission of the RMP paper Dirac had formulatedhis hypothesis that all the negative energy states were filled – and thatholes in the negative energy sea corresponded to protons. At Michigan Fermispoke of Tamm’s and of Oppenheimer’s work pointing out the difficultywith that interpretation – namely that the hydrogen atom would be unstablesince protons and electrons could annihilate via two photon emission – andstressed the necessity of including negative energy states contributions in theorder to derive the Klein-Nishina formula and be able to recover theThomson limit from it.We next shall look at a problem that Fermi treated with Bethe in 1932,namely the derivation of the interaction potential between two charged particles.Kragh (1991) and Roqué (1991) have given thorough expositions ofthe background to this paper, namely the theory of Møller scattering and thecontroversies over the derivations by Breit and others of the electron-elec-4 Thus his second Rendiconti paper already described the particles by the Dirac equation.201

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtron interaction potential that included both magnetic and retardationeffects:(47)Suffice it to say here that Møller made use of correspondence arguments –still in the vogue in the Copenhagen at the time – to derive the scatteringmatrix element for the transition from the initial two-electron state to thefinal one after the scattering and that Breit had made heavy use of theHeisenberg-Pauli formalism whose consistency was in the question andwhose clarity was not always readily discernable. There was also the questionof the dependence of the result on the particular gauge that is adopted,whether one works in the Lorentz gauge in the which both transversal as wellas longitudonal and time-like photons are exchanged and the initial state ofthe charged particles are free-particle states, or one works in the radiationgauge where only transverse photons are exchanged and the Coulomb interactionis part of the unperturbed Hamiltonian. The aim of Bethe and Fermiwas to indicate the relation between the two approaches, and more importantly,how perturbation theory could be used to generate transparentresults. Again transcribing their perturbation theoretic treatment into modernterminology, they consider the change in the time of the two-electronamplitude:(48)where Φ I is the initial state (an eigenfunction of H 0 ), a two-electron statespecified by appropriate quantum numbers and the photon vacuum. Onereadily derives that to lowest order of perturbation theory the amplitude thatat some later time t the two electron system is in the state Φ F (again a twoelectron state and no photons present) is given by(49)which is to be compared with the amplitude202

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)that would be computed on the assumption that in the Schrödinger picturethe two electrons obey the equation(50)and interact via a potential V. A comparison of (49) and (50) [after takingthe appropriate photon vacuum expectation value in Eq. (49)] yields theBreit interaction for V stemming from one-photon exchange. It is clear fromtheir derivation that they considered the force between the charged particlesas arising from the exchange of the photons between them.Some technical remarksThere is one aspect of the derivations of the description of physical processesin the Fermi QED papers that I have not commented upon. It will berecalled that in the decomposition of the scalar and vector potential Fermiassigned a different phase to each the degrees of freedom. These differentphases will therefore be present in the computed answers to the variousprocesses that Fermi analyzed. The simplicity of the final expressions resultedfrom an averaging over these phases. The physical meaning of these phaseaveraging is not readily apparent.It will be recalled that in the section 3 of the Dreimännerarbeit Jordan rederivedEinstein’s result for the mean square fluctuations of the electromagneticenergy at frequency in the thermal equilibrium at temperature T inthe a volume v of a cavity(51a)(51b)Jordan actually only treated a one-dimensional system: the transverse vibrationsof a string of length L, described by an amplitude u(x,t)203

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE(52a)(52b)The q k (t) are the “coordinates” describing the system and by virtue of theequations of motion their time dependence is given by:(53)Jordan then computed the mean square fluctuations of the energy in thesubinterval (o, a) of the string. To arrive at Einstein’s result Jordan had totake time averages of the q k ’s and claimed that this time averaging was equivalentto a phase averaging over the phases Φ κ . In some sense the phase averagingenforces the locality of the description requiring the fields at differentspace-time points to be independent degrees of freedom with independentquantum fluctuations.Wightman (1996)has suggested that the departures from Einstein’s formulaif the phase averaging is not taken represents the quantum mechanical versionof the interference effects discussed by Ornstein and Zernike (1919) andby Ehrenfest (1925) 5 . The justification of the phase averaging must thereforehave recourse to an analysis of the measuring apparatus and the extent towhich it is sensitive to possible frequency dependent phase correlations.The electromagnetic mass paperBethe visited Rome in 1931 and in 1932 as a Rockefeller Foundation fellow.He later recalled that:Between the two visits work in the field theory had gone on and Fermi,like so many other of the great theorists, had tried to explain away thedivergences of Quantum electrodynamics.Fermi’s paper (Fermi 1931) was a response to a paper on the self-energyproblem that Heisenberg had published the year before in the Zeitschrift fürPhysik. In his introductory statement in his paper Heisenberg commented that:5 See Wightman 1996 for a detailed history of this controversy.204

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)In classical theory, the field strengths E and H become arbitrarily large inthe neighborhood of the point-charge e, so that the integral over the energydensity (1/8π)(E 2 + H 2 ) diverges. To overcome this difficulty, onetherefore assumes a finite radius r 0 for the electron in classical electron theory.The radius is related to the mass m of the electron in the order of magnituderelation r 0 ~ e 2 /mc 2 : the integral over the energy density is then ofthe order mc 2 . In quantum theory, not only this radius r 0 but possiblyanother length λ 0 = h/mc, which is characteristic of the electron, plays a rolein the self-energy in a superficial consideration in terms of the correspondenceprinciple, one would suspect that the self energy of the point-likeelectron must also become infinite in quantum theory.In, fact Oppenheimer (1930) and Waller (1930) have indeed shown thata perturbation method which proceeds in powers of e does not yield finitevalues for the self-energy [of a point-like electron].But instead of considering a finite sized electron, Heisenberg suggestedthat one divide space into cells of the finite size r 0 3 , and that one replacesthe present differential equations by difference equations... [T]he self energyof an electron would be finite in such as lattice world. [But] the statementthat a smallest length exists is no longer relativistically invariant, andno way is presently known to harmonize the requirement of relativisticinvariance with the fundamental introduction of a smallest length. In themeantime it therefore seems more correct not to introduce the length r0into the foundation of the theory but to hold fast to relativistic invariance.Heisenberg then proceeded to analyze the self-energy of an electron movingwith a speed nearly that of light, in which case its rest mass can be neglected,and thus “we always calculate... with m = 0.” Under those circumstancesHeisenberg believed that the self energy must remain finite ondimensional ground.The one particle Hamiltonian Heisenberg worked with is given by:with p and q and Φ and E satisfying the usual commutation rules.The total momentum operator fro the system is given by(54)(55)205

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEHeisenberg then noted that the electron coordinates can be completelyeliminated from the Hamiltonian by using the total momentum so that itbecomes:(56)For an electron under the influence of no force Heisenberg claims that theequationmust hold. He therefore looked whether solutions wherein(57)exist – and came to the conclusion that[t]he one electron could thus be treated correctly without an infinite selfenergy if there were solutions of vacuum electrodynamics without a zeropointenergy. Unfortunately, such solutions do not exist... A solution ofthe basic equations...has therefore not been found for the time being; itis also not probable that one will achieve a solution without substantialmodification of the quantum theory of wave fields. The purpose of thispaper was to show that the difficulties of field theory do not come directly fromthe infinite self-energy of the electron but that rather the foundations of fieldtheory still require modification. (emphasis added)(58)In his paper written slightly later, Fermi (1931) also investigated the problemof the self-energy of an electron. Fermi was cognizant of the fact that thedivergences resulted from the point character of the charges which wasreflected in the local nature of the stipulated interaction: p i·A(x i ) or υ i·A(x i )and in the form of the Coulomb interaction. Fermi undertook to explore theconsequences of assuming that the charge on an “elementary” particle wasextended – fully aware that this destroyed the relativistic invariance of the theory.Fermi’s model is similar to Lorentz’s: electrons were objects with finiteextension. Moreover, Lorentz made a distinction between electromagneticmass, m ele , and material mass, i.e. mechanical mass, m 0 , the electromagneticmass being the inertia that the charged particle had by virtue of its charge.206

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)The total mass, identified with the experimentally determined mass, isLorentz thought that all the mass of the electron was electro-magnetic, i.e.that m 0 = 0. Fermi in his investigation echoed these views.Fermi made the charge frequency (scale) dependent to reflect its distributednature. His argument for doing so was as follows: if the electron has afinite radius its various parts will present the same phase as far as the wavelengths that are large in the comparison with the electron radius are concerned.On the other hand, for wave lengths of the order of or smaller thanthe electron’s radius different interior points will react with different phases.The electron thus interacts differently with radiation of different frequency –effectively it presents a smaller charge for high frequencies – with theobserved charge some kind of average charge. Fermi thus in the Hamiltonianmakes the charge of each particle frequency dependent: e i = e i ( ).Following Heisenberg, Fermi when characterizing the one particle state ashaving a charge e, momentum p and energy E, required that this state vectormust be an eigenfunction of the total momentum operator, G, (i.e of field +of particle + momentum stemming from the interaction between charge andfield) with eigenvalue p. He then investigated the chiral case, [i.e. the formulationwhen the mechanical mass in the Dirac equation for the chargedparticle is set equal to zero], to see whether he could find states Φ which satisfiedthe requirementsand(59)(60)The joint requirement can be satisfied since G and H commute with oneanother: [G, H] = 0.). In fact, Fermi explicitly exhibited the state vectors thatsatisfied the equation G Φ = p Φ.He then pointed out where Heisenberg had gone wrong. Heisenberg’sassumption that in the full quantum electrodynamical description the forcefree electron must satisfy the Dirac equation(61)207

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwas incorrect. As a result of its interaction with the [quantized] electromagneticfield the equation the electron obeys should be taken to be(62)where m em is the electromagnetic mass the electron acquires by virtue of theinteraction. Fermi therefore inquired whether there are solutions that satisfy(63)with m em to be determined. For the chiral case, Fermi formulated a perturbationtheoretic approach, and to lowest order found an approximate solutionfor which(64)Fermi commented that by virtue of the dependence on h the generation ofthe electromagnetic mass was a strictly quantum mechanical phenomenon.Note that the chiral symmetry is broken!Fermi thus discovered an early case of anomalous or quantal symmetrybreaking, namely that the symmetry of the classical theory need not survivequantization. The introduction of the frequency dependent charge was a regularizationprocedure that allowed the symmetry breaking to be exhibited.As far as we have ascertained, Fermi’s paper fell on deaf ears. During the1930s – except for Kramers’ papers in 1938 – the relativistic invariance of theformulation took precedence over structural modeling and calculations.Thus there is no reference to either Heisenberg’s 1930 self-energy paper norto Fermi’s 1931 paper in Weisskopf 1934 papers wherein he calculated theself-energy of the electron in hole theory and ascertained that to orderα=e 2 /hc the self-energy diverges logarithmically. 3Fermi and the Lamb ShiftShortly after finishing his QED and β-decay researches Fermi turned tonuclear physics and devoted most of his activities to his neutron work.Although he did not publish any further theoretical papers during the 1930sdealing with these subjects it is clear that he kept abreast of theoretical developmentsin the these fields. There are two occasions that I know which elicit-208

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)ed his interest in the QED. In the 1947 after Bethe had completed and circulatedhis calculation indicating that a major part of the Lamb-Retherfordexperimental result on the 2s-2p level shift in the hydrogen could be explainedas a non-relativistic quantum electrodynamical effect, the task at hand becameto carry out a relativistic calculation using the full hole theoretic formalism tojustify Bethe’s introduction of a cut-off at mc 2 . French and Weisskopf, whohad started such a calculation before the Shelter Island conference at whichLamb had presented his data, continued their calculation, but now made useof Kramers’ideas on mass renormalization that had been discussed at ShelterIsland and thus simplified somewhat the subtraction of infinities. At Cornell,Bethe assigned the problem to one of his graduate students, Scalettar.Similarly, Lamb at Columbia started on a hole theoretical calculation duringthe early part of the summer of 1947, and was soon joined by Norman Kroll.Fermi, who was spending the summer 1947 at Los Alamos, upon receiving acopy of Bethe’s preprint explored a relativistic calculation. His first step wasto understand the Bethe calculation – which he redid, in the collaborationwith Uehling, who was also visiting Los Alamos, but they obtained an expressionfor the Lamb shift which was 4/3 times larger than Bethe’s formula.The factor 4/3 [was] due... to the inadequacy of our assumption that the[intermediate] states can be described by plane wavesFermi wrote Uehling after speaking to Bethe. Furthermore,A point that is not explained in the Bethe’s paper but which he explainedto us in the Los Alamos is the procedure for justifying that the recoil ofthe light quantum can be disregarded. This can actually be done by usingan only slightly more complicated sum rule and I do not understand whyBethe did not follow this more complete procedure in the writing hispaper since it would have made the result more convincing.Fermi continuedThe point that still is quite unsatisfactory is of course the upper limit ofthe logarithm in the Bethe’s formula (11). Apparently several people(Bethe, Weisskopf and Schwinger) have tried unsuccessfully to carry out arelativistic calculation of this upper limit. Also Teller and I tried the sameand we believe that we have a method that seems to be practical thoughprobably far from simple. This method consists in the describing the[intermediate] state n as plane waves plus a first approximation[Coulomb] correction which is necessary and sufficient to correct for thefactor 4/3 discussed above.209

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi gave the problem “of the electromagnetic energy level shift in therelativistic case” to Marvin L. Goldberger who was a graduate student atChicago at the time. Goldberger wrote Bethe in the early October 1947 toask him whether “our work is sufficiently different to warrant both Mr.Scalettar and me to work on the problem. Clearly, if our work is merely repetitionof his, we will drop our program.” The approach Goldberger was toemploy was the Fermi-Teller proposal to use “for the intermediate state [inthe hole theoretic generalization of theterm in the Bethe formula the first order Coulomb perturbation of the planewaves... [since] with this device the problem appears to be not too difficult.”Bethe promptly answered him and informed him thatWe are using a very similar method to yours which effectively amounts toa Born approximation on the intermediate state. However, the calculationis by no means simple even with this method... In the some calculationswhich I did in the August, I was able to...demonstrate the convergence ofthe result. Moreover, I found that the result is similar to the non-relativisticcase. Scalettar is now checking my arguments and especially calculatingexplicitly the result in the order to obtain the numerical value. There areapproximately twenty different terms which have to be integrated...Because of the considerable complication of the calculation I should findit desirable that the calculation be done at several places ndependently.You may be able to find a simple method. The main reason against furtherduplication is that in the addition Scalettar, also Weisskopf and Lambare engaged in the similar calculations.Evidently Goldberger dropped the problem.The second occasion for which Fermi came to review developments in QEDafter the war was in the lectures he delivered in Rome and in Milan in the fallof 1949 at the invitation of the Fondazione Donegani. The Rome lecture wasdevoted entirely to the recent developments in QED. In it Fermi reviewedLamb and Retherford’s experiment that established that the 2P 1/2 and 2S 1/2energy levels in atomic hydrogen were not degenerate (as stated by the Diracequation for an electron in a Coulomb field) but were separated by 0.033 cm –1 .He then outlined the Bethe calculation for the Lamb shift, carefully going overthe physics involved in mass renormalization, and proceeded to explicate whatTomonaga, Schwinger, Feynman and Dyson had accomplished. (Fermi 1950).210

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)A third review of QED by Fermi is contained in his Silliman lectures on“Elementary Particles” which he delivered at Yale in the winter of 1950.His opening remarks were a succinct overview of the state of affairs inQED and QFT:Perhaps the most central problem in theoretical physics during the lasttwenty years has been the search for a description of the elementary particlesand their interactions. The radiation theory of Dirac and the subsequentdevelopment of quantum electrodynamics form the present basis forour understanding of the electromagnetic field and its associated particles,the photons... The field theories of other elementary particles are patternedon that of the photon. The assumption is made that for each type of elementaryparticle there exists an associated field of which the particles are thequanta. In addition to the electromagnetic field an electron-positron field,a nucleon field, several meson fields, etc., are also introduced.The Maxwell equations that describe the macroscopic behavior of theelectromagnetic field have been known for a long time. It is therefore naturalto assume that these are the basic equations one should attempt toquantize in constructing a quantum electrodynamics. This has been donewith considerable measure of success. In the past two or three years the lastremaining difficulties associated with the infinite value of the electromagneticmass and the so-called vacuum polarization have been largelyresolved through the work of Bethe, Schwinger, Tomonaga, Feynman andothers. They have been able to interpret satisfactorily the Lamb shift in thefine structure of hydrogen and the anomaly of the intrinsic magneticmoment of the electron as due to the interaction with the radiation field.... Less convincing are the attempts at a similar description of fields aboutwhich we have much scantier experimental knowledge.FeynmanWe have already quoted Bethe on the influence of Fermi’s QED work andin the particular of the RMP exposition of the theory on an entire generationof physicists during the 1930s. Here we merely want to draw attentionto the important influence that Fermi’s RMP article had on Feynman.Already in his PhD thesis Feynman adopted Fermi’s approach to QED in hisinvestigation of whether one can give a description of the interactionbetween charged particles that eliminated explicit reference to the electromagneticfield by integrating out the oscillator degrees of freedom correspondingto it, in his Lagrangian formulation of quantum mechanics. Theopening remarks of section 11 of his dissertation are the following:211

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThe problem which we discuss in the this section is the quantum analogueof the problem discussed in the section 4 of the first part of the paper.Given two atoms A and B, each of which interacts with an oscillator O, towhat extent can the motion of the oscillator be disregarded and the atomsbe considered as interacting directly? This problem has been solved in thea special case by Fermi who has shown that the oscillators of the electromagneticfield which represent longitudonal waves could be eliminatedfrom the Hamiltonian, provided an additional term be added representinginstantaneous Coulomb interactions between the particles. Our problemis analogous to his except that in the general case, as we can see fromthe classical analogue, we shall expect that the interaction will not beinstantaneous, and hence not expressible in the Hamiltonian form.(Feynman 1942)Finally, as is apparent throughout Feynman’s “Mathematical Formulationof the Quantum Theory of Electrodynamics” – the last paper which he wroteon his post-war QED work, but which in fact was the point of departure forall his QED researches – the foundation for his formulation of QED wasFermi’s 1932 Reviews of Modern Physics article.EpilogueWe will let Bethe’s insights into Fermi’s way of doing physics constitute ourconcluding remarks:My greatest impression of Fermi’s method in theoretical physics was of itssimplicity. He was able to analyze into its essentials every problem, howevercomplicated it seemed to be. He stripped it of mathematical complicationsand of unnecessary formalism. In this way, often in half an hour orless, he could solve the essential physical problem involved. Of coursethere was not yet a mathematically complete solution, but when you leftFermi after one of these discussions, it was clear how the mathematicalsolution should proceed.This method was particularly impressive to me because I had come fromthe school of Sommerfeld in Munich who proceeded in all his work bycomplete mathematical solution. Having grown up in Sommerfeld’sschool, I thought that the method to follow was to set up the differentialequation for the problem (usually the Schrödinger equation), to use yourmathematical skill in finding a solution as accurate and elegant as possible,and then to discuss this solution. In the discussion finally, you would findout the qualitative features of the solution, and hence understand the212

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)physics of the problem. Sommerfeld’s way was good one for many problemswhere the fundamental physics was already understood, but it wasextremely laborious. It would usually take several months before youknew the answer to the question.It was extremely impressive to see that Fermi did not need all this labor.The physics became clear by an analysis of the essentials, and a few orderof order of magnitude estimates. His approach was pragmatic...Fermi was a good mathematician. Whenever it was required, he was ableto do elaborate mathematics; however, he first wanted to make sure thatthis was worth doing. He was a master at achieving important results witha minimum of effort and mathematical apparatus.By working in this manner he clarified the problems very much, especiallyfor younger people who did not have his great knowledge. For instance,his formulation of quantum electrodynamics is so much simpler than theoriginal Heisenberg and Pauli that it could be very easily understood. Iwas very much intimidated by the Heisenberg-Pauli article, and could notsee the forest from the trees. Fermi’s formulation saw showed the forest.The same was true in the paper we wrote together, concerning variousformulations of relativistic collision theory. Fermi’s formulation of neutrondiffusion, the age theory, has been extremely fruitful in making quickcalculations of neutron diffusion even in complicated cases. I could multiplythis list easily, just from my own experience with Fermi and his work.(Bethe in Segrè 1970).REFERENCES01. BETHE H.A. 1930. “Über die nichtstationäre Behandlung des Photoeffekts.” Annalen derPhysik 4:443-449.02. BETHE H.A. 1955. “Remarks at the Memorial Symposium in the honor of Enrico Fermi.”Reviews of Modern Physics 27/3, p.253.03. BETHE H.A. and FERMI E. 1932. “Über die Wechselwirkung von zwei Elektronen.” Zs. FürPhysik 77:296-306.04. BREIT G. 1929. “The effect of retardation on the interaction of two electrons.” PhysicalReview 34:555-573.05. BREIT G. 1933. “The Quantum Theory of Dispersion.” Part VI and VII.Reviews of ModernPhysics 5/2:91-140.06. DIRAC P.A.M. 1927a. The quantum theory of the emission and absorption of radiation.Proceedings of the Royal Society A 114 243-265.07. DIRAC P.A.M. 1927b. The quantum theory of dispersion. Proceedings of the Royal SocietyA 114:710-728. 243, 710, 1927)08. FERMI E. 1926. “Argomenti pro e conto la ipotesi dei quanti di luce”. Nuovo Cimento.3:47-54.213

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE09. FERMI E. 1927. “Sul meccanismo dell’emissione nella meccanica ondulatoria.” Rend. Lincei5:795-800.10. FERMI E. 1929a. “Sopra l’elettrodinamica quantistica.” Rend. Lincei 9:881-887.11. FERMI E. 1929b. “Sulla teoria quantistica delle frange di interferenza”. Nuovo Cimento.7:153-158. 4112. FERMI E. 1930. “Sopra l’elettrodinamica quantistica.” Rend. Lincei 12:431-435.13. FERMI E. 1931. “La masse eettromagnetiche nella elettrodinamica quantistica”. NuovoCimento. 8:121-132.14. FERMI E. 1931. “Sur la théorie de la radiation”. Annales de L’Institut Henri Poincaré1:53-74.15. FERMI E. 1932. “Quantum Theory of Radiation”. Reviews of Modern Physics 4:87-132.16. FERMI E. 1950. Conferenze di Fisica Atomica. Entry 240 in volume 2 of Fermi 1965. Pp.744-755.17. FERMI E. 1951. Elementary Particles. New Haven: Yale University Press.18. FERMI E. 1965. Collected Papers (Note e memorie). 2 v. Chicago: University of ChicagoPress.19. FEYNMAN R.P. 1942. The Principle of Least Action in the Quantum Mechanics. PhD.Dissertation. Princeton University.20. FEYNMAN R.P. 1950. “The mathematical formulation of the quantum theory of electromagneticinteraction. Phys. Rev. 80:440-457.21. HEISENBERG W. 1930. “Die Selbstenergie des Elektrons.” Zeitschrift fur Physik 65:4-13.22. HEISENBERG W. and PAULI W. 1929. “Zur Quantendynamik der Wellenfelder.” Zeits. fürPhysik 56:1-61.23. HEISENBERG W. and PAULI W. 1930. “Zur Quantendynamik der Wellenfelder. II” Zeits. fürPhysik 59:168-190.24. JORDAN P. and KLEIN O. 1927. “Zum Mehrkörperproblem der Quantentheorie.” Zeits.Physik 45:751-763.25. JORDAN P. and WIGNER E. 1928. “Über das Paulische Äquivalenzverbot.” Zs. f. Physik 47:631-651.26. KRAGH H. 1991. “Relativistic Collisions: The Work of Christian Møller in the Early 1930s.Archive for History of Exact Sciences 43:299-328.27. LANDAU L. and PEIERLS R. 1930. “Quantenelektrodynamik im Konfigurationsraum.” Zs.f. Physik 62:188-200.28. LOW F. 1952. “Natural Line Shape.” Physical Review 88:53-57.29. PAULI W. 1979. Wissenschaftlicher Briefwechsel mit Bohr, Einstein, Heisenberg U.A.BAND I:1919-1929. Hermann, A., von Meyenn, K, and Weisskopf, V. Eds. Berlin:Springer Verlag.30. ROQUÉ X. 1991. “Møller Scattering: a Neglected Application of Early QuantumElectrodynamics.” Archive for History of Exact Sciences 43:197-264.31. SEGRÈ E. 1970. Enrico Fermi Physicist. Chicago: University of Chicago Press.32. SOMMERFELD A. and SCHUR G. 1930. “Über den Photoeffekt in the der K-Schale derAtome.” Annalen der Physik 4/5:409-432.214

Sam SchweberFERMI AND QUANTUM ELECTRODYNAMICS (QED)33. WEISSKOPF V. and WIGNER E. 1930. “Berechnung der naturlichen Linienbreite auf Grundder Diracschen Lichttheorie.” Zs f. Physik 63:54-73.34. WEISSKOPF V. 1931. “Zur Theorie der Rezonanzfluoreszenz.” Annalen der Physik (5) 9:23-66.35. WEISSKOPF V. 1934. “Über die Selbstenergie des Elektrons.” Zeitschrift fur Physik 89:27-39.36. WEISSKOPF V. 1934. “Berichtung zu der Arbeit: Über die Selbst-energie des Elektrons.”Zeitschrift fur Physik 90:817-818.37. WENTZEL G. 1926. “Zur Theorie des photoelektrischen Effekts.” Zs f. Physik 40:574-38. WIGHTMAN A. 1996. “How it was learned that quantized fields are operator -valued distributions.”Forschritte Phys. 44:143-178.ENDNOTES1. “The light-quantum has the peculiarity that it apparently ceases to exist when it is in oneof its stationary states, namely, the zero state, in which its momentum, and therefore alsoits energy, are zero. When a light-quantum is absorbed it can be considered to jump intothis zero state, and when one is emitted it can be considered to jump from the zero stateto one in which it is physically in evidence, so that it appears to have been created. Sincethere is no limit to the number of light-quanta that may be created in this way, we mustsuppose that there are an infinite number of light-quanta in the zero state, so that the N 0of the Hamiltonian (1.3.24) is infinite.” Dirac 1927a.2. Fermi repeatedly returns to these solutions. See for example, page 115 of Fermi’sNotebook I . Reel 69 of Archives for the History of Quantum Physics.3. The self-energy calculations by Heisenberg and Fermi were carried out before Dirac hadformulated his hole theory wherein all the negative energy states of the Dirac equationsare filled, and holes in that distribution would correspond to positrons. The calculationsby Oppenheimer and by Waller had indicated that to lowest order of perturbation theorythe self energy of an electron diverged linearly in a pre-hole theory.Sam SchweberObtained his PhD in theoretical physics from Princeton University in 1952. Hethereafter was a postdoctoral fellow with Gian Carlo Wick at Pittsburgh andwith Hans Bethe at Cornell. Since 1955 he has been at Brandeis Universitywhere he is presently the Koret Professor of the History of Ideas and professorof Physics. Since the early 1980s he has focused his research interests on thehistory of science and the history of modern physics in particular. He is a facultyassociate in the department of the history of science at Harvard University.He is the author of a textbook on relativistic quantum field theory (1961), andmore recently of a history of quantum electrodynamics (1994), and of a studyin the parallel lives of Hans Bethe and J. Robert Oppenheimer (2000).215

Michelangelo De MariaFermi and Applied Nuclear Physicsduring the War (1939-1945)I will discuss the fundamental role played by Enrico Fermi in the conception andrealization of the first nuclear reactor. In particular, I will analyse his scientificcontributions to the “pile”, from his choice of carbon as “moderator” to the latticearrangement of graphite and uranium, from his theory of reactors to the so-called“exponential experiments”. I will also examine his crucial role in the “ignition” ofthe “Plutonium project”. Such a role was played by Fermi in a manifold, rapidlychanging context. Indeed during the war years, physicists and Fermi in particularbecame active protagonists of the abrupt shift from the “little science” pattern ofresearch, typical of Fermi and his group at Columbia University in 1939-1941,to the “big science” pattern, which he started to practice in 1942-1944.Moreover, for the first time physicists became scientific advisors and consultantsof politicians, military and industrialists, and participated in the decision-makingprocess of the most important choices in the war.Fermi e la fisica nucleare applicata negli annidel conflitto bellico (1939-1945)Il mio intervento è centrato sul ruolo fondamentale avuto da Enrico Fermi nellarealizzazione del primo reattore nucleare. Viene esaminato il suo contributoscientifico alla “pila”, dalla scelta del carbonio come “moderatore”, allacombinazione di grafite ed uranio, dalla teoria dei reattori ai cosiddetti“esperimenti esponenziali”.Viene preso in esame anche il ruolo cruciale da luiavuto nell’ignizione del “Progetto Plutonio”, in un contesto rapidamente mutevole.Durante la guerra i fisici, e Fermi in particolare, furono attivi protagonisti dellarepentina svolta dalla “little science”, tipiche di Fermi e del suo gruppo allaColumbia University nel 1939-1941, alla “big science” che egli iniziò a metterein atto nel 1942-1944. Inoltre per la prima volta i fisici divennero consiglieri,scientifici e consulenti di politici, militari ed industriali, prendendo parteattivamente ai processi decisionali sui più importanti snodi del conflitto.217

Dominique PestreNew Large Accelerators in the Worldin the Forties and Eearly FiftiesThis paper presents half a dozen stories involving protons and physicists, electronaccelerators and high politics. The aims of the study are two-fold. The first is tooffer a series of historical analyses describing how decisions were arrived atconcerning some of the largest accelerators constructed from the 1930s to the1970s throughout the world. Accelerators are the basic tools of what manyconsider to be the most fundamental physics undertaken during the last halfcentury, and they are expensive and technically complex machines.My second aim is to reflect upon the decision-making processes as they occurredin XXth Century big physics. “Spontaneously”, I would say, one might betempted to imagine such processes as being of a linear, rational, “scientific” kind– the final decision resulting from an exhaustive analysis of all possible solutionsand of their relevance for the unresolved problems of physics. My study beliesthe systematic dominance of such a process and suggests, on the contrary, theplaying out of different logics of a completely different kind.I nuovi grandi acceleratori realizzati nel mondo negli anniquaranta e nei primi anni cinquantaQuesta relazione riporta una serie di eventi riguardanti protoni e fisici,acceleratori di elettroni ed alta politica con un duplice obiettivo.Il primo è quello di offrire una serie di analisi storiche riguardanti le modalitàdecisionali su alcuni dei più grandi acceleratori costruiti nel mondo tra gli anni30 e gli anni 70. Gli acceleratori, macchinari complessi ed estremamentecostosi, sono gli strumenti basilari di quella che molti considerano la fisicafondamentale della seconda metà del secolo scorso. Il secondo è fare unariflessione sui processi decisionali del ventesimo secolo nella “big physics”.Credo che si possa essere facilmente portati a pensare che tali processi altronon fossero che la naturale conseguenza di un processo logico lineare erazionale, di impronta scientifica, la decisione finale di una analisi esaustiva diogni soluzione possibile e della loro attinenza con i quesiti irrisolti della fisica. Ilmio studio smentisce questa tesi e suggerisce, al contrario, che su tali decisioniabbiano influito una logica di natura completamente diversa.219

Giulio MalteseEnrico Fermi and the Birth of High-Energy Physicsafter World War IIThe motivation of the work is to outline the influence that Fermi exerted on thebirth and the rapid growth of high-energy physics in the period 1946-1954,after his return to Chicago from Los Alamos till his untimely death in 1954. Thisinfluence is manifold, as it ranges from Fermi’s role as a founder of the socalled“Chicago School” of physics, where many important scientists camefrom, to contributions to theory, like his interpretation of the Conversi, Pancini,and Piccioni experiment or his and Yang’s bold hypothesis concerning thecomposite nature of pions. Other areas where Fermi played a major roleinclude the policy of science in the post-war years and the path-breakingexperimental work he did on pion-nucleon scattering, that eventually led to thediscovery of the 3-3 resonance. Fermi’s influence on the development ofmodern physics can be seen also in his systematic pushing towards the use ofelectronic computers, which he regarded as an effective mean to helpresearch. In the concluding remarks Fermi’s attitude as a theoretical physicistwill be discussed, and his outlook of theoretical physics will be put in theframework of physics as it was in the fifties.221

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEEnrico Fermi e la nascita della fisica delle alte energiedopo la seconda guerra mondialeQuesta relazione si prefigge lo scopo di delineare l’influenza esercitatada Fermi sulla nascita ed il rapido sviluppo della fisica delle alte energienegli anni 1946-1954, dopo il suo ritorno a Chicago da Los Alamos efino alla sua morte prematura nel 1954. Tale influenza si manifestò invari modi, e spazia dal ruolo di Fermi come fondatore della cosiddetta“Chicago School”, dove si formarono molti importanti scienziati, acontributi teorici come l’interpretazione dell’esperimento di Conversi,Pancini e Piccioni, o all’audace ipotesi, formulata assieme a Yang, sullanatura composita dei pioni.Altri settori nei quali Fermi giocò un ruolo di primo piano vanno dallapolitica della scienza negli anni del dopoguerra al suo pionieristicolavoro sperimentale sulla diffusione del pione-nucleone, che condussealla scoperta della risonanza 3-3.L’influenza di Fermi sullo sviluppo della fisica moderna può esserericonosciuta anche nella sua spinta verso l’utilizzo dei calcolatorielettronici, che Fermi considerava uno strumento molto efficace per laricerca. Il commento conclusivo riguarderà l’atteggiamento di Fermi comefisico teorico e la sua opinione sulla fisica teorica verrà posta nelcontesto dello stato della fisica agli inizi degli anni cinquanta.222

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIIntroduction: Enrico Fermi and a new field of physicsOf the almost sixteen years that Enrico Fermi spent in the US, since he fledfrom Europe at the end of 1938 to his untimely death in 1954, his bestknown achievements are the first self-sustained chain reaction (Chicago,December 2, 1942) and the first test of a fission atomic bomb (Alamogordo,July 16, 1945). In the latter enterprise, Fermi was an influential member ofthe most incredible team of physicists ever assembled in the history of science.The consequences of those successes went well beyond the communityof scientists and marked the history of mankind in the 20 th century. Thisis probably the reason why Fermi’s achievements in the postwar years, whileat least comparable to the ones quoted above, are less widely known.Fermi’s astonishing contributions to physics continued during the years1946-1954, a period that witnessed the rapid flourishing of “high-energynuclear physics”, as both a follow-on of wartime military projects, as far asfunding and science organization were concerned, and as a consequence ofthe will that many physicists, including Fermi, displayed to go back to purescience after focusing on applied physics in wartime years.Enrico Fermi was one of the key actors in this new field of physics in theUS after World War II. He deeply influenced the birth and rapid growth ofhigh-energy physics in the period 1946-1954, after his return to Chicagofrom Los Alamos till his death in 1954. Fermi’s contributions ranged fromhis role as a founder of the so-called “Chicago School” of physics, wheremany important particle physicists came from, to theoretical achievements orideas, like his interpretation of the Conversi, Pancini, and Piccioni experimentor the bold hypothesis concerning the composite nature of pions thathe and Yang put forward in 1949. An influential member of the communityof physicists, Fermi was President of the American Physical Society during1953. He served (1947-1950) as a member of the General AdvisoryCommittee (GAC) of the Atomic Energy Commission (AEC). In these andother capacities, Fermi strongly favored the development of high-energyphysics, pushing towards particle accelerators and electronic computers, thathe considered as the fundamental tools of particle physicists. As an experimentalphysicist, using the Chicago 450 MeV synchrocyclotron Fermi performeda path-breaking work that eventually led to the discovery of the pionnucleon3-3 resonance and put the isospin concept at the center of the stagein the study of strong interactions.Fermi was deeply interested in all fields of the physics of “fundamental” particles,a term he preferred to “elementary”. He taught physics to a generation223

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEof young scientists, many of whom played a major role in the revolution thatmarked the development of physics in the second half of the 20 th century. Hetook lively part to the debate on the inadequacy of theory to account for thegrowing number of facts that experiments continuously brought to the surfaceat the beginning of the fifties. In those times his pragmatic outlook oftheoretical physics was especially suited for the status of the discipline, driven,as it was, by experimental discoveries. Young students at Chicago in hislate years mostly knew “this” Fermi, and “this” Fermi will be the subject ofthe present paper.A major shiftIn 1945, at the age of 44, Enrico Fermi was the greatest neutron physicistin the world. He mastered this subject so thoroughly that he could safely saythat he felt neutrons were, so to speak, a sort of “relatives” to him. 1However, just when he was at the top of his fame as a neutron physicist andhe was widely considered an “oracle” at Los Alamos laboratory, he decideda major change and set out to tackle the “high-energy nuclear physics” as itwas then called that field of physics that would eventually give rise to themodern physics of elementary particles. It was a paradigm shift comparableto the one Fermi had made in 1932, when he had left atomic and molecularphysics, which he considered by then well established, to devote himself andhis group to the more promising field of neutron physics. In his biographyof Enrico Fermi, Segrè recalls what was the context, at Los Alamos in 1945,where this decision was taken: “One could go on with nuclear physics, whilewaiting for the instruments to tackle elementary particles to be ready; theshift, however, was necessary, to keep staying in the forefront of physics. Inthe mean time, one could start preparing himself, studying everything wasthen known, and working to make available instruments required by futurework. Fermi, Allison and I kept talking of all these things while going downthe steep walls of the Cañon de Frijoles and then stepping along the rivertowards the Rio Grande in a strange and exotic landscape made of Indianruins, vividly colored rocks, cactuses and piñones”. 21 E. FERMI, “Conferenze di Fisica Atomica”, FNM, vol. 2, paper no. 240, p. 756. The following abbreviationsare used: EFP, Enrico Fermi Papers, Department of Special Collections, University of ChicagoLibrary; EAP, Edoardo Amaldi Papers, Department of Physics, University of Rome I; FNM, EnricoFermi, Note e Memorie (Collected Papers), Accademia Nazionale dei Lincei and University of ChicagoPress, Rome and Chicago, 1965; PR, Physical Review.2E. SEGRÈ, Enrico Fermi, fisico, Zanichelli, Bologna, 1987, p. 170, my translation.224

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IITo be sure, Fermi had started thinking to high-energy nuclear physics evenbefore. In 1944, when working at Hanford at the start-up of the first plutoniumproduction reactor, Fermi told Leona Marshall of his plans to build abetatron after the war. Eventually a betatron was not the kind of machinethat was best suited for the research Fermi had in mind, but his goal wasclear: he wanted to devote himself to particle physics, “to find out all therewas to know about nuclear forces”. 3Fermi left Los Alamos with his family on December 31, 1945. He had beenappointed Charles H. Swift Distinguished Service Professor of Physics at theInstitute of Nuclear Studies of the University of Chicago. However, “at theend of the war, the physicists who returned to the University of Chicago toform the Institute of Nuclear Studies found a physics department with bareshelves”. 4 The building of the Institute was still to come, as Fermi wrote toSegrè in June 1946: “During the winter and spring I have done practicallyall my work at Argonne and I expect to continue the same way until we shallhave some beginning of a building of our own probably about one year fromnow;” 5 thus, “it was reasonable, therefore, that we turned to the excellentheavy water reactor facility at the Argonne Laboratory with its high thermalneutron flux, to investigate aspects of neutron physics which had beenbypassed in the drive to the wartime objectives”. 6Together with Leona Marshall and others, Fermi in 1946-1947 devotedhimself to neutron physics, and especially to neutron scattering, givingimportant contributions to the study of the diffraction of neutrons by crystallinesubstances and investigating the hypothesis of a neutron-electroninteraction. 7 However, experimental activity at Argonne started decreasing asFermi got more and more involved into his activity as a teacher and, as helater said, as a “student” of the new theoretical physics.The “Chicago school”In his letter to Segrè of June 24, 1946, Fermi also spoke of his activity asa teacher: “I have been giving one official course and some unofficial teach-3 L. MARSHALL LIBBY, The Uranium People, Charles Scribner’s sons, New York, 1979, p. 108.4 L. MARSHALL, introduction to papers nos. 227-231, 234 and 235, FNM, vol. 2, p. 578.5 E. Fermi to E. Segrè, June 24, 1946, EFP, box 11.6L. MARSHALL, introduction to papers nos. 227-231, 234 and 235, FNM, vol. 2, p. 578.7See FNM, vol. 2, papers nos. 226-231 and 234-235.225

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEing to a small group of students”. 8 Fermi’s was an understatement. As Segrèput it, “Soon the rumour spread that Fermi was about to create a new schoolof physics, and a group of extraordinary students gathered at Chicago”. 9Between 1946 and 1953, Fermi gave twenty-three courses, 10 teaching tomany first-class students. Among them was Chen Ning Yang who laterrecalled: “Fermi gave extremely lucid lectures. In a fashion that is characteristicof him, for each topic he always started from the beginning, treated simpleexamples and avoided as much as possible ‘formalisms’. (He used to jokethat complicated formalism was for the ‘high priests’). The very simplicity ofhis reasoning conveyed the impression of effortlessness. But this impressionis false: The simplicity was the result of careful preparation and of deliberateweighing of different alternatives of presentation”. 11In addition to giving regular courses, Fermi created a sort of ”late afternoongraduate school of physics”, again described by Yang: “it was Fermi’shabit to give, once or twice a week, informal unprepared lectures to a smallgroup of graduate students. The group gathered in his office and someone,either Fermi himself or one of the students, would propose a specific topicfor discussion. Fermi would search through his carefully indexed notebooksto find his notes on the topic and would then present it to us. I still have thenotes I took of his evening lectures during October 1946 – July 1947. It coveredthe following topics in the original order: theory of the internal constitutionand the evolution of stars, structure of the white dwarfs, Gamow-Schönberg’s idea about supernovae (neutrino cooling due to electron captureby nuclei), Riemannian geometry, general relativity and cosmology,Thomas-Fermi model, the state of matter at very high temperatures and density,Thomas factor of 2, scattering of neutrons by para and ortho hydrogen,synchrotron radiation, Zeeman effect, “Johnson effect” of noise in circuits,Bose-Einstein condensation, multiple periodic system and Bohr’s quantumcondition, Born-Infeld theory of elementary particles, brief description ofthe foundation of statistical mechanics, slowing down of mesons in matter,slowing down of neutrons in matter […] The fact that Fermi had kept overthe years detailed notes on diverse subjects in physics, ranging from the purelytheoretical to the purely experimental, from such simple problems as the8 E. Fermi to E. Segrè, June 24, 1946, EFP, box 11.9 E. SEGRÈ, Enrico Fermi, cit., p. 171, my translation.10 V.L. TELEGDI, “Enrico Fermi in America”, in: Symposium dedicated to Enrico Fermi on the occasion of the50th anniversary of the first reactor, Atti dei Convegni Lincei, vol. 104, pp. 71-90, Rome, 1993, p. 81.11C.N. YANG, introduction to paper no. 239, FNM, vol. 2, p. 673.226

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIbest coordinates to use for the three-body problem to such deep subjects asgeneral relativity, was an important lesson to all of us. We learned that thatwas physics. We learned that physics should not be a specialist’s subject;physics is to be built from the ground up, brick by brick, layer by layer. Welearned that abstractions come after detailed foundation work, not before”. 12Several Fermi’s students were awarded the Nobel Prize in physics: C. N.Yang and T.D. Lee (1957), O. Chamberlain (1959), J. Steinberger (1988),J. I. Friedman (1990). In addition to them we have to mention J. W. Cronin(1980), a young student at the Institute of Nuclear Physics at the time of lateFermi, and M. Gell-Mann (1969), who between 1952 and 1954 was a youngteacher at the Institute for Nuclear Studies.Mention must also be made of Emilio Segrè, who shared the Nobel Prizein 1959 with Chamberlain and was the first of Fermi’s students in Italy.Finally, Maria Goeppert Mayer, whose work on the nuclear shell model wasawarded the Nobel Prize in 1963, acknowledged a decisive suggestion shehad from Fermi in her quest.Most of his students were aware of the privilege they had to study under theguidance of such a great teacher. In 1954 Chamberlain wrote to him: “I am verygrateful to you for the time and effort you have invested in me in the past. If Iam to be regarded as a decent physicist, it is mostly because of your training”. 13According to Steinberger “Fermi’s courses […] were models of transparentand simple organization of the most important concepts. He went to agreat length to show those of us who had finished the courses and wereworking on our Ph.D., theses how to attack a variety of simple, general problemsin different branches of physics, by gathering us together one or twoevenings a week […] proposing a problem, and then, perhaps later, goingthrough the solution”. 14Friedman described the atmosphere at the Institute for Nuclear Studies: “Itis difficult to convey the sense of excitement that pervaded the Departmentat that time. Fermi’s brilliance, his stimulating, crystal clear lectures that he12C.N. YANG, Introduction to paper no. 239, FNM, vol. 2, pp. 673-674. This way of teaching, typical ofFermi’s style, dated back to his Italian years; see, for example E. SEGRÈ, Autobiografia di un fisico, IlMulino, Bologna, 1995, pp. 66-67; E. Amaldi, “Commemorazione del Socio Enrico Fermi”; E. Persico,“Commemorazione di Enrico Fermi”; F. Rasetti, “Enrico Fermi e la Fisica Italiana”, in: C. BERNARDINIand L. BONOLIS (Eds.), Conoscere Fermi, Società Italiana di Fisica, Bologna, 2001, p. 27, 39, 50.13 O. Chamberlain to E. Fermi, February 2, 1954, EFP, box 11.14 J. STEINBERGER, “A particular view of particle physics in the fifties”, in: L.M. BROWN, M. DRESDEN, L.HODDESON, (Eds): Pions to Quarks: Particle Physics in the 1950s, Cambridge University Press,Cambridge, 1989, pp. 307-308.227

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEgave in numerous seminars and courses, the outstanding faculty in theDepartment, the many notable physicists who frequently came to visit Fermi,and the pioneering investigations of pion proton scattering at the newly constructedcyclotron all combined to create an especially lively atmosphere. Iwas indeed fortunate to have seen the practice of physics carried out at its‘very best’ at such an early stage in my development. I also had the great privilegeof being supervised by Fermi, and I can remember being overwhelmedwith a sense of my good fortune to have been given the opportunity to workfor this great man. It was a remarkably stimulating experience that shaped theway I think about physics”. 15Emilio Segrè, his first student in Italy and later a Nobel prizewinner in1959 recalled Fermi’s style in his lectures for graduate students: “His lectureswere absolutely informal and not prepared in advance. We gathered in theafternoon at the Institute and maybe some initial conversation suggested himthe topic for his lecture. If, for example, we asked him to clarify the problemof capillarity, Fermi would improvise a magnificent talk on the mathematicsof capillarity […] in other cases the level was quite higher and Fermiexplained to us the last paper he had read: in this way we became familiarwith the famous Schrödinger’s papers on wave mechanics […] Fermi’s teachingconcerned almost exclusively theoretical physics and he made no distinctionbetween students that were supposed to become theorists or experimentalists.He himself, while being first of all a theoretician, worked also asan experimenter. His knowledge and his interests concerned all fields ofphysics, and he duly read several papers. He preferred practical problems anddistrusted theories too abstract or generic; however, whatever problem inwhatever field of physics – classical mechanics, spectroscopy, thermodynamics,solid state theory, and so on – fascinated him and stimulated his ingenuityand his sense of physics […] A curious aspect of Fermi’s style was his slowpace, even when he dealt with simple problems. A simple-minded observermight have wondered why Fermi wasted so much time in elementary algebra;however, when difficulties occurred that would have stopped a less brilliantscientist, Fermi could dispose of them without changing his speed. Hegave the impression of a steam-roller that proceeded slowly but that couldnot be stopped […] When he had discovered a new method he stored it inhis memory, and he often applied it later to problems that looked quite differentfrom the one that had originated the method itself”. 1615J.I. FRIEDMAN, autobiography, http://www.nobel.se.physics.228

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIEven more than a teacher, Fermi was actually, to quote Gell-Mann’s words,“the meson that kept the Institute together”. At his funeral, his friend S.K.Allison said that “the Institute is his Institute, for he was its outstandingsource of intellectual stimulation. It was Enrico who attended every seminarand with incredible brilliance critically assayed every new idea or discovery. Itwas Enrico who arrived first in the morning and left last at night, filling eachday with his outpurring of mental and physical energy”.According to V.L. Telegdi, “it is imaginable […] that some other physicist(or group of physicists) might have obtained the research results that Fermiachieved while at Columbia and in Chicago (including the realisation of thefirst nuclear chain reaction), but it defies the bounds of human imaginationto speculate that any other man or woman might have played Fermi’s role asa teacher (in the broadest sense of this term). Through the influence of hisstudents, Fermi effectively revolutionized the training of physicists in theUnited States and, hopefully, in the whole Western world”. 17All of the Nobel prizes listed above were awarded for discoveries made inthe field of elementary particle physics; more generally, many of Fermi’s studentsspent their scientific careers in high-energy physics. It can safely beassumed that the first great contribution that Fermi gave to elementary particlephysics was the “Chicago School” of physics that he created.From mesotrons to pions: Fermi and the experiment of Conversi,Pancini, and PiccioniIn 1934-1935 the Japanese physicist Hideki Yukawa put forward his theoryof nuclear forces, implying the existence of a new particle (variously namedas “Yukon” or “mesotron”) that played the role of quantum of the nuclearforce field and was supposed to have a mass of µ≈200m e (m e being the massof the electron). In 1936-1937 Carl Anderson and Seth Neddermeyerobserved in cosmic rays a sort of “heavy electron” with a mass similar to thatof the particle hypothesized by Yukawa. In the spring of 1937 it was hypothesizedfor the first time that the particle observed by Anderson andNeddermeyer could actually be Yukawa’s particle.Then it followed a period (1938-1943) in which physicists measured the16P. DE LATIL, Fermi: la vita, le ricerche le testimonianze, Edizioni Accademia, Milano, 1974, pp. 170-171, my translation.17 M. Gell-Mann’s biography, Santa Fe Institute, http://www.santafe.edu; S.K. ALLISON, “Enrico Fermi1901-1954”, Physics Today, no. 8, 1955, p. 9; V.L. TELEGDI, “Enrico Fermi in America”, cit., p. 71.229

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEproperties of the mesotron (mean lifetime and decay properties), trying to fitit into the framework of Yukawa’s theory, albeit with increasing difficulties.It was a series of experiments, carried on in 1943-1946 by the Italian physicistsMarcello Conversi, Ettore Pancini and Oreste Piccioni that eventuallydemonstrated that mesotrons behaved in a way that could hardly fit intoYukawa’s scheme. Basically, according to theory, slow positively chargedmesotrons traversing the matter should prefer to decay rather than beabsorbed by a nucleus, since Coulomb repulsion should prevent them fromreaching the nucleus. On the other hand, negative Yukawa particles shouldstrongly prefer absorption to decay. While in the Conversi et al. experimentpositive cosmic ray mesons behaved the way the theory said, and negativecosmic ray mesons were absorbed in iron, again as expected, negative cosmicray mesons were not absorbed in a light element like carbon! 18Immediately, Conversi, Pancini and Piccioni communicated this result toEdoardo Amaldi, who was then in Washington, about to complete a threemonthtrip to the US. Looking for major wisdom, Amaldi wrote to Fermi:“I think you’ll be interested in the last data from M. Conversi, E. Pancini, O.Piccioni on the death of mesons of both signs [...] It may be inferred fromthese results that in iron only positive mesons decay, and that in carbon bothpositive and negative mesons decay, with equal probability”. 19Fermi realised the importance of the matter and started working on it. Hesoon replied to Amaldi: “Thanks a lot for your letter from Washington, inwhich you tell me of the results of the experiments by Conversi, Pancini andPiccioni on the decay of mesotrons in carbon and in iron. Teller and I havemade some calculations and discussions on the meaning of these experiments,and our conclusions are summarized in the enclosed manuscript. Wewould like to publish it or something very similar as a letter to the Phys. Rev.and naturally we would like to ask Conversi et al. for the permission to quotetheir results”. 20 Two generations of Italian physicists, ranging from theyoung Pancini, Conversi and Piccioni, to the elder Amaldi, the former “boyof Via Panisperna”, and finally to Enrico Fermi, “the Pope” and the leaderof that group, were involved in executing and analyzing what is today consideredthe experiment that initiated the era of high-energy physics.18 For more details see A. PAIS, Inward Bound: Of Matter and Forces in the Physical World, OxfordUniversity Press, Oxford, 1986, chapter 18.19 E. Amaldi to E. Fermi, November 28, 1946, EFP, box 9, my translation.20E. Fermi to E. Amaldi, January 3, 1947, EFP, box 9, my translation.230

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIFurthermore, it was through Amaldi and Fermi that the news of the experimentwas spread in the US. 21Soon, the experimental result of the Italian physicists became a stimulatingresearch topic at the Institute for Nuclear Studies. Jack Steinberger, then ayoung student, recalled: “For me, particle physics began in 1947, when I wasa graduate student at the University of Chicago. Enrico Fermi gave a seminaron the results of the Conversi, Pancini and Piccioni experiment [...] Itwas a beautiful and important experiment, and Fermi’s explanation wasextraordinarily lucid, as well as stimulating and exciting”. 22 Fermi (who hadalready studied in 1939 the anomalous absorption of cosmic rays in air)devoted himself to analyze the outcome of the Conversi et al. experiment,together with Teller. It appeared that the result obtained by Conversi and hisassociates pointed toward a very weak interaction between cosmic ray (“µ”)mesons and nucleons. Teller recalls that “Weisskopf had arrived at a similarconclusion and through correspondence we arranged a short joint note”. 23The analysis by Fermi, Teller and Weisskopf demonstrated that the time ofcapture from the lowest orbit of carbon was not less than the time of naturaldecay, i.e. 10 -6 s. This was in disagreement with the estimate of the theoryfor a factor ranging from 10 10 to 10 12 . The interaction between µ-mesonsand nucleons was therefore much weaker than demanded by Yukawa’s theory.In a second and more detailed paper, Fermi and Teller looked for an alternativeexplanation to the effect discovered by Conversi et al. They hypothesizedthat the time of capture in carbon was so long that the relatively greatnumber of meson decays might take place during the time of capture. Fermiand Teller therefore studied the capture mechanism in depth. They foundthat the capture time is much shorter (from 10 -9 to 10 -13 s) with respect tothe average lifetime of µ-mesons (2x10 -6 s), and the hypothesis of identifyingµ-mesons and mesotrons was definitely proved to be fallacious. 24The discussion of the Italian experiment was one of the two major themesat the Shelter Island Conference (held on June 2-4, 1947), the first of a series21 M. CONVERSI, E. PANCINI, O. PICCIONI, “On the Disintegration of Negative Mesons”, PR, vol. 71(1947), pp. 209-210. The paper was published on February 1, 1947.22 J. STEINBERGER, “A particular view of particle physics in the fifties”, in: L.M. BROWN, M. DRESDEN, L.HODDESON, (eds): Pions to quarks, cit., p. 307.23E. TELLER, introduction to paper nos. 232 and 233, FNM, vol. 2, p. 615. The joint paper was: E.FERMI, E. TELLER, V. WEISSKOPF, “The decay of negative mesotrons in matter”, PR, vol. 71 (1947),pp. 314-315, also in FNM, vol. 2, paper no. 232.24E. FERMI and E. TELLER, “The capture of negative mesotrons in matter”, PR, vol. 72 (1947), pp. 399-408, also in FNM, vol. 2, paper no. 233.231

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEof three conferences organized by J.R. Oppenheimer devoted to theoreticalphysics as well as to theoretical implications of available experimental results.In particular, there was substantial concern due to the apparent difficulty inreconciling the high rate of production of µ-mesons in the high atmospherewith the weak interactions that these mesons showed while traversing matter.Oppenheimer ventured to hypothesize that this situation might eventuallymean a breakdown in the “customary formalism of quantum mechanics”. 25The analysis by Fermi, Teller and Weisskopf emphasized the striking discrepancybetween the value of the lifetime observed for the negative µ-mesonand the value that should be expected if µ-meson were responsible fornuclear forces. It played a major role in leading to a new theory, formulatedby Marshak and Bethe at the Shelter Island Conference, where the authorsput forward the so-called two-meson hypothesis, according to which the µ-mesons investigated by Conversi et al. were not the Yukawa particle, butmerely one of its decay products. This hypothesis was soon confirmed by thediscovery of the π-meson or “pion” in the cosmic rays by Powell et al. atBristol. 26 High-energy nuclear physics had just begun.The coming of the Big Science eraIt is well known that the post-war years marked the birth of the so-calledBig Science. A lot of words have been spent to describe what Big Science was,and I will not add mine to this substantial corpus of writings. For the purposeof the present paper, it suffices to quote a letter from Segrè to Fermi ofFebruary 1946, soon after both of them had come back home from LosAlamos: “We are now settled again in our old house, without telephone.Being back to civilization after suffering for shortage of water is not that bad.At Radiation [Lab] orgies of first class engineering are going on, but for thetime being practically nothing as to detecting end of machines. TheRadiation Lab looks pretty much like Los Alamos and war projects and iseven more industrial than Los Alamos was. It seems to me that they rely25 R.E. MARSHAK, “Particle physics in rapid transition: 1947-1952”, in: L.M. BROWN, L. HODDESON,(eds.): The Birth of Particle Physics, Cambridge University Press, Cambridge, 1983, pp. 376-401, onpp. 379-381.26 R.E. MARSHAK and H.A. BETHE, “On the Two-Meson Hypothesis”, PR, vol. 72 (1947), pp. 314-315;C.M.G. LATTES, H. MUIRHEAD, G.P.S. OCCHIALINI, C.F. POWELL, “Process involving ChargedMesons”, Nature, vol. 159 (1947), pp. 694-697; see also R.E. MARSHAK, Meson Physics, McGraw-Hill,New York, 1952, pp. 194-195.232

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IImostly on money from Groves”. 27 Segrè’s words show the two most distinctivefeatures of Big Science, namely the coming of new cooperative projects,on a scale never seen before, and the strict connection between military andpeacetime organisations, later testified by the fact that the three federal fundingagencies that supplied the bulk of support for American particle physicsin the post-World War II decades, namely the Atomic Energy Commission(AEC), the Office for Naval Research (ONR), and the National ScienceFoundation (NSF) directly grew out from the Manhattan EngineeringDistrict (MED). 28Fermi’s attitude towards changes implied by the new organization of sciencewas many-sided, and cannot be easily subsumed under just one interpretativekey. In January 1946 he wrote to his Italian friends E. Amaldi andG. C. Wick: “Also in the US physics has undergone deep changes, due to thewar. Some are for the best: now that people got convinced that physics canbe used to make atomic bombs, everybody keeps talking about funds of severalmillions of dollars. It’s impressive that the biggest concern regardingmoney will be to figure out enough things to buy. To be sure, there are alsoserious drawbacks. The most serious is represented by military secret. In thisrespect the general hope is that a good deal of the scientific results that arestill kept secret will be published in the near future; for the time being, however,things proceed quite slowly. Another drawback is that a substantial partof the public opinion is convinced that wartime scientific successes weremostly due to the super-organization of scientific enterprise. Therefore, theyconclude that super-organization is the best way to promote scientificprogress also in peacetime. The majority of physicists believe that this wouldbe a mistake. However, there are always candidates to the role of superorganizerswho think differently. Finally, many physicists are now much morebusy with politics than with science, and spend their time at Washington inpleasant conversations with Senators and Congressmen”. 29Thus Fermi was not altogether in favour of changes brought in by the postwarmetamorphosis occurring in science. One year later, his concerns wereeven deeper than that, as he explicitly spoke of a “crisis”: “The crisis through27 E. Segrè to E. Fermi, February 7, 1946, EFP, box 11, my translation.28 L.M. BROWN, M. DRESDEN, L. HODDESON, “Pions to quarks: particle physics in the 1950s”, in: L.M.BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., pp. 10-11.29 E. Fermi to E. Amaldi and G.C. Wick, January 24, 1946, EAP, box E1, my translation; also in: E.AMALDI, Da via Panisperna all’America, edited by G. BATTIMELLI and M. DE MARIA, Rome, EditoriRiuniti, 1997, pp. 166-167.233

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwhich Science has been going in the last two years […] to a large extent hasbeen due to the sudden recognition, of part of the public and theGovernment of the tremendous role that Science can have in human affairs.The importance of this role was already known before. But the dramaticimpact of the development of the atomic bomb has brought it so vividly intothe public consciousness that scientists have found themselves, unexpectedlyand sometimes unwillingly, to be in the spotlight […] There is at present agreat scarcity of trained research men […] Now the enrollment of studentsin the scientific departments is large. I hope that very few of them are attractedby the new glamour that science has acquired. The profession of theresearch man again must go back to its tradition of research for the sake ofuncovering new truths. Because in all directions we are surrounded by theunknown and the vocation of the scientist is to drive back the frontiers of ourknowledge in all directions, not only in those that show promise of moreimmediate gains or more immediate applause”. 30 Fermi’s last statements givestriking evidence of the need he felt to go back to “purity” in science.Fermi was however a strong advocate of some aspects of high-energyphysics. He belonged to the generation that, quoting Schweber’s words,“had come of age with quantum mechanics” and, besides him, included peoplelike Hans A. Bethe, Julius R. Oppenheimer, Ernest O. Lawrence, IsidorI. Rabi, to name just a few. During the war they had been associated to militaryprojects, and as Johann Von Neumann said, they had become “betterscientists and impurer men”, i.e. wartime projects had requested them tobecome more and more involved into applied science projects. 31When the war ended, many of them, and especially the nuclear physicistswho had worked at the Metallurgical Laboratory and at Los Alamos, “soughtways to become once again purer men and purer scientists. Guaranteeing anddemonstrating the peaceful uses of atomic energy was one avenue forredemption […] A second avenue to purity was unraveling the secrets ofnature at the subnuclear level. For many physicists the wartime experiencehad reinforced the notion that only pure physics – physics for physics’ sake –was ‘basic’ or ‘fundamental’ physics and ‘good’ physics. High-energy physics30 E. FERMI, unpublished address given at the Union College on the Commencement Day of year 1947,EFP, box 53.31 See S. SCHWEBER, “A Historical Perspective on the Rise of the Standard Model”, in: L. HODDESON, L.M. BROWN, M. RIORDAN, M. DRESDEN, (eds.): The Rise of the Standard Model. Particle Physics in the1960s and 1970s, Cambridge University Press, Cambridge, 1997, p. 646; see also J. Von Neumann toO. Veblen, May 21, 1943, quoted in S. Schweber, cit., p. 657.234

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIoffered fertile ground for both purification and ‘good’ physics. Most of themembers of the GAC [the General Advisory Committee of the AEC, whereFermi served from 1947 to 1950], and […] many of those serving on theadvisory committee to ONR – the bodies that decided on the support ofhigh-energy physics after World War II – were nuclear physicists that hadbeen associated with Los Alamos. Their support of high-energy activities wasimportant for the growth of high-energy physics. In fact, these men –Bacher, Rabi, Oppenheimer, Lawrence, Fermi and so on – were some of themost convincing advocates of high-energy physics, and the spectacular floweringof the field owes much to their effectiveness as proponents […] Theywere also statesmen who could interface between the scientific and the politicalrealms and their political and diplomatic efforts within the councils ofstate made possible the construction of the laboratories and the requisitesubsequent funding”. 32Fermi was aware that, for particle physics “to go back to its tradition ofresearch for the sake of uncovering new truths” new facilities were needed,namely accelerators and computers. We have already seen that he was thinkingof a betatron as early as 1944. Plans to purchase from General Electric a100 MeV betatron for the Institute of Nuclear Studies were being discussedin the Fall 1945. It was expected to be able to produce mesons in order toinvestigate the nature of nuclear forces. The assembling of the machine wasstrewn with several difficulties, and it became evident later that a 100 MeVmachine accelerating electrons could not produce mesons for the requiredinvestigations. It was therefore proposed to modify the original project,transforming the original machine into a one that could operate either as abetatron or as a synchrotron. Eventually, the betatron at Chicago startedoperating partially during the year 1950-1951 and was employed mostly toinvestigate the properties of gamma rays. In the end, it was not so importantfor the physics Fermi had in mind, for which a synchrocyclotron like the oneoperating at Berkeley was better suited. A project to build a synchrocyclotronat Chicago started in 1947, Fermi being one of the main proponents. Themachine started operating in the spring of 1951, and for some time it wasthe most powerful particle accelerator in the world. Being able to accelerateprotons at 450 MeV, this machine allowed Fermi and his group to performfundamental experiments of scattering of pions impinging on nucleons.32 S. SCHWEBER, “A Historical Perspective on the Rise of the Standard Model”, cit., p. 657 and 646.235

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi had a long standing interest in numeric calculation. In 1928 he hadcomputed the solution of the differential equation of the Thomas-Fermiatom using a small desk calculator. In 1945 he had shown a lively interest inthe electro-mechanical accounting machines then used at Los Alamos for scientificcalculations, and he had proposed to solve a numerical problem withthem. 33 With the coming of the Big Science era, Fermi promptly realized thatelectronic computers were the natural tools to process the big amount ofdata coming out of accelerators and to help sorting out the intricacies of thetheories of nuclear forces.Speaking in 1947 on the future of nuclear physics he said: “Theory is usuallyrather helpless in attacking a thoroughly new problem unless it is supportedby experimentation. For this reason, there are now great hopes offurther progress. New experiments will become possible with the developmentof giant cyclotrons, like the one recently operated at Berkeley, andother large accelerating machines, which are now being planned and developedin several Institutions. These machines will permit to study in the laboratoryparticles of energies approaching those of cosmic rays. It seems justifiableto expect that their investigation in the laboratory may offer valuableleads for the exploration of nuclear properties. Many physicists hope that itmay even be possible to produce artificial mesotrons and to demonstratedirectly their connection with nuclear forces postulated by Yukawa. Theoverall problem of the nucleus, however, will not be solved by the knowledgeof the forces alone. Many nuclei are of extreme complexity and containhundreds of neutrons and protons closely packed together, so that evenif the laws of their dynamics were understood, their application to such acomplex system would present a formidable mathematical problem. Itscomplexity is such that the hopes of finding exact solutions by conventionalmethods of analysis are exceedingly small and it appears more probablethat numerical methods will have to be used. I would like to point out theimportance that electronic computing machines will have in this respect.The ENIAC, an early model of this type of machines, has been developedin Philadelphia during the war and is now operating successfully. Somepromising results in its application to problems of nuclear physics alreadyhave been obtained. But the men who are responsible for the Eniac developmentare not resting on their present achievements and work is activelygoing on to build what may properly be called an electronic mathematical33See N. Metropolis’ introduction to paper no. 256, FNM, vol. 2, p. 861.236

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIbrain. I put great hopes in the help that the physicists will be able to deriveby these very promising developments”. 34In order to process the results that in 1952 started to come out from Chicago(as well as from other groups) on pion-nucleon scattering, and particularly inorder to investigate on phase-shifts, Fermi decided to use the MANIAC I, thefirst of a series of three electronic computers that his friend Nick Metropolis hadbuilt at Los Alamos. He soon became fluent in writing the code for variousproblems to be processed by the MANIAC. In 1953-1954 he became interestedin the project of having a big electronic computer at Chicago.A proposal was submitted to AEC in the Spring 1954 and it was favourablyconsidered. This led to a more detailed proposal, submitted in July 1954.“George” – that was to be the name of the Chicago computer – was supposedto start operating in the spring of 1955. However, Fermi died in thefall of 1954 after his last journey to Italy. On that occasion, he was requestedby two researchers of the University of Pisa – Marcello Conversi andGiorgio Salvini – of his opinion concerning how to spend a substantialamount of money at that time available for the University of Pisa.According to the line he was pursuing at Chicago, Fermi’s prompt suggestionwas to build an electronic computer, as he wrote to the rector of theUniversity of Pisa: “On the occasion of my stay at the Varenna SummerSchool, Professors Conversi and Salvini mentioned that Pisa Universitymight have at its disposal a great amount of money for the progress and thedevelopment of Italian research. On being questioned about the various possibilitiesof employing such funds, I thought that the idea of building an electroniccomputer in Pisa was by far the best. An electronic computer wouldconstitute a research instrument from which all science and research activitieswould profit, in a way that is currently inestimable”. 35According to Metropolis, who worked with him on the MANIAC, “Fermihad early recognized the potential capabilities of electronic computers; hissustained interest was a source of stimulation to those working in the field;but it was his direct approach and complete participation that had the greatesteffect on the new discipline. His curiosity extended beyond the calculationproblem at hand; he raised questions about the general logical structure34E. FERMI, “The future of nuclear physics”, address given on the occasion of the award to Fermi of theFranklin Medal of the Franklin Institute, April 16, 1947, EFP, box 53.35 E. Fermi to E. Avanzi, August 11, 1954. Translation as in G. DE MARCO, G. MAINETTO, S. PISANI, P. SAVINO,“The Early Computers of Italy,” IEEE Annals in the History of Computing, vol. 21 (1999), pp. 28-36,on p. 32.237

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEof computers, and his remarks were always of a penetrating nature. […]Finally it may be mentioned that Fermi, in the summer of 1952, raised thequestion of the feasibility of automatically scanning and measuring, as well asanalysing, nuclear particle tracks in emulsions of photographs. Only a preliminaryformulation of this problem was possible, but it was clear that Fermihad anticipated the intense efforts that would be made later”. 36Fermi served as a member of the GAC – the consulting committee of theAEC – from 1947 to 1950. In this capacity, he had the task to advise on projectsand funding requests. Among those, requests for particle accelerators werethe most conspicuous, as new ideas allowed to build more and more powerfulmachines and as it was clear that particle accelerators were to take over cosmicrays as far as particle production was concerned. In 1941 Kerst had inventedthe betatron, and in 1945 the principle of phase-stable acceleration, proposedby Vekser and McMillan, allowed to approach relativistic energies and was soonput to use in the 184’’ proton-synchrocyclotron at Berkeley and in a numberof electron-synchrotrons with energies near 300 MeV.In 1947 a debate arose concerning Lawrence’s proposal of building a 6-GeV proton-synchrotron at Radiation Lab, in addition to the other machinesat that time almost completed or underway (the mentioned 184’’ synchrocyclotron,a 330 MeV electron-synchrotron and a linear accelerator). 37 Allthese machines were supported by the Manhattan Engineering District(MED) and its successor, the AEC “at a level thirty times that of prewar laboratorybudget”. 38 In November 1947 “Fermi questioned the need for moreenergetic machines before those under construction at the BerkeleyRadiation Laboratory were completed and their energy ranges explored andhe worried that ‘it would harm science to have [the GAC] endorse whatappeared to be an unthoughtful project.’” 39 Eventually, the AEC decided tofund a smaller and upgradable machine at Berkeley, and another proton-synchrotronat Brookhaven, on the East Coast. The Berkeley Bevatron (whicheventually achieved 6.2 GeV) and the Brookhaven Cosmotron (3 GeV) startedoperating in early 1954 and in Spring 1953, respectively, and were todominate the scene of particle accelerators in the 1950s.36 N. METROPOLIS, introduction to paper no. 256, FNM, vol. 2, p. 861.37 Lawrence’s initial proposal concerned a 10-GeV machine, later halved to 5 GeV “to avoid the appearanceof greed” and finally raised to 6 GeV following the advice of E. McMillan and W. Panofsky, whoargued that 6 GeV, “the energy thought necessary for nucleon creation, might be a more scientificgoal,” R. Seidel, “The postwar political economy of high-energy physics”, in: L.M. BROWN, M.DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 498.38 Ibidem.238

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIContributions to theoryAs soon as Fermi completed his experimental activity on neutrons at theArgonne, he came back to theory. On February 2, 1948 he wrote: “I havefor a few months retired from active work in experimental physics, andbecame a theoretical physicists, or at least, a student of theoretical physics.This is a practice that I have had for many years, to interrupt for a while theexperimental work and devote myself to learning and understanding whathas been done in theory in the meanwhile”. 40New contributions to theory soon appeared. In the summer of 1949 Fermiand Yang prepared a paper where they questioned whether the pion was a fundamentalentity or a composite particle formed by the association of a nucleonand an antinucleon. 41 This model accounted for pion’s triplet isospin andits otherwise rather surprising negative intrinsic parity. The authors knew theywere proposing just a tentative idea, as Yang recalled: “As explicitly stated inthe paper, we did not really have any illusions that what we suggested mayactually correspond to reality […] Fermi [however] considered the questionwe raised as worthy of publication”. 42 Today we know that none of the mentionedparticles is elementary. The question raised by Fermi and Yang exerteda deep influence of the development of physics, giving rise to a vein ofresearch in this field. Their model directly inspired Sakata, who in 1956 generalizedthe idea to include strangeness by taking the lambda hyperon to be athird fundamental constituent of a triple (formed also by proton and neutron)of particles that, together with their antiparticles, were to be the basic constituentsof all the hadrons. Sakata’s Nagoya associates developed this idea,pointing out that the group SU(3) was the appropriate generalization of theisospin group SU(2), which was the basis of the Fermi-Yang model. The latterexerted its influence also on the quark models of the 1960s. 43Next, Fermi tackled the problem of preparing a rough but reliable theoreticalframework for the experimental data which were about to come out39 Ibidem.40E. Fermi to J. Stearns, February 2, 1948. EFP, box 11.41E. Fermi and C. N. Yang, “Are mesons elementary particles?”, PR, vol. 76 (1949), p. 1739, also inFNM, vol. 2, paper no. 239.42C.N. YANG, introduction to paper no. 239 in FNM, vol. 2, p. 674.43 See L.M. BROWN, M. DRESDEN, L. HODDESON, “Pions to quarks: particle physics in the 1950s”, in: L.M. BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 18; L.M. BROWN, M. RIORDAN,M. DRESDEN, L. HODDESON, “The Rise of the Standard Model: 1964-1979”, in: L. HODDESON, L.M.BROWN, M. RIORDAN, M. DRESDEN, (eds.): The Rise of the Standard Model. Particle Physics in the 1960sand 1970s, cit., p. 10; E. SEGRÈ, Enrico Fermi, cit., p. 174.239

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEfrom accelerators. Initial experiments seemed to indicate that pi-mesons werepseudoscalar particles, coupled to the nucleon field through gradient(pseudovector) coupling. This situation had consequences which were justthe reverse of the situation in QED, where the strength of elecron-photoninteraction decreases with increasing energy, thereby ensuring the convergenceof radiative cross-sections at high energies. The smallness of the couplingconstant in the electron-photon interaction (α=2πe 2 /hc≈1/137) isanother feature leading to finite cross sections in QED in the relativistic limit.These two features justify in QED the use of weak coupling theory and theapplication of standard perturbation methods even at relativistic electronenergies. In pi-meson theory, however, the situation was just the opposite,since due to the nature of the coupling between pi-meson and nucleon, themeson-nucleon interaction increases with increasing energy. Furthermore,the coupling constant between nucleon and meson is much higher than inQED. Thus, as Marshak wrote in his textbook on mesons in 1952, “it wouldappear to follow that, at high energies, multiple meson processes shouldoccur with appreciable probability and the perturbation-theoretic methodsshould break down”. 44 For all these reasons, Fermi deemed appropriate toleave aside the perturbation theoretic approach and to build a different theoreticalframework.Anderson recalls: “During 1949-1950 Fermi began to prepare for thedevelopments in high energy physics which were starting to come out ofBerkeley [where the 170-inch cyclotron started operating in November 1946and produced its first artificial mesons in early 1948], and would soon becoming from many other laboratories as well. In particular, he began to preparehimself and his colleagues and students at Chicago for the experimentswhich they would soon be able to do with the pi-mesons from the newcyclotron nearing completion in the Institute for Nuclear Studies. Fermi […]needed a framework in which to set the information which came to him […]for this he developed simplified methods for calculating the orders of magnitudeof the pertinent quantities, the cross-sections of the processes of interests.His position was that the meson theories were not correct anyway, sowhy take the trouble to calculate anything with them exactly. Fermi’s methodswere a boon for experimentalists, who had difficulty in following thesophisticated way in which the theorists liked to put forth their theories”. 4544 R.E. MARSHAK, Meson Physics, cit., p. 275.45H.L. ANDERSON, introduction to papers no. 241 and 242, in FNM, vol. 2, p. 789.240

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIAccording to Segrè, Fermi once compared this effort of organizing availableexperimental data into a theoretical framework to the work that one mighthave done in Lorentz’s times, before quantum mechanics, in order to explainatomic spectra. 46Fermi’s method consisted in assuming that “as a result of fairly stronginteractions between nucleons and mesons the probabilities of formation ofthe various possible numbers of particles are determined essentially by thestatistical weights of the various possibilities. […] When two nucleons collidewith very great energy in their center of mass system this energy will be suddenlyreleased in a small volume surrounding the two nucleons. […] Thisvolume will be suddenly loaded with a very great amount of energy. Since theinteractions of the pion field are strong we may expect that rapidly this energywill be distributed among the various degrees of freedom present in thisvolume according to statistical laws. One can then compute statistically theprobability that in this tiny volume a certain number of pions will be createdwith a given energy distribution”. 47Fermi’s theory was not the first one; before him other authors, likeHeisenberg and Lewis had proposed multiple meson production theories, toaccount for processes occurring at relativistic nucleon energies. 48 Fermi’smethod was taken quite seriously and was used for a long time. In order to testit at high energies, Fermi in 1953 was one of the first experimenters to use the1.5 BeV Cosmotron, the proton-synchrotron that started operating fully atBrookhaven in the spring of 1953. 49 In 1953 Fermi worked out a tentative statisticaltheory of production of strange particles in pion-proton collisions.There are several other topics in theoretical particle physics which Fermiwas interested in and where he occasionally gave some remarkable suggestions.They range from V-particles to nucleon number conservation, fromparity conservation to the nuclear shell-model. A thorough examination goesbeyond the scope of the present paper. Here I will just give some examples.46 E. SEGRÈ, Enrico Fermi, cit., p. 174.47E. FERMI, “High Energy Nuclear Events”, Progr. Theor. Phys., vol. 5 (1950), pp. 570-583, also in FNM,vol. 2, paper no. 241, on p. 790; see also E. FERMI, “Angular Distribution of the Pions produced inHigh Energy Nuclear Collisions”, PR, vol. 81 (1951), pp. 683-687, also in FNM, vol. 2, paper no.242.48 See R.E. MARSHAK, Meson Physics, cit., p. 282ff.49 See: E. FERMI, “Multiple Production of Pions in Pion-Nucleon Collisions”, Academia Brasileira deCiencias, vol. 26 (1954), pp. 61-63, also in FNM, vol. 2, paper no. 263; “Multiple Production of Pionsin Nucleon-Nucleon Collisions at Cosmotron Energies”, PR, vol. 92 (1953), pp. 452-453; Errata corrigein PR, vol. 93 (1954), pp. 1434-1435, also in FNM, vol. 2, paper no. 264.241

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi was among those who received a preprint of the paper by Rochesterand Butler announcing the discovery of the fist V-particle, which heacknowledged with interest. 50 The new particles started to raise considerableinterest at the beginning of the fifties, and soon became one of the most puzzlingtopics in theoretical physics. While in his Silliman Lectures, given atYale in the spring of 1950, 51 Fermi made no mention of the new particles,only a year later, in 1951, he was taking them quite seriously. During the secondRochester Conference (January 11-12, 1952) one full day was devotedto new particles, and in that year the first theoretical ideas on the new particlesemerged. 52 The puzzle coming with V-particles was the contrastbetween their relatively high production rate, which showed that they werestrongly interacting particles and their long lifetimes, which showed that theydecayed by the weak interaction. Feynman reported in 1951 that Fermi andW. Fowler had conjectured that a steep potential barrier between nucleonand pion might suppress Λ-hyperon decay without inhibiting its production.In particular, Fermi remarked that this would be the case if the Λ-hyperonpossessed a spin of, say, 13/2. 53 Also Feynman favoured the idea of states ofhigh angular momentum for V-particles with respect to the idea of associatedproduction, that had been put forward in 1952 by Abraham Pais. 54 In avisit to Caltech Fermi and Feynman discussed the hypothesis and the two ofthem collaborated a little bit at long distance on the idea of high angularmomentum as an alternative explanation. 55In the same year (1951), using an approach similar to the one suggestedby Fermi in his statistical production theory, Sachs suggested that neutral V-particles were merely an excited state of the neutron. In order to account forthe very long lifetime of this state, Sachs suggested that the nucleon had a50G.D. ROCHESTER and C.C. BUTLER, Nature, vol. 160 (1947), p. 855; E. Fermi to G. D. Rochester,December 3, 1947, quoted in A. PAIS, Inward Bound, cit., p. 512.51 E. FERMI, Elementary Particles, Yale University Press, 1951.52 In 1952 Marshak’s textbook (R.E. MARSHAK, Meson Physics, cit.) was the first to contain a chapter onnew particles. See also H.A. BETHE and F. DE HOFFMANN, Mesons and Fields, Row, Peterson andCompany, New York, 1955, vol. 2, chapter 51.53 A. PAIS, Inward Bound, cit., p. 518; “From the 1940s into the 1950s”, in: L.M. BROWN, M. DRESDEN,L. HODDESON, (eds): Pions to Quarks, cit., p. 351. Feynman’s remark is dated June 7, 1951, and wasa note added to his lectures on high-energy physics: R.P. FEYNMAN, “High-energy phenomena andmeson theories”, unpublished notes of lectures given at Caltech, January-March 1951.54 A. PAIS, “Some Remarks on the V-Particles”, PR, vol. 86 (1952), pp. 663-672.55 M. GELL-MANN, “Strangeness”, in: Colloque International sur l’Histoire de la Physique des Particules,Paris, July 21-23, 1982, Journal de Physique, vol. 12, Colloque C-8, supplément au n. 12, Decembre1982, pp. 395-408, on p. 398.242

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIvery complex structure involving many mesons in virtual states. The excitationwas therefore distributed over many degrees of freedom, so the probabilityfor formation of that state that led to the disintegration might be possiblyvery small. Just before publication Sachs sent the manuscript to Fermi,asking for his opinion; Fermi, however, who was soon to leave to LosAlamos, was too busy to examine it in detail. 56Later, in 1953, Fermi pondered the matter more deeply. He confessed tohis former student Uri Haber-Schaim: “I still am very puzzled at the propertiesof these various particles and I hope very much that some of them maymerely turn out to be alternate modes of disintegration, which would makethe interpretation a little bit easier”. 57Fermi also sketched a theory of V-particles as states of high values of angularmomentum (angular momentum selection rules were to slow down thedisintegration rate). 58More or less at the time he wrote his attempt (early Fall 1953), Gell-Mannwent to visit Fermi in Chicago, and explained to him the strangeness scheme,that he had worked out during the summer. “He sounded very skeptical”Gell-Mann recalled later “when I told him about explaining the strange particlesby means of displaced isotopic spin multiplets. He said he was convincedmore than ever that high angular momentum was the right explanation”. 59 Alittle frustrated, Gell-Mann had however the chance, one or two days later, ofseeing a letter that Fermi’s secretary was writing to G. Cocconi, who was theninvestigating on the consequences of Fermi’s and Feynman’s proposal of highangular momentum. In his reply, Fermi warned Cocconi that there was inChicago Gell-Mann “speculating about a new scheme involving displaced isotopicspin multiplets and perhaps that was the explanation of the curious particlesrather than high angular momentum”. 60 While Gell-Mann recoveredfrom his depression, he became a little angry with Fermi for having been skepticalat his strangeness scheme a few days earlier.Fermi, however, was not fully convinced. In February 1954, he wrote toCocconi: “If Pais and Gell-Mann are right, the long lifetime is due to a selec-56 R.G. SACHS, “On the Nature of the V-Particles”, PR, vol. 84 (1951), pp. 305-307; see also R.G. Sachsto E. Fermi, June 14, 1951, and Fermi’s reply of July 5, EFP, box 11.57 E. Fermi to U. Haber-Schaim, May 12, 1953, EFP, box 10.58 EFP, Notebook D1, box 45. The theory is sketched in entries dated October 2 and 3, 1953.59 M. GELL-MANN, “Strangeness”, in: Colloque International, cit., p. 401.60M. GELL-MANN, “Strangeness”, in: Colloque International, cit., p. 401, Gell-Mann’s paraphrase ofFermi’s letter.243

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtion rule that permits only pair interaction. I am not sure that this is finallyproved and the alternate interpretation of strange particles as states of highangular momentum is still possible”. Thus, apparently, still in 1954 Fermifavored the interpretation of the nature of strange particles as states of highangular momentum with respect to Pais’ associate production or Gell-Mann’s and Nishijima’s, scheme based on the new strangeness quantumnumber. 61Fermi played an important role, in a discussion with Gell-Mann that tookplace in a class at the University of Chicago in 1954, in giving some hintsthat eventually led Gell-Mann to propose, together with Abraham Pais, theconcept of “particle mixture”. From Gell-Mann’s account of the episode, itemerges that he feared quite a bit Fermi’s objections: “Whenever Enricocame to a seminar, a lecture, a colloquium, or a course, if he didn’t like somethinghe interrupted. The interruption was not a minor matter; it continueduntil Enrico felt happy about what the speaker was saying, which often tookessentially forever, that is to say the seminar ended, Enrico was still nothappy, and the speaker never finished what he was going to say. If it was acourse, as in this case, the course could be blocked for a week or two, whileat each class he came in and started objecting where he had left off at the endof the previous class”. 62Now, according to Gell-Mann’s strangeness scheme, charged kaons had tohave isospin 1/2. But this implied that there had to exist two distinct neutralK-mesons, K° and K’°, that were one the anti-particle of the other.However, they had to decay in exactly the same manner and differed only forstrangeness quantum number (S = +1 for K° and S = –1 for K’°). Accordingto the most plausible reconstruction, Fermi objected that, for K° and K’° tobe considered distinct particles, one should be able to “see” such a differencein the laboratory, for example from decay mode or lifetime data. To be sure,the name “particle” should be reserved to objects with a unique lifetime. 6361 E. Fermi to G. Cocconi, February 24, 1954, EFP, box 9. See also: M. GELL-MANN, “Isotopic spin andnew unstable particles”, PR, vol. 92 (1953), pp. 833-834; T. NAKANO and K. NISHIJINA, “Charge independencefor V-particles”, Progr. Theor. Phys., vol. 10 (1953), p. 581. For an historical account see A.PAIS, Inward Bound, cit., chapter 20; A. PAIS, “From the 1940s into the 1950s”, and L.M. BROWN, M.DRESDEN, L. HODDESON, “Pions to quarks: particle physics in the 1950s”, in: L.M. BROWN, M.DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 351 and pp. 19-21.62 M. GELL-MANN, “Strangeness”, in: Colloque International, cit., p. 402.63 See: J.W. CRONIN, “The Discovery of CP Violation”, in: L. HODDESON, L.M. BROWN, M. RIORDAN,M. DRESDEN, (eds.): The Rise of the Standard Model, cit., pp. 114-115; A. PAIS, Inward Bound, cit., p.521; V.L. FITCH and J.L. ROSSITER, “Elementary particle physics in the second half of the twentieth244

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIGell-Mann recalls that Fermi “finally came up with a clinching argument. Hesaid, ‘I can write K° = A + iB, where A and B are both real fields with definitecharge conjugation, and you have in each case a neutral particle that isits own charge conjugate’. Gell-Mann, who had already gone through anobjection like this by an anonymous referee just a few months before, wasready for Fermi’s objection: “Yes, that’s true” he replied “but in the productionof strange particles, because of strangeness conservation, it is the K°and the K°’ that matter; in the decay, if it is into pions or photons or both,then it will be your A and B that matter and that have different lifetimes”. 64That was the seed of the idea of particle mixtures. A year later, Gell-Mannand Pais were led to analyze the whole matter in the light of charge-conjugationinvariance and to conjecture that, as far as decay is concerned, the trueparticles should be K 1 and K 2 (Fermi’s original A and B, respectively), havingdefinite and different lifetimes and definite behaviour with respect tocharge conjugation. K° and K’° having definite strangeness, are to be consideredin the production processes, and are linear combinations of K 1 andK 2 . 65 Furthermore, only K 1 decays into π - π + , while K 2 does not have a longerlifetime, about 100 times longer, supposing the decay mode to be K 2 →π -+ π + + γ. On the other hand, K° and K’° particles, with definite strangeness,are “real” objects insofar as production phenomena are concerned. The conceptof particle mixture was soon confirmed by experiments carried out atBrookhaven in 1955 and was one of the pieces of new physics that nature wasto teach human beings through neutral kaons. 66A very important question that Fermi helped to raise was the possible existenceof a spin-orbit interaction in the shell model of nuclei, a hint he gaveMaria Goeppert Mayer, who was working in 1948-1949 with “nuclear magicnumbers”, describing the existence of unusually stable configurations of neutronsor of protons whatever the associated number of the other nucleons.Maria Mayer was awarded in 1963 the Nobel Prize for the invention of theshell model of nuclei and acknowledged Fermi’s suggestion in her Nobelcentury”, in: L.M. BROWN, A. PAIS, B. PIPPARD (Eds.), Twentieth Century Physics, 1995, vol. 2, p. 658.I take pleasure in thanking Prof. J. W. Cronin, who took part to the mentioned class and gave me someadditional information on the discussion between Gell-Mann and Fermi.64 M. GELL-MANN, “Strangeness”, in: Colloque International, cit., p. 402.65M. GELL-MANN and A. PAIS, “Behavior of Neutral Particles under Charge Conjugation”, PR, vol. 97(1955), pp. 1387-1389.66See also A. PAIS, Inward Bound, pp. 521-522; L.M. BROWN, M. DRESDEN, L. HODDESON, “Pions toquarks: particle physics in the 1950s” and W. CHINOWSKY, “Strange Particles”, in: L.M. BROWN, M.DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., pp. 22-23, p. 334 and p. 338.245

PROCEEDINGS OF THE INTERNATIONAL CONFERENCELecture: “At that time Enrico Fermi had become interested in the magicnumbers. I had the great privilege of working with him, not only at thebeginning, but also later. One day as Fermi was leaving my office he asked:‘Is there any indication of spin-orbit coupling?’ Only if one had lived withthe data as long as I, could immediately answer: ‘Yes, of course, and that willexplain everything’.” 67Finally, it is worth mentioning the issue of the conservation of parity, thatwas to be unveiled by two students of Fermi, C.N. Yang and T.D. Lee. Yangreported that Fermi was “always very much interested in the question of parityconservation”. Segrè ventured to say that Fermi might have had some suspicionabout parity conservation since he frequently stated “criptically” that“nobody had ever changed right into left-hand in space”.While it is impossible to know what Fermi exactly meant, an indirect contributionthat he gave to this discovery can be discerned in Pais’ words aboutYang’ and Lee’s analysis of parity conservation: “Lee and Yang faced thechallenge […] they started a systematic investigation of the then status ofexperimental knowledge concerning the verification of the space reflexioninvariance and charge conjugation invariance. Their conclusion was that forone group of interactions neither invariance had so far been established […]The work of T.D. and of Frank, as they are affectionately called, is characterizedby taste and ingenuity, by physical insight and formal power. Theircounsel is sought by theorist and experimentalist alike. In this they havemore than a touch of the late Fermi”. 68Pion scattering and nucleon structureIn 1951 Fermi came back to experimental physics, as his colleague andfriend H.L. Anderson recalls: “in the spring of 1951 the big synchrocyclotronat Chicago started operating. It could accelerate protons at 450 MeVand a copious number of pions could be produced with these. The machinehad been built with the idea that Fermi would be the principal user and when67 M. GOEPPERT MAYER, “The shell model”, in: Nobel Lectures, Physics, 1963-1970, Elsevier, Amsterdam,1972, pp. 20-37, on p. 29; “On Closed Shells in Nuclei. II”, PR, vol. 75 (1949), pp. 1969-1970, onp. 1970; E. SEGRÈ, Enrico Fermi, cit., p. 175; C.N. YANG, introduction to paper no. 239, FNM, vol.2, p. 674.68 A. PAIS, Inward Bound, cit., pp. 532-533; C.N. YANG, introduction to paper no. 238, FNM, vol. 2, p.673; see also Proceedings of the International Conference on Nuclear Physics and the Physics ofFundamental Particles. University of Chicago, September 17 to 22, 1951, p. 2 and 109; E. SEGRÈ,Autobiografia di un fisico, cit., p. 346.246

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIit was finally complete he spent a great deal of time familiarizing himself withits operation, laying out the pion beams and measuring their intensity andenergy”. 69An “International Conference on Nuclear Physics and the FundamentalParticles” was held at Chicago from September 17 to 22, 1951, on the occasionof the inauguration of the cyclotron. Approximately 200 scientistsattended, and forty of them came from foreign countries. The conferencealmost coincided with Fermi’s 50 th birthday, which was celebrated informallyby some of his old friends at the breakfast table. Fermi delivered the firstpaper of the conference. He listed some 21 “fundamental” particles, expressinga belief in the existence of antinucleons, still to be discovered. He alsoexpressed his conviction that “philosophically, at least some of these 21 particlesmust be far from elementary. The requirement for a particle to be elementaryis that it [has to] be structureless. Probably some of these 21 particlesare not structureless objects. They may even have some geometricalstructure, if geometry has any meaning in such a small domain”. 70The initial experiments aimed at measuring the transmission of first negativeand then positive pions through liquid hydrogen targets. The firstresults, obtained with negative pions, seemed to indicate that pions behavedas pseudoscalar particles, thereby allowing to rule out at once several mesontheories. Further results with π - gave evidence that the interaction betweenpions and protons was strong and of range of the order of the pion Comptonwavelength. This result confirmed that pions must play a central role innuclear interactions. The real surprise, however, came from a comparison ofthe cross sections for π + and π - . Let us consider the processes:(A) π - + p → π - + p (elastic scattering)(B) π - + p → π° + n (charge exchange scattering)(C) π - + p → γ+ n (radiative capture)(D) π + + p → π + + p (elastic scattering)The π + measurements started in mid-December 1951 and soon broughtnew news. Results showed that σ(π + ) (where σ is the cross-section) was 2-3times bigger than σ(π - ). This was a puzzling result, due to the greater mul-69 H.L. ANDERSON, introduction to paper no. 246, FNM, vol. 2, p. 825.70 E. FERMI, “Fundamental Particles”, Proceedings of the International Conference on Nuclear Physicsand the Physics of Fundamental Particles. University of Chicago, September 17 to 22, 1951; also in:FNM, vol. 2, pp. 825-828, p. 826.247

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtiplicity of reactions involving π - (processes A, B, C) with respect to reactionD, the only one involving π + . According to Anderson: “This anomaly puzzledFermi very much. I recall the day [December 21] we were measuringthis cross section. Fermi was running the counters. He had a stopwatch inone hand, a slide rule in the other, the desk calculator was clattering away,and his eyes were keeping a close watch on the flashing neon indicators todetect any possible misbehavior. After he recorded each count, he would calculatethe cross section. He kept shaking his head because it kept coming outso high. There was so little for me to do that I just sat back and began to gothrough my mail. On this day there was a preprint of a paper by KeithBrueckner on meson nuclear scattering. ‘Enrico,’ I said after glancing at oneof the curves, ‘here’s a guy who seems to think the π + cross section shouldbe higher than the π - .’ Fermi was disparaging in his retort. ‘How should heknow anything about it?’. ‘But Enrico’ I persisted, now taking the trouble toscale off Brueckner’s curve, ‘this fellow Brueckner says we ought to be gettingabout 120 millibarns for the cross section.’ ‘We’re getting even morethan that’ admitted Fermi. ‘Let me have a look at that paper.’ Then, ‘Willyou take over for 20 minutes while I go up to my office?’ I suppose he consultedhis ‘Artificial Memory’ for he was back in 20 minutes with a broadgrin. ‘The cross sections will be in the ratio 9:2:1 for the π + :π°:π - scattering,’he announced [i.e. the following relationship holds: σ(D):σ(B):σ(A)=9:2:1].This would be the case if the dominant interaction which took place was forthe state of isotopic spin 3/2”. 71Thus it was taken the path that would have shed some much needed lighton the pion-nucleon scattering processes and on the behavior of nuclearforces. The concept of isotopic spin (or isospin), that had been introduced in1932 by Heisenberg, was suddenly brought at the center of the stage. It wasunderstood that, as far as one can neglect the contribution of electromagneticforces, isospin is a conserved quantity in processes involving nuclearforces. This in turn provided some hint on the existence of symmetries andon the possibility to organize hadrons in isospin multiplets. The scatteringresults obtained by Fermi for process (D), when interpreted in the light ofBrueckner’s theory, showed that scattering was dominated by the state wheretotal isospin T of the pion-nucleon system and the total angular momentumJ were both 3/2. The discovery of a strong peak in the σ(π + ) centered at 15571H.L. ANDERSON, “Meson Experiments with Enrico Fermi”, Rev. Mod. Phys., vol. 27 (1955), pp. 269-272, on p. 270.248

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIMeV (in the center of mass system) was the first hint of the existence of anuclear resonance, even if it took some years before this was generallyacknowledged, soon after Fermi’s death. The resonance was later to bedenoted by “3-3 resonance” or “∆”, a multiplet with charges ∆ ++ , ∆ + , ∆°, ∆ – .Its role in πN (pion-nucleon) scattering is that of a real particle, beingformed according to the reaction π+N → ∆ and decaying according to thereaction ∆ → π+N. Besides total angular momentum (3/2), isospin (3/2),and parity (even) it has a definite value of mass (1232 MeV/c 2 ) and lifetime(10 -23 s), thereby showing all the attributes of an unstable particle. ∆ was thefirst of a long series of nuclear resonances, to be discovered later, at differentenergies. It had a great impact on the development of theoretical physics asit provided, for example, a hint on the composite nature of nucleons.Back to Fermi’s experimental results, it has to be emphasized that they providedtheoreticians with a tool – isospin – independent of perturbation theorywhich could hardly be applied to nuclear interactions, since the magnitudeof the interaction made perturbative methods - that had proven to beso useful in QED – useless. According to Pais: “Relations likeσ(D):σ(B):σ(A):=9:2:1 came as a blessing; theorists had at least somethingto offer their experimental colleagues. Moreover, since isospin has nothing todo with perturbation theory meson theories, it could serve as a reliable guideto what needed explanation by alternative theoretical methods. Isospin doesnot, of course, suffice to inform how it should be explained that, for example,a certain state dominates at a certain energy, as in the Chicago experiments.Symmetry saves, but only up to a point”. 72Soon three letters were sent to the Physical Review, all of them received onJanuary 21, 1952. 73 Fermi’s experiments raised the interest of theoreticians,who hoped that these experiments may hold the key to the understanding ofnuclear forces.Richard Feynman, then in Brazil, corresponded with Fermi, sending predictions,based on different meson theories, concerning nucleon-pion crosssections. In his reply Fermi employed a method based on the analysis of thephase shifts. The method was not new, but “Fermi’s adoption of the tech-72 A. PAIS, Inward Bound, cit., pp. 486-487.73H.L. ANDERSON, E. FERMI, E.A. LONG, R. MARTIN, D.E. NAGLE, “Total cross section of negative pionsin hydrogen”; E. FERMI, H.L. ANDERSON, A. LUNDBY, D.E. NAGLE, G.B. YODH, “Ordinary andexchange scattering of negative pions by hydrogen”; H.L. ANDERSON, E. FERMI, E.A. LONG, and D.E.NAGLe, “Total cross section of positive pions in hydrogen”; PR, vol. 85 (1952), p. 934, p. 935 and p.936. Also in FNM, vol. 2, papers nos. 248, 249, 250.249

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEnique revived the interest in it, and it came into wide usage thereafter”. 74 Atthe second Rochester conference, held on January 11-12, 1952, Fermi “wasquite excited about the new experimental results and about his letter toRichard P. Feynman on phase shifts”. 75Reporting on Brueckner’s interpretation of his own results, Fermi assertedthat “One can therefore interpret the experimental results by postulating theexistence of a broad resonance level T=3/2 in the band of energy 100-200MeV, with the consequence that practically all the scattering comes throughT=3/2 in this energy region”. 76 However, even if he had initially worked outin detail the resonance hypothesis, Fermi was publicly much more cautiousand even doubtful about the existence of a resonance level. 77His attitude was perfectly adequate: “soon after Rochester II, C. N. Yangpointed out an ambiguity in the phase-shift analysis of the πN scatteringexperiments [see below], and it took several years before the T=3/2, J=3/2πN resonance […] was placed on a completely sure footing. […] But it is fairto say that after Rochester II, the concept of isospin invariance of the πNinteraction, and consequently the search for other symmetry principles,moved into the forefront of theoretical thinking in particle physics.Moreover, the methods developed to confirm the ∆ resonance were used toestablish the existence of scores of hadronic resonances in succeeding years.The determination that the pion was a pseudoscalar particle, that the πNinteraction was isospin-invariant, and that the first excited state of N possessedthe quantum numbers T=3/2, J=3/2 seemed to provide a reasonablestarting point for a dynamical theory of the strong πN interaction”. 78The next task was to obtain more detailed information about the scatteringprocess. This could be done by making angular distribution measurements.It was expected that at low energies only s-and p-waves are important.74 H.L. ANDERSON, introduction to papers no. 251 and 255, FNM, vol. 2, p. 844; E. Fermi, “Letter toFeynman,” January 18, 1952, FNM, vol. 2, paper no. 251, pp. 844-846. See also: R. Feynman to E.Fermi, December 19, 1951, EFP, box 9.75 C.N. YANG, “Particle physics in the early 1950s,” in: L.M. BROWN, M. DRESDEN, L. HODDESON, (eds):Pions to Quarks, cit., p. 41. Fermi’s letter to Feynman was reproduced as Appendix 3 in the conferenceproceedings.76 E. FERMI, in “Proceedings of Second Rochester Conference, Jan. 1952”, unpublished mimeograph,edited by A.M.L. MESSIAH and H.P. NOYES, p. 26.77 See: H. ANDERSON, “Early history of physics with accelerators”, in Colloque International sur l’Histoirede la Physique des Particules, cit., pp. 101-161, on p. 130ff; see also “Proceedings of Second RochesterConference, Jan. 1952”, cit., p. 31ff and p. 37ff.78 R.E. MARSHAK, “Scientific impact of the first decade of the Rochester conferences (1950-1960),” in:L.M. BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., pp. 651-652.250

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIs 1/2 p 3/2 pTable 1. Phase shifts and1/2states for the pion-protonT=3/2 α 3 α 33 α 31 scatteringT=1/2 α 1 α 13 α 11Then the following equation holds, between the differential cross sectionand the scattering angle:dσ/ dΩ = a + b cosθ + c cos 2 θ (1)Taking spin 0 for the pion, and knowing that spin is 1/2 for nucleons, onehas three possible states: s 1/2 , p 1/2 and p 3/2 , since total spin can be 1/2 and3/2. These three states can exist in either of the isotopic spin states T=1/2and T=3/2. Thus we have six different states. Therefore, six phase shifts candescribe the scattering as reported in Table 1.For each energy, measurements at three angles for each of the processes π +→ π + , π - → π°, π - →π - , would give nine experimental values for the crosssections, which, though affected by experimental errors, would allow to determinethe six phase shifts, which in turn would give detailed information on thescattering process and on the hypothesized existence of a resonance. Fermi hadanalysed the data in terms of phase shifts initially using desk calculators. In thatperiod, the first of a series of three electronic computers, the MANIAC I(MAthematical Numerical Integrator and Computer) had become operationalon March 15, 1952. Since the relationships between cross sections and phaseshifts is not a simple one and had to be repeated many times, and in order toinclude experimental data obtained by the Columbia and Carnegie groups,Fermi proposed to use the new computer at Los Alamos. 79 Mathematically, ithad been decided to adopt a least-squares type of fit was to make maximum useof the data. The problem was therefore to find the six phase shifts α 1 … α 6 thatminimize the quantity M in the following equation:9M(α 1 ...α 6 ) = ∑ [σ i (computed) – σ i (measured)] 2 / ε i2(2)i = 1where the ε i are the experimental errors in the measurements of cross sectionsσ i .79 See H. L. Anderson, “Meson Experiments with Enrico Fermi”, cit., p. 271; N. Metropolis, introductionto paper no. 256, FNM, vol. 2, p. 861.251

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEAs Anderson recalled, “The MANIAC fascinated Fermi and he had beenitching to get his hands on it. Now he had a problem to put to the machine.Metropolis would teach him how, and he could feed in his questions, watchthe machine digest them, and gather the answers as they rolled out”. 80 Themachine actually found the set of phase shifts. The problem was that it foundtoo many. “For some years following” Anderson recalled “the experts in pionphysics talked about the different possible solutions. There was the Fermisolution and the Yang solution; then a new one called the Fermi-Metropolissolution, also the Steinberger solution and finally the Bethe-De Hoffmannsolution”. 81 Fermi struggled hard in the last two years of his life to discoverthe solution to the phase shift problem. He spent the summer of 1952 andof 1953 working with MANIAC, at Los Alamos; moreover, in 1952-1954he intensively corresponded with Metropolis from Chicago. In the fall of1953 Fermi’s work was expanded and extended by Hans Bethe, Frederic DeHoffmann, Nick Metropolis and E. Alei, who used new data that began toemerge from other laboratories. A number of techniques were used to discriminatebetween the sets of phase shifts found by the MANIAC. AfterFermi’s death it came out that “the Bethe-De Hoffmann solution, which wasreally Fermi’s original choice extended properly in the higher energy region,was most probably the correct one”. 82 Thus, the existence of the 3-3 pionnucleonresonance was firmly established.Epilogue: Fermi’s outlook of theoretical physicsand physics in the fiftiesTo complete my overview on Fermi’s contributions to high-energy physics,I plan to examine Fermi’s attitude towards theoretical particle physics in thecontext of the crisis that theoretical physics went through in the early fifties.First of all, Fermi was a very peculiar theoretician, as Anderson has empha-80 H.L. ANDERSON, “Meson Experiments with Enrico Fermi”, cit., p. 271.81 H.L. ANDERSON, introduction to papers no. 257 and 258, FNM, vol. 2, p. 871.82 H.L. ANDERSON, introduction to papers no. 257 and 258, FNM, vol. 2, p. 871. See also H.L.ANDERSON, “Meson Experiments with Enrico Fermi”, cit., p. 272; F. DE HOFFMANN, N. METROPOLIS,E. ALEI, H.A. BETHE, PR, vol. 95 (1954), p. 1586; H.L. ANDERSON, E. FERMI, R. MARTIN, D.E.NAGLE, “Angular distribution of pions scattered by hydrogen,” PR, vol. 91 (1953), pp. 155-168 (alsoin FNM, paper no. 257); E. FERMI, M. GLICKSMAN, R. MARTIN, D.E. NAGLE, “Scattering of negativepions by hydrogen,” PR, vol. 92 (1953), pp. 161-163 (also in FNM, paper no. 259); E. FERMI, N.METROPOLIS, E. ALEI, “Phase shift analysis of the scattering of negative pions by hydrogen,” PR, vol.95 (1954), pp. 1581-1585 (also in FNM, paper no. 260).252

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIsized in a panel discussion: “We’ve been discussing [...] about how [...] theexperimentalists are not very much inspired by the theory, and the theoristssomehow manage to anticipate some of the developments in working out someof their ideas. But I want to mention another kind of theorist, because of myfamiliarity with Fermi’s work. He was the kind of theorist who didn’t work thatway at all. If you examine all the theoretical works of Fermi, and there weresome very distinguished ones, as you know, they were always done with theidea of explaining some experimental fact. [...] At the end of almost every paperin which he made a theoretical development, there was always a calculation toshow that the theory gave some agreement with the experiment”. 83Secondly, at the beginning of the fifties, Fermi appeared as a disenchantedtheoretician. When he realised the severe drawbacks of the available mesontheories, Fermi soon got convinced that there was something deeply wrongwith the theory itself and that it was not worth it to use it extensively in calculationsthat might prove to be altogether wrong. That was the motivationfor his statistical theory of multiple meson production that he used as aguideline in his investigations. This attitude began to emerge as early as1951, when he was already involved in experimental research on pion-nucleonscattering.In October, speaking to an audience of three thousand people assembledin the Chicago Civic Opera House for the twentieth anniversary meeting ofthe Institute of Physics in Chicago, he said that “when the Yukawa theoryfirst was proposed, there was a legitimate hope that the particles involved,protons, neutrons and pi-mesons, could be legitimately considered as elementaryparticles. This hope loses more and more its foundation as new elementaryparticles are rapidly being discovered [...] Of course, it may be thatsomeone will come up soon with a solution to the problem of the meson,and the experimental results will confirm so many detailed features of thetheory that it will be clear to everybody that it is the correct one. Such thingshave happened in the past. They may happen again. However, I do notbelieve that we can count on it, and I believe that we must be prepared fora long hard pull”. 84At the beginning of the fifties Fermi was convinced that theoretical physicswas going towards a new revolution, like the one represented by the intro-83H.L. ANDERSON, in: L.M. BROWN, L. HODDESON, (eds.): The Birth of Particle Physics, cit., p. 268, firstround-table discussion.84 E. FERMI, “The Nucleus”, Physics Today, vol. 5 (March 1952), pp. 6-9, also in FNM, vol. 2, paper no.247, p. 834.253

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEduction of quantum mechanics, some twenty-five years before. He was doubtfulthat quantum mechanics held within a region (that he called “contact”)having the size of the range of nuclear forces, i.e. 10 -13 cm, and he believedthat current physics could only explain facts occurring outside nucleus.At the Chicago Conference, in September 1951, he said: “It is desirable toarrange experimental data so as to exhibit most clearly the features whichcome from fundamental particle interactions taking place at ‘contact’, namelywithin about 10 -13 cm. This may be done by assuming quantum mechanicsholds in regions outside ‘contact’(there is little doubt in my mind that itdoes), and using it to remove from consideration phenomena which do notdepend on what happens in the ‘contact’ volume. The result is a compressedexpression of experimental results, in which the nature of fundamental interactionsbetween particles may be more easily discernible”.“Within a volume corresponding to 10 -13 cm” he added “there are lionswhich will eat us if we get within”. 85 As we have seen, also Oppenheimershowed a similar standpoint at the Shelter Island Conference in 1947. Yangremarked that in 1945-1955 “physicists born before 1905 seemed to havegeneral reservations [...] whether or not quantum mechanics were applicableinside of ‘the electron radius’ [...] On the other hand, in that same period,younger physicists, those of my generation, seemed to have very little inclinationto question the validity of quantum mechanics”. 86 This would not be thefirst instance of a generational difference within the community of physicists.Fermi conjectured that the revolution he foreshadowed in physics mighteventually demand new mathematics and new geometry, to deal with regionsinside “contact”: “Perhaps the introduction of a finite size of the elementaryparticles or even a granular geometry such as is suggested by Heisenberg andSnyder may be clues to the solution”. 87 Thus Fermi showed some influencefrom Heisenberg’s S-matrix theory, i.e. a theory based only on observablesquantities, which banished distances shorter than 10 -13 cm and time intervalsshorter than 3x10 -24 s. 88Facing such a disparaging situation, Fermi thought that theoretical physicsshould go back to the origins of science and proceed adhering strictly to the85 E. FERMI, “Fundamental Particles”, cit.; also in: FNM, vol. 2, pp. 825-828, p. 827.86 C.N. YANG, “Particle physics in the early 1950s,” in: L.M. BROWN, M. DRESDEN, L. HODDESON, (eds):Pions to Quarks, cit., p. 42.87 E. FERMI, Elementary Particles, cit., p. 24.88 See, for example, H. RECHENBERG, “The early S-matrix theory and its propagation (1942-1952),” in:L.M. BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 552.254

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IIevidence provided by experimental data. At the Chicago Conference heasserted that “Theoretical research may proceed on two tracks: 1. Collectexperimental data, study it, hypothesize, make predictions, and then check.2. Guess; if nature is kind and the guesser clever he may have success. Theprogram I recommend lies nearer the first track”.One month later, at the Institute of Physics Anniversary he was moreexplicit, asserting that “it is difficult to say what will be the future path. Onecan go back to the books on method (I doubt whether many physicists actuallydo this) where it will be learned that one must take experimental data,collect experimental data, organize experimental data, begin to make workinghypotheses, try to correlate, and so on, until eventually a pattern springsto life and one has only to pick out the results. Perhaps the traditional scientificmethod of the textbooks may be the best guide, in the lack of anythingbetter”. 89 Fermi’s recommendations were followed in some cases in whichthe observations were exceedingly puzzling, like the case of K-mesons: “thesenior physicists took the general attitude of Enrico Fermi: Collect evidence,but make no assumptions about the identity of any of these K-mesons untilthe evidence allows no other possibility”. 90In analysing Fermi’s role in the physics of the early fifties, one should alsokeep in mind the status of theoretical physics as it was in those years and, inparticular, its relationship with experimental physics: “In recent years, whentheory called for new particles (such as the W and the Z), experiments obliginglyprovided them, but in the fifties experiment outran theory and producedsurprise after surprise. Neither the muon nor the strange particles wereexpected, nor were they welcomed, for the most part, for they destroyed whatmight have been a consensus for a new unification. Without the muon, physicistshad anticipated a closed system in which the electron, proton, and neutronwere the constituent particles of matter, while the photon and Yukawameson were field quanta that carried the electromagnetic and strong interactions.Add the neutrino for weak interactions, and complete the picture byincluding the antiparticles of the fermions. The muon changed all that”. 91In the context of the fifties, where theoretical physics had to face anincreasing number of “surprises” coming from experiments it seems that a89 E. FERMI, “Fundamental Particles”, cit.; also in: FNM, vol. 2, pp. 825-828, p. 827; “The Nucleus”, cit.,p. 834.90R.H. Dalitz, “K-meson decays and parity violation,” in: L.M. BROWN, M. DRESDEN, L. HODDESON,(eds): Pions to Quarks, cit., p. 435.91 L.M. BROWN, M. DRESDEN, L. HODDESON, “Pions to quarks: particle physics in the 1950s”, in: L.M.BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 4.255

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEphysicist like Fermi, who was used to work with experimentalists, who himselfwas an excellent experimentalist, and a pragmatic theoretician, used tofocus on experimental evidence, possessed to the highest extent the abilitiesand the attitude so badly needed by the way physics was in the fifties.Fermi’s influence may well have gone beyond his own activity as a researcher,since he actually taught a style of making physics to a generation of physiciststhat with their discoveries were to revolutionize this discipline between thefifties and the sixties. It has already been noted the pragmatism of the postwargeneration of U.S. theorists and the somewhat pragmatic spirit of theories likethe S-matrix and the one grounded on the dispersion relations that played animportant role in the fifties. 92 There are several reasons for this and a detailedanalysis of those reasons is beyond the aim of this paper. However, it can besafely said that among those reasons, Fermi’s influence played a significant role,and the fact that many protagonists of the just mentioned theoretical fields hadbeen his students or collaborators is per se revealing.Did the revolution that Fermi foreshadowed actually happened in physics?With hindsight we can say “yes and no”. On the one hand, quantum mechanicsstill holds and no region where it is not applicable has been found. On theother hand, theoretical physics has undergone deep changes since the earlyfifties, and we may well venture to say that a true revolution has occurred withthe introduction of quarks, QCD and electroweak theory. Quantum field theories,whose validity seemed confined to quantum electrodynamics at Fermi’sage, have been brought again into the forefront of physics, after the importanceof non-Abelian gauge theories was properly recognised.As a concluding remark, I would like to show Fermi’s standpoint concerningone of the issues that were to raise considerable debates in modern times,i.e. the intrinsic usefulness of particle physics, or, in other words, the rationalebehind investing huge amounts of money to support more and moreexpensive facilities and experiments. He was a man deeply committed to science,and he believed that “the vocation of a scientist is to drive back thefrontiers of our knowledge in all directions”. He had a deep faith in theintrinsic usefulness of doing fundamental particle physics anyway, whatevercomplex or abstract this research might be.This is testified by his words in an address he gave just before that momen-92 See, for example, A. PICKERING: “From field theory to phenomenology: the history of dispersion relations,”and S. SCHWEBER, “Some reflections on the history of particle physics in the 1950s,” in: L.M.BROWN, M. DRESDEN, L. HODDESON, (eds): Pions to Quarks, cit., p. 587 and pp. 671-674.256

Giulio MalteseENRICO FERMI AND THE BIRTH OF HIGH-ENERGY PHYSICS AFTER WORLD WAR IItous Rochester II conference, where he foreshadowed the debates later tocome: “Some of you may ask. What is the good of working so hard merelyto collect a few facts which will bring no pleasure except to a few long-hairedprofessors who love to collect such things and will be of no use to anybodybecause only few specialists at best will be able to understand them? Inanswer to such question I may venture a fairly safe prediction. History of scienceand technology has consistently taught us that scientific advances inbasic understanding have sooner or later led to technical and industrial applicationsthat have revolutionized our way of life. It seems to me improbablethat this effort to get at the structure of matter should be an exception tothis rule. What is less certain, and what we all fervently hope, is that man willsoon grow sufficiently adult to make good use of the powers that he acquiresover nature”. 93While the view concerning the high-energy particle physics has meanwhileperhaps changed, Fermi’s last statement is more than ever modern, its scopenot merely concerning physics, but the whole realm of science.This research has been partially supported by the Italian Embassy in the US. I wish to thank themanagement and the staff of the Department of Special Collections of the University of ChicagoLibrary for kind and effective help in my research on Fermi’s paper.Giulio MalteseHe is with Ibm as a Research staff member working on automatic speechrecognition. Since 1987 he has been doing research in the history of science,focusing on the history of rational mechanics, on the development ofgeneral relativity, and on the history of physics in Italy in the 20th century. Asa contract professor he has given courses on history of mechanics at the universitiesof Genoa and Rome (“La Sapienza”). He has also given courses andseminars on the foundations of mechanics and of electrodynamics. He is amember of the Group for the history of physics at the Department of physicsof “La Sapienza” University of Rome; of the Italian Society of Physics, and ofthe Italian Societies for the History of Science and for the History of Physicsand Astronomy. He authored three books on the history of mechanics andseveral papers on various topics concerning the history of physics. He is currentlyfocusing on Enrico Fermi’s role in the development of physics in the fortiesand the fifities during Fermi’s stay in the United States (1939-1954).93 E. FERMI, “The Future of Nuclear Physics,” unpublished address, Rochester, January 10, 1952, EFP,box 53.257

Robert SeidelEnrico Fermi, High-Energy Physicsand High Speed ComputingThe field of high-energy physics saw early applications of the computer as ascientific instrument, both for data analysis and as a controller of the acceleratorand other detectors. The transfer of this technology from wartime militarylaboratories to peacetime high-energy physics laboratories shows how EnricoFermi conceived the computer as a scientific instrument in high-energy physics.Enrico Fermi, la fisica delle alte energieed il calcolo ad alte prestazioniIl campo della fisica delle alte energie utilizzò le prime applicazioni delcomputer come strumento scientifico, sia per quanto riguardava l’analisi dei datisia come strumento di controllo dell’acceleratore ed altri rivelatori. Il trasferimentodi tale tecnologia dai laboratori militari di guerra ai laboratori di fisica delle alteenergie in tempo di pace, mostra la concezione che Enrico Fermi aveva delcomputer come strumento scientifico nella fisica delle alte energie.259

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEComputers and World War IIComputers are the transcendent instruments of experimental high-energyphysics at the end of the 20 th century. They are involved in high-energyphysics experiments from the cradle to the grave. Computers design newaccelerators, detectors, and other experimental apparatus, computers operatethis apparatus tirelessly during the extended periods of time required to conductsuch experiments and computers sort, interpret, analyze, and presentthe results. Peter Galison has even suggested that in modern high-energyphysics experiments, they take over many the traditional role of the physicistsin high-energy physics experiments. 1Enrico Fermi stands at the forefront of those physicists who brought thecomputer into the service of high-energy physics. He saw that the techniquesdeveloped at Los Alamos for the design of nuclear weapons could be transferredto more peaceful studies of nuclear behavior. He initiated a researchprogram before his death in 1954 that eventually transformed the study ofhigh-energy physics and was directly responsible for the introduction of computerdata analysis techniques less than a decade later. This is the story Iwould like to tell you today.The early history of computers is well-known, and the contributions ofphysicists like Howard Aiken, John Atanasoff, John Mauchly, and other pioneersin the construction of computers has been the subject of several conferencesover the past decade to celebrate the semi-centennial of the electroniccomputer.The exigencies of World War II accelerated the development of thesemachines and, more importantly perhaps, saw enhanced use of the electromechanicalcomputers associated with the firms of Burroughs, IBM, andNCR, including work on code-breaking machines in England and theUnited States that was hidden from history for a quarter of a century. Evenfor the better-known machines, there is a great deal that remains shroudedin secrecy about their early operations. ENIAC, for example, ran a program– which is still classified – to evaluate Edward Teller’s design of the classicalsuper (H-bomb) in late 1945. Most of the early computers were used to runsimilar programs for Los Alamos in the postwar decade, and those programstypically stressed the capacity of the machines.During World War II at Los Alamos, the calculations required to predictthe behavior of implosion designs of fission weapons were performed on1 PETER GALISON, Image and Logic: A Material Culture of Microphysics (Chicago, 1997), 391-2.260

Robert SeidelENRICO FERMI, HIGH-ENERGY PHYSICS AND HIGH SPEED COMPUTINGIBM business machines. Enrico Fermi, who came to Los Alamos in 1944 aftercompleting his work on the design of nuclear reactors for plutonium production,took a particular interest in the newly installed IBM machines, accordingto Nicholas Metropolis, who, with Richard Feynman and other computationallyinclined physicists, had assembled them to replace teams of human“computers” who had performed the necessary calculations previously.Fermi’s F-Division also housed Edward Teller, who had abandoned hisearly interest in implosion to work on the design of a fusion weapon, a designwhich Fermi had stimulated by suggesting the possibility of triggering afusion bomb with a fission bomb to him in 1942.Fermi devoted most of his efforts at wartime Los Alamos to the perfectionof their reactor, and it is unclear whether he provided Teller with more thanmoral support for his work. We do know that Fermi attended a meeting atLos Alamos in the spring of 1946 that discussed the ENIAC’s results, andalthough different attendees reported varying views of the potential revealedfor the super by these calculations, Teller wrote the final report of the meetingin his usual optimistic fashion.Interdisciplinary use of computersSince the IBM electromechanical computers at Los Alamos were collocatedwith other tools of nuclear physics: accelerators, reactors and detectors, itwas a propitious place for a synergistic interaction between the more fundamentalaspects of nuclear physics and calculation. The interdisciplinary use ofcomputers at Los Alamos to solve weapons related problems developed techniquesuseful in nuclear physics studies. Indeed, Fermi calculated a numericalformula for atomic masses that he had derived at Los Alamos soon afterthe atomic bombs were dropped on Japan, apparently recognizing theadvantages of electromechanical over analogue and manual computation.Fermi sought to translate that potential to the University of Chicago afterWorld War II by hiring Nick Metropolis to develop a computer for theInstitute of Nuclear Studies – now the Enrico Fermi Institute for NuclearStudies – which he agreed to head after leaving Los Alamos.Nor was he alone in attempting to beat computational swords into academicplowshares. John von Neumann, who had worked on both the atomicbomb and the ENIAC, and who suggested the 1945 calculation to which Ihave referred, sought military funds to build a computer of his own design atthe Institute for Advanced Study in Princeton in 1946. When military fund-261

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEing for von Neumann’s IAS machine faltered, the AEC picked up the tab, inlarge part because von Neumann had become an important asset to the LosAlamos weapons design program.In the meantime, Los Alamos physicists continued to elaborate machine calculation.One example may serve to illustrate this. The Monte Carlo techniquewas developed to study neutron diffusion in critical assemblies at LosAlamos by von Neumann, Stan Ulam, and Nicolas Metropolis. It rapidlyspread to other applications in nuclear weapons design and statistical calculations.Ulam, like Metropolis, left Los Alamos after the war to pursue an academiccareer, but both men returned as consultants and, ultimately, as staffmembers. Von Neumann was at Los Alamos every summer as a consultant.The shortage of theoretical physicists in the postwar era required the laboratoryto make extensive use of such agreements, and put a premium on lighteningthe burden of the thought process whenever possible.The invention of Monte Carlo techniques resulted from the interactions ofMetropolis, von Neumann and Ulam, who colonized fields of physics researchin their crusade to popularize their techniques. While statisticians found littlenovel in them, and most other mathematicians did not have access to computers,Monte Carlo techniques were useful in a number of applications ofinterest to physicists including meteorology, turbulent behavior in fluids, andNewtonian mechanics. 2 The development of numerical hydrodynamics andweather forecasting owed not a little to their efforts.The FERMIACFermi developed the first “Monte Carlo” computer, the FERMIAC, tomodel the processes of fission, scattering, and absorption of neutrons in aspherical assembly composed of several materials. Since each of these processeshad measurable cross sections, but competed, statistical weights had to becalculated for each interaction, and then applied to the operation of the device.Monte Carlo techniques readily lent themselves to electro-mechanical andelectronic calculation, and Los Alamos mathematicians and physicists developeda series of codes to perform them. These were sufficiently large to warrantbeing named after large mammals and their offspring, e.g. Hippo andBaby Hippo. Like many modern software programs, these codes were klugesand required years to write. Since the electronic computers capable of running2Von Neumann (1946).262

Robert SeidelENRICO FERMI, HIGH-ENERGY PHYSICS AND HIGH SPEED COMPUTINGthem weren’t built yet, this was less of a problem than it might have been.In the meantime, Fermi led a new initiative at the University of Chicago todevelop a different kind of numerical assault on the nucleus intended toreveal not so much how the nucleus split apart or fused with other nuclei,but rather how it was held together and interacted with mesons. As thefamous experiments of Marcello Conversi, Ettore Pancini and OrestePiccioni here in Rome had shown, positive and negative mesons wereabsorbed in different fashion by carbon and iron, and this in turn led to thediscovery of the pi-meson as well as the elaboration of a theoretical explicationof it by Bethe and Marshak. 3 This was a problem that fired Fermi’s interestsat Chicago and led him into high-energy physics. The Office of NavalResearch [ONR] provided the opportunity for Fermi to realize some, butnot all, of his dreams at Chicago. As Herbert Anderson, Fermi’s close associatein this period, recalled, the Director of ONR traveled to Chicago to seeFermi and asked him “Look, Fermi, isn’t there something you would like todo? I’d like to get you the money for it.”After discussing the matter with Fermi and Teller, Anderson offered tobuild anything Fermi wanted, a computer, a cyclotron, or a betatron. Tellerrecommended a computer, but Fermi preferred a synchrocyclotron, largerthan Berkeley’s, which Anderson and other members of the Institute forNuclear Studies began to build. 4 The high-energy proton synchrocyclotronat Berkeley inspired the Institute for Nuclear Studies, among others, to copythe new technique of frequency modulation first applied in the 184-inchcyclotron. The Chicago machine, whose energy was greater than that of theBerkeley machine, would, he hoped, be capable of extending knowledge intonew energy regions and producing pions.The University of Chicago, the Office of Naval Research and the AtomicEnergy Commission paid for the construction of the accelerator underFermi’s supervision as part of a multifaceted program of nuclear physicsresearch. 5 The decision to forego a computer, however, meant that3 DONALD H. PERKINS, “Cosmic-ray-work with emulsions, 1940s to 1950s, in HODDESON, ET AL., Pionsto Quarks (Cambridge, 1989), 90-1. Fermi’s compatriot, Bruno Pontecorvo, initiated a similar researchprogram at Dubna. See BRUNO M. PONTECORVO, Establishment of the weak-interaction notion, loc. cit.,p. 369-372.4 HERBERT L. ANDERSON, “The Cyclotrons in my Life,” Los Alamos National Laboratory Report LALP88-15 (August, 1989).5 “Research in Atomic Structure and Energy in the Institute of Nuclear Studies, the Institute of Metalsand the Institute of Radiobiology and Biophysics”, The University of Chicago. Fund Raising Brochuredated June 15, 1946.263

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEMetropolis spent most of the next two years working at Princeton with Johnvon Neumann, where he participated in the design of the computer at theInstitute for Advanced Study and the modification of the ENIAC for storedprogramoperation.The connection between Chicago and Los Alamos were also strengthenedby Edward Teller who, like Fermi and Metropolis, spent summers at the NewMexico laboratory working on the problem of the Super bomb. OtherChicagoans with a pied-a-terre at Los Alamos included Harold Agnew,Herbert Anderson, and Anthony Turkevich. Besides designing the analogcomputer named after him, Fermi took an interest in the development of theMonte Carlo technique, a form of which he had used in the 1930s. Duringhis summers at Los Alamos as a consultant, he was constantly in the companyof Ulam, and, after his return to the laboratory to build a computer in1948, Metropolis. Metropolis, disappointed by the slow pace of computerdevelopment at the University of Chicago, readily accepted Los Alamos’sinvitation to build a von-Neumann machine there.When the team of Eugene Gardner and Cesar Lattes succeeded in manufacturingthe first pions in the 184-inch in 1948, Fermi began to plan experimentsusing them with the Chicago synchrocyclotron.The nature of the mesons which carried the nuclear force was an importantfocus of theoretical and experimental physics in the postwar era, as Fermipointed out a significant shortcoming of theory in Elementary Particles, hisSilliman Lectures at Yale in 1950.A great deal of work has been devoted to the field theory of mesons firstproposed by Yukawa in his attempt to explain nuclear forces. The meson ofYukawa should be identified with the π-meson of Powell (briefly called herepion). The µ-meson of Powell (called here muon) is instead a disintegrationproduct of the pion, only weakly linked to the nucleons and therefore of littleimportance in the explanation of nuclear forces. The Yukawa theory hasproved a very valuable guide in experimental research and probably containsmany correct leads to a future theory. In particular it is partly responsible forthe discovery of the production of mesons in the collision of fast nucleons.On the other hand, the attempts to put this theory in a quantitative formhave had very mediocre success. Often a ponderous mathematical apparatusis used in deriving results that are no better than could be obtained by asketchy computation of orders of magnitude. This unsatisfactory situationwill perhaps improve only when more experimental information becomesavailable to point the way to a correct understanding. The purpose of this264

Robert SeidelENRICO FERMI, HIGH-ENERGY PHYSICS AND HIGH SPEED COMPUTINGdiscussion is not to attempt a mathematical treatment of the field theoriesbut rather to exemplify semi-quantitative procedures that are simple and maybe helpful in the interpretation of experiments. There are several cases inwhich not much would be gained by a more elaborate mathematical treatmentsince a convincing treatment has not yet been discovered. In othercases the qualitative discussion presented here may serve as an introductionto more complete elaborations of the subject. 6The desire for such a semi-quantitative understanding of pion-proton scatteringled Fermi to devise a heuristic theory based upon the available phasespace for interactions between pions and the s- and p- shells of protons.This involved several simplifying assumptions, including the one that the sand p but not d-waves, were involved in the interaction. Although this producedorders of magnitude as an heuristic guide to such reactions, accordingto Herbert Anderson, I.I. Rabi believed that if such statistical methodsworked, there was nothing new to learn in high energy physics. Fermi’s oversimplifiedtheory served as a standard against which to measure experimentalresults of multiple production of mesons and reveal non-statisticalprocesses. 7The MANIACThe phase-shift analysis, however, required the solution of nine equations.Preliminary attempts to do so manually had convinced him that the computercould accelerate the solution. By the use of the least squares method,equations governing the statistical analysis of phase shift-angles of scatteringof pions of s- and p- waves could be approximated. Fermi brought the problemto Los Alamos in the summer of 1952 where he ran it on Metropolis’srecently completed machine, the MANIAC.In order to run the calculation, Fermi converted it into hexagesimal computercode.He also programmed the machine himself.Fermi returned to the University of Chicago in the fall, and presented aseries of lectures advertising numerical techniques using digital computers atChicago and Argonne. The presentation of the results of MANIAC’s calcu-6 ENRICO FERMI, Elementary Particles, Yale University Silliman Memorial Lectures, 1950 (New Haven:Yale University Press, 1951) p. 3. See ch. 4, esp. pp. 79-84, for Fermi’s invocation of statistical methods.265

PROCEEDINGS OF THE INTERNATIONAL CONFERENCElations at the Rochester Conference at the end of the year, however, did farmore to establish the computer as a participant in the work. As Fermi put it:“With the use of an electronic computer the phase shifts can be computedin five minutes, since there is one code for all calculations. With eachcalculation only taking about five minutes, one can learn something of themathematics of the problem by varying the conditions a little... the phaseshifts are then used to calculate the cross section. The results invariablywant the cross section to look as they do experimentally. In this calculationon the S and P phase shifts are used”.Dramatically, Fermi then presented the new data for which the conferencehad been waiting, first remarking that the courier when he got here handedhim a small piece of paper on which there were written, as is proper for somethingthat comes from Los Alamos, certain numbers which then had to bedecoded. In this case, they converted from binary to decimal notation...using the program.Fermi noted that the calculated cross section represented the observedcross section very well: “The phase shifts have no business to represent theobservations so well. That is, for the nine measurements this set is inconsistentstatistically with the errors given. The most striking difference from theprevious results is in ...phase shifts.... of...angles [extremely sensitive] to achange in cross section [that] varied all over the map”. 8The phase shift for the pion-nucleon interactions identified the first “resonance,”presaging a flood of short-lived “particles” over “a period of manyyears when the newest sets of phase shifts were reported at nearly every conferenceon particle physics”. Although other solutions fit the data as well asFermi’s, the Chicago group admitted that their data did not extend farenough in energy to support the resonance hypothesis.’ By 1953, Fermi stillargued that the experimental facts might be explained in some other way. 9Fermi’s tentative interpretation of the numerical and experimental results7 FERMI, Coll. Pap., II, 780. FERMI, “High Energy Nuclear Events,” Progress in Theoretical Physics 5(1950) 570-583. Fermi compared the predictions of this technique to cosmic-ray results in order toascertain its validity. FERMI, “Angular Distribution of the Pions Produced in High Energy NuclearCollisions,” PR 81 (1951) 683-687.8 FERMI, “Report on Pion Scattering,” Proceedings of the Third Annual Rochester Conference (Dec. 18-20, 1952), pp.859-60.9 ROBERT L. WALKER, “Learning about nuclear resonances with pion photoproduction,” in LAURIE M.BROWN, MAX DRESDEN, and LILLIAN HODDESON, eds., Pions to Quarks: particle physics in the 1950s:based on a Fermilab Symposium (Cambridge University Press, 1989) 117-118.266

Robert SeidelENRICO FERMI, HIGH-ENERGY PHYSICS AND HIGH SPEED COMPUTINGof his pion-proton experiments did not diminish the interest awakened in thenew computational techniques he announced. In addition, Fermi posed thefeasibility of automatically scanning and measuring, as well as analyzing,nuclear particle tracks in photographic emulsions in the summer of 1952.Computational physicsWhen Luis Alvarez applied computers to the problem of data analysis ofbubble chamber film in the late 1950s, he hired two of Fermi’s students,Arthur Rosenfeld and Frank Solmitz, to write the computer programs forthis work.Another of Fermi’s students, Darragh Nagel, built one of the first computerdesigned and controlled proton accelerators, the Los Alamos MesonPhysics Facility. Nicolas Metropolis returned to Chicago after Fermi’s deathto found a computer research institute and build MANIAC III. Metropolisand his associates completed the work on phase shift analysis that Fermi hadbegun at Chicago. The Institute for Computer Studies and the ArgonneNational Laboratory, which built the AVIDAC, the ORACLE andGEORGE computers in the 1950s, also carried forward the work whichFermi pioneered in Chicago. Indeed, Fermi initiated the project when heapplied to the AEC and ONR for funds to build a computer at the Universityof Chicago in 1954. 10Edward Teller was also very influential in promoting the use of computersin the Institute for Nuclear Studies, although, as in so many of his enthusiasms,he sought to go too far and too fast to suit Fermi’s taste. He found anequally enthusiastic colleague in Ernest Lawrence after he went to theUniversity of California Radiation Laboratory where he was responsible forthe introduction of computers for weapons design and other purposes at theRadiation Laboratory’s Livermore branch. 11 There, under the direction ofSydney Fernbach and Berni Alder, computational physics became, in the10 See Fermi’s “Preliminary Proposal for High Speed Electronic Computer” to George A. Kolstad,Director of Physics Research section of the Research Division of AEC, dated April 16, 1954 and notesand correspondence with Kolstad in May 1954, including a telephone conversation from Kolstad toFermi in which he stated the research division would recommend acceptance and recommending finalproposal “stress particularly the educational value….how far we want to copy the Oracle and …majornew components that we would plan to install….space that could be allotted to the machine, includingair conditioning and other specifications and [what personnel and what kind of new personnel aswell [sic] as a tentative time schedule”. Fermi Papers XI:5, University of Chicago.11 Cf. Inter alia, McKenzie, Seidel (1997).267

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1960s, a major enterprise, although the most visible and fruitful applicationsin high energy physics were made at the main branch of the Laboratory inBerkeley by Alvarez, who also enjoyed Lawrence’s enthusiastic support inadapting the computer. Von Neumann, whose logical design of these computerslong survived both his IAS machine and him, left a comparable institutionallegacy at Princeton in the Matterhorn project, which applied computationaltechniques developed in support of hydrogen bomb developmentto the problem of controlled nuclear fusion.As in so many other areas, Enrico Fermi blazed a trail in the use of thecomputer as a scientific instrument. The pioneering activity in high-energyphysics at Chicago has often been overshadowed by activity at the Universityof California Radiation Laboratory and Brookhaven National Laboratory inthe years following the completion of the Cosmotron in 1952 and theBevatron in 1954, as well as by the development of the hydrogen bomb,another application of physics born of Fermi’s ideas. I have tried to showhow, despite his continuing involvement in the application of nuclear physics,Fermi left another legacy in high-energy physics, and provided the ideas,inspiration, and individuals who used the computer as they settled the highenergyfrontier.Robert W. SeidelHe is Professor of the History of Science and Technology at the University ofMinnesota, Minneapolis. He has served as Director of Charles BabbageInstitute for the History of Information Processing and as the administrator ofBradbury Science Museum at Los Alamos National Laboratory. He is coauthor(with John Heilbron) of Lawrence and his Laboratory, volume I of AHistory of the Lawrence Berkeley Laboratory (Berkeley: University ofCalifornia Press, 1990).268

Nina ByersWomen in Physics in Fermi’s TimeIn the first half of the 20 th century, Fermi’s time, women breached barriers tohigher education and became major players in physics. There were many inaddition to Marie Curie who made original and important contributions tophysics such as Emmy Noether, Marietta Blau, Irene Joliot-Curie, Lise Meitner,Maria Goeppert Mayer and others less well known. This talk will be aboutthese women, their struggles to work in the field, and some of their importantcontributions.Le donne nella fisica al tempo di FermiNella prima metà del ventesimo secolo, al tempo di Fermi, le donneruppero le barriere che circondavano l’educazione superiore e divennerofigure di rilievo nel campo della fisica. Molte donne oltre a Marie Curiecontribuirono in modo originale e rilevante alla fisica, come ad esempioEmmy Noether, Marietta Blau, Irene Joliot-Curie, Lise Meitner, MariaGoeppert Mayer e molte altre meno note. Qui si parlerà di queste donne,della loro lotta per occupare una posizione in questo settore e di alcuni deiloro rilevanti contributi alla fisica.269

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntroductionProbably most people, particularly in English speaking countries, would thinkof one, two, or at most three women in physics in Fermi’s time. But in fact thereare many who deserve to be recognized as having made important discoveries,contributions of lasting value to physics. At UCLA we have collected informationabout twentieth century women who have made original and importantcontributions to physics before 1976, and find there are at least eighty-sixexamples. Brief biographies outlining the scientific lives and major contributionsof these women can be found at the website http://www.physics.ucla.edu/~cwp.In this paper, we give some outstanding examples.Before launching the subject, which is women in physics in Fermi’s time, afew brief historical remarks are in order. Before the proliferation of printingpresses in the nineteenth century books on science were relatively inaccessibleto women and there were very few female physicists. Women did not haveopportunities to study and work in institutions of higher learning. Therewere exceptions among aristocratic women; for example, Émilie du Châtelet(1706-1749) who translated Newton’s Principia into French and bestedVoltaire in a physics competition.Just as the Renaissance came to Italy in advance of other countries ofEurope, so Italy was more advanced in the entrance of women into institutionsof higher learning. Laura Bassi (1711-1778) was a professor of physicsin University of Bologna studying electrical phenomena along with her husband.She was perhaps the first woman to be professor of physics in aEuropean university.The landscape as regards there being female physicists in Europe andAmerica radically changed toward the end of the nineteenth century. MarieCurie (1867-1934) published her first important paper in 1898. It was on asystematic study of the uranic rays Becquerel had discovered. She found thatsimilar radiation emanated from atoms other than uranium. Consequently ina following paper, authored with her husband Pierre, the word radioactivitywas introduced to refer generically to what had previously been referred toas the emanation of uranic rays [1]. Pierre was a professor in the Sorbonnewhere Marie was a doctoral student. Before joining with her to studyBecquerel’s uranic rays, he had been studying in his laboratory magneticproperties of substances.In addition to Marie Curie, there were other women physicists whose workwas at the cutting edge of physics at that time. There were several whose discoveriesare of lasting value. One is Agnes Pockels (1862-1935), a German270

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEwoman whose studies initiated the field of surface physics. Since her experimentalwork was highly original and in a new field of investigation, she failedto get it recognized in her own country. She wrote about it to Lord Rayleigh,who began to publish his own studies in surface physics more than ten yearsafter she began hers. Rayleigh was so impressed with her experimental methodsand results that he had her letter translated from the German and publishedit in Nature [2]. He wrote a brief introduction which reads in part:“I shall be obliged if you can find space for the accompanying translationof an interesting letter which I have received from a German lady, whowith very homely appliances has arrived at valuable results respecting thebehaviour of contaminated water surfaces. ... I hope soon to find opportunityfor repeating some of Miss Pockels’ experiments”.Pockels’ studies of surface tension were forerunners of the Nobel Prizewinning work of Irving Langmuir.Another female physicist who worked before Fermi’s time was KristineBjerrum Meyer (1861-1941) who won the 1899 Gold Medal of the DanishAcademy of Science and Letters for her paper [3] on an equation of state forliquids similar to that of van der Waals for gases.Finally I’d like to mention Henrietta Leavitt (1868-1921) whose discoveryof the period-luminosity relation in light from Cephid variable stars in theMagellanic Clouds led to, and still enables, determination of intergalactic distances.Women in Physics in Fermi’s TimeI take Fermi’s Time to be from 1922, when he took his doctorate inphysics in Pisa, up to his premature death in 1954 and have chosen to discusssome women who have made important contributions to fields ofphysics in which he engaged himself. They are presented chronologically, followingthe timeline of Fermi’s life in physics; viz.,1922-1924: Fermi in Leiden and Göttingen1. Tatiana Ehrenfest-Afanaseva {statistical mechanics}2. Emmy Noether {general theory of relativity}1925-1927: Fermi in Florence3. Marietta Blau {photographic method of measuring particle tracks}271

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1928-1938: Fermi in Rome4. Irène Joliot-Curie {artificial radioactivity}5. Ida Noddack {suggested chemical analysis might reveal uranium fission}6. Lise Meitner {nuclear fission}1939-1954: Fermi in United States7. Leona Woods Marshall Libby {work with Fermi in Los Alamos andChicago}8. Maria Goeppert Mayer {shell model of the nucleus}.The sections in this paper on Emmy Noether and Marietta Blau are muchlonger than the others in consideration of the fact that they contributed soimportantly to progress in physics in the twentieth century and relatively littleis known about them, generally speaking. Relatively little is also knownabout the first woman on the list, Tatiana Ehrenfest-Afanaseva although shewas co-author of a classic treatise on the foundations of statistical mechanicswith her husband Paul Ehrenfest. She studied physics before her marriageand the marriage may have set an example to Fermi who later married theyoung physics student, Laura Capon.Laura however discontinued her physics studies after she married [4].1922-1924In 1922 Fermi received his doctorate from the University of Pisa and tookup a two year fellowship which he spent in Göttingen and Leiden. He was ayoung man and went abroad to see the world and become acquainted withforeign physicists. He did theoretical physics in this period writing papersmainly on general relativity and also on statistical mechanics and thermodynamics.Before he left Pisa in 1922, he had obtained the remarkable result inthe general theory of relativity that space is Euclidean in the neighborhood(infinitesimal) of a worldline [5]. While in Göttingen he may have metEmmy Noether who was then a well known mathematician and had foundimportant results in the general theory. In 1918 she published a very importantpaper for physics which solved a big problem, the problem of energyconservation in the general theory of relativity. In Leiden he most likely metTatiana Ehrenfest-Afanaseva, the wife of Paul Ehrenfest who became a lifelongfriend. Sadly Ehrenfest died in Leiden in 1933.272

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIME1. Tatiana Ehrenfest-AfanasevaTatiana Afanaseva (1876-1964) lived in St. Petersburg before she marriedPaul Ehrenfest. In Russia, at that time, women were not admitted to universities.There were, however, special university-level institutions that allowedwomen to take courses in engineering, medicine, and teaching. She attendeda women’s pedagogical school and the Women’s Curriculum which shadowedthe imperial university. Martin Klein, in his biography of PaulEhrenfest [6], wrote the following about her:“Paul Ehrenfest was not the kind of thinker who develops his ideas slowlyin the solitude of his study. He had to talk about them, to work them outby discussing and arguing them with a critical and competent colleague,and Tatyana was willing and able to play this role. Her quick and extraordinarilylogical mind was a natural foil for his more inventive one, and herurge to probe to the very bottom of an idea was as deep as his own”.Together they wrote the classic treatise on the foundations of statisticalmechanics and statistical thermodynamics [7] which was important in thedevelopment of those fields. Fermi wrote papers on the ergodic hypothesiswhile in Leiden that Segrè characterizes as subtle papers. This hypothesis wasa central concern of Paul and Tatiana Ehrenfest. Perhaps Tatiana and PaulEhrenfest themselves personally as well were instrumental in the developmentof Fermi’s thinking which led him, after the discovery of quantummechanics and Pauli’s exclusion principle, to the discovery of quantum statisticsfor identical particles which obey the exclusion principle. This isknown as Fermi-Dirac statistics, having been independently discovered byP.A.M. Dirac.2. Emmy Noether (1882-1935)During his fellowship in Göttingen, Fermi may have attended lectures ofEmmy Noether, a mathematician whose work profoundly influenced twentiethcentury physics. She was a member of the group David Hilbert and FelixKlein had assembled at the University. Following Hilbert and Klein, she tookan interest in mathematical physics, particularly in the general theory of relativity.Shortly after her arrival in Göttingen in the summer of 1915, AlbertEinstein came and gave a series of lectures on the general theory which wasthen not yet complete. Almost simultaneously with Einstein’s completion ofthe theory in November (he had been working on it for eight years), Hilbertdiscovered a Lagrangian formulation which solved the problem with the the-273

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEory that Einstein was confronting earlier in the year. With this problemsolved they had a consistent field theory, but there was the vexing physicalproblem with the theory that it didn’t seem to have an energy conservationlaw such as is found in classical field theories. Hilbert asked Emmy Noetherto look into this problem and she solved it with the discovery of theoremswhich, collectively, physicists call Noether’s Theorem [8]. This relates symmetriesand conservation laws. Their importance for our understanding ofbasic physics cannot be overstated. For example, Feza Gürsey wrote [9]:“Before Noether’s Theorem the principle of conservation of energy wasshrouded in mystery, leading to the obscure physical systems of Mach andOstwald. Noether’s simple and profound mathematical formulation didmuch to demystify physics”.The Theorem to which he refers consists of two theorems, which she calledtheorem I and theorem II. She proved them and their converses in a landmarkpaper read to the Königl. Gesellschaft der Wissenschaften zu Göttingen(Royal Society of Sciences of Göttingen) by Felix Klein in 1918. PresumablyKlein presented it because Noether was not a member of the Society; it seemslikely she wasn’t even there when the paper was read. Records of the Societywere lost in the Second World War and we do not know when women werefirst admitted; counterpart societies in London and Paris did not admitwomen until after World War II. The Royal Society (London) elected its firstfemale member in 1945 and the Académie des Sciences of Paris in 1962;both were established in the seventeenth century.Though the general theory of relativity was not in the main line of herresearch, she wrote several papers on the theory. In a letter to Hilbert,Einstein expressed his appreciation of her work and wrote:“Yesterday I received from Miss Noether a very interesting paper oninvariant forms. I am impressed that one can comprehend these mattersfrom so general a viewpoint. It would not have done the Old Guard atGöttingen any harm had they picked up a thing or two from her. She certainlyknows what she is doing”.Emmy Noether’s main line of research was the development of modernalgebra. She had returned to writing papers and lecturing on this subjectwhen Fermi was in Göttingen. Nathan Jacobson wrote about her achievementsin this period [10]:“Abstract algebra can be dated from the publication of two papers byNoether, the first a joint paper with Schmeidler and a truly monumental274

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEwork Idealtheorie in Ringbereichen [which] belongs to one of the mainstreamsof abstract algebra, commutative ring theory, and may be regardedas the first paper in this vast subject ...”Historians of mathematics see the creation of modern abstract algebra inthe years 1921-1933 in the work of Emmy Noether, Emil Artin and theirschool [11]. Prominent mathematicians came from all over Germany andabroad to consult with Noether and attend her lectures. Though Fermi wentto Göttingen to study physics with Max Born, and Noether was in the mathematicsdepartment, it seems reasonable to conjecture that Fermi attendedsome of her lectures.It is remarkable that Noether was never appointed to a paid position in thefaculty of the University of Göttingen. Her biographer Auguste Dick wrote[12]: “Was it because she was Jewish? There were several Jewish Ordinarii inGöttingen. Was it because she was a member of the Social Democratic Party?Or was it her firm stance as a pacifist that was frowned upon?”. Today wemight also ask what role did gender discrimination play? For more than adecade after receiving her Ph.D. in 1908 from the University of Erlangen,Emmy Noether worked unpaid in Erlangen and Göttingen teaching anddoing mathematical research. During this period she published fifteen papersin important mathematical journals, became a member of the prestigiousCircolo Matematico di Palermo and the Deutsche MathematikerVereinigung (DMV) [German Association of Mathematicians], and gave twolectures to the DMV.At the invitation of David Hilbert and Felix Klein, in 1915 she joined theirgroup in Göttingen but was refused appointment as lecturer (Privatdocent)by the University Senate. The stated reason the University refused to appointher was because she was a woman. This so enraged Hilbert that he stormedout of a Senate meeting saying “I do not see that the sex of a candidate is anargument against her admission as Privatdocent. After all, we are a Universitynot a bathing establishment!”. After WWI more liberal attitudes prevailedand in 1919 the University granted Noether Habilitation. This enabled herto give University lectures and be paid for them. Before that her lectures hadbeen announced as those of Professor David Hilbert with the assistance ofDr. E. Noether.After March 1933 Emmy Noether was not allowed to lecture in theUniversity. Jews were not allowed to teach in the University after Hitler cameto power. In 1934 women, Jewish or not, were dismissed from theirUniversity posts in accordance with the Nazi policy of Kirche, Kinder, Küche275

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEfor women. Later when there was a manpower shortage in Germany womenwere allowed back in the workforce. Hermann Weyl wrote about Noether inthis period [13]:“A stormy time of struggle like this one we spent in Göttingen in thesummer of 1933 draws people closely together; thus I have a vivid recollectionof these months. Emmy Noether – her courage, her frankness, herunconcern about her own fate, her conciliatory spirit – was in the midstof all the hatred and meaness, despair and sorrow surrounding us, a moralsolace”.She soon emigrated. She had only two job offers. One was from SomervilleCollege, Oxford which was able to offer her room and board and a smallstipend, and the other from a women’s college in Pennsylvania, Bryn MawrCollege, where she was offered a visiting professorship paid in part by theRockefeller Foundation which was subsidizing jobs for German refugee scientists.She accepted the Bryn Mawr position and in addition weekly went bytrain to the Institute for Advanced Studies in Princeton to give an invitedcourse of lectures [14].Again gender discrimination worked against her because undoubtedlyotherwise, on the basis of her eminence as a mathematician, she would havebeen given a paid position in the Institute in Princeton. Emmy Noether’suntimely death in 1934, owing to a post-operative infection, led Einstein towrite a memorial Letter to the Editor of the New York Times which readsin part:“In the realm of algebra, in which the most gifted mathematicians havebeen busy for centuries, she discovered methods which have proved ofenormous importance. Pure mathematics is, in its way, the poetry of logicalideas. In this effort toward logical beauty, spiritual formulas are discoverednecessary for deeper penetration into the laws of nature. ...There is, fortunately, a minority [of people] who recognize early in theirlives that the most beautiful and satisfying experiences open tohumankind are not derived from the outside, but are bound up with thedevelopment of the individual’s own feeling, thinking and acting. Thegenuine artists, investigators and thinkers have always been persons of thiskind. However inconspicuously the life of these individuals runs itscourse, none the less the fruits of their endeavors are the most valuablecontributions which one generation can make to its successors’’. [15]276

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIME1925-1927In this period, Fermi made one of his most important contributions tophysics. Following the discovery of quantum statistical mechanics for photonsby Bose, extended to ordinary molecules by Einstein, and the Pauli exclusionprinciple, he developed quantum statistical mechanics for identical particlesthat obey the Pauli principle [16]. In these years, in Vienna, Marietta Blau discoveredthat photographic emulsions could be used to study particle tracks.Years later, in the founding days of particle physics when he studied pion-nucleoninteractions in Chicago, Fermi made very extensive use of this method.3. Marietta Blau (1894-1974)Marietta Blau, working in the Radium Institute at the University of Vienna,began the development of what later became known as nuclear emulsions, aphotographic method of detecting particle tracks which Fermi employed togreat advantage in the post WWII period in Chicago. She was the first physicistto show that proton tracks could be separated from alpha-particle tracksin emulsion. Indeed the final paragraph of her ground breaking 1925 paper[17] concludes: “The method of photographic detection of H-particles [protons]was developed ... to obtain pictures of H-particles, which struck thephotographic plate with parallel incidence. As with the alpha particles, theresults were series of points clearly defining a direction, where each series correspondsto the track of an H-particle. With the aid of absorption experimentsand of comparison experiments where the H-radiation source of paraffin wasreplaced by a layer of soot with an equivalent content of carbon, it was shownthat the photographic material blackening can only be explained by the effectof H-particles and not by possibly existing radiation”.From 1923 until 1938 she worked unpaid in the Institute in Vienna. Thehead of the Institute provided funds for her experimental work but no salary.When applying for a regular paid position she was told her chances were slimbecause she had two strikes against her – she was a Jew and a woman.Fortunately she had financial support from her family, prominent publishersof sheet music in Vienna. When the Nazi Anschluss occured she happened tobe working in the Curie Institute in Paris and, being Jewish, was not able toreturn to work in Vienna.While at the Institute in Vienna she worked with the British firm Ilford todevelop stable, thick photographic emulsions which would provide for bettermeasurements of particle tracks. She was remarkably successful. This work277

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwas precursor to the further developments by Nobel Laureate C.F. Powell;see below. Another woman, Hertha Wambacher, came to work with her inthe Institute. They prepared and exposed photographic plates at high altitudesand observed nuclear disintegrations caused by cosmic rays. Thesewere called Blau-Wambacher stars. In 1932, just after Chadwick discoveredthe neutron, she showed that neutrons can be detected by observing recoilprotons in nuclear emulsions [18]. This was, and still is, a preferred way ofdetecting neutrons.After Hitler took over Austria in 1938, she became a Nazi refugee and herlife was difficult. She went back to Vienna to bring her mother out and, witha recommendation of Albert Einstein, became professor in the TechnicalUniversity of Mexico City. But the conditions of work there for an experimentalphysicist were very poor. She left for the United States in 1944 witha job in the International Rare Metals Refinery in New York. After the war,she pioneered development of photomultiplier tubes for particle physicsdetectors and in Brookhaven National Laboratory carried out early studies ofmultipion productions by pions [19]. She had research associate appointmentsat Columbia University and then at Brookhaven National Laboratory,and in 1955 an associate professorship at the University of Miami. None ofthese American appointments were suitable for a physicist of her ability andaccomplishment. And from a practical point of view, they did not provideretirement benefits or health insurance. In 1960, in declining health,Marietta Blau returned to Vienna.C.F. Powell is usually credited with the development of the photographicmethod of studying particle tracks. Indeed his 1950 Nobel citation reads“for his development of the photographic method of studying nuclearprocesses and his discoveries regarding mesons made with this method” andthe biographical notes read in part [20]:“In 1938, he undertook experiments in cosmic radiation and employedmethods of directly recording the tracks of the particles in photographicemulsions and employed similar methods for determining the energy ofneutrons, that is, by observing the tracks of the recoiling protons. Thelength of the track of a charged particle in the emulsion was found to givean accurate measure of its range and the great advantages of this methodfor experiments in nuclear physics were soon clearly established”.Indeed he did much to develop the method but Marietta Blau is key to thestory of how he came to use it. This is the story as told by A.M. Tyndall for278

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEwhom Powell was working in Bristol University at that time. In 1938 WalterHeitler, also a Nazi refugee, came to Bristol and asked Tyndall for funds toexpose photographic plates to cosmic rays at high altitudes telling him “therewas this method of studying particle tracks developed by two women inVienna which was so simple even a theorist could do it”. Tyndall found thefunds and Heitler exposed a stack of plates on a mountain site.Powell had come to work on a Cockcroft generator that was not yet workingand joined with Heitler in the study of cosmic rays. He evidently foundthat this Blau-Wambacher photographic method had promise and the rest ishistory. There is a good problem here for historians to document and explainwhy after the war Marietta Blau was not appointed to a position appropriateto her talent and accomplishments. She was well known in Europe before thewar, having been nominated several times for the Nobel Prize and havingwon (with Hertha Wambacher) the prestigous Lieben Prize of the VienneseAcademy of Science.Some Bristol physicists recollect that she was overlooked after the warbecause of her association with Hertha Wambacher, who had been a Nazi.The irony of this is that Blau was a Jew who had to flee the Nazis in 1938.Even before the Anschluss, Austria had a strong Nazi Party (though illegalsometimes) and there were influential Nazi Party members in scientific aswell as other institutions. It seems likely that Blau found it necessary to maintainassociation with Wambacher in those years in order to continue herwork. And then, of course, there is the question of gender discrimination.Speaking about Blau’s inferior employment status in Brookhaven NationalLab in the early fifties, Maurice Goldhaber remarked “Women were nottreated very well in those days”.1928-1938Fermi built up a premier school of physics in Rome. Many young men wholater were very famous and accomplished physicists came to study and workwith him. There he characteristically worked both in experimental and theoreticalphysics. He carried on experimental studies in nuclear physics andgave us the Fermi Theory of Weak Interactions. After Irène and FrédéricJoliot-Curie’s discovery of artificial radioactivity and Chadwick’s discovery ofthe neutron, he systematically studied the radioactivity produced by neutronbombardment of stable isotopes. He became expert in neutron and nuclearphysics. But he had the misfortune of overlooking the phenomenon of neu-279

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtron induced fission. This despite the paper of a chemist, Ida Noddack, whosuggested that the radioactivity he observed resulting from neutron collisionswith uranium might be evidence for such an effect. In this period, twowomen, Irène Joliot-Curie and Lise Meitner, who did discover nuclear fissionwith the help of chemists O. Hahn and F. Strassmann, made major contributionsto physics. Time and space limitations require them to be discussedmore briefly than Blau and Noether. There are very good referenceswhere more information about them can be found. Here I will give some discussionabout Ida Noddack, though she has been discussed already by severalspeakers in this Conference.4. Irène Joliot-Curie (1897-1956)For a brief summary of the scientific life and accomplishment of IrèneJoliot-Curie, one could do no better than to read from the obituary by JamesChadwick in Nature, 177, 964 (1956):“Irène Joliot-Curie was born in the stirring days of radioactivity when herparents [Marie and Pierre Curie] were making great discoveries, she grewup with radioactivity, and all her life was devoted to its study. In 1926 shemarried Frédéric Joliot and there began a collaboration of husband andwife in scientific work rivaling in productive genius even that of her parents.The most outstanding of their joint papers were published in theyears 1932-1934. In the first of these, on the radiation excited in berylliumby alpha-particles, they reported a very strange effect which providedthe clue to the discovery of the neutron.Then, after studying the conditions of excitation of neutrons by theimpact of alpha-particles on various elements, they turned for a time tothe “materialization” of positive electrons through the action of gammaraysof high energy. This was followed by a systematic study of the radiationsemitted from the lighter chemical elements under the impact ofalpha-particles, which through the light of intuition – and good technique– led them, in early 1934, to their beautiful discovery of artificial radioactivity.An interesting feature of this discovery is that it was so long in coming;for the phenomenon of artificial activity had been expected, andsought for, since the earliest days of radioactivity. For this discovery theJoliot-Curies were awarded the Nobel Prize for Chemistry in 1935.About two years later with P. Savic, she examined in detail the artificialradioelements produced by the irradiation of uranium by slow neutrons,analysing the products and identifying them chemically, and she camewithin a hair’s-breadth of recognizing that the phenomenon involved inthe production of these elements was that of fission”.280

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEChadwick himself won a Nobel Prize for his discovery of the neutron. Hevery generously remarks here that a paper of F. and I. Joliot-Curie provideda clue to his great discovery. After the announcement of his discovery theymade one of the first determinations of the neutron mass and concluded hisparticle would be unstable and decay to proton and electron.As regards gender discrimination, Irène Joliot-Curie’s professional life wasfar less burdened by it than her predecessors. This must have been due in partto the fact that her mother, as well as her father and her husband, were activefeminists and committed to the cause of social justice. (During WWI, withher mother she ran mobile X-ray machines which traveled from camp tocamp diagnosing soldiers’ wounds). Some of the positions she held were:1918-46 Assistant to Marie Curie, Radium Institute; 1936 Undersecretaryof State for Scientific Research, Léon Blum’s Popular Front Government (4months); 1946-56 Director, Radium Institute; 1946-50 Director, FrenchAtomic Energy Commission; 1937-56 Professor, Sorbonne.5. Ida Tacke Noddack (1896-1979)Ida Tacke Noddack was a distinguished chemist with many publications inscientific journals, chemical journals in particular. In 1925, she discoveredthe missing element 75 with W. Noddack and O. Berg. They named it rheniumafter the Rhine River.In a now famous paper, “Über das Element 93”, Zeitschrift fürAngewandte Chemie 47: 653 (1934), she suggested that the radioactivitywhich Fermi observed resulting from neutron bombardment of uranium,which he proposed might be evidence for production of the transuranic element93, might instead be caused by disintegration of the uranium nucleusinto several heavy fragments – a process now known as fission. She suggestedthis could be determined by chemical analysis, and indeed chemical analysesby radiochemist Otto Hahn with Fritz Strassmann and Lise Meitner,much to their surprise, confirmed her suggestion in 1939. E. Segrè, Fermi’scoworker in Rome, wrote that “the possibility of fission, however, escaped usalthough it was called specifically to our attention by Ida Noddack. The reasonfor our blindness is not clear”.In the paper which reported the discovery of rhenium, the authors alsoreported evidence for another missing element, the element 43 which theynamed masurium. This was, and is still, a disputed discovery because allknown isotopes of this element are highly radioactive with half-lives muchshorter than the age of the earth. In 1937, C. Perrier and E. Segrè found and281

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEidentified this element in an irradiated foil in the Berkeley cyclotron andnamed it technetium. It is conjectured that what is considered as Noddack’spremature report of the discovery of element 43 is responsible for the neglectof her prescient 1934 paper that correctly draws attention to the fact thaturanium fission may be responsible for the neutron induced radioactivityFermi observed in uranium. She also has been criticised for not following upher own suggestion and performing chemical analyses of the reaction productsof neutron irradiated uranium herself. It was such a chemical analysis inLise Meitner’s lab that produced the evidence for nuclear fission.Perhaps a contributing factor in Ida Noddack’s paper not having receivedthe attention it deserved was political. There is evidence that some colleaguesobserved her husband Walter in a Nazi uniform and Professor J.P. Adloff ofStrasbourg University reports [22a]:“Together with her husband, Ida Noddack was appointed to ourUniversity by the Nazis when Alsace was annexed by Germany duringWW II. They held a position probably from 1942 to 1944 when the Naziswere thrown out by the Liberation army. They managed to cross theRhine back to Nazi Germany. Walter Noddack was professor of chemicalphysics (we say chimie physique) at Strasbourg University and was helpedby his wife Ida. Nothing is known about the scientific work of the coupleduring this period. In fact, the list of publications of the Noddacks lacksany entry from 1940 to 1951. In a 1954 paper the authors write ‘in 1944an important enrichment of masurium had been obtained, but then allpreparations were lost and the work was interrupted for 5 years’. It is notknown if the enrichment of masurium was carried out in Strasbourg”.6. Lise Meitner (1878-1968)Lise Meitner was an Austrian Jewish woman who came from Vienna witha doctorate in physics to Berlin in 1907 after Ludwig Boltzmann died.Collaborating with Otto Hahn, she became renowned as an experimentalnuclear physicist. Their many accomplishments before and just after WWIincluded the discovery of element 91, protactinium. She became head of theradiophysics department of the Kaiser Wilhelm Institute, Berlin-Dahlemfrom 1918 to 1938, and the head of the radiochemistry department. Theythen worked separately until 1934 when Meitner invited Hahn to join her inreproducing and studying Fermi’s new discoveries bombarding uraniumwith neutrons. Before that, in the twenties, she made many important contributionsincluding discovery of radiationless atomic transitions two years282

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEbefore Auger, though the effect is widely known as the Auger effect; experimentalconfirmation of the Klein-Nishina formula for Compton scattering;and most important for Fermi’s work, confirmation of Chadwick’s observationof the continuous electron energy spectrum in nuclear beta decay [21].In this time her reputation as a very careful and reliable experimentalist wasextremely high so that her confirmation of Chadwick’s results convincedeveryone including Wolfgang Pauli that they were observing new physics.Very soon thereafter Pauli proposed the existence of the neutrino.Implementing Pauli’s proposal, Fermi constructed his Theory of WeakInteractions whose quantitative predictions led to confirmation of the existenceof the neutrino.Lise Meitner is most famous for her discovery of nuclear fission. She and hernephew O.R. Frisch named the process and explained it [22]. The experimentaldiscovery was carried out with radiochemists O. Hahn and F. Strassmannwhom she invited to join her effort when she began to study neutron nucleusinteractions in uranium. She expected to confirm Fermi’s experiments in whichhe observed radioactivity that he reported as indicating production of newtransuranic elements. She must have felt that having chemists in the groupwould be valuable in confirming those results and studying the new elements.The three of them found something surprising. After very careful analysis, theyfound that the observed radioactivity was due to the disintegration of the uraniumnucleus into smaller nuclear fragments. By that time Austria had beenannexed by Nazi Germany and, being a Jewish woman, Meitner could nolonger work in Berlin. Before the Anschluss she was able to continue her workin Germany as an Austrian national. In 1938 she escaped to Stockholm and theexperimental results, which were obtained in her laboratory were publishedwithout her name as coauthor though she had initiated the investigation andparticipated in all its phases. This discovery led to Fermi’s constructing the firstself-sustaining nuclear chain reaction, nuclear reactors, and the atomic bomb.For an in depth discussion of Lise Meitner’s life and work, including herclose collaboration with Otto Hahn for over half a century, see Ruth LewinSime’s fascinating biography Lise Meitner: a life in Physics, University ofCalifornia Press, Los Angeles 1996.1939-1954During the war years 1939-1945, Fermi was engaged in creating the firstself-sustained nuclear chain reaction, and improving nuclear reactors for283

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEpower generation and for producing plutonium for atomic bombs. He was aleading scientist in the Manhattan Project to build the atomic bombs.During most of those years, and afterward at the University of Chicago, heworked closely with a young physicist, Leona Woods Marshall. After the warhe returned to Chicago where he also had a close collegial relationship withNobel Laureate Maria Goeppert Mayer. Owing to limitations of space andtime, in this paper I can only give unduly brief mention of these two women.But there are excellent references for more information. Leona WoodsMarshall Libby has written an autobiographical account of her work withFermi and others in the Los Alamos Laboratory and in Chicago (see below).There are numerous good references where one can read about MariaGoeppert Mayer; in particular, her biography in “Nobel Lectures, Physics1963-1970”, Elsevier Publishing Company, Amsterdam, 1964-1970 and“Maria Goeppert Mayer, A Biographical Memoir” by Robert G. Sachs inBiographical Memoirs vol. 50, National Academy of Sciences (1979).7. Leona Woods Marshall Libby (1919-1986)Leona Woods Marshall was an experimental physicist who worked closelywith Fermi in the Manhattan Project and after the war at the University ofChicago. She wrote an autobiographical account of this work entitled TheUranium People, published by Charles Scribners & Sons (1979).8. Maria Goeppert Mayer (1906-1972) Nobel Prize in Physics 1963Maria Goeppert Mayer was a brilliant theoretical physicist, the only womanafter Marie Curie to have been awarded a Nobel Prize in Physics. Marie andPierre Curie, with Henri Becquerel, received a Nobel Prize in Physics in1903. In studies of nuclei, Maria Mayer discovered the magic numbers andtheir explanation in terms of the nuclear shell model with strong spin-orbitcoupling. For this she won the 1963 Nobel Prize in Physics, with J.H.D.Jensen who had independently proposed the strong spin-orbit coupling. Itis appropriate here, in this Conference celebrating Enrico Fermi, to bringattention to Fermi’s role in Mayer’s Nobel Prize winning work. In her shortbut very famous paper “On Closed Shells in Nuclei II” she gives a summaryof the evidence for the spin-orbit explanation of magic numbers, and endsthe paper with the following sentence: “Thanks are due to Enrico Fermi forthe remark, ‘Is there any indication of spin-orbit coupling?’ which was theorigin of this paper” [23].284

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEThroughout her life Maria Mayer made important contributions to manyfields of physics including chemical physics, molecular physics, atomicphysics, statistical mechanics and, of course, nuclear physics. With her husbandJoe, she wrote a classic textbook, Statistical Mechanics, from whichmany generations of students benefited.Having obtained her doctorate from the University of Göttingen in 1930,she worked in universities unpaid until 1960! In 1930 she married JosephEdward Mayer, an American physical chemist, and went with him to JohnsHopkins University in Baltimore, Maryland. This was when no universitywould think of employing the wife of a professor. She endured the indignityof working as a ‘Volunteer’ in universities until she was appointed to a fullprofessorship in the University of California in 1960. She kept working, shesaid, “just for the fun of doing physics”.ConclusionIn conclusion I want to reiterate that, owing to limitations of ability, time,and space, I have not been able to do justice to the lives and accomplishmentsof the women mentioned here. Hopefully more will be written aboutthem and others who also have made important contributions to progress inphysics. Rather than to focus attention on a fewer number of women, I havechosen to bring fourteen to your attention to emphasize the fact that thereare many successful women physicists who tend to go unrecognized in ourprofession.I am very grateful to Professor Carlo Bernardini, Luisa Bonolis and theOrganizing Committe of the International Conference “Enrico Fermi andthe Universe of Physics” for inviting me to speak to the Conference aboutwomen in physics in Fermi’s time.ACKNOWLEDGMENTAdvice of my colleague at UCLA Professor S. A. Moszkowski has been very helpfulin the preparation of this manuscript.REFERENCES01. S. CURIE, “Radiations from Compounds of Uranium and of Thorium”, Comptes Rendus126: 1101 (1898). M. et MME. CURIE, “New Radio-Active Element in Pitchblende”,Comptes Rendus 127: 175 (1898).285

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE02. Surface Tension, Nature 43: 437 (1891); Letter from Lord Rayleigh.03. K. BJERRUM MEYER, “Om overensstemmende Tilstande hos Stofferne”, Royal DanishAcademy of Science and Letters series SN 6.IX.3, pp. 155-225 (1899).04. L. FERMI, “Atoms in the Family: my life with Enrico Fermi”. [Chicago] University ofChicago Press [1954]05. E. SEGRÈ, “Enrico Fermi, Physicist”, University of Chicago Press, (1970). In this book,Fermi’s papers are referenced according to the numbering in “The Collected Papers ofEnrico Fermi”, University of Chicago Press (1962, 1965): e.g., [FP 11] is paper number11 in the Collected Papers {this is his important paper on the ergodic theorem}and [FP3] is his 1922 paper “On the Phenomena Occurring near a World Line”.06. M.J. KLEIN, “Paul Ehrenfest Volume I: The Making of a Theoretical Physicist”, North-Holland Publishing Co. (1970).07. P. and T. EHRENFEST, “Begriffliche Grundlagen der statistischen Auffassung in derMechanik”, Encyklopädie der mathematischen Wissenschaften, vol. 4, part 32(1911);English translation by Michael J. Moravcsik, Cornell University Press (1959).08. E. NOETHER, “Invariante Variationsprobleme”, Nachr. d. König. Gesellsch. d. Wiss. zuGöttingen, Math-phys. Klasse (1918), 235-257. English translation: M.A. TAVEL,Transport Theory and Statistical Physics, 1(3), 183-207 (1971).09. N. BYERS, “E. Noether’s Discovery of the Deep Connection Between Symmetries andConservation Laws, Israel Mathematical Conference Proceedings Vol. 12, 1999”. Seehttp://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html.10. Emmy Noether Collected Papers, ed. Nathan Jacobson, Springer-Verlag 1983.11. NICOLAS BOURBAKI, “Elements of the History of Mathematics”, Masson Editeur, Paris1984; English translation by John Meldrum, Springer-Verlag, Berlin Heidelberg 1994.Henri Cartan, Andre Weil, Jean Dieudonne, Claude Chevalley, and AlexanderGrothendieck wrote collectively under the name of Nicolas Bourbaki.12. A. DICK, “Emmy Noether (1882-1935)”, Birkhauser 1981; English translation by H. I.Blocher.13. H. WEYL, Scripta Mathematica III. 3 (1935) 201-220; an English translation of thismemorial lecture is given in Ref. 12.14. O. TAUSSKY TODD, in Emmy Noether in Bryn Mawr, B. SRINIVASAN and J. SALLY (eds.),New York-Berlin, 1983.15. A. EINSTEIN, Letter to the Editor of the New York Times, May 5, 1935. The full text mayalso be found in ref. 12.16. E. FERMI, “On the Quantization of the Perfect Monatomic Gas”, presented to theAcademia Lincei, February 1926. [FP30 & 31]17. M. BLAU, “The photographic effect of natural H-rays” (in German), SBAWW(Sitzungsberichte Akademie der Wissenschaften in Wien) IIa 134: 427 (1925) (Englishtranslation by Sven Reiche and James Rosenzweig posted on the Web athttp://www.physics.ucla.edu/~cwp/articles/blau/blau-rosenz.html).18. M. BLAU and H. WAMBACHER, “Photographic detection of protons liberated by neutrons.II”, ibid., 141: 617 (1932).19. M. BLAU, “The multiplier phototube in radioactive measurements”, RSI 18: 715 (1947).286

Nina ByersWOMEN IN PHYSICS IN FERMI’S TIMEM. BLAU, M. COULTON and J.E. SMITH, “Meson production by 500 MeV negative pions”,Phys. Rev. 92: 516 (1953).20. Nobel Lectures, Physics 1942-1962, Elsevier Publishing Company, Amsterdam, 1964-1970.21. L. MEITNER, “Das beta-Strahlenspektrum von UX1 und seine Deutung”, Z. Phys. 17: 54-66 (1923). H.H. HUPFIELD and L. MEITNER, “Uber das Absorptiongesetz fur kurzwelligegamma-Strahlung”, Z. Phys. 67: 147 (1930). L. MEITNER and W. ORTHMANN, “Uber eineabsolute Bestimmung der Energie der primaren beta -Strahlen von Radium E”, Z. Phys.60:143 (1930).22. L. MEITNER and O.R. FRISCH, “Disintegration of Uranium by Neutrons: A New Type ofNuclear Reaction”, Nature 143: 239 (1939); “Products of the Fission of the UraniumNucleus”, Nature 143: 471 (1939); “New Products of the Fission of the ThoriumNucleus”, Nature 143: 637 (1939).23. M. GOEPPERT MAYER, “On closed shells in nuclei II”, Phys. Rev. 75: 1969 (1949). See also“On closed shells in nuclei”, Phys. Rev. 74: 235 (1948).Nina ByersIn the summer of 1948, Enrico Fermi gave a course of lectures on QuantumMechanics in Berkeley, California. That was the beginning of Professor Byers’career in physics. The next step was graduate study with Fermi at theUniversity of Chicago. After receiving her Ph. D. in Physics from Chicago in1956, she has held appointments to the faculties of University of Birmingham,England; Institute of Theoretical Physics, Stanford University; Institute forAdvanced Study, Princeton; University of California at Los Angeles; OxfordUniversity; and held research appointments at the European Organization forNuclear Research (CERN) and Fermi National Accelerator Laboratory(FNAL). She is Fellow of the American Physical Society (APS) and theAmerican Association for the Advancement of Science (AAAS) and wasOfficial Fellow and Janet Watson Visiting Fellow of Somerville College,Oxford.287

Harold AgnewDocuments on Fermi’s LifeI had the privilege of starting my relationship with Enrico Fermi at ColumbiaUniversity in January 1942. I assisted him with his experiment with a smallexponential pile there. We subsequently moved to Chicago and constructed CP-1 ,where I was present when he brought into being man’s first nuclear chainreaction. I then left and went to Los Alamos but returned to Chicago in 1946where I studied under Fermi and Herbert Anderson who was his closestcolleague since Fermi’s arrival in the United States. My wife, daughter and I hadthe privilege of living with the Fermi’s during the summer of 1946. It was duringthis period that we really became close friends and we really got to knowEnrico, Laura, Nella, and Julio. Our relationship continued after I left Chicagoand rejoined the Los Alamos Scientific Laboratory. Fermi visited the Laboratoryfrequently especially during the summers. He and Laura were clearly verytalented individuals. When one examines Fermi’s contibutions during the 20 thcentury I don’t believe anyone has made more meaningful contributions toscience and technology.289

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEDocumenti sulla vita di FermiHo avuto il grande privilegio di conoscere Enrico Fermi alla Columbia Universitynel gennaio del 1942. Fui suo assistente nell’esperimento che effettuò con unapiccola pila esponenziale. Poi ci trasferimmo a Chicago dove costruimmo il CP-1, e fui presente quando Fermi realizzò la prima reazione nucleare a catena.Mi trasferii in seguito a Los Alamos, per ritornare a Chicago nel 1946, dovestudiai sotto la guida di Fermi ed Herbert Anderson, che era stato il suocollaboratore più stretto sin dal suo arrivo negli Stati Uniti. Mia moglie, mia figliaed io avemmo il privilegio di vivere con la famiglia Fermi durante l’estate del1946, e fu in questo periodo che diventammo buoni amici e conoscemmo piùintimamente Enrico, Laura, Nella e Giulio. La nostra amicizia continuò quandolasciai Chicago per tornare nel Laboratorio Scientifico di Los Alamos, che Fermivisitò frequentemente, in special modo durante le stagioni estive. Lui e Lauraerano chiaramente delle persone eccezionalmente dotate, e studiando icontributi scientifici e tecnologici dati da Fermi nel ventesimo secolo il suoineguagliato primato in questo senso appare evidente.290

Harold AgnewDOCUMENTS ON FERMI’S LIFEThe Manhattan ProjectIn January 1942 I went to the University of Chicago to join the ManhattanProject. I was immediately sent to Columbia University to work with EnricoFermi. When I first met him the only unusual thing that I noticed was thatall of his pants pockets had zippers. All four of them. At the time he was conductingexperiments using a large pile of graphite. The structure was entirelyencapsulated with a sheet metal cover and was evacuated using mechanicalvacuum pumps.The pile had a radium berrylium neutron source at its center and we measuredthe slowing down of the neutrons using indium foils which were activatedby the source’s neutrons. We would insert the foils at different levelsin the pile for a specific time, then remove them and run about 100 ft to thecounting room where there was a set of Geiger counters. We did this hourafter hour for about 10 hours each day. Fermi not only directed the work butactually took on a shift the same as the rest of us. Inserting the foils, runningto the counting room with the activated foils and then taking the data. Hewas one of us. This always distinguished Fermi. He clearly was a genius butacted with no pretentiousness. He was a very unassuming person. He had awonderful sense of humor.The array of counters in their lead shields all had names, taken from theWinnie the Pooh books. They were named Pooh, Pigglet, Heffelump, etc.For non-nuclear safety reasons he decided to move the experiments toChicago and we started to build CP-1, the first man-made chain reaction.One day a several ton load of graphite blocks was delivered around 4 pm. Wehad to unload the truck so along with the rest of us Fermi took off his coatand pitched in and helped unload the truck. This was Fermi. He not onlysupplied the brains at Chicago but when needed also supplied the brawn.Chicago is cold in the winter and people went ice skating there near theUniversity. Fermi had never ice skated and decided he would. We all went tothe rink, got Fermi a pair of skates and after a few falls Fermi caught on andbefore the end of our first session was skating as well as anyone else. He wasan excellent athlete and loved to compete. He liked to play tennis especially.Later on when I returned to Chicago as a graduate student we used to playtennis during the lunch hour. This required checking out a net and setting itup on the court. The professor and student took turn with this task. He wasa very regular person. Not at all impressed with his position. The only sportat which he was a failure was in fly fishing for trout. Segrè who was a verygood fly fisherman never let Fermi forget that at this sport he was no good.291

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEAfter the warIn 1946, after the war, housing was very scarce in Chicago. I was unableto find a place for my family to live. Fermi who had a fairly large house suggestedthat my wife, small daughter and I come live with them. His wifeLaura wanted to visit her sisters in Italy and when she was gone my wifeBeverly could run the house and do the cooking etc. for Fermi and his childrenGiulio and Nella. We did this for almost three months until I found aplace for us to live. Being part of the family for three months was a wonderfulexperience. Fermi preferred non-spicy food and always diluted the redwine we had for dinner half with water. We stayed on for a month or so afterhis wife Laura returned.One evening she told Fermi that she had gone to the local appliance storeand put her name on a waiting list for a General Electric dishwasher. [Afterthe war appliances were scarce and one had to sign up on waiting lists forappliances, car etc.] I was astounded. Fermi had been the major consultantfor General Electric who were building reactors at Hanford for the productionof plutonium. I said “Enrico you know the president of General Electric.Just tell him you want a dishwasher and he will send you one tomorrow”.Fermi thought for a second and said: “No that wouldn’t be fair for others,we will wait our turn in line.” This was classic Fermi.Fermi liked to swim. Sometimes after work his team of which I was a memberwould go to Lake Michigan. On one day he decided we would swimacross a little bay. I had been a varsity swimmer in high school so thought Iwas pretty good. But after about 15 minutes in the choppy cold water ofLake Michigan I was falling behind. Fermi who swam with what I would calla “dog paddle” style swam back to me and asked if I was O.K. I said Ithought so but clearly my Australian crawl swimming style wasn’t best forchoppy Lake Michigan. I barely made it to the other side of the bay and withdifficulty climbed up the sea wall and sat down. Fermi said: “Meet you backwhere we started” and plunged back in and swam back to our starting point.I had difficulty just walking back. Fermi was known by his colleagues as the“Pope”. This made it all very clear that he was the supreme authority on all matters.He held this position in all of our minds as an accepted fact. No big deal.Just an accepted realization that he really knew more than the rest of us or anyoneelse involved in our scientific work. Fermi especially liked young people.He, in his position, entertained a lot but preferred to have young people.The top floor of his Chicago house had a large room in which he wouldinvite students to come and square dance, I usually did the calling and a292

Harold AgnewDOCUMENTS ON FERMI’S LIFEgood time was had by all. He and Laura had these parties about once amonth. When he had dinner parties for his peers he always said “ We needto dilute so and so” and “so and so” with some young people”. The “so andso’” are too stuffy. Chicago had an open enrollment system for graduatestudies but required a 3 day written examination to decide one’s future.Choices were, flunk and out, pass with a master’s degree and out, or passwith option for going on for a doctorate, if you could find a faculty sponsor.I was terrified about taking the exam because I felt my peers were muchsmarter than me. [Subsequently 4 of my classmates have received a NobelPrize in physics, and they were not all the really smart ones] The tests weregiven so that those scoring the written results had no idea as to whose papersthey were grading.I kept putting off taking the test but Laura Fermi kept urging me to do so.I went to Fermi and asked what he suggested I read. He said he had no ideabecause he didn’t read much. I asked how he always knew what was goingon. He said people came and told him and explained things to him. Then hesaid, which amazed me, that there were people who said they immediatelyunderstood things but he wasn’t one of those. He said it took him a longtime to understand what people were explaining to him but many times herealized that they really didn’t understand what they were describing to himbut he did. He also volunteered that one who was very quick to say heunderstood even before the person finished was Oppenheimer, but a lot ofthe time Oppenheimer really didn’t understand the technical information theway Fermi understood it. He told me that if you really understood [Fermi’sway of understanding] about ten things in physics you could know almosteverything. I had been getting a weeks lecture on Brillouin zones, which Inever understood, and asked him about it. He went to a small blackboardand in less than 5 minutes developed the whole theory and at the time Ithought I understood it. But as was with most of Fermi’s lectures they wereso clear and so simple that you really thought you understood all but whenone tried to repeat it afterwards on ones own became lost.Very much like eating Chinese food end up very full and satisfied but shortlyvery empty and hungry. Of all his colleagues of his vintage, Fermi’s favoritefor his intellectual ability was Edward Teller. He told me this and years laterLaura Fermi and his daughter confirmed this when I raised the question.Among his young people I believe Fermi thought Dick Garwin was thebrightest and I also believe this even to this day. This is just a short snapshotof my interaction with Fermi.293

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThere are many other stories such as how he saved our nuclear weapon programwhen he came up with the idea that plutonium from Hanford wouldbe different than that produced in a cyclotron and had Segrè confirm hisworry, but I will stop now and show a video I made from a home movieabout two years before his death. Also there is a short segment showing howgood a sport he was.Harold M. AgnewFormer Director Los Alamos Scientific Laboratory, Former President GeneralAtomics, New Mexico State Senator 1955-61, Member US NationalAcademy of Sciences, Member US National Academy of Engineering,Recipient E.O.Lawrence Award, and Enrico Fermi Award from the US AtomicEnergy Commission, Scientific Advisor to the Supreme Allied CommanderEurope (NATO) 1961-1964. Flew as Scientist on Hiroshima Mission August6,1945 with 509 th Composite Group US Army Air Corps, Member Councilof Foreign Relations, Fellow American Physical Society and AmericanAssociation for the Advancement of Science, Adjunct Professor University ofCalifornia San Diego. I received a B.A. in chemistry from the University ofDenver in 1942 and a Masters and Ph.D. from the University of Chicago in1949 (under Fermi).294

Giovanni GallavottiFermi and the Ergodic ProblemThis paper discusses some aspects of Fermi's early work on the quasi-ergodichypothesis, partly in relation to his last work, which showed that the hypothesiswas false in cases of interest to physics.Fermi e il problema ergodicoSi discutono alcuni aspetti del lavoro giovanile di Fermi sull'ipotesi quasiergodica in relazione anche al suo ultimo lavoro dal quale l'ipotesi risulta falsain casi di interesse fisico.295

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEBoltzmannBoltzmann’s ergodic hypothesis became controversial. In a way for the firsttime, perhaps, the description of the World by continuum models, like pointparticles sysceptible of occupying a continuum of positions in a continuumphase space, was replaced by discrete conceptions in an argument that hadmajor physical consequences.Boltzmann viewed the world as discrete and infinitesimal calculus as a toolto approximate sums and ratios whose evaluation was needed in the physicaltheories. Therefore the energy surface consisted of finitely many cells thatcould be labeled and counted and that time evolution simply permuted in asingle cycle: this is the “ergodic hypothesis”. In this context it was natural tosuppose that each cell visited in due time all others: he even estimated thetime for this to happen, for a cm 2 of Hydrogen in normal conditions to beabout (!) 10 1019 · 10 -13 sec (a similar estimate had been made earlier byThomson) [3].Once the hypothesis is accepted together with Boltzmann’s theory of therelaxation times (qualitatively solved in general by the vastity of the“Boltzmann’s sea” [1,2] and quantitatively analyzed in the case of rarefiedgases via the Boltzmann’s equation) the time averages could be computed byaveraging over cells. The latter could then be “conveniently approximated”by the integrals over phase space which have become familiar to all of us andwhich lead to the Boltzmann-Maxwell statistics, following ideas that alsoMaxwell and Thomson developed independently or largely shared.A strict interpretation in the context of classical mechanics of point particlesmoving in a continuum became the hypothesis that a typical trajectorymoving on the energy surface visited all its points: and it seems that mostphysicists and mathematicians followed such an interpretation at least untilthe 1930’s. The manifest impossibility of this, divulged by the influentialreview of the Ehrenfests [4], was pointed out by mathematicians and physicists.And it led to the formulation of a physically nebulous hypothesis calledthe quasi ergodic hypothesis (see footnote 99 in [4]) which basically proposedthat every point of the energy surface, but a set of zero volume, evolved coveringdensely the surface itself.PoincaréIn modern Physics, starting with the 1930’s, the ergodic hypothesisbecame quite different from the quasi ergodic hypothesis (and essentially296

Giovanni GallavottiFERMI AND THE ERGODIC PROBLEMidentical to Boltzmann’s hypothesis). The weaker quasi ergodic hypothesis,nevertheless, is interesting in its own. While it is easy to exhibit importantphysical systems which do not verify the ergodic hypothesis [15], even in themodern sense, it is still an open problem to prove that systems of the type consideredby Fermi generically verify the quasi ergodic hypothesis.One of the main mathematical reasons in favor of the quasi ergodic hypothesisrested, perhaps, on a theorem by Poincaré (see for instance [5]) statingthat a Hamiltonian system very close to an integrable cannot admit constantsof motions depending analytically on the phase coordinates and on the perturbationstrength µ other than the functions of the energy.It is, at first, surprising that in the middle of the storm in which quantummechanics was being conceived Fermi, working in the early 1920’s Göttingen,devoted himself to studying the esoteric (quasi) ergodic problem. Consideringa l -degrees of freedom system, l > 2, with Hamiltonian H 0 + µH 1 whichis a perturbation of an integrable Hamiltonian H 0 he correctly proved [6,7]that, for generic perturbing energy functions H 1 , there could not exist evena single surface of dimension 2l - 2 embedded in the 2l - 1 dimensional energysurface and analytic in the phase coordinates and in µ, for small µ.FermiFermi tried to deduce [6,9] from his theorem the generic validity of thequasi ergodic hypothesis: stating that it would become generically true underan arbitrarily small perturbing force. In fact he defined “quasi ergodic” a systemsuch that any open set σ on the energy surface generates a set of pathswhich cover the whole energy surface (a definition not exactly coincidingwith the one mentioned above). His line of reasoning was the following: ifnot there would exist two open regions whose points had trajectories whichdid not visit the other region and which would therefore be separated by acommon boundary S. Assuming that S is a smooth surface of dimension 2l - 2(to separate into disjoint sets the 2l - 1 dimensional energy surface) dependinganalytically on µ one derives a contradiction with his theorem, just quoted,stating the generic non existence of such surfaces. The assumption is confinedto a footnote “added in proof” at the bottom of the paper.The proof was criticized because the smoothness of the surface was to beproved for the argument to be convincing. Fermi’s answer [12] was not satisfactoryalthough he seemed to consider the objection not very relevantfrom a physical point of view.297

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEWhy did he not continue to investigate the subject until 1954 when, in his lastmajor scientific contribution, he discovered (with Pasta and Ulam) [14] thatindeed the objections raised to the work of his youth were likely to beextremely serious? [15].In order to understand one has to take into account that very likely Fermibecame interested in a proof of the ergodic hypothesis because he was inGöttingen and he was probably involved in the critiques being raised to theattempts of founding quantum mechanics on the adiabatic invariants [18].The adiabatic invariants approach, at the time (1923) under intense analysis,was based on Ehrenfest’s principle which considered systems admittingaction-angle coordinates with cyclic actions and prescribed that the actionintegrals ∫ o γip → ⋅dq → over independent cycles γ i should be integer multiples ofPlanck’s constant h. The principle rested heavily upon the existence of a continuumof models connecting the Hamiltonians of the systems of interest.For instance, in a typical example, the harmonic oscillator and the Kepleriantwo body system can be continuously transformed into each other by consideringthe one parameter family of Hamiltonian functions H µ .1 1 gH µ = – p → 2 + (1 – µ) – ω 2 q →2 – µ –– 0 ≤ µ≤12 2 ⎜q ⎢as the parameter µ varies between 0 and 1. By using the adiabatic invariantsone could, in this case, derive the Bohr-Sommerfeld quantization rules forthe Hydrogen atom from those of the harmonic oscillator (and viceversa).Immediately after the work on the quasi ergodic hypothesis Fermi publisheda series of remarkable papers showing that the approach to quantummechanics based on the Ehrenfest principle led to incorrect results in thecases in which the family of interpolating Hamiltonians H µ was not integrableby quadratures for some intermediate µ: note that one cannot definethe adiabatic integrals ∫ op→ ⋅dq → for the Hamiltonian systems corresponding tosuch µ’s [10,11].Thus it seems likely that Fermi must have considered his work importantas a fundamental critique to the adiabatic invariants approach to quantummechanics (even to an extent warranting a bilingual publication, german [6]and, split in two parts, italian [7,9]. Although he did not achieve a proof ofthe validity of the quasi ergodic hypothesis his result certainly cast a darkcloud over the quantization based on the adiabatic invariants and it strengtheneddoubts already (quietly) raised by Einstein in an earlier paper [13] thatFermi did not know. This might explain also why he did not seem to pay298

Giovanni GallavottiFERMI AND THE ERGODIC PROBLEMmuch attention to the critiques to his work: whether or not it proved thequasi ergodic hypothesis (without the assumption added in proof it did not!)its main part was correct and it made, together with the accompanyingworks, the quantization based on the adiabatic invariants untenable.One can imagine that the very young Fermi, in the austere ambiance of thefamous german university of the early twenties, left to the reader to draw hisown conclusions about the knell that his work rang for the adiabatic principle:perhaps he did not yet feel strong enough to withstand the consequences ofa direct critique to a theory as established as the “early quantum mechanics”:in the quasi ergodicity paper the word “adiabatic invariant” is not even mentioned,neither in the german original nor in the italian versions, see [17].The discovery of stability of non-ergodic behaviorIn discussing the works of Fermi on ergodic theory one has to mentionwhat is perhaps his most important contribution to the subject: namely theeffective lack of ergodicity of classical systems with energy close to theground state (minimum value).The discovery was made via an experimental work that has had a verystrong influence in the years that followed it: the experiment was proposedby Fermi as an application of the new powerful electronic computingmachines. Not only it marked the beginning of a new subject, moleculardynamics, which is becoming more and more important but it also gavestrong evidence that simple systems believed to be ergodic were not such, atleast for practical purposes. A harmonic chain of several (64) oscillators andwith fixed extremes was considered: it appeared quite clearly that in presenceof a small nonlinear perturbation an initial datum in which all the energy wasconcentrated on a single normal mode of the linear system did not evolve insuch a way that energy would become shared among all the modes of the system[14,16]. No equipartition was realized during the times of observation.The result was clearly in contrast with the beliefs of most physicists at thetime who were convinced that over a rapid time scale the energy wouldbecome shared by all the modes. The possibility that the sharing would occurover time scales of enormous size of course could not be excluded: but suchan explanation would undermine the theoretical bases of statistical mechanics.Essentially at the same time Kolmogorov [19] achieved a theoretical andrigorous proof that indeed a generic perturbation of an integrable systemwould be such that in phase space there would be a set of positive volume299

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwhose points would evolve on trajectories that would not fill densely phasespace. This means that, in the modern sense of the word, such systems arenot ergodic. However excluding the 2-degrees of freedom case it remainspossible (and likely) that they verify the quasi ergodic property in the senseof Fermi, i.e. in the sense that the trajectories emanating from any open setin phase space fill densely the energy surface.Strictly speaking the result of Kolmogorov did not apply to the systemsconsidered in the experiments by Fermi and collaborators: and in fact a completetheory of the latter systems is still under investigation although remarkablecases have been understood, see [20] for a review.Therefore the work of Fermi and collaborators remains a landmark in thePhysics literature and, by posing and partially answering a major question,marks the return of the problems of nonlinear mechanics among the interestsof Physicists after they had been for several decades a subject left tomathematicians.REFERENCES01. BOLTZMANN L., Theoretical Physics and philosophical writings, ed. B. Mc Guinness, Reidel,Dordrecht, 1974. See p. 206.02. BRUSH S., Gadflies and geniuses in the history of gas theory, Synthese, 11-43, 1999. See p.28. See also UHLENBECK G.E., “An outline of Statistical Mechanics”, in Fundamentalproblems in Statistical Mechanics, vol. II, ed. E.G.D. Cohen, North Holland, Amsterdam,1968. See p. 3, fig. 2.03. GALLAVOTTI G., Statistical Mechanics, Springer Verlag, Berlin, 1999. See p. 140 and Sec.1 and Sec. 3.04. EHRENFEST P., “Adiabatic invariants and the theory of quanta”, Philosophical Magazine,33, 500-513, 1917. Ristampato in18.05. GALLAVOTTI G., “Quasi integrable mechanical systems”, ed. K. Osterwalder and R. Stora,Les Houches, XLIII, 1984, Phenomènes Critiques, Systèmes aleatories, Théories de jauge,Elsevier Science, 1986, p. 539-624.06. FERMI E., “Beweis dass ein mechanisches normalsysteme im algemeinen quasi ergodischist”, Physikalische Zeitschrift, 24, 261-265, 1923. Reprinted in 8 , paper n. 11a.07. FERMI E., “Generalizzazione del teorema di Poincaré sopra la non esistenza di integrali diun sistema di equazioni canoniche normali”, Nuovo Cimento, 26, 101-115, 1923.Reprinted in 8 , paper n. 15.08. FERMI E., Note e Memorie (Collected papers), Accademia dei Lincei and University ofChicago Press, vol. , 1961, e vol. II, 1965.09. FERMI E., “Dimostrazione che in generale un sistema meccanico è quasi ergodico”, NuovoCimento, 25, 267-269, 1923.10. FERMI E., “Il principio delle adiabatiche ed i sistemi che non ammettono coordinate angolari”,Nuovo Cimento, 25, 171-175, 1923. Ristampato in 8 , lavoro n. 12.300

Giovanni GallavottiFERMI AND THE ERGODIC PROBLEM11. FERMI E., “Alcuni teoremi di meccanica analitica importanti per la teoria dei quanti”,Nuovo Cimento, 25, 271-285, 1923. Ristampato in 8 , lavoro n. 13.12. FERMI E., “Uber die existenz quasi-ergodisher systeme”, Physikalische Zeitschrift, 25, 166-167, 1924. Ristampato in 8 , alla fine del lavoro n. 11a.13. EINSTEIN A., “Zum Quantensatz von Sommerfeld und Epstein”, Verhandlungen derDeutschen physikalischen Gesellshaft, 19, 82-92, 1917. Italian reprint in GRAFFI S., Le radicidella quantizzazione, “Quaderni di Fisica Teorica dell’Università di Pavia”, Pavia, 1993,ISBN 88-85159-09-5.14. FERMI E., PASTA J., ULAM S., Studies of nonlinear problems, “Los Alamos report LA-1940”,1955, printed in 8 , Vol. II, p. 978-988.15. BENETTIN G., GALGANI L., GIORGILLI A., “Boltzmann’s ultraviolet cut-off andNekhoroshev’s theorem on Arnold diffusion”, Nature, 311, 444-445, 1984. AndBENETTIN G., GALGANI L., GIORGILLI A.: The dynamical foundations of classical statisticalmechanics and the Boltzmann-Jeans conjecture, Edited by S. Kuksin, V.F. Lazutkin, J.Pöschel, Birkhauser, 1993.16. FALCIONI M., VULPIANI A., “Il contributo di E. Fermi ai sistemi non lineari: l’influenza diun articolo mai pubblicato”, in Conoscere Fermi, edited by C. and L. Bonolis, p. 274-289,Editrice Compositori, Bologna, 2001, ISBN88-7794-284-3.17. GALLAVOTTI G., La meccanica classica e la rivoluzione quantica nei lavori giovanili diFermi, edited by C. Bernardini and L. Bonolis, p. 76-84, Editrice Compositori, Bologna,2001, ISBN88-7794-284-3.18. VAN DER WAERDEN B.L., Sources of quantum mechanics, Dover, 1968 (this is a collectionof the main papers on matrix mechanics with an important critical introduction).19. KOLMOGOROV N., “On the preservation of conditionally periodic motions”, DokladyAkademia Nauk SSSR, 96, 527- 530, 1954. See also: Benettin, G., Galgani, L., Giorgilli,A., Strelcyn, J.M.: “A proof of Kolmogorov theorem on invariant tori using canonicaltransormations defined by the Lie method”, Nuovo Cimento, 79 B, 201- 223, 1984.20. RINK B., “Symmetry and resonance in periodic FPU chains”, Communications inMathematical Physics, 218}, 665-685, 2001.Giovanni GallavottiBorn in 1941, Mr. Gallavotti received his physics degree from the Universityof Rome in 1963. At the University of Florence, taught the introductory physicscourse (1964-65) and neutron physics (1965-66). Researcher at IHES in Paris(1966-68) and at Rockefeller University in New York (1969-70), associateprofessor of institutions of higher analysis (Rome, 1970-72), full professor since1972 (mathematical methods in physics, rational mechanics, mathematicalphysics, fluid mechanics and advanced mechanics), visiting professor of theoreticalphysics at Nijmegen (1973-74), faculty member at the LinceoInterdisciplinary Centre (1986-89). Received the Italian President's NationalAward in 1997. Member of the Scientific Boards of IHES (1998-2003), and,as of 2000, of ESI in Vienna and the Institut Henri Poincaré in Paris.Author of 180 articles in international journals, numerous monographs, fourbooks in Italian (three of them also published in English translations) and onein English, and 14 monographic entries for the Italian Encyclopaedia.301

Tullio ReggeFermi and General RelativityThe contributions of Enrico Fermi to the theory of relativity are all contained inhis early papers. Paper N. 1, the first one in his collected papers, deals withthe inert mass of a rigid system of electric charges and in particular for aspherically symmetrical one. It turns out that the final result does not agree withEinstein’s principle of equivalence.The riddle is solved in Paper N. 2 where Fermi evaluates the effect of auniform gravitational field on a system of electric charges and recoversagreement with general relativity. Paper N. 3 is the most important one andthe so called Fermi theorem thereby contained is still widely quoted in alltreatises which deal with absolute differential calculus, for instance byJ.L.Synge, (Relativity, the General Theory, Amsterdam 1960). The theorem,among other things, proves the existence of a locally intertial coordinatesystem in the neighbourhood of a timelike geodesic. The paper is related toN. 2. As Persico points out in his comment (p. 17) Fermi ... felt theopportunity of a more systematic treatment of this and othe similar problems,by means of a system of spacetime coordinates particularly fitted to follow thebehaviour in time of phenomena happening in a small spatial region”. PaperN. 8 returns briefly on general relativity.It is evident from his late contributions that general relativity was not the centralelement of interest of Fermi but that he nevertheless felt at ease in it. EmilioSegrè aptly comments in the introduction to the collected works (p. XXV) thatFermi had no difficulty in using abstract mathematics with the most rigorousstandards if he saw it fit for his vision.There is no doubt that his primary interest was physicsand that mathematics was a tool. In spite of this the maturityand power of this early contribution is prodigious.303

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFermi e la relatività generaleIl contributo dato da Enrico Fermi alla teoria della relatività è tutto contenutonelle sue prime pubblicazioni. Il Documento n. 1 “Sulla dinamica di unsistema rigido di cariche elettriche in moto traslatorio”, riguarda la massainerte in un sistema rigido di cariche elettriche ed in particolare un sistemasferico simmetrico, ed i suoi risultati finali sono in netto contrasto con ilprincipio di equivalenza di Einstein.Il problema viene risolto nel Documento n. 2 “Sull’elettrostatica di un campogravitazionale uniforme e sul peso delle masse elettromagnetiche”, in cuiFermi valuta gli effetti di un campo gravitazionale uniforme su di un sistema dicariche elettriche, riconciliandosi con la teoria della relatività.Il Documento n. 3 “Sopra i fenomeni che avvengono in vicinanza di unalinea oraria” è il più importante, e la teoria cosiddetta fermiana ivi contenutaè ancora ampiamente citata in tutti i trattati sul calcolo differenziale assoluto,come ad esempio da J.L. Synge (Relativity, the General Theory, Amsterdam1960). Il teorema, tra l’altro, dimostra l’esistenza di un sistema locale dicoordinate inerziali in un ambito temporale geodetico.L’origine di tale Documento è probabilmente collegata al Documento n. 2,come afferma Persico nella sua relazione (pag. 17): “Fermi …sentì l’esigenzadi una trattazione più sistematica di queste ed altre questioni attraverso unsistema di coordinate spaziali particolarmente indicate a seguire l’andamentonel tempo di quei fenomeni che avvengano in uno spazio limitato”.La pubblicazione n. 8 “Sul peso dei corpi elastici”, si sofferma di nuovobrevemente sulla relatività generale. Appare evidente dai suoi ultimi scritticome la relatività generale non costituisse per Fermi l’elemento centrale diinteresse, cosa che non gli impedì di occuparsene agevolmente.Emilio Segrè afferma nell’introduzione alle sue Opere Complete (pag. XXV)come Fermi non avesse alcuna difficoltà nell’utilizzare la matematica purasecondo standard rigorosi da lui stesso applicati. Nonostante il suo interesseprincipale fosse la fisica e la matematica rappresentasse per lui solo unostrumento, la maturità e la potenza di questi suoi primi contributi sonocomunque prodigiosi.304

Nicola CabibboFermi’s Tentativo and Weak InteractionsI will discuss Fermi’s beta-decay paper, and some of the further work byFermi’s close collaborators, Majorana, Wick, Pontecorvo. I will also discussrecent advances in the understanding of weak interactions, in particular quarkmixing and neutrino oscillations.Il tentativo di Fermi e le interazioni deboliMi soffermerò sulle pubblicazioni Fermiane riguardanti il decadimento beta,e su alcuni lavori posteriori di suoi collaboratori come Majorana, Wick ePontecorvo, nonché sui recenti progressi nella comprensione delle interazionideboli, particolarmente per quel che riguarda la mescolanza dei quark e leoscillazioni neutriniche.305

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntroductionThe December 1933 issue of “La Ricerca Scientifica”, the journal of theConsiglio Nazionale delle Ricerche, contained an article by Enrico Fermi,“Tentativo di una teoria dell’emissione dei raggi beta”, “a tentative theory ofbeta rays” 1 . The title was far too modest: the theory is still valid today, afternearly seventy year.Fermi’s “tentativo” did not have an easy life. According to Franco Rasetti,one of Fermi’s closest friend and collaborator, an english version of the paperwas rejected by Nature as too abstract. Attempts to locate copies of this manuscriptor other documents relating to this episode have failed, but we hopethat new evidence might emerge in the future.Fermi attributed β decay to the action of a new type of force which actsbetween elementary particles which is now called the weak force or weakinteraction. A number of other physical processes can today be attributed toweak interactions essentially in the form presented by Fermi’s paper.The study of weak interaction has led to important discoveries, amongwhich, in the fifties, the violation of specular symmetry (P) and of chargesymmetry, (C). A few years later the study of K 0 mesons led to the discoveryof the violation of time reversal symmetry (T) and of the symmetrybetween matter and anti-matter (CP). The last few months have seen theannouncement of two new example of (CP) violation, one again in thedecays of K 0 mesons, the second in the decay of B 0 mesons, which containa heavy quark of type b.Weak interactions are of great interest because they allow the transformationof one elementary particle into another, thus revealing the intimate connectionbetween different particle types.The study of some problematical aspects of Fermi’s theory has led in thesixties to the formulation of a unified theory of weak and electromagneticinter-action, which contains as limiting cases Maxwell’s theory of electromagnetismand Fermi’s theory of weak interaction.Beta Decay in 1933Of the three types of radioactive emission, two, the α and γ rays, did not1 Reprinted in Note e Memorie – Collected Papers, Vol. I, Accademia dei Lincei and University of ChicagoPress, 1962. Franco Rasetti wrote an interesting introduction to the beta decay papers. An excellenttreatment of the subject is in A. PAIS, Inward Bound, Oxford University Press, 1986.306

Nicola CabibboFERMI’S TENTATIVO AND WEAK INTERACTIONSpose substantial conceptual problems. An α disintegration, such asRa 88226 → Rd 86 222 + He 24(1)is a true dis-integration, a rearrangement of the protons and neutrons presentin the initial Radium nucleus to form the daughter Radon and Heliumnuclei. Many details remained to be clarified, but in 1933 the nature of alphaemission was well understood, and the essential fact were well interpreted byGamow’s successful 1927 theory.In γ radioactivity photons are emitted. Although many details were missingin 1933, this phenomenon was clearly a close analogue of photon emissionin atoms, i.e. a transition between two different quantum states of thesame nucleus.The nature of β radioactivity was only clarified with Fermi’s paper. It waswell known that β rays are electrons, but which was their origin? BeforeChadwick’s discovery of the neutron, the current hypothesis was that nucleiwere composed by protons and electrons. An Helium atom, for instance,would have contained four protons, providing most of the mass, and twoelectrons.In the proton-electron model of the nucleus a β decay would have beensimilar to an α decay, the emission of an electron already present in the nucleus,a true dis-integration.In fact the proton-electron model had failed an important test withRasetti’s determination, in 1929, of the statistics of nitrogen’s atoms, a resultwhose meaning was however fully appreciated later, e.g. in Heisenberg’s1932 paper on nuclear structure. After the discovery of the neutron the transitionto the modern proton-neutron model was very rapid. But if electronsare not present in the nucleus, what happens in β decay?There was in fact a more serious problem posed by β decay: α and γ rays areemitted with an energy equal to the difference between the energies of the initialand final nucleus, so as to guarantee the overall conservation of energy; inβ decay, on the contrary, electrons are emitted, in any given transition, with acontinuous energy spectrum. Niels Bohr was led to propose that energy is notexactly conserved in β decay. A very strange proposition, but it originatedfrom the father of atomic physics, and could not be easily discarded.The solution of this second puzzle was found by Wolfgang Pauli: in β decaya second particle was emitted together with the electron, so that the twowould share in different ways the available energy. This would certainlyexplain why the electron appears with a range of energies. The “second par-307

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEticle” would have been neutral, and available data excluded that it could bea photon: a new particle, then, never observed before.Pauli was very prudent with his idea, which he probably considered tooextreme, and he did not publish it. He wrote of the idea to close friends inthe famous “Dear radioactive ladies and gentlemen” letter, where he calledthe new particle a “neutron”. He discussed it in the corridors of physics conferences,but never officially.Pauli discussed his idea with Fermi in 1931, during the Rome conferenceon nuclear physics, and on this occasion Fermi proposed 2 that the correctname was not “neutron”, but “neutrino”, more suited to a very light particle.The two must not have discussed the matter again; while Pauli readilyadopted the name proposed by Fermi, Fermi himself kept using the nameproposed by Pauli.In his talk at the International Conference on Electricity (Paris, 1932) he said:“... Si potrebbe pensare ad esempio, secondo un suggerimento di Pauli,che nel nucleo atomico si trovino dei neutroni che sarebbero emessi contemporaneamentealle particelle beta. ...” (We can think that, accordingto Pauli’s suggestion, the atomic nucleus contains neutrons which areemitted together with the beta particles).To a question from the audience he answered that these “neutrons” couldnot be those recently discovered by Chadwick, but much lighter particles. In1932 Fermi was still thinking in terms of the emission of particles alreadypresent in the atomic nucleus. The 1933 paper would have proposed a radicallydifferent solution.Fermi’s theory of Beta DecayChadwick’s neutron expelled the electron from the atomic nucleus, and leftlittle space for Pauli’s neutrino. The modern view of the nucleus had its officialsanction in the Solvay Conference in october 1933, where Heisenberg’stheory was widely discussed. It is generally assumed that Fermi started workingon his beta decay theory just after this conference, completing the workin just two months. I frankly suspect that he must have started consideringthe problem much earlier than that. His interest in the subject is well shownby his talk in Paris the previous year (although he was not then able to pro-2The Pauli hypothesis had already been discussed by Fermi with his collaborators. According to a recollectionby E. Amaldi, he had proposed the name neutrino during one of these discussions with Fermi.308

Nicola CabibboFERMI’S TENTATIVO AND WEAK INTERACTIONSpose the correct theory), and the proton-neutron model of the nucleus hadbeen essentially accepted in Rome due to Majorana’s unpublished work.Majorana had turned down Fermi’s proposal to present his work at theSolvay meeting.At the core of Fermi’s theory is the idea that the electron and neutrino arenot preexisting in the nucleus, but are created anew at the time of their emission.To accept this idea one would have to renounce the well-establishedone that an electron is a particle endowed with a certain amount of materialsolidity and persistence.There was of course the example of the photon, a particle which is createdwhen light is emitted, and destroyed when light is absorbed. These processesare well understood in the quantum theory of the electromagnetic field,developed by Dirac soon after the birth of Heisenberg’s quantum mechanics.That this formalism could be applied to the creation and absorption of anyparticle, electron included, had been shown since 1927 by Jordan and Klein.The formalism of quantized fields, proposed by Jordan and Klein for all particles,must have struck a note very close to Fermi’s scientific interests . Thetheory of quantized field naturally lead to the description of particles which areidentical in the quantum sense, particles which must necessarily obey either theBose-Einstein statistic, as photons do, or, as is the case with electron, the statistiche had himself discovered in 1926, the Fermi-Dirac statistics.Fermi had not used the Jordan-Klein formalism in his famous lectures onQuantum Electrodynamics: it was not needed for his discussion of processeswhere electron are not created or destroyed, and Fermi was very thrifty in hischoice of tools. But when the need arose, the tool was ready.According to Fermi the beta decay of a nucleus is due to a new type of interactionwhich causes the transformation of a neutron inside the nucleus into aproton, with the simultaneous production of an electron-neutrino 3 pair:N → P + e + ν (2)Fermi introduced the hypothesis that this process is quite analogous to thatin which a proton emits a photon,P → P + γ. (3)To the photon emitted in eq. 3 corresponds the electron-neutrino pair in eq. 2.3According to present conventions the neutral particle emitted in beta decay together with a negativeelectron is an antineutrino. In this paper I use the term neutrino to denote either a neutrino or an antineutrino,except in the following when I will touch on Majorana’s neutrino theory.309

PROCEEDINGS OF THE INTERNATIONAL CONFERENCETo shed some light on the analogy Fermi had in mind we may look at theproton in eq. 3 as a radio antenna: the transition of the proton from a higherenergy quantum state to a lower energy state activates an electric currentwhich causes the emission of electromagnetic waves – the photon. In Fermi’sview what happens in beta decay, eq. 2, is that the transformation of a neutroninto a proton activates a new kind of current, today called a weak current,which causes the creation of the electron-neutrino pair.The analogy between beta decay and photon emission is both a productiveone and a very happy one. It is productive, because it allowed Fermi to proposea definite mathematical form for the interaction giving rise to betadecay 4 , and a very happy one because this form proved to be essentially correct,the only needed modification having been due to the discovery of parityviolation in 1956.According to the modern view, a more precise similitude could be establishedbetween beta decay and electromagnetic induction: a variable currentin a circuit generates an electromagnetic field which can than induce a currentin a second circuit – the principle of operation of electric transformers.In Fermi’s theory we can see a kind of short-circuit between the weak currentof the neutron-proton transition and a corresponding current whoseactivation lead to the production of the electron-neutrino pair.In unified theories, which reached maturity at the end of the sixties, the relationshipbetween weak and electromagnetic interaction is much closer thanFermi could have suspected. As in the case of electromagnetic induction, theinteraction between weak currents is mediated by a field, whose quanta, theW, have been discovered at the beginning of the eighties. Fermi’s analogy hasbeen proven correct at a deeper level, since we now know that weak and electromagneticinteractions are different manifestation of the same force, nowcalled the electro-weak force. Since the W has a very large mass, Fermi’s originaltheory remains in most case an excellent approximation.In the 1933 paper Fermi presented the mathematical structure of the theoryas well as its application to the study of beta radioactivity. He was able toshow that beta decays can be subdivided in two classes: the allowed decays,which can proceed in the limit where one neglects the motion of nucleons4 The analogy led Fermi to choose a “vector” form for the new interactions. Although Fermi did not discussin his paper the general case, which was published later by Uhlenbeck and Konopinsky, many –among them Wigner – were convinced that he was aware of this possibility, but choose the most attractiveform.310

Nicola CabibboFERMI’S TENTATIVO AND WEAK INTERACTIONS(proton and neutron) within the nucleus, and the forbidden ones, whichdepend on this motion, and proceed at a rate which is roughly a hundredtime lower than that of allowed decays. Only with Fermi’s work the wellknown fact that certain beta decays have a much larger transition rate thanothers found a quantitative explanation.An important result of Fermi’s work is the determination of the energeticdistribution of the emitted electrons. Fermi was able to show that the studyof the high-energy end of this distribution can be used to establish an upperlimit to the mass of the neutrino, and that available data favoured a very smallneutrino mass. The method proposed by Fermi has in recent years led to thecurrent limit (≈10eV, 50000 times smaller than the mass of the electron) onthe mass of the neutrino emitted in beta decay.Fermi’s theory contains a single free parameter, today called the Fermi constant,G, which determines the strenght of weak interactions, and can bedetermined by measuring the decay rate of one of the allowed decays. G hasthe dimension of the inverse of a mass squared – with good approximationG≈(300 M P ) –2 ,where M P is the mass of a proton. The large mass appearingin the denominator, 300 M P , is the reason why Fermi interactions are veryweak in low energy phenomena, which include all of the radioactive decays.The actual strenght of Fermi’s weak interactions increases with energy, and amore complete theory, such as the modern unified theory, becomes essentialfor processes of very high energy.Weak interactions after Fermi’s paperWhile Fermi himself was not actively devoted to the exploration of weakinteractions after 1934, many of his students and collaborators, both in Italyand the United States, gave important contributions, among whom G.C.Wick, B. Pontecorvo, E. Majorana, T.D. Lee, C.N. Yang, M. Gell-Mann, R.Garwin, J. Cronin, together with many others.Gian Carlo Wick applied the theory to beta decays with positron emission,and predicted the possibility of K capture, where a nucleus, instead of emittinga positron absorbs one of the inner electrons in the atom, so that only aneutrino is emitted.Bruno Pontecorvo studied inverse beta decay, the process where a neutrinois absorbed by a nucleus and an electron is emitted, and proposed thatthis process could be used to establish the existence of the neutrino.Pontecorvo’s method was in fact applied in the Cowan-Reines experiment in311

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1956. In later years Pontecorvo proposed to carry out experiments withbeams of high energy neutrinos, an experimental program which was developpedstarting from the sixties and which led to important discoveries,among which the existence of different neutrino types associated with thedifferent leptons – the electron, muon and tau.The greatest contribution by Bruno Pontecorvo is his proposal of a newphenomenon – neutrino oscillations, where a neutrino can oscillate betweendifferent identities, an electron-neutrino transforming for example into amuon-neutrino or a tau-neutrino 5 . Recent years have seen the discovery oftwo different examples of neutrino oscillations, the first arising in muon-neutrinosproduced in the atmosphere by cosmic rays, the second in electronneutrinosemitted from the Sun. Neutrino oscillations are becoming one ofthe hottest items in High Energy Physic research.Ettore Majorana proposed an alternative neutrino theory, where neutrinoand antineutrino coincide. This idea, reformulated in the light of the discoveryof parity violation (T.D. Lee and C.N. Yang, 1956), remains very muchalive today, and is invoked to explain the existence of the very small neutrinomasses implied by the discovery of neutrino oscillations.The discovery of parity violation in 1956 led to the modernly acceptedform of the weak interaction theory. The new form, the so called V- A theory(R. Feynman and M. Gell-Mann, Marshak and Sudarshan, 1958) is veryclose to that proposed by Fermi: beta decay and other weak interactionprocesses are still due to the interaction of two currents 6 , but these currentsdo not have a definite behaviour under specular reflection. The new developmentsvindicated the correctness of Fermi’s analogy between weak andelectromagnetic processes, and at the same time concentrated the attentionon the structure of the weak currents. In carrying the analogy to theextreme, Feynman and Gell-Mann proposed a strict relationship betweencertain terms in the weak current and corresponding terms in the electromagneticcurrent, leading for instance to the existence in beta decay of a phenomenonsimilar to magnetism, the weak magnetism, which was succesfullyidentified a few years later.The impact of Fermi’s 1933 paper goes well beyond the study of weakinteractions. Fermi’s paper was the first in which quantum field theory wasused in the modern sense, and it must thus be considered the first modern5 In his original proposal Pontecorvo actually considered neutrino-antineutrino oscillations.6 We now know that this interaction is mediated by a field whose quanta are the W bosons.312

Nicola CabibboFERMI’S TENTATIVO AND WEAK INTERACTIONSpaper on the physics of elementary particles. Among the many instances ofthe influence of this paper on subsequent work, one that stands out is certainlyYukawa’s paper on the meson theory of nuclear forces.Quark mixing, the unified theory, the violation of CPThe discovery of strange particles in 1953 greatly enlarged the range ofphenomena arising from weak interactions. The main decay mode of particlessuch as the K mesons or the hyperons (Λ,Σ,Ξ) do not involve the emissionof electron neutrino pairs, e.g.K + →π+ + π 0 , Λ→ P+ π – (4)a new kind of interaction between weak currents. The new particles also haddecay modes similar to the ordinary beta decay (eq. 2), e.g.Λ → P+e – +ν, (5)The beta decays of strange particles posed a very annoying problem, in thatthey seemed to be well described by Fermi’s theory, but with a constant G′substantially smaller than the one determined from ordinary beta decay, G′≈0.2 G. This result ran against the generally accepted belief, inspired byFermi’s analogy, that the strenght of weak interactions should be, as is thecase for electromagnetic forces, universal in nature. I solved this problem in1963 by proposing that in fact weak interactions are characterized by a singleuniversal Fermi constant, but that their strenght is in effect shared inunequal terms between processes involving the usual particles – ordinarybeta decay – and those involving strange particles. This sharing is determinedby a new constant, θ and is essentially a quantum phenomenon, a mixing ofnormal and strange particles as acted upon by weak interactions.The mixing phenomenon has a simple expression in the language ofquarks. Beta decay (eq. 2) is due to a transformation of a d quark into an uquark, while the beta decay of strange particles (eq. 5) is due to the correspondingtransformation of an s quark, the elementary processes being in thetwo cases:d → u + e – + ν, s→ u + e – + ν (6)Since the two transitions lead to the same final state, there must be a linearsuperposition of the two initial state which maximizes the transition amplitude,corresponding to a transition313

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE(cos(θ)d + sin (θ)s) → u+ e - + ν, (7)so that the Fermi constants for the two decays would be in the ratiocos(θ)/sin(θ). My proposal of the weak mixing phenomenon led to detailedpredictions on different decays of strange particles, which have been checkedin a succession of experiments, lastly in 1998 when a team led by R. Winstonat the Fermi Laboratory near Chicago was able to study in detail the betadecay of the Ξ 0 hyperon.An essential ingredient in the transition to the modern unified theoryappeared in 1969 when S. Glashow, J. Iliopoulos and L. Maiani showed thatcertain difficulties in the theory could be eliminated by the existence of afourth quark, the charm quark, c, with clearly specified weak interactions.The early seventies saw impressive experimental results: the discovery of thefirst particles containing the charm quark, and that of an entirely new formof weak interactions, the neutral current interaction, the hallmark of the unifiedmodel. The triumph of the unified model was sanctioned with the discovery,in 1982, of the W and Z bosons. In the course of the last decadeexperiments at the LEP e + e - collider at CERN have collected an impressiveset of high precision checks of the unified electro-weak theory.The mixing story has an interesting sequel. In 1973 Kobayashi andMaskawa noted that if six different types of quarks exist (only four whereknown at the time) the mixing phenomenon I had proposed would offer anexplanation for the violation of the CP symmetry observed in 1964 by J.Cronin and V. Fitch in the decay of K 0 mesons. The mixing among six quarktypes is described by a matrix, the CKM matrix, whose elements determinethe amplitude and phase of the possible quark transitions caused by weakinteractions. A non-vanishing phase in one or more of the matrix elementleads necessarily to the violation of the CP symmetry. It turns out that CPviolating phases in the CKM matrix are closely interconnected and determinedby a single parameter, so that the observation of CP violation in theK-meson decays leads to definite predictions for the CP violation which canbe observed in other transitions, such as those which involve the heavierquarks.The credibility of this proposal was boosted by the discovery, in 1976, of afifth quark, the b, known as beauty quark. The sixth, the top quark, was discoveredin 1996. This summer two different groups working at Stanford inthe USA and at KEK in Japan have verified a crucial prediction of the theory,the existence of well defined violation of the CP symmetry in the decay314

Nicola CabibboFERMI’S TENTATIVO AND WEAK INTERACTIONSof B 0 mesons. The exploration of CP violation phenomena represent todaythe top priority in the study of weak interactions phenomena.The discovery of two different instances of neutrino oscillation opens up alarge new chapter in the physics of weak interactions. Neutrino oscillationsare in fact described by a mixing matrix which is the analogue of the CKMmatrix for quark mixing. In 1978 I noted that neutrino oscillation can displayCP violation phenomena, and that in fact CP violation represents a rulerather than the exception. Unravelling the subtleties of neutrino oscillationwill require a protracted effort which is just now beginning.Nicola CabibboCabibbo is Professor of Elementary Particle Physics at the Roma University “LaSapienza”. He is President of the Pontificia Accademia delle Scienze. He hasbeen President of the Istituto Nazionale di Fisica Nucleare (INFN) and of theEnte per le Nuove tecnologie, l’Energia e l’Ambiente (ENEA). He discoveredthe phenomenon of “quark mixing” in which a new fundamental constantappears: the “Cabibbo angle”. Besides the field of the elementary particleshe has obtained important results on the interaction of high energy electromagneticradiation with crystals and on the trapping of magnetic flux quantain superconductors. He has given important contributions in the realizationof the parallel supercomputers now called APE. He is member of many academiesin Italy and abroad.315

Jay OrearEnrico Fermi, the ManExcerpts from some documentsOne of the purposes of this talk is to give the audience a feeling for EnricoFermi, his personality, sense of humor, etc. by making use of some of mymemories plus the few recordings that are available of him via audio tape andfilm. Those who have never seen Fermi alive can get an idea of what he waslike from the following sources: (1) the film The World of Enrico Fermi, (2) thevideo of the 10th anniversary of the first nuclear chain reaction produced by SeeIt Now of CBS TV news, (3) the audio tape of Fermi’s lecture entitled Physics atColumbia University, The Genesis of The Nuclear Energy Project, and (4) Fermi’spersonal notes and slides on his talk as retiring president of the AmericanPhysical Society in Jan. 1954. Items (1) and (2) contain live speeches by Fermi.Also I will show quotes and TV clips from a day-long symposium on Fermi heldat Cornell University on Oct.14, 1991. These speakers knew him first hand andcame to similar conclusions as what Fermi was like as a person. I will give someexamples of Fermi’s famous “intuition” and his remarkable sense of humor.317

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEL’uomo Enrico FermiEstratti da alcuni documentiUno degli scopi di questa relazione è dare agli ascoltatori uno spaccato dellasua personalità e del suo senso dell’umorismo attraverso alcuni dei miei ricordie delle registrazioni su nastro e video. Coloro che non hanno mai visto Fermida vivo possono farsene un’idea dal film “Il mondo di Enrico Fermi”, dal videodel decimo anniversario della realizzazione della prima reazione a catena,prodotto dalla See It Now della CBS Tv News, dalla registrazione su cassettadella relazione di Fermi “La Fisica alla Columbia University, Genesi delProgetto Energia Nucleare”, dalle note di Fermi e dalle slide del suo discorsodi addio dall’incarico di presidente della Società Americana di Fisica nelgennaio del 1954. Il film ed il video contengono discorsi dal vivo di Fermi.Mostrerò inoltre clip ed interventi tratti da un simposio su Fermi tenutosi allaCornell University nell’ottobre del 1991. Gli oratori lo avevano conosciuto dipersona e sono arrivati alle medesime conclusioni nel formulare un giudizio suFermi come persona. Fornirò anche alcuni esempi della famosa “intuizione” edel notevole senso dell’umorismo di Fermi.318

Jay OrearENRICO FERMI, THE MANIntroductionOne of the purposes of this talk is to give a feeling for Enrico Fermi theman, his personality, creativity, intuition, sense of humor, how he related tostudents as well as being a great scientist and teacher. The approach is tomake use of my first hand memories and experiences as well as those of others.Some of his close friends have exchanged anecdotes and have spoken atmeetings devoted to Fermi. There have been symposia, dedications, birthdaycelebrations and 3 reunions of his former grad students. Much of such materialhas gone unpublished. I have had the privilege to be (a) one of his lasttwo grad students and postdocs, (b) the primary organizer of a Fermi symposiumat Cornell University on Oct. 14, 1991, (c) the organizer of two ofthe three Fermi student reunions and (d) a speaker at 4 of the 100 th birthdaycelebrations in 2001. So I am in a special position to put together newmaterials on Fermi. If these various first hand contacts come to commonconclusions about Fermi’s characteristics, then it is likely that those conclusionsare correct. After the Cornell symposium several attendees suggestedthat I edit these new materials into a book before they were forgotten.Fortunately it was all video taped by the Cornell physics department and inmy retirement I have finally found time to get it transcribed and and see howit fits in with other sources of knowledge about Fermi. The two main sourcesof similar material are the biographies by Laura Fermi and Emilio Segrè. Myapproach is mainly that as seen by a grad student and postdoc, whereas LauraFermi’s approach is as a wife and Segrè’s relates more to his earlier career.The Cornell Fermi Symposium, Oct. 14, 1991In the early 1990’s those most close to Enrico Fermi were rapidly dyingoff; e.g., Laura Fermi, Herb Anderson, and Leona Marshall. A few otherswere alive, but some of those were no longer capable of giving a public lecture.By 1991 many of us felt that Fermi’s contribution to the world was soexceptional that it should be well documented by first hand observers. Ourgoal was to invite all those close acquaintances before it was too late. Theoccasion of the 1991 Bethe lectureship at Cornell University provided aunique gathering of close first hand observers. Dick and Lois Garwin, Hansand Rose Bethe, Bob and Jane Wilson, Val and Lia Telegdi, Boyce and JaneMcDaniel and Jay Orear would all be at the same place at the same time andthat would be October 1991 in Ithaca, NY at the time of Dick Garwin’sBethe lectureship. Garwin agreed that it would be a good idea to invite the319

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEsurviving Fermi acquaintances and spend one day of Garwin’s Lectureshipsharing our memories of Fermi. Since I was the chairman of the BetheLecture Committee, I was able to make the arrangements. In our early planningwe invited Carl Sagan to be the master of ceremonies. Orear, Garwinand Sagan did most of the planning and organizing. We tried to invite allwho had known Fermi personally and most of them were able to come. Theprogram was as follows:WELCOME DALE CORSON, CHANCELLOR 9 AMINTRODUCTION CARL SAGAN 9:10PILGRIMAGES TO ROME HANS BETHE 9:30FILM AND AUDIO CLIPS JAY OREAR 11THE FOUNTAIN IN ROME JOE MCEVOY 11:20EXPERIMENTS IN THE ‘40’S AL WATTENBERG 11:35LUNCHNOON-2 PMCOLUMBIA, LOS ALAMOS HAROLD AGNEW 2 PMPRE-CHICAGO YEARS BOB WILSON 2:15THE FERMI FAMILY JANE WILSON 2:35FERMI AT CHICAGO VAL TELEGDI 2:50CHICAGO – LOS ALAMOS DICK GARWIN 4:10FERMI & TECHNOLOGY JOHN PEOPLES 4:30LOS ALAMOS INVENTIONS PERCE KING 4:45RECEPTION AND DINNER BREAK 5:45A DIFFERENT PERSPECTIVE NELLA FERMI 8:00PANEL DISCUSSION ROSENFELD, ET AL. 8:30I think all the speakers came to the same assessment of Fermi as expressedby Val Telegdi: “None of the great scientists who worked at Chicago everhad a greater impact on his immediate and world-wide surroundings thandid Enrico Fermi. Nobody in the history of modern physics possessed greaterversatility than he. He had just as great achievements in pure theory as inconcrete experimental work. He could with equal ease solve abstract problemsor design and build with his own hands astonishingly useful experimental‘tools’.... To these qualities he added those of an exceptionally lucidlecturer and expositor. As well as an active and patient thesis supervisor. …But it defies the bounds of human inspiration to speculate that any otherman or woman might have played Fermi’s role as a teacher in the broadersense of this term. Through the influence of his students, Fermi effectively320

Jay OrearENRICO FERMI, THE MANrevolutionized the training of students in the United States and one hopes inthe whole world”.This summary of Telegdi’s must be correct if so many independently-mindedfirst-hand observers would come to the same conclusions as they did atthis symposium. I also feel, as does Telegdi, that scientists all over the worldare being exposed to Fermi’s way of looking at science and doing science. Asimilar and even stronger appraisal of Fermi was expressed by our first speaker,Hans Bethe.He said:“My conversations with Fermi showed me a completely new approach tophysics. I had studied with Sommerfeld, and Sommerfeld’s style was tosolve problems exactly. You would sit down and write down the differentialequation. And then you would solve it, and that would take quite along time; and then you got an exact solution. And that was very appropriatefor electrodynamics, which Sommerfeld was very good at, but itwas not appropriate at all for nuclear physics, which very soon entered allof our lives. Fermi did it very differently, and Dale Corson alreadydescribed it very well, namely he would sit down and say, “Now, well, letus think about that question”. And then he would take the problem apart,and then he would use first principles of physics, and very soon by havinganalyzed the problems and understood the main features, very soon hewould get the answer. It changed my scientific life. It would not havebeen the same without having been with Fermi; in fact I don’t knowwhether I would have learned this easy approach to physics which Fermi practicedif I hadn’t been there”.Another sign of Fermi’s strong positive influence on his students and othersis the large number who became Nobel Prize winners. There were Leeand Yang for the correct theory of non-conservation of parity, OwenChamberlain for the discovery of the antiproton, Jack Steinberger for themuon flavored neutrino, and Jerry Friedman for measurements of the quarksin electroproduction. Dick Garwin was also a student of Fermi and he led theexperimental discovery of parity violation in pion-muon and muon-electrondecay. The Nobel Prize has not been awarded for this, but it certainly shouldhave. Jim Cronin was formally a grad student of Sam Allison. However hisoffice was next door to Fermi’s office and he frequently visited with us andattended Fermi’s courses. Cronin received the Nobel Prize for the discoveryof CP violation. Maria Mayer was not a Fermi student, however she was ayoung faculty member who consulted and worked with Fermi. She gives321

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEcredit in her paper on the shell model to Enrico for supplying key ideas. Ithink it is fair to say that the shell model is a joint product of the two of them.Back in Fermi’s Italian days Emilio Segre was a student and Hans Bethe wasa postdoc. Both have received the Nobel Prize. This is a total of 10 followersof Fermi receiving Nobel Prizes in a short period of time. I don’t knowof any other physicist who has left such a strong mark on his followers. A possible11 th is Murray Gell-Mann who joined Fermi on the Chicago faculty asa young instructor; Millie Dresselhaus has told me the story of how Fermi ata party had patted Murray on the back and predicted that he will become aNobel prizewinner.I think the probability that an existing Nobel prizewinner give birth toanother winner is less than 1/10. So if this is a purely random process, theprobability of one winner giving birth to 10 other winners would be onetenth to the 10 th power or one in ten billion which is essentially impossible.The explanation lies in the fact that Fermi was the best trainer or teacher ofthem all.I was asked at the time of the Cornell symposium to edit a book presentingthe dozen or so invited talks. The book that has evolved is one thatattempts to reveal the real person, his personal traits, his sense of humor, hisfamous intuition and creativity. I have chosen those talks which help revealFermi’s personality and I have devoted a chapter to each such speaker. Eachtalk is verbatim from the Cornell video tapes. I have at times added somecomments of my own. This first part has evolved from my Cornell talk withconsiderable additional material and analysis consistent with the above goals.I am very grateful to the other speakers who so kindly let me use their papers.Also I wish to thank Cornell University and its Physics Department for theirsplendid cooperation in making the 1991 Symposium such a great success.I have been invited at least 7 times to give talks about Enrico Fermi. Inthese talks I have drawn upon some of the following audio and video sources:(1) the 50 minute film The World of Enrico Fermi produced by Gerry Holtonof Harvard, (2) the video of the 10 th anniversary of the first nuclear chainreaction produced by See It Now of CBS TV news, (3) the audio tape ofFermi’s 1954 lecture entitled Physics at Columbia University, The Genesis ofThe Nuclear Energy Project, (4) Fermi’s personal notes and slides on his talkas retiring president of the American Physical Society in Jan. 1954, and (5)To Fermi – With Love, an audio recording produced by Argonne NationalLab making use of 16 friends of Fermi plus a commentator. The video See ItNow contains live speeches by Fermi, Arthur Compton, Leo Szilard, and322

Jay OrearENRICO FERMI, THE MANLeona Marshall. Both videos show a re-enactment of the famous phone callof Arthur Compton to Vanover Bush which gave the good news toWashington using the code: “The Italian Navigator has safely arrived in theNew World”.My first meetings with FermiMy first course with Fermi was Quantum Mechanics taken in the FallQuarter of 1947. I was just one face out of many. But I really met him in amore unconventional way. That same Quarter I also had registered for aphysical education course called Social Dancing. Early in the course one ofthe coeds in the class invited me to a dance party at a girlfriend’s house. Aswe were walking to the house that night she happened to mention the nameof her girlfriend as Nella Fermi, an art major. I asked whether her friend wasthe daughter of the Fermi. Being an art major, my date had never heard ofEnrico Fermi. But once I entered the door, I was greeted by the warm faceof my quantum mechanics instructor. Fermi did recognize my face and heasked me what I thought of his quantum mechanics course. The party was asquare dance with Harold Agnew as the caller. Many were Nella’s friends andEnrico’s co-workers. I was an indirect guest of Nella and not Enrico. I wasinvited as a friend of a friend of Fermi’s daughter. These Fermi square danceswere held once a month. I was better than the average square dancer. Fromthen on I was on the guest list of the Fermi family. The guest list was workedout by Nella, Laura, and Enrico. Harold Agnew did the calling and suppliedthe dance records. Both he and I have the impression that Nella and herfather enjoyed working together in organizing those parties.I can give an idea of what a good sport Enrico was by relating one experienceat those monthly parties. Sometimes between the sets of dancing, therewere party games. I proposed a group version of Twenty Questions. I suggestedthat the guesser be one of the best logical thinkers. So Enrico waschosen and he gladly agreed to step out of the room. Then I proposed to therest of the crowd that we not choose any object for him to guess, but insteadwe answer “yes” if his guess ends in a vowel, “no” if his sentence ends in aconsonant and “sometimes yes and sometimes no” if the sentence ends in a“y”. So we called Enrico back into the room and stood in a circle aroundhim. He could choose anyone in the circle to answer his first yes or no question– and so on. He rather quickly realized that he should ask some redundantquestions and then he remarked: “I think you have made up a story323

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwith some built-in contradictions”. I replied to him: “How could we allcome up with the same crazy story and be in complete agreement with eachother?” He never did discover the vowel-consonant code and finally had togive up.Not much later by coincidence I encountered Enrico skating by himself ata University ice skating rink. He greeted me and it seemed only natural tojoin him. It was clear that he enjoyed young people and we got to know eachother fairly well in this and subsequent tête-à-têtes on ice. It was not beneathhim to associate freely with students and to treat them as equals. In fact Ithink he enjoyed young physics students more than some of his older colleagues.Another example of his enjoyment of young people was that he ate lunchin the large student cafeteria (the Hutchinson’s Commons) rather than theMen’s Faculty Club where most of his fellow faculty members ate. The centerlong table at the student cafeteria became known informally as the Fermitable; however anyone was welcome. Several of those who frequented thattable later became Nobel Prize winners. In the Chicago physics departmentthe younger grad students felt that some of the older grad students (like Lee,Yang, Chew, Goldberger, Garwin, Wolfenstein, Steinberger, Rosenbluth)were better teachers on the whole than the faculty at that time (except, ofcourse, for Fermi who was clearly the best). Fermi was a modest person andliked to be treated as one of the crowd. Just to give one example of his modesty,even though one of his many great achievements was the discovery ofFermi statistics, he always referred to it as “Pauli statistics”.My coursework with FermiMy next Fermi course a year or so later was when he first taught NuclearPhysics at Chicago. I had been studying and working problems with classmatessuch as Art Rosenfeld and Bob Schluter. We had a system of refiningour classroom notes together and we realized that with a little extra effort,we could type them on mimeograph stencil sheet masters and make our classnotes on nuclear physics available to the entire department. All three of ushad training in touch-typing. The department chairman liked our proposaland offered to pay for the materials and we would provide free labor. Duringthe first few days of preparing the wax stencil sheets my father suggested thatwe switch from mimeograph to photo-offset. Then it would be especiallyeasier to make the many drawings and equations. My father recommended a324

Jay OrearENRICO FERMI, THE MANfirm in Michigan that charged almost the same as the mimeograph process.Whenever we got stuck we usually consulted T.D. Lee or Frank Yang. Onlywhen their response was not satisfactory did we consult Fermi. As one mightexpect, in those rare cases when Lee and Yang could not understand a partof the lecture, then neither did Fermi. Fermi’s office door was always wideopen and any stranger or friend was always welcome to enter (as long as heor she observed the no smoking sign on his desk).Many have remarked on how simple Fermi made things seem in his lectures.But then after the lecture it was not so simple to reconstruct his reasoning.I do not blame this on any over-simplifying on the part of Fermi. Itis because understanding of physics requires many successive steps of not tooobvious reasoning. For this reason Art, Bob and I would occupy a nearbyempty classroom immediately following each Fermi lecture and try to makesure that we each really understood the lecture we had just heard. It usuallytook us more than an hour to convince ourselves that we understood theone-hour lecture.When we made the choice to switch over to the easier and superior systemof photo-offset we were not aware of another advantage: now the number ofcopies could be unlimited rather than restricted to about 500. It quicklybecame clear that the “whole world” wanted copies of these Fermi lecturenotes. No nuclear physics book of this breadth or talent had yet appeared onthe market. Fermi’s contract with the University of Chicago required thatany outside money he might earn must be given to the University. So the distributionand sales now were delegated to the University of Chicago Press.They paid me $333.34 and Rosenfeld and Schulter $333.33 each for ourservices. As Telegdi has pointed out, this way of teaching the whole world isjust one of the ways Fermi has left his mark on almost all physicists.Teaching of the Fermi approach was not restricted to the West. The U. ofChicago Press edition was copyrighted 1950, but a Russian language editionappeared in 1951 that was in violation of international copyright agreements.It was in widespread circulation in Eastern block nations. In fact a radicalChicago student who went to a Moscow peace conference brought back acopy for me.A second-order effect that reached an even larger audience was a collegetextbook entitled Fundamental Physics by Jay Orear, published in 1961. Iwrote in the Preface: “My greatest debt is to Enrico Fermi, who not onlytaught me much of the physics I know, but also how to approach it. As ateacher, Fermi was well known for his great ability to make the most difficult325

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtopics seem beautifully simple in a clear, direct way with little mathematics,but much physical insight. The goal I have been aiming at is to try to presentthe spirit and excitement of physics in the way that Fermi might havedone”. This first college physics textbook used no calculus. But 8 years laterI wrote a second more advanced version which did teach calculus along withthe physics.I have one more personal example of how Fermi left his mark on the entireinternational physics community. Fifty years ago (or 2 years before Fermi’sdeath) most physicists were not very knowledgeable about statistical inference.In my thesis I had to find the best 3-parameter fit to my data and alsothe errors of those parameters in order to get the pion-proton phase shiftsand their errors. Fermi showed me a simple analytical method. I spent thesummer of 1958 working with L. Alvarez and one of my assignments was towrite what I had learned from Fermi about statistics as a UCRL report.These statistics notes were revised in 1982 as a Cornell preprint. Countingboth editions, thousands of copies were distributed all over the world at nocost to scientists living in both sides of the iron curtain.Here is one last anecdote of the grad student days where Fermi was treatedas one of the gang. In those days the University of Chicago neighborhoodwas not as safe as one would like. Even Fermi’s son Guilio had been attacked.And so had my brother. Art Rosenfeld and I had done some “research” ontear-gas guns which were disguised as fountain pens. We discussed things likethat with Fermi and he agreed that a surprise object which could incapacitatethe attacker would be of some advantage. So we ordered 3 such kits by mailfor us. As soon as they arrived, Fermi took his into his machine shop and hemodified the trigger mechanism so it would have a quicker response. Art andI were satisfied with the original design and we had some worries thatFermi’s modification might some day backfire in his pocket.In that same period I had found a mail order company that sold inexpensivedosimeters complete with battery chargers. I told Fermi that I felt a personaldosimeter was more important than a personal fallout shelter. The shelter coulddo harm if it contained some undiscovered radiation after an attack. And I hadlived through the Bikini atom bomb tests where I returned to a ship with someremnant radiation zones that could be found with the help of my personal surveymeter. I offered to include an extra kit for Fermi in my order and he agreedwith my reasoning and gladly joined in on the order. At times like that wethought of him as a fellow grad student. Not only was he fascinated with new“gadgets” just as we were, but he really treated us as equals.326

Jay OrearENRICO FERMI, THE MANFermi intuitionTo me, intuition is a kind of mental telepathy and mental telepathy is supernatural;i.e., by definition it is “outside of nature” - it does not exist. So nowlet me give you some examples of Fermi’s famous “intuition”. About one orso months after the Berkeley Bevatron had been running on both electronicand nuclear emulsion antiproton searches there were still no positive results.Murray Gell-Mann had just returned from Berkeley with these negativeresults, which he was relating to Fermi and me in the hall just outside ouroffice doors. Murray said now we know there is no anti-proton. But Fermisaid in a very definitive and loud manner: “There IS an antiproton”. We gradstudents used to say that “Fermi had an inside track to God”. Within amonth of that definitive pronouncement Fermi was proven correct.Another example was his explanation of the cosmic ray vs. nuclear emulsiondata of neutral and charged V-particles plus the tau particle (a chargedparticle coming to rest and decaying into 3 charged pions). The measuredmasses of these particles differed by a few standard deviations. Both Fermiand I independently felt that God would not have created so many newbosons of almost the same mass. The simpler explanation was that theseobservations were different decay modes of the same particle and that someof the mass measurements must have had larger errors than claimed. Fermisupervised the Chicago nuclear emulsion group and we knew that nuclearemulsions could determine masses more accurately than the cloud chambers.In 1953 Fermi taught a Particle Physics course. I sat in on the course andtook detailed notes. My notes reveal two more examples of what might becalled intuition. On my pages dated April 11, 1953 Fermi explains the intrinsicparity of the pion as two spin 1/2 sub-particles in an L=1 orbit around eachother and with the intrinsic and orbital angular momenta opposed to give atotal spin zero of the composite particle. A spatial inversion would give achange in sign or odd parity for the composite. This is the present quark modelof the pion years ahead of its time. On pages of the same date Fermi gets evenintrinsic parity for the neutrino in one reaction and odd intrinsic parity inanother reaction. So two different parities for the same neutrino. (This is nowknown to be true). I asked Fermi in class: “Suppose there is an antineutrino inthe other reaction?” He said, “Let me think about that”. Later that day hecalled me into his office and said that he still has the problem that he gets bothparities for the neutrino. He admitted that he still did not understand the neutrino.I like to speculate that if he had known about the two-component neutrinoin the Pauli Notes, he might have beaten Lee and Yang by 3 years.327

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThe most famous example of Fermi’s so-called intuition has to do with hisNobel-prize winning discovery of how slow neutrons can produce largeramounts of artificial radioactivity. It is true that he was the first to slow downa beam of neutrons with a slab of paraffin. But there is at this time a disputewhether he first tried a lead filter with no result and then followed it withparaffin resulting in a hundred-fold increase in the induced radioactivity. Onone side of the dispute is a famous quotation by Chandrasekhar.Chandrasekhar had told Segrè that Fermi told him in a conversation aboutthe scientific method: “When finally, with some reluctance, I was going toput it [the lead filter] in its place, I said to myself; ‘No, I do not want thispiece of lead here. What I want is a piece of paraffin.’ It was just like that withno advance warning, no conscious prior reasoning”. This is one of the reasonswhy we students would joke about Fermi having an inside track to God.Segrè who was in another room at that time doesn’t seem to remember thatdetail, but he cannot trust his memory. Chandrasekhar admits he did notwrite down verbatim what Fermi said to him but he feels he can trust hismemory.On the other hand Laura Fermi in her Atoms in the family tells a differentstory. On page 98 she says: “They placed the neutron source outside thecylinder and interposed objects between them. A plate of lead made theactivity increase slightly. Lead is a heavy substance. Fermi said, ‘let’s try alight one next, for instance, paraffin’ ”. Laura Fermi’s book was proofread byher husband. Too bad that Enrico Fermi, Laura Fermi, Segrè, Pontecorvo,or Chandrasekhar are no longer available to settle this dispute. I can think of5 reasons that support Laura Fermi’s version (1) The Chandrasekhar versionis admittedly not verbatim. (2) The Laura Fermi version is verbatim (she waswriting a book while interviewing her husband and her husband did proofreadher entire book). (3) It was a lead box which was giving Fermi and hisgroup inconsistent results and which they supposedly decided at that time tostudy in a more systematic way. (4) The heavier elements gave more complicationslike artificial radioactivity (and even fission which they did not understandat the time) whereas the lighter elements did not. So it made moresense to start with that which is expected to give complications. (5) If Fermiat the last minute had changed their agreed upon logical plan without anywarning to Segrè, Segrè would have been annoyed and have a reason forremembering something so out of Fermi’s character. At the Rome Congresshonoring Fermi’s 100 th birthday it seemed most of the audience was on theside of Chandrasekhar. However a compromise theory was proposed that the328

Jay OrearENRICO FERMI, THE MANlead experiment was done the day before the paraffin was “impulsively”selected. Whether or not the lead was used, the fact that paraffin was selectedearly on is a good example of uncanny intuition.One last example of good intuition is whether Fermi believed in the Fermi-Metropolis phase shifts as defined in paper 260 of the Collected Papers of E.Fermi, Vol. II, U. of Chicago Press, 1965. In the paper delivered by ValTelegdi at the Cornell Symposium, Telegdi says the Fermi-Metropolis fit“favored by Fermi did not correspond to the proposed resonance”. WhatTelegdi should have said is that “the world data at that time favored theFermi-Metropolis phase shifts but Fermi favored the resonance fit”. It is truethat the full set of world data at that time taken together gave a better goodness-of-fitto the Fermi-Metropolis solution than to the solution where thep-wave phase shift went through a resonance. And it was this resonance fitthat Fermi personally always favored. In an earlier talk I remember HerbAnderson making a statement similar to Telegdi’s. These statements mightcause readers to rule out Fermi as the discoverer of the first excited state ofthe nucleon. What Telegdi and Anderson should have said is that in theirpaper the Fermi-Metropolis solution gives a better goodness-of-fit value thanthe resonance solution. One must keep in mind that Fermi and Metropoliswere doing a fit to the combined world data. At that time the resonance solutionfit every combination of world data until the first “measurement” of thepi plus- proton total cross section was reported from Columbia University.They reported a total cross section considerably smaller than required by a p-wave resonance. They had exposed nuclear emulsion to positive pions at theresonance energy at a position near the center of the Nevis cyclotron. It wasa difficult experiment because of the heavy background and the scanning efficiencyfor finding all the elastic scatterings is expected to be low. Fermi andI felt all along that the scanning efficiency must have been lower than whatthe Columbia scanners had estimated. If the Columbia data could have beencorrected for this then the Fermi-Metropolis fit would be ruled out. (Laterexperiments at the Cosmotron using external pi plus beams at and beyondthe resonance energy proved that the Columbia cross section was way toolow). Fermi was so confident that there was a resonance that he tried torepeat the Columbia experiment using the Chicago cyclotron with HoraceTaft as the grad student in charge. This involved mounting some nuclearemulsions and shielding near the center of the vacuum tank where residualradiation levels were significant. Members of our nuclear emulsion grouptook turns working short shifts inside the tank. Of course we wore film329

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEbadges and dosimeters and made sure no one was exposed to more than 300mr per week. Fermi as a member of the group insisted on taking the samedosage as Taft, Orear, Rosenfeld, and others. (The others may have been BobSwanson and Jerry Friedman). We pointed out to Fermi that he already hadaccumulated more lifetime dosage than we, and that we preferred that he notcrawl inside the cyclotron as we were doing. But he was an egalitarian and hefelt strongly about this and he was our boss. (Nobody had any hint that hewould die from cancer in the following year). We did find some elastic scatteringsin our exposures but we also found heavy background that would swampout the signal at the needed exposure levels. So we were unable to disprove theColumbia experiment as the Cosmotron did shortly after Fermi died.My last example is a case where his remarkable intuition failed him. Hehimself later referred to it as his great mistake. When his Rome group irradiateduranium with neutrons in 1934 they observed more than the usualamount of radioactivity. They had expected to get radioactivity fromtransuranic elements. But their chemistry and halflives didn’t fit in a way sothat they could prove that what they saw was due to transuranic elements. AGerman chemist, Ida Noddack, actually published that what they saw was fission,which seemed a wild idea at that time. Apparently her idea was too wildto be taken seriously. According to Segrè, Fermi’s knowledge of nuclearenergy states was such as to make him think fission was not possible. Ferminever wanted to publish an experimental result unless he was sure of it. IfFermi had published that he had seen fission, the half-sized pieces wouldhave an excess of neutrons and these neutrons would give rise to more fissionsmost likely in a chain reaction. Then both Germany and the U.S. mighthave had atom bombs in time for World War II. The world should be gratefulfor this one mistake of Fermi! I like to make the following analogybetween the two great Italian Navigators. The first in 1492 found a wholenew world, but thought it was China; the second in 1934 found fission, butthought perhaps it was just transuranic isotopes.Fermi humorHans Bethe in his talk at the Cornell Symposium gave an example of Fermi’shumor when Fermi was at the age of 29. Not only was he a full professor, buthe was a member of the Royal Academy with the title of His Excellency Fermi.The driveway to the Physics Institute also led to an important governmentaldepartment that sometimes had “classified” meetings and on such occasions330

Jay OrearENRICO FERMI, THE MANthe driveway was closed to the physics people. On one of those days Fermicame driving and when the guards stopped him he said “I am the driver toHis Excellency Fermi. And His Excellency would be very annoyed if you didn’tlet me in”. And as he told the story later, Fermi emphasized that he hadtold the whole truth: he was the driver to the Excellency Fermi, and indeedHis Excellency would have been very annoyed.Fermi chose to inject quite a bit of humor into his retirement lecture as thePresident of the APS (American Physical Society) on Jan. 29, 1954. On thenext day Fermi gave a second lecture in honor of the 200 th anniversary ofColumbia University that he also sprinkled with humor. Both of these lecturesgive a good idea of his personality and style of humor. Unfortunatelyno audio or visual recording exists for the first, but the entire second lectureexists on audio tape and is transcribed in Physics Today and Segrè’s book.(a) The Ultimate AcceleratorThis is the unofficial title we physicists gave to the retiring president lecture.Fortunately Fermi typed out one page of notes for it with his ownhands (he did know how to type). Parts of this one page are discussed below.We shall see that he does plan jokes days in advance and from the taped lecturewhere we can hear both Fermi laughter and audience laughter we notethat he laughs heartily at his own jokes. As far as I can tell, the style of humorand delivery shown in these documents are just as I remember and to methey give some feeling of his humble, friendly and cheerful personality. Mycomments are in italics.The first sentence of his page of notes says: “Congratulate Society on Loosingmediocre President and getting eccellent one”. (Spelling has not been corrected).This first joke is one of self-deprecation.Next sentence: “Counting number of papers... most active branches... solidstate physics in which, perhaps mistakenly, we believe... nuclear Physics inwhich we cannot make that mistake. Since Yukawa…first suspected and thenknown…”. As a father of solid state physics and meson physics he can get awaywith criticizing them.Now he explains his criticism of nuclear physics: “But, to our dismay we gota lot more… many so called elementary particles… and because in addition…each… many names…number of names… stupendously great… even morethan the number… which large enough”. He finds it humorous that there areeven more names than there are particles. “But to solve the mysteries higherenergy data are needed. But cosmic rays above 25 BeV only one per cm 2 at331

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEan inconvenient location.For these reasons… clamoring for higher and higher…”.Fig. 4: Semi-log plot of beam energy vs. the year of accelerator completion.Courtesy Cornell accelerator group. Line is drawn through the highest protonenergies obtained up to 1954. The accelerators after 1954 are also shownand they still tend to lie on the line determined by the pre-1954 accelerators.In his talk his Fig. 4 was a similar plot of MeV versus time and also cost vs.time (of the existing accelerators showing extrapolation to 1994). Fermi’s predictedvalue at 1994 is an energy of 5×10 9 MeV at a price of 170 B$. (Remarkablythis energy could have been built in 1994, and at a lower price of about11 B$ by using colliding beams. The highest energy colliding beams wereachieved at Fermi National Accelerator Laboratory in 1988 at an equivalentbeam energy of 2×10 9 MeV).Fig. 5: Central Laboratory Building at Fermi National Laboratory where theworld’s highest equivalent beam energy of 2×10 9 MeV was achieved in 1988.Next Fermi makes a preliminary design for a single ring proton acceleratorof energy 5×10 9 MeV: “Preliminary design…8000 km, 20,000 gauss”Such a single ring would give the desired energy, but the radius of 8000 km or5000 mi would put the orbit 1000 mi above the surface of the earth! This isshown in Fermi’s Slide 3. By now the audience must have been in hysterics. Theywere still talking about it when they came back to Chicago. Fermi’s Slide 3 showsa single beam accelerator in orbit 1000 miles above the surface of the earth.“What we can learn impossible to guess… main element surprise… somethings look for but see others… Look for multiple production… antinucleons….strange particles…puzzle of long life times… large angular moment?…double formation? At present more probable…”.Fermi’s intuition was working well: this energy was achievable in 1994. Acolliding beam version could have been built well under his estimated cost,but Congress ruled that the cost of ~10 B$ was too much. He was correctin predicting that the main element would be surprises ( like strangeness,charm, and bottom and top quantum numbers, heavy leptons, electro-weakunification, the 6 quarks and 3 different kind of leptons, the fantastic successof the standard model, non-conservation of parity, etc). His preference for332

Jay OrearENRICO FERMI, THE MAN“double formation” which is now called conservation of strangeness was alsocorrect. I feel that Fermi was close to solving the puzzle of long lifetimes forstrongly produced particles.“…tried to photograph what I saw in the ball… and made slide.Slide 5 – Strange particles in pion nucleon collisions.…should realize this picture retouched…”His Slide 5 must be Fermi’s last joke in this talk. Unfortunately I was notable to find it among his papers.(b) Physics at Columbia in the 1940’sThe following contains eight of the many jokes in this talk that are on tape.One can hear Fermi as well as the audience laughing while giving the joke.Sometimes he starts laughing before reaching the end of the joke.1. “I don’t know how many of you know Szilard; no doubt many of you do.He is certainly a very peculiar man, extremely intelligent (laughter). I seethat this is an understatement (laughter). He is extremely brilliant and heseems somewhat to enjoy, at least that is the impression he gives to me, heseems to enjoy startling people”.2. “And in fact help came along to the tune of $6000 a few months after andthe $6000 were used in order to buy huge amounts – or what seemed atthat time when the eye of physicists had not yet been distorted – (laughter)what seemed at that time a huge amount of graphite. So physicists onthe 7 th floor of Pupin Laboratories started looking like coal miners (laughter)and the wives to whom these physicists came back tired at night werewondering what was happening. We know that there is smoke in the air,but after all ... (laughter). (The film shown near the start of my talk showeda machinist stripped to the waist machining a block of graphite. It was producinga black cloud of graphite and the machinist was Fermi himself).3. It was the first time when apparatus in physics, and these graphite columnswere apparatus, was so big that you could climb on top of it – and you hadto climb on top of it. Well cyclotrons were the same way too, but anywaythat was the first time when I started climbing on top of my equipmentbecause it was just too tall – I’m not a tall man (laughter).4. Now graphite is a black substance, as you probably know. So is uraniumoxide. And to handle many tons of both makes people very black. In factit requires even strong people. And so, well we were reasonably strong,but I mean we were, after all, thinkers (laughter). So Dean Pegram again333

PROCEEDINGS OF THE INTERNATIONAL CONFERENCElooked around and said that seems to be a job a little bit beyond your feeblestrength, but there is a football squad at Columbia (laughter – an injoke: Columbia’s football team lost almost all its games) that contains adozen or so of very husky boys who take jobs by the hour just to carrythem through college. Why don’t you hire them?PoliticsAfter the first H-bomb test the possibility of a Cobalt bomb producing widespreadradioactive contamination was rather obvious. Art Rosenfeld and I askedFermi for his opinion on this and he spoke freely to us. He gave a response I didnot expect. He said our military leaders would not rely on a weapon whoseeffects had never been tested and that the long range air patterns are too unpredictable.Now that I am older and perhaps wiser, I agree with Fermi on this.Bob Wilson in his Cornell talk criticized the common opinion thatOppenheimer was more liberal than Fermi. (This is in agreement with astatement in Segrè’s book that Fermi was more liberal than Oppenheimer,Condon, and Compton). Wilson gave the pending May-Johnson Bill ongovernment control of atomic energy and research as an example. He, Fermi,and others felt that the May-Johnson would permit too much governmentsecrecy in fundamental research. Wilson said that Oppenheimer was for it butultimately Fermi strongly opposed it and supported an alternate civilian controlbill. Here are the words used by Wilson in his Cornell Symposium talk:“Still, to my surprise, [Opppenheimer] was backing that bill [May-Johnson],and giving advice to Senator Fulbright. It mystified me. At that time, he alsoread a letter that he had from Fermi, who wasn’t in Washington, then. Fermi,on the other hand, did criticize the bill, and did not approve it. He criticizedit because of the secrecy measures, which he thought were too much, and healso criticized it because he thought it was overly organized, and that thatwould be something that keep the young scientists, particularly, from makingsuggestions and making inventions, and might dampen their creativeabilities. I think that was absolutely correct. Well, okay for that. After thelunch, five of us young physicists were so impressed by Fulbright that wewent around to see him. There was Curtis, from Oakridge, and Borst, andRabivinich, from Chicago… I’ve forgotten all of them … a small tier of halfa dozen or so who went to see Fulbright, and spent the whole afternoon withhim. We found out that he was very astute in the way in which he was ableto ask us questions about that which we had already made up our minds, andcould advise him about. It was a nice afternoon. I got to know the other sci-334

Jay OrearENRICO FERMI, THE MANentists from the other laboratories – the Radiation Laboratory in Boston, andwell as the people from Chicago. That evening (and I’m finally coming tomy story!) a dinner had been arranged by Watson Davis, who you are probablynot familiar with, but he was the person in Science Service, and heplayed a very valuable role in science at that time, and he was very much ofa liberal person, and he helped in organizing the young scientists tremendously.In any case, he had the idea of having a dinner, at which there werescientists sitting around a rather large table, and between each scientist, wasa politician. So, a senator, a scientist, a senator, a scientist, and all the wayaround (all senators, I believe, except for Wallace, who came, I believe, witha person named Neumann, a mathematician from Yale, who was to becomevery important). The kind of people who were there … there wasOppenheimer, and Fermi was now in town, and Szilard, Shapely… therewere half a dozen young scallywags, of which I was one, and that made upthe dinner. Well, it started off … of course the senators had heard aboutOppenheimer, but not about Fermi .. so they asked a few questions of Oppy,about various aspects of nuclear bombs. One of them asked the question ofFermi, then. These were all social questions, about what we should do aboutnuclear energy. Could it be kept secret? Could other nations do that? Thesewere bright people asking these questions. I’m afraid that Oppy, because ofhaving to back the May-Johnson Bill before Fulbright, was a little confused,and so he tended to be a little bit wooly in responding, and he could be thatwithout much trouble at all (Audience laughter). Fermi was about the clearest,and could speak very simply and with great understanding, had been listeningto us when we had been like gnats, arguing around him… my apprehensionshad not been justified. The senators, when they heard the firstanswer from Fermi, with his clarity, directed all their questions to Fermi.There were a lot of questions and, each time they asked questions of Fermi,I had not much confidence, because I thought he’d say, ‘Well, I don’t reallyknow about that. What do we know about sociology, what do we knowabout politics?’ I could just see him doing that. (Audience laughter). He wasnot like that at all. He went right down our party line, without deviating inone way. Now, with Wallace present, with Fulbright present, with Toby, whowas the senior Republican, there, I think it was one time that it made a bigdifference that somebody spoke out clearly and forcefully, and that man wasEnrico Fermi”.Fortunately there were enough liberals in Congress to defeat the May-Johnson Bill. And when Oppenheimer’s security clearance was revoked,Fermi testified on his behalf before Congress. Behind the scenes, Fermi privatelytried without success to persuade Edward Teller not to testify againstOppenheimer.335

PROCEEDINGS OF THE INTERNATIONAL CONFERENCECarl Sagan in his Cornell talk quoted a strong warning by Fermi not tomake an H-bomb. Carl said: “In the October 1949 report of the GeneralAdvisory Committee to the U.S. Atomic Energy Commission, there was anaddendum by Enrico Fermi and I. I. Rabi. This was a report on whether itwas a good idea to build the first thermonuclear weapon, and the main report,signed by Robert Oppenheimer and others said, ‘The extreme danger tomankind, inherent in the proposal by Edward Teller and others, to develop athermonuclear weapon, wholly outweighs any military advantage’ and theaddendum, by Fermi and Rabi, made that point even more strongly. It said,“The fact that no limits exist to the destructiveness of this weapon makes itsvery existence, and the knowledge of its construction, a danger to humanity.It is an evil thing.’ Which is, to my mind, a very strong statement” (end ofSagan’s quote). Again Fermi took a stronger position than Oppenheimer.After World War II Fermi was in my opinion unjustly criticized byCommunists and some liberals in Italy for his work on the A and H bombs.But during the war Fermi knew that we were in what was thought to be aclose race with Germany in producing an A-bomb. It was believed thatGermany had a head start. If Hitler had beaten us to the A-bomb, he couldhave forced a US surrender.And after the war Fermi’s anti-H-bomb statements indicate that he advocateda joint US-Soviet agreement not to work on thermonuclear weapons.But again we were in an even closer race – this time with the Soviet Union.Stalin’s regime was the first to acquire and test a solid and compact H-bomb.It is not Fermi’s fault that the political leaders of both sides would not listento scientists such as Fermi, Rabi, Bethe, Wilson and Szilard. It is a shame thatsome citizens of Italy were rejecting their modern day equivalent of Galileo.Fermi had brought Italian physics up from the bottom to the top in a veryshort time.After the defeat of Hitler, Fermi and Oppenheimer were consulted byPresident Truman to choose between military use or a demonstration explosionof the first A-bomb. Fermi felt that the Japanese military leaders were ina kamakazi state of mind. They were too fanatical to be influenced by a testexplosion. But surprise use on a city of military value might result in a surrender.And if not, it should be followed by a second city of military valueplus an offer to let the people keep their emperor. This was an offer theemperor and the people could not refuse. At least in hindsight we see thatFermi gave advice that resulted in a prompt Japanese surrender and a savingsof hundreds of thousands of lives.336

Jay OrearENRICO FERMI, THE MANFermi and creativityPerhaps the most famous example of Fermi’s extraodinary creativity is hisbeta decay paper in 1933. Fermi first submitted it to Nature for publication,but it was rejected. The referees thought it was too far fetched and impossible.They didn’t like the four-particle interaction which created an electronand neutrino out of nothing and they didn’t like taking the neutrino so seriously.After Pauli had proposed the neutrino in 1930, most physiciststhought of it as some kind of bookkeeping procedure. They didn’t think ofit as a “real” particle that had an interaction cross section. And Fermi’s theorydid predict a well defined energy-dependent interaction collision crosssection with protons. Fermi liked to reason by analogy and he felt that ifthere could be electron-positron pair production in nature, there could alsobe electron-neutrino pair production.He then submitted the paper to a less prestigious Italian journal where it wasfirst published. Segrè on pages 73 and 74 comments: “Fermi’s paper, writtenat the end of 1933 has stood the test of time with singular success; in fact,except for the nonconservtion of parity, even today very few changes wouldhave to be made to it. …and his uncanny choice of the vector interaction wascorrect”. (The most famous example of his extraordinary intuition).In 1951 Fermi said in an unpublished speech: “Theoretical research mayproceed on two tracks: 1. Collect experimental data, study it, hypothesize,make predictions, and then check. 2. Guess; if nature is kind and the guesserclever he may have success. The program I recommend lies nearer to thefirst track”. He referred to track 2 as a big leap where great progress can bemade all at once. He must have had his beta decay paper in mind as an exampleof “track 2”. To me, it is an example of high creativity in science. I don’tthink any other physicist in 1933 was close to producing this theory of theweak interaction. But, like any other discovery, it would have come probablya few years later. Except in this remarkable case it took 25 years before othersmade the final improvement.To me Fermi’s weak interaction was a greater intellectual leap thanNewton’s checking the ratio of the acceleration of a falling apple to thefalling Moon. Fermi was truly a great theoretical physicist, a great experimentalphysicist, a great teacher at all levels, and a great engineer. Newtonwas also a great theorist, experimentalist, mathematician, and engineer (Ilove his reflecting telescope), but perhaps not one of the best teachers.Maxwell and perhaps Galileo were in the same league as Fermi and Newton.They also were excellent in both theory and experiment.337

PROCEEDINGS OF THE INTERNATIONAL CONFERENCESegrè has made a collection of the 270 most important papers of Fermi andpublished them in two volumes by the University of Chicago Press. Some ofthese papers have given birth to entire new fields of physics. Segrè also lists13 books. I have read only a few of these papers and books. My short list ofnoteable discoveries is (1) the first understandable paper in quantum electrodynamics,(2) Fermi statistics and theory of solids, (3) the Thomas-Fermimodel of the atom, (4) the weak interaction and beta decay theory, (5) neutroninduced radioactivity which includes transuranic isotopes and not fullyunderstood fission products, (6) first self-sustained nuclear reactors, (7)nuclear reactor patents and design, (8) neutron diffraction applications tosolid state physics, (9) the A-bomb, (10) thermonuclear weapons, (11) pionbeam designs, (12) his role in creating the nuclear shell model, (13) pionprotonelastic scattering, (14) discovery of the L=1 excited state of the proton,(15) acceleration of cosmic rays, (16) the approach to equilibrium.In this paragraph I shall attempt to deal with the question of who is the bestphysicist in history. This is really a meaningless question unless the criteria forjudging are made clear. Should it be the best theoretician of all time, the bestexperimentalist, or the best combined theoretician and experimentalist?Should technological contributions that are beneficial to the human race becounted? How about weapons technology that are helpful to one’s country?But in spite of these difficulties, Physics World, the house organ of the BritishInstitute of Physics did take a poll of its readers in December 1999 asking whois the best physicist in history without specifying any criteria. According totheir results the top 10 physicists in history are: Einstein, Newton, Maxwell,Bohr, Heisenberg, Galileo, Feynman, Dirac, Schrodinger, Rutherford. I wasdisappointed that Fermi was nowhere on the list. At that same time Timemagazine named Einstein as its person of the century and put him on thefront cover of their centennial issue. I am very happy with Einstein being chosenby non-scientists, most of whom never heard of Fermi. If the criteria werethat the physicist must be tops in theory, experiment, engineering, teachingthat is felt over the entire planet, no mixing of science with the supernatural,and beneficial contributions to mankind then I think I might choose Fermi.But I am not enough of a historian of science to make expert comparisonswith Maxwell and Galileo. I have read a book of Einstein quotations and I donot agree with all of them. Also I feel that quantum mechanics would notwork if “God did not play dice with the universe”. Einstein made some greatdiscoveries in theory, but he was not an experimentalist or engineer. It hasbeen said that he was not even aware of the relevance of the Michelson-338

Jay OrearENRICO FERMI, THE MANMorley experiments to special relativity. Most physicists feel that quantummechanics is much more important to physics than gravitation.I know that highly creative people in physics tend not to learn by studyingtextbooks in the conventional manner. Instead they try to work all the interestingproblems. If such a person has trouble with a problem, he then goesto that part of the text. We know that Fermi used books in such a manner. Ialso know that Lee and Yang studied together in such a manner. I recentlylearned that Fermi when he was 16 and 17 learned much of physics from a5000 page set of volumes by the Russian Chwolson. He first did a quick runthroughthe French edition to eliminate the 1000 pages he already knew.Then he spent several months on the remaining 4000 pages until he hadmastered them. I do not know whether he used the method of working backfrom the problem sections. I do know that through most of his life if he wastold of a new discovery, he would work it out for himself first in order toachieve a true understanding.Educators are interested in how to train for creativity. Perhaps they couldget some clues by studying the methods used by people like Fermi, Garwin,Lee and Yang when they were young.Jay OrearProfessor Emeritus of Physics, Cornell University Graduate student U. ofChicago Sept. 1946 to June 1953 receiving Ph.D. in particle physics undersupervision of Enrico Fermi. Post-Ph.D. Research Associate of Enrico FermiJune 1953 to Aug. 1954.Instructor and then Assistant Professor, Columbia University Sept. 1954 toJune 1958.Associate to full Professor 1958 to 1995, Cornell University. Then EmeritusProfessor.Associations with Fermi: My Ph.D. was to confirm the pion-proton phase shiftsdiscovered by Fermi. He was also the first to measure the signs of thosephase shifts. Authored “Notes on Statistics for Physicists” 1958, revised1982 (based on Fermi conversations).Co authored “Nuclear Physics” 1949 U. of Chicago Press (based on notesof Enrico Fermi’s course with A. Rosenfeld and R. Schluter). FundamentalPhysics, John Wiley & Sons 1963 and Physics, Macmillan, 1979 (collegeintroductory textbooks with a Fermi approach). With help from R. Garwinand C. Sagan organized a symposium “Memories of E. Fermi”, Oct. 1991at Cornell University. Organized reunions of Fermi thesis students Oct.13,1991 and Dec.3, 1992.339

John L. HeilbronExperimental Nuclear Physicsin the Thirties and FortiesElementary particle physics, long the exemplar of big science, has alsocultivated a reputation for purity. It traces these character traits to the nuclearphysics of the 1930s and 1940s, when, however, purity and bigness did notfrequently coincide. Big nuclear science, as represented most conspicuously byE.O. Lawrence’s cyclotron laboratory at Berkeley, pursued philanthropic andindustrial support and gave promises and sometimes realizations of usefulapplications in return. None of the fundamental experimental discoveries inparticle physics during the 1930s – the neutron, the deuteron, artificialradioactivity, neutron activation, fission – was made in a cyclotron laboratory;and only one – the transmutation of light nuclei by proton bombardment – wasmade with any sort of accelerator. Those who made the major discoveries,among whom Fermi’s group in Rome stood out, used small-scale, desk topapparatus. The two directions in experimental nuclear physics came togetherduring the Manhattan project like the separated parts of a critical mass. In thelate 1940s, the cyclotron became the tool of choice for many particle physicists.This development was abetted by a new design created during the last waryears, by the replacement of cyclotrons by piles in the quantity production ofisotopes, and by plenty of government money.341

PROCEEDINGS OF THE INTERNATIONAL CONFERENCELa fisica nucleare sperimentalenegli anni Trenta e QuarantaLa fisica delle particelle elementari, per lungo tempo modello della“big science”, ha coltivato anche una sua reputazione di purezza.Tali tratti caratteristici risalgono alla fisica nucleare degli anni 30 e 40,un’epoca in cui peraltro purezza e grandezza non coincidevanofrequentemente.La “big science” nucleare, come rappresentata efficacemente dalLaboratorio del Ciclotrone di E.O. Lawrence a Berkeley, era in cerca disostegni filantropici e industriali, in cambio dei quali prometteva e talvoltarealizzava utili applicazioni.Nessuna delle fondamentali scoperte sperimentali della fisica delleparticelle avvenute negli anni 30 – il neutrone, il deuterio, la radioattivitàartificiale, l’attivazione neutronica, la fissione – fu realizzata in unlaboratorio del ciclotrone, ed una sola (la transmutazione di nuclei leggeritramite bombardamento protonico) fu fatta con qualche tipo di acceleratore.Coloro che realizzarono tali scoperte, tra i quali spiccava il gruppo diFermi a Roma, utilizzarono macchinari a piccola scala, da tavolo.Le due direzioni della fisica nucleare sperimentale conversero nel ProgettoManhattan, come le due parti separate di una massa critica. Alla fine deglianni 40 il ciclotrone divenne lo strumento principe per molti fisici delleparticelle. Tale sviluppo fu favorito da un nuovo disegno tecnico sorto negliultimi anni del conflitto, dalla sostituzione dei ciclotroni con le pile nellaproduzione degli isotopi e dai consistenti finanziamenti governativi.342

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESCyclotron laboratories did not make the big discoveriesin the 1930sIt is a great honor and greater challenge to speak to you about a subject inwhich Enrico Fermi played so prominent a part, and about which so muchhas been written and said. I have no credentials for the task except a longstandinginterest, awakened in a course on quantum mechanics I took withEmilio Segrè. He taught from the English translation of the textbook usedin Rome in the 1930s. My class came to know this book, by Fermi’s boyhoodfriend Enrico Persico, by heart. Our unusual devotion was inspired bySegrè’s periodic absences from Berkeley to visit Fermi, then terminally ill inChicago. Each time he left, Segrè threatened to give us an examination onhis return. Instead he would tell us about Fermi.Segrè and Fermi quickly accommodated to what generous people callAmerican culture. They fit in perfectly with the gigantic physics of World WarII and made good use of large accelerators and reactors. But they retainedtheir preference and ability to work in small groups. It is only slightly overschematicto say that they fused the small-group, low-cost, physics researchof prewar Rome with the interdisciplinary high-cost cyclotron developmentpioneered by Ernest Lawrence in Berkeley.Particle accelerators came to dominate experimental “high-energy” physics inthe late 1940s. By then they could achieve energies and intensities that madepossible the creation of particles previously observable only, and infrequently,in cosmic rays; and the physicists who operated them had become more interestedin exploiting the power of the machine than increasing it. The war freedcyclotroneers to do physics. During the 1930s, Lawrence had to raise fundsfrom philanthropic organizations or government agencies concerned withmedical problems. Most of the operating time of the Berkeley cyclotrons wentto manufacturing isotopes of biological, chemical, or pharmaceutical interest.Reactors developed during the war took over these manufacturing jobs after it.Cyclotron laboratories did not make the big discoveries – the Nobel-prizewinning discoveries – in nuclear physics in the 1930s. The prize-winning discoverersused apparatus of traditional desk-top size and modest cost.Without the obligation to improve their instrumentation beyond what wasnecessary to the object in hand, or to develop large means of production tomeet the expectations of funders, European nuclear physicists had the leisureto discover the neutron, artificial radioactivity, neutron excitation, and fission.The only major discovery made at a cyclotron laboratory was the transmutationof light nuclei by protons accelerated in the machine built by John343

PROCEEDINGS OF THE INTERNATIONAL CONFERENCECockcroft and E.T.S. Walton at Cambridge. This apparent exception in factreinforces the rule. Cockcroft and Walton continued to tinker with theiraccelerator after it had become capable, both in fact and theory, of disintegratinglithium; and they would have kept at their improvements indefinitelyif their boss, Ernest Rutherford, had not ordered them to try the experimentfor which they had built the machine and he had raised the money.Enrico Fermi’s group did not need orders to do physics. Their single-mindedpursuit of neutron activation was the exemplar of small-scale nuclearphysics during the 1930s. It came to an end owing to the dispersal of thegroup on, and even before, Fermi’s emigration to the United States in 1938.But by then the vein that they had mined had played out. Fermi’s next moves– across the Atlantic and to the problem of realizing a controlled self-sustainingchain reaction – placed him within or in charge of a large crew and apparatus.That marked a turning point not only in exploitating atomic energy butalso in bringing physicists broadened in small-scale work into collaborationwith machine builders narrowed by large-scale constructions. The strength ofthe combination revealed itself in the atomic bomb and, less dramatically, inthe rapid postwar progress of accelerator physics in the United States.My purpose today is to illustrate this general development by comparingFermi’s group with Lawrence’s. The leaders, Fermi and Lawrence, were thesame age – Lawrence too is celebrating his centennial this year. Both werecharismatic and convivial and commanded the loyalty of their coworkers. Eachreceived the Nobel prize in physics and other high honors. National laboratoriesin the United States have been named after them. They reached the highestlevels of governmental advising and generally agreed about nuclear policy.As scientists, however, they had little in common. Fermi took up nuclearphysics deliberately, Lawrence by chance. Fermi stayed a theorist, Lawrencebecame a fund raiser. Fermi had a traditional liberal education and spoke severallanguages. Lawrence knew neither languages nor cultures. I can also reportthat Lawrence was tall and Fermi short – a metrological difference that wouldnot be worth mentioning had it not extended to most of their close associates.The Berkeley group – Lawrence, Edwin McMillan, Luis Alvarez, and GlennSeaborg – all were over ten percent taller than Fermi, Segrè, Edoardo Amaldi,and Oscar d’Agostino. The men matched their machines. Franco Rassettiescapes the generalization, but then he marched to his own tune.Both groups took an interest in themselves. We have autobiographies ofAlvarez, Amaldi, Seaborg, and Segrè, biographies of Fermi by his wife and bySegrè, and much about Lawrence from Alvarez and Seaborg. Biographers344

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESand historians from outside the groups have also contributed their bits. Wedo not lack information for a comparative history broader and deeper than Ihave time to suggest.The “Golden Thirties”In RomeThe Physics Institute on the Via Panisperna boasted an establishment torival the Vatican. It had an Eternal Father in the person of its director, OrsoMario Corbino, who protected Fermi’s group from academic and worse politics,and procured funds and assistance as necessary; a Divine Providence,that is, G.C. Trabacchi, who furnished critical radium emanation for thegroup’s radon-beryllium neutron source from the School of Public Heath; aPope, Fermi himself, infallible in physics; a Cardinal Vicar, Rassetti, whosometimes substituted for the pope; a Grand Inquisitor, Ettore Majorana,never satisfied with an answer; a Cardinal De Propaganda Fidei, Persico, socalledfor his textbook and other advertisements of quantum theory; and aPrefect of the Libraries, Segrè, a connoisseur of the physics literature, alsoknown for his touchiness as the basilisk, a fabulous beast that can freeze otheranimals by the chill of its glance. 1Fermi’s little church had switched its attention from the periphery of theatom to its nucleus during the early 1930s in the hope of establishing itself,and thereby Italy, as a leader in some branch of physics. In a famous speechof 1929 no doubt formulated with Fermi’s help, Corbino had pointed tonuclear physics as the obvious new frontier; and his insistence that the necessaryexperiments would have to be led by theory implied an advantage tothe Rome group under the infallible Fermi. Still, Corbino’s speech, whichalso hinted at the possible exploitation of atomic energy, scarcely made a program,and Fermi’s group prepared for its transition by visiting other laboratoriesin Europe and the United States to learn experimental techniques andforeign languages that might come in handy. Then, in 1931, they held aninternational conference on nuclear physics, the first ever, which brought theleading brains engaged with the nucleus to Rome for easier picking. The discoveryof the neutron in 1932 at last gave them a secure direction. 21 HOLTON, Minerva, 12 (1970), 194-5; L. FERMI, Atoms (1954), 46-8; SEGRÈ, Mind (1993), 51.2 HOLTON, Minerva, 12 (1974), 181, 183, 186; SEGRÈ, Fermi (1970), 65-8.345

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThey had already prepared a radon-beryllium source and various detectorswhen they heard about the discovery of excited radioactivity by Frédéric Joliotand Irène Curie early in 1934. Joliot and Curie had used alpha particles fromnatural sources to create an activity lasting a few minutes. Fermi saw that neutronswould be a more effective agent than alpha particles, since they wouldnot be repelled by the nucleus’s positive charge; an inference sufficiently obviousbut not, therefore, an obvious reason to replace alpha particles by neutronsin the experiment. The neutron yield from a radon-beryllium source isvery low; and it took some imagination to suppose that the greater efficiencyof neutrons more than compensated for their lesser number. The Rome groupmade a concerted effort to irradiate samples of every element they could procure.In their rush they fell off the periodic table. They identified some activitiesthey had provoked in uranium with elements 93 and 94, to which theygave the ancient names ausonium and hesperium. They were in fact fissionfragments. 3 The true ausonium and hesperium are neptunium and plutonium,first made on the earth by a cyclotron in Berkeley.The yield of new isotopes accelerated in October 1934 when Fermi madea discovery that he later rated as his most important. 4 For reasons he couldnever specify adequately, he placed a piece of paraffin in the path of the neutronsfrom his Rn-Be source. The emerging or moderated neutrons were farmore effective than those that fell directly on the target. Fermi reasoned thatthe neutrons lost energy in the collision with hydrogen atoms in the wax andthat slow neutrons made better agents provacateurs than fast ones. The inferencewent against experience with charged particles, whose capacity to provokenuclear reactions increased rapidly with their energy. The discovery ofthe different efficiencies of fast and slow neutrons had literally earth-shakingconsequences. The theory of atomic piles and nuclear bombs depends criticallyon an understanding of the relative probabilities of fission and captureas a function of the velocity of the impacting neutrons. 5On Corbino’s urging, the Rome group took steps to share in the profit ofany future industrial exploitation of neutron activation. They applied almostimmediately after their discovery of the peculiar efficiency of lethargic neutronsfor an Italian patent on the process and also on some of the products.3 SEGRÈ, Fermi (1970), 72-8; AMALDI, in Weiner, History (1977), 298-316; AMALDI, Riv. stor. sci., 1(1984), 3-23.4 S. CHANDRASEKHAR, quoting a conversation with Fermi, in Fermi, Coll. papers, 2 (1965), 296-7, andSEGRÈ, Fermi (1970), 80. Cf. Oscar d’Agostino, in CARDONE and MIGNANI, Fermi (200), 69-73.5 HOLTON, Minerva, 12 (1970), 160.346

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESThey received the patent in 1935 and soon secured it world-wide. After thewar they pressed their claims against the U.S. government, which had usedtheir patented process in the piles that made plutonium. Eventually the U.S.Atomic Energy Commission (AEC) paid $400,000 for the patent, not much,perhaps, for an invention of world-historical importance, but over ten timesthe cost of all the experiments in nuclear physics done by the Rome groupduring the 1930s. 6The group began to disintegrate in 1935. That year Segrè won the chair inphysics at the University of Palermo. Secondary members of the group driftedaway. In 1938 Fermi went to Stockholm to receive his Nobel prize –essentially for the achievements recorded in the patent application of 1935plus the discoveries of ausonium and hesperium – and continued from theceremony to a professorship in Columbia University in New York City. Hiswife was Jewish. Segrè, also Jewish, was visiting Berkeley when Mussoliniproclaimed the racial laws; he decided to remain in Lawrence’s Lab and sentfor his family. Rassetti, though without Jewish connections, also emigrated,to Canada, and later to the United States. He did not adjust to the Americanpostwar regime in nuclear physics and, although hired as a professor ofphysics, preferred to indulge an interest in natural history that he had cultivatedsince childhood. 7 Big science is not for everyone.Fermi had spent the summer of 1935 in Ann Arbor, Michigan, whereEuropean physicists gathered annually for a summer school. There hereceived a letter from Lawrence containing a milligram of radiosodium madeat the cyclotron. Fermi could scarcely believe his counters. He had expecteda microgram. In 1936 Segrè went to Berkeley to see the machine that couldmake so magnificent an activity. He found nothing there to resemble thegreat laboratories and leading physicists of Europe. Lawrence was cordial,open, boyish, enthusiastic, and generous; he invited Segrè to dinner and gavehim some old cyclotron parts to take back to Italy. 8Neither Lawrence nor his collaborators thought that this scrap might containanything useful that they could not recreate, much enlarged, in the upgradedcyclotron they then were building. Back in Palermo Segrè separated someradioactive phosphorus from the scrap and gave it to his colleagues in biology6 SEGRÈ, Mind (1993), 244-7.7 AMALDI, Da via Panisperna (1997), 69-80; BATTIMELLI and DE MARIA, in ibid., 17-37; AMALDI, 20 thcentury physics (1998), 147-52, 173-80.8 SEGRÈ, Mind (1993), 112-16.347

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEto feed to rats. Early in 1937 he received another nice piece of cyclotron junk.He digested it with the help of Palermo’s professor of metallurgy, Carlo Perrier.Among its many radioactive products they identified iosotopes of the missingelement of atomic number 43, which they later named technetium. “Thecyclotron evidently proves to be a sort of hen laying golden eggs”, the basiliskwrote Lawrence announcing the Nobel-prizeworthy discovery. He and Perriermade the same point more soberly in the paper describing their work. “[T]hisresearch, carried on months after the end of the irradiation and thousands ofmiles from the cyclotron, may help to show the tremendous possibilities of theinstrument”. 9 Lawrence responded with characteristic enthusiasm to Segrè’screative use of cyclotron scrap. What impressed him most, however, was notthe identification of technetium – experience had taught him to be wary aboutclaims based on complex radiochemistry – but the resourceful use of what heregarded as “trivial amounts of radiophosphorus”. 10In BerkeleyIn 1935, just before Lawrence sent Fermi the amazing millicurie ofradiosodium, Lawrence had set his sights on a minimum production of 10 mCia day. In the late summer of 1937, after many changes in design, the Berkeleycyclotron, now with pole pieces 37 inches in diameter, could deliver morethan a curie of radiosodium, over a million times what Fermi had considereda useful amount two years earlier. And, in marked contrast to earlier models,the 37-inch ran reliably, much to the irritation of Berkeley’s chemists, whocould detect its neutrons in their laboratories 100 meters away. 11We know the main reason for the scramble to improve the machine and,after its attainment of reliability as well as power, to regiment its builders inshifts to oversee its performance. Lawrence had promised something to thefoundations that supported his work: radioactive tracers for biologicalresearch, large quantities of radioisotopes for pharmaceuticals, and strongparticle beams for the direct radiation of tumors. 12 Similar indications andexpectations paid for the building of cyclotrons by Lawrence’s students outsideof Berkeley. 13 But even the big beam took a day and a half to make the9 HEILBRON and SEIDEL, LAWRENCE (1989), 365-7; hereafter cited as HS.10 HS, 36711HS, 271, 277.12 HS, 214-18.13HS, 266-8.348

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESamount of radiophosphorus needed for a single therapeutic dose. That,together with the constant work to keep the machine going and improve itsproductivity, occupied most of the time of Lawrence’s group. As the cyclotrongained strength, however, so did the desire of a few of its attendants to dosome physics with it. But how to pay the bills and do science simultaneously?Robert Wilson, then beginning the career that would make him the builderof Fermi Lab, found a way. He put small probes of material to be made hotfor the doctors inside the vacuum chamber, where the beam current wasstrongest, and left the diminished emergent beam for physics and chemistry.This win-win situation did not produce as much science as it promised, however,because by the time Wilson had made his case, the laboratory hadbecome preoccupied with building a super-cyclotron with 60-inch polepieces. Amaldi passed through Berkeley in 1939 as the behemoth nearedcompletion. He was impressed. He hoped, in vain as it turned out, to build asimilar colossus as part of Mussolini’s grand universal exposition of 1942. 14When news of the discovery of fission reached Berkeley toward the end ofJanuary 1939, the 60-inch serfs could not be kept at their tasks. J. RobertOppenheimer, who, with his students, did the theoretical work, such as itwas, of the laboratory, immediately proved that fission was impossible. Thatdid not stop Luis Alvarez, whose acute mind seldom missed an opportunity,from looking for fission fragments created by neutrons in the 37-inchcyclotron. He found them using an ionization counter. Others obtained nicetracks of receding fragments in a cloud chamber. Oppenheimer changed hisdiagnosis from “impossible” to “unbelievable”. By this time the call of the60-inch could not be ignored. The laboratory did not follow up the intriguingquestion, raised by physicists around the world, whether fission releasedmore neutrons than required to induce it. Strong indications that fission gavearound two electrons on average for every one absorbed were obtained by,among others, Joliot in Paris and Fermi in Columbia using Rn-Be sources. 15Berkeley’s response to fission – immediately confirming and enlarging adiscovery made in Europe – had an air of déjà-vu. The same thing had happenedin the case of artificial radioactivity. As soon as news of the results ofJoliot and Curie arrived in Berkeley, Lawrence checked them with deuteronsaccelerated in the cyclotron. “To our surprise [he wrote] we found thateverything we bombarded... is radioactive”. The cyclotron had been making14 HS, 279-80; AMALDI, Da via Panisperna (1997), 75-6, 121.15 HS, 441-7.349

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEartificial radioisotopes for months; Lawrence could have made the discoveryof Joliot and Curie by examining the fillings in his teeth. “We looked prettysilly [one of Lawrence’s junior collaborators wrote]. We could have made thediscovery at any time”. 16The discovery of artificial radioactivity created a program at Berkeley similarto that of Fermi’s group in Rome – with notable differences. Thecyclotroneers obtained their neutrons from a process identified byRutherford and Cockcroft while trying to understand some odd resultsobtained in Berkeley. This process fused deuterons to make helium-3 and aneutron (or hydrogen-3 and a proton). Merely by letting ionized heavyhydrogen loose in the cyclotron, the Berkeley group made fast neutrons inplenty and closed off all probable paths to the discovery of the efficacy ofslow ones.Lawrence sprayed his fast neutrons on elements that might be transformedinto what he called “synthetic radium”. 17 In September 1934 he found whathe wanted. He bombarded table salt with deuterons and obtained, by (d,p),radioactive Na-24, which Fermi’s group had already made in two differentways, by (n,α) on aluminum and (n,p) on magnesium. But whereas Fermimerely pointed to the reactions and moved on, Lawrence seized uponradiosodium as a place to linger. He also tried to patent his (d,p) process toelude Fermi’s patent on Na-24 made via neutron excitation. The patentexaminer would not allow it for technical reasons having nothing to do withthe Rome work. It did not seem an important setback to Lawrence. He hadalready patented the cyclotron. Since he believed that the cyclotron wouldremain the only neans of producing radioisotopes in abundance, he thoughthimself protected sufficiently. He worried rather about how to increase productivity.18With men like McMillan and Alvarez, who joined Lawrence in the mid1930s, the Berkeley laboratory could not limit itself to the improvement ofapparatus, the manufacture of radioelements, and the hunt for new reactions.The detection of the mass-three isobars produced by deuteron fusion indicatesthe sort of physics the lab managed to sandwich between its bread-andbutteractivities. Energy measurements indicated that He-3 slightly exeededH-3 in weight. Majority opinion therefore held the helium isotope to be16 HS, 178-9.17 HS, 186.18 HS, 196-7.350

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESradioactive and the hydrogen isotope stable. The authoritative Hans Betheassigned He-3 a half-life of around 5000 years. Alvarez decided to employ thenew 60-inch cyclotron, idle for want of adequate shielding, in a search for stableH-3. While tuning the machine, he noticed a burst of mass-three particleswhen the source was not hydrogen but helium derived from a well in Texaswhere it had lain for geologic ages. He-3 turned out to be the stable isobar.Alvarez then sought evidence of a radioactive H-3 in the problematic activitiesdiscovered in Berkeley. He found it in a product earlier obtained byMcMillan, which had been misidentified as an isotope of beryllium. Lawrenceapplied this discovery immediately. He wrote to a major supporter, theRockefeller Foundation: “Radioactively labelled hydrogen opens up a tremendouslywide and fruitful field of investigation in all biology and chemistry”. 19The Big-Time FortiesThe bombs of Berkeley and ChicagoThe possibility of fission bombs did not excite the leaders of nuclear physicsin the United States in 1940. In so far as they thought the release of atomicenergy likely, they favored engineering (and controlling!) a chain reaction innatural uranium. They changed their minds in the fall of 1941 on learningtwo results obtained by refugee physicists living in England: the calculationsof Otto Frisch and Rudolf Peierls, which promised a big bang with only tenkilograms of U-235, and Franz Simon’s estimate that a gaseous diffusionplant covering only forty acres could produce a kilogram of pure U-235 aday. Lawrence immediately proposed to study the electromagnetic separationof the uranium isotopes on a grand scale, using cyclotroneering techniquesand a huge new magnet – with pole pieces 184 inches in diameter – that hewas building with a grant from the Rockefeller Foundation. Indeed, only bymobilizing the magnet for war could he obtain the steel and other strategicwar materials needed to complete it. He asked for and received $400,000from the government, the easiest money he had ever raised. 20Meanwhile, Fermi had been investigating the possibility of a self-sustainingchain reaction in natural uranium interspersed with a graphite moderator. It19 HS, 368-73; ALVAREZ, Adventures (1987), 68-70.20 HEWLETT and ANDERSON, New world (1962), 33-44; RHODES, Making (1986), 320-5, 339-40; HS,504-9.351

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEwas understood that a product of the pile would be plutonium and that plutoniummight be as explosive as U-235. Fermi, Segrè, and Lawrence met toplan the use of the 60-inch cyclotron to make enough plutonium to investigateits fission properties. The work, done by Segrè and Seaborg, made clearthat plutonium could serve in a bomb. Then came Pearl Harbor, a flood ofmoney, transfer of the Columbia work and personnel to Chicago, and theassembly, under Fermi’s direction, of the first self-sustaining pile. It wentcritical almost exactly a year after the United States declared war on Japanand Germany. 21The two projects then went forward in parallel as part of the ManhattanEngineer District, the code name given to the bomb business when the U.S.Army Engineers took it over in 1942. Fermi’s project industrialized underDupont and moved to Hanford, Washington; although he lost control ofdevelopment and criticized some decisions of Dupont’s engineers, heremained close to the project and continued to make contributions to it.Lawrence and his engineer-physicists guided the electromagnetic separationwork during its development phase and at Oak Ridge, Tenessee; but eventuallyit too was industrialized. Gigantic production plants arose in thoseremote places to house and service the uranium piles, plutonium separationtanks, and “calutrons”, or banks of mass spectrographs, for the electromagneticseparation of U-235. The Hanford industry based on Fermi’s pile producedall the material for the bomb that destroyed Nagasaki. Lawrence’scalutrons supplied some of the enriched uranium for the Hiroshima bomb. 22Fermi and Lawrence remained high in the councils of the ManhattanDistrict because of their essential contributions to it and because GeneralGroves, the project’s supreme commander, liked and trusted them. The generalfound in each, and in abundance, the qualities needed to push the workto success. Lawrence provided enthusiasm, unquestioning patriotism, and anundefeatable conviction that all technical obstacles could be overcome.Fermi provided scrupulously honest, even downplayed, technical assessments,authoritative opinions, and uncannily clever ideas. In return for thegeneral’s trust and in keeping with their middle-class backgrounds and highresponsibilities, Fermi and Lawrence identified more strongly with the militarythan most of their colleagues in the Manhattan District. Perhaps for this21 HEWLETT and ANDERSON, New world (1962), 54-6, 68, 88-9, 108-13; RHODES, Making (1986), 395-401, 428-42; HOLL, Argonne (1997), 15-20.22 HEWLETT and ANDERSON, New world (1962), 105-7, 112-14, 129, 141-59, 184-94, 207-24; RHODES,Making (1986), 407-15, 431-2, 487-500.352

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESreason as well as for his power of reasoning Fermi ranked with the directorsof the District’s major laboratories – Oppenheimer at Los Alamos, Lawrenceat Berkeley, and Arthur Compton at Chicago – and, like them, had the constantcompany of a bodyguard. 23In the spring of 1945, the Secretary of War asked the three directors andFermi to serve as a panel of experts to an Interim Committee he had set upto advise him about the use of the bomb and the future of atomic energy.Thus did Lawrence and Fermi, friendly rivals in small matters for a decade,find themselves collaborators on questions of immense moral and technicalsignificance. They turned out to have the same opinions. They concurred inthe unanimous recommendation that the bomb should be used withoutwarning on a target of military significance near a populated area. In theiropinion, no other demonstration, for example, a blast in an unpopulatedarea, would have a good chance of bringing Japan’s military government tosurrender. They also advised that in the immediate postwar period the governmentcontinue to support their activities at one billion dollars a year. 24Fermi, Lawrence, and Oppenheimer displayed their identification with theArmy and the cause of atomic energy immediately after the war in their supportof a proposal pushed by the military to establish an Atomic EnergyCommission (AEC) as successor to the Manhattan District. This proposalvested extraordinary powers in the army and the commission over employees,raw materials, facilities, and finances. Rank-and-file scientists organizedto defeat it and formed an unlikely alliance with the Bureau of the Budget,which opposed an organization able to run roughshod over civil rights anddo its business insulated from the executive authority of the president.Lawrence and Fermi were among the five or ten percent of Manhattan scientistswho did not join one of the federations that lobbied for a less restrictive,less secret, atomic science. Lawrence declared himself to be opposed inprinciple to scientists’ organizations not directed to the immediate pursuit ofscience and Fermi, though willing to talk politics privately, declined to bedrawn publicly. 25 Fermi expressed reservations through channels about themore permissive proposals that superseded the bill he had favored, and theresultant legislation, which established the AEC, bore traces of his interven-23 SEGRÈ, Fermi (1970), 102-3, 125-6, 136; GROVES, Now it can be told (1962), 61-2, 296-7, 377;CHILDS, Genius (1968), 355-6.24 HEWLETT and ANDERSON, New world (1962), 356-9, 367-8; RHODES, Making (1986), 649-51, 696-7, 750-9.25 SMITH, Peril (1965), 49-50, 148, 166-7, 249, 383, 395.353

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtion. The result satisfied him sufficiently that he accepted appointment to thenew commission’s General Advisory Committee (GAC), chaired byOppenheimer, for a three-year term beginning with the commission’s birthon January 1, 1947.Partial demobilizationFermi had been able to continue his studies of reactors and neutron physicsin 1943 and 1944 at the pile built to his specifications at the ManhattanDistrict’s laboratory at Argonne near Chicago. He began to distance hmselffrom the subject, however, as it became industrialized; and, as a member ofthe GAC, he gave priority to weapons over reactors. With the majority of theGAC, he doubted that economic nuclear power could be available withintwenty years. The only reactor project to which he assigned a high prioritywas a power plant for the propulsion of ships and submarines. TheManhattan District had started a propulsion project, which the GAC consideredweak and desultory. What to do about it? Fermi proposed the obvioussolution: call in Lawrence to chair a committee to oversee the project andinject the enthusiasm and vitality it lacked. The GAC endorsed the proposalbut the commission rejected it. On the other hand, Fermi opposedLawrence’s proposal to build a high-flux reactor mear Berkeley on theground that Lawrence’s staff did not have the necessary skill or experience. 26While serving on the GAC, Fermi was also building up an important schoolin theoretical physics in Chicago and championing high-energy physics elsewhere.27 Although he continued to range over most of physics, he decidedto shift his main concern from the nucleus to its constituents, thus duplicatingthe move from the atom to the nucleus that had proved so productive inthe 1930s. One of his earliest contributions, which had important implicationsfor Berkeley, developed from his analysis of an experiment done in Italyin hiding during the war by Marcello Conversi, Ettore Pancini, and OrestePiccioni. 28 Working in a cellar where only they and cosmic rays penetrated,they managed to capture electronically the decays of a few mesotrons. (Theseparticles had been detected in 1937 at Caltech in a cloud chamber adaptedto the study of cosmic rays.) Fermi’s analysis of the life times of the particlesobserved by Conversi, Pancini, and Piccioni indicated that they could not be26 HEWLETT and DUNCAN, Atomic Shield (1962), 31-2, 117-18, 209, 217, 383; SEGRÈ, Fermi (1970), 131-2.27 BONOLIS, in BERNARDINI and BONOLIS, Conoscere Fermi (2001), 364-77.28 ROSSI, Cosmic rays (1964), 127-8; PICCIONI, in BROWN and HODDESON, Birth (1983), 222-9, 239-40;CONVERSI, in ibid., 243-8; FERMI, Coll. papers, 2 (1965), 615-17.354

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESthe carriers of nuclear force proposed by Hideki Yukawa. The upshot wasthat the mesotron found in cosmic rays could not be Yukawa’s particle – adistinction confirmed by evidence of the transformation of a charged Yukon(a π meson) into a mesotron (a µ meson). This golden event took place in aphotographic emulsion exposed to cosmic rays by Giuseppe Occhialini, whohad studied under Persico and no doubt learned his quantum mechanicsfrom the famous text. At the time, 1947, Occhialini was working in Bristolwith Cecil Powell and the Brazilian Cesar Lattes. 29Meanwhile Berkeley had commissioned the 184-inch cyclotron, or, to betechnical, synchro-cyclotron, which worked on a principle invented byMcMillan. Theorists had warned in 1939 that the conventional cyclotronwould not produce the 100 MeV deuterons that Lawrence promised theRockefeller Foundation because their relativistic increase in mass wouldthrow them out of phase with the accelerating radio-frequency field.McMillan suggested that if the particles were injected into the machine indiscrete bunches and the frequency of the field altered appropriately as theygained energy, they could stay in phase with the acceleration. With othermodifications of the original design, McMillan’s principle of phase stabilityenabled Berkeley’s physicists and engineers to double the energy originallypromised, to 100 MeV per nucleon. Although that was just enough to makemesons, the Berkeley physicists did not look for them when the 184-inchstarted running in November 1946. Only late in 1947 did they begin thesearch. Eugene Gardiner, who had received his Ph.D. in 1943 underLawrence with a thesis on calutron sources, oversaw a group that exposedemulsions in the paths of mesons created in a target struck by the synchrocyclotronbeam. They found nothing using the emulsions made for them byEastman Kodak. Success came with Lattes, who brought the emulsions usedby the Bristol group and the experience to recognize meson tracks. InFebruary 1948 Berkeley registered the first machine-made mesons. 30These mesons were charged. Theories of cosmic rays by Oppenheimer andothers had predicted an uncharged pion, which could not easily be spottedin the sea of particles in the 184-inch machine. No matter. McMillan hadbuilt an electron synchrotron with the special support and blessing ofGeneral Groves. Pions generated via the synchrotron decayed into photons29 ROSSI, Cosmic rays (1964), 131-41; LATTES, in BROWN and HODDESON, Birth (1983), 307-10;MARSHAK, in ibid., 376-86.30 MARSHAK, in BROWN and HODDESON, Birth (1983), 386-7; HEILBRON, SEIDEL, and WHEATON,Lawrence (1981), 51-60.355

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEdetected by coincidence counters. By then, 1950, Lawrence had alreadystarted on a new machine. The synchro-cyclotron produced particles of severalhundred million electron volts; its successor, the Bevatron, paid for bythe AEC, would scale up by an order of magnitude and operate on a newprinciple. It would confine particles to orbits of fixed radius within a narrowcircular evacuated ring that ran through a series of small bending magnetswhose fields would be adjusted to correct for the relativistic increase in mass.When the laboratory received permission to proceed with the Bevatron in1948, it hoped to accelerate protons to around six billion electron volts,which, according to the calculations of Fermi and others, might be sufficientfor the creation of antiprotons. In fact, the design of 1948 would not havereached 6 GeV because it provided for a large gap to accommodate the circulatingparticles within the magnets that held them in their orbits.Designers worried that they could not control the beam sufficiently to permita smaller gap, which would have allowed a stronger field and the confinementof more energetic particles. 31As the frame of the bevatron rose above San Francisco Bay, the SovietUnion detonated its first atomic bomb and the GAC debated the merits of acrash program for a fusion bomb. Fermi had favored research into thermonuclearexplosives, but he joined the rest of the GAC in recommendingto the commissiom that it not rush for the so called “super”. They invokedboth moral and technical reasons for their advice: since a thermonuclearbomb could be made as large as its maker pleased, there was no natural limitto the devastation it could wreak, and, moreover, no one knew how to makeone. The commissioners accepted this advice and referred the decision toPresident Truman. The decision distressed Lawrence and Edward Teller,who pushed their views as high as they could reach. They were helped by therevelation of atomic espionage and the outbreak of the Korean War. 32Truman authorized a crash program. Lawrence rushed to do his part, which,he decided, was to make nuclear and thermonuclear explosives in large quantitiesby both particle accelerators and a high-flux reactor. As we know, thecommission, acting on Fermi’s advice, turned down the reactor. But it sunka large amount of money into Lawrence’s factories for making explosiveiostopes in his favorite manner – by bombardment.31 HEILBRON, SEIDEL, and WHEATON, Lawrence (1981), 76-8; HEILBRON, in De Maria et al.,Restructuring (1989), 172-4.32 HEWLETT and DUNCAN, Atomic Shield (1962), 530-7, 581-4.356

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIESThe first stage of a suitable production accelerator was built in the early1950s at a disused airbase not far from Berkeley in the Livermore Valley. Themachine did not run in circles like the cyclotron, but in a straight line, usinghuge oscillators and long drift tubes to hurry and control the beam withinthe greatest nothingness – that is, the largest vacuum – ever created by man.The design scaled up the proton linac that Alvarez had built from radar oscillatorsand other parting gifts to Lawrence from General Groves. This largeand expensive business came to an early end when the commissioners realizedthat they could obtain the raw materials for fission and fusion bombsmore cheaply in other ways. 33Lawrence’s initiative had two grand consequences, however. For one, the siteof the production accelerator became the nucleus of the Lawrence LivermoreLaboratory. For another, when the builders of the prototype production acceleratorreturned to Berkeley to finish the Bevatron, they brought with themexperience with beam control and high vacuum systems that made them confidentthey could reduce the gaps between the pole pieces enough to reach 6GeV. And so the great machine came into full-scale operation in November1954 with the capacity to make antiprotons. Once again, the need to do practicalwork made a Berkeley accelerator capable of prodigious physics. 34In keeping with tradition, however, most of the early experiments at theBevatron concerned particles discovered elesewhere – pions and also kaons,the strange particles first detected by cosmic-ray physicists in photographicemulsions in 1947. The exotic life-styles of kaons occupied the attention ofseveral groups at Berkeley, including Segrè’s. The information they collectedhelped prompt the invention of the concept of hypercharge and the discoveryof the non-conservation of parity. Early in 1955, Segrè’s group and others,each in its own way, began to look for antiprotons. Segrè’s won inOctober 1955, using advanced counters and up-to-date magnets designedwith the help of Piccioni. The machine men then turned the tables on theobservers of nature’s direct bounty. Segrè sent film exposed not to the heavensbut to the Berkeley Bevatron to Amaldi’s cosmic-ray scanners in Rome,where they soon found a minuscule cataclysmic explosion in which anantiproton ended its career. 35 At last, an accelerator had made and studiedparticles not previously found in cosmic rays and had opened a field of33 HEILBRON, SEIDEL, and WHEATON, Lawrence (1981), 62-75.34 HEILBRON, in DE MARIA ET AL., Restructuring (1989), 176-84.35 Ibid., 185-91.357

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEresearch not adumbrated by more modest instruments. The manufacture anddetection of the antiproton marked the full realization of the potential ofLawrence’s machine, and vindicated his twenty years of devoted effort tomake his cyclotron the ultimate tool in fundamental physics.Lawrence had further satisfaction in the success of Seaborg, whose group,persisting in the old game, made one transuranic element after another in ahigh-intensity, moderate-energy, cyclotron erected below the Bevatron on ahill overlooking the Berkeley campus. Two of these superheavy elements,which rejoice in the unlikely names berkelium and californium, celebrateLawrence and his laboratory. Another, number 100, bears a name that comesmore readily to the mind and tongue: fermium.REFERENCES01. ALVAREZ L. W. Adventures of a physicist. New York: Basic Books, 1987.02. AMALDI E. “Il caso della fisica”. In Le consequenze culturali delle leggi razziali. Accademiadei lincei. Atti dei convegni, vol. 84. Rome: the Academy, 1990. Pp. 107-133. In AMALDI,20 th century physics (1988), 141-67; 168-90 (English tr.).03. AMALDI E. “Personal notes on neutron work in Rome in the 30s and post-war Europeancollaboration in high-energy physics”. In CHARLES WEINER, ed. History of twentieth centuryphysics. New York: Academic Press, 1977. Pp. 294-351. (International School ofPhysics “Enrico Fermi”, course LVII, July-August 1972.)04. AMALDI E. Da via Panisperna all’America. Ed. GIOVANNI BATTIMELLI and MICHE-LANGELO DE MARIA. Rome: Riuniti, 1997.05. AMALDI E. “Neutron work in Rome in 1934-36 and the discovery of uranium fission”.Rivista di storia della scienza, 1 (1984), 1-24. In AMALDI, 20 th century physics (1998), 5-28.06. AMALDI E. 20 th century physics: Essays and recollections. A selection of historical writings. Ed.GIOVANNI BATTIMELLI and GIOVANNI PAOLONI. Singapore: World Scientific, 1998.07. BATTIMELLI G. and DE MARIA M. “Prefazione”. In AMALDI, Da via Panisperna (1997),15-55.08. BONOLIS L. “Cronologia dell’opera scientifica di Enrico Fermi”. In CARLO BERNARDINIand LUISA BONOLIS, eds. Conoscere Fermi nel centenario della nascita. Bologna: EditriceCompositori, 2001. Pp. 319-77.09. BROWN L.M. and HODDESON L. eds. The birth of particle physics. Cambridge: CambridgeUniversity Press, 1983.10. CARDONE F. and MIGNANI R. Enrico Fermi e i secchi della sora Cesarina. Metodo, prejudizioe caso in fisica. Rome: Di Renzo, 2000.11. CHILDS H. An American genius. The life of Ernest Orlando Lawrence, father of the cyclotron.New York: Dutton, 1968.358

John L. HeilbronEXPERIMENTAL NUCLEAR PHYSICS IN THE THIRTIES AND FORTIES12. CONVERSI M. “The period that led to the 1946 discovery of the leptonic nature of the‘mesotron.’” In BROWN and HODDESON, Birth (1983), 242-50.13. FERMI E. Collected papers. Ed. EDOARDO AMALDI ET AL. 2 vols. Chicago: University ofChicago Press, 1962-65.14. FERMI L. Atoms in the family. Chicago: University of Chicago Press, 1954.15. GROVES L.R. Now it can be told. The story of the Manhattan project. New York: Harpers,1962.16. HEILBRON J.L. “The detection of the anti proton”. In MICHELANGELO DE MARIA ET AL.,eds. The restructuring of physical sciences in Europe and the United States 1945-1960.Singapore: World Scientific, 1989. Pp. 161-217.17. HEILBRON J.L. and SEIDEL R.W. Lawrence and his laboratory. A history of the LawrenceBerkeley Laboratory. Vol. I. Berkeley: University of California Press, 1989.18. HEILBRON J.L., SEIDEL R.W. and WHEATON B. Lawrence and his laboratory. Nuclear scienceat Berkeley 1931-1961. Berkeley: University of California, Office for History ofScience and Technology, 1981.19. HEWLETT R.G. and ANDERSON O.E. Jr. The new world, 1939-1946. University Park:Pennsylvania State University Press, 1962. (A history of the United States Atomic EnergyCommission, vol. 1.)20. HEWLETT R.G. and DUNCAN F. Atomic shield, 1947-1952. University Park: PennsylvaniaState University Press, 1962. (A history of the United States Atomic Energy Commission,vol. 2.)21. HOLL J.M. with HEWLETT R.G. and HARRIS R.R. Argonne National Laboratory, 1946-96.Urbana: University of Illinois Press, 1997.22. HOLTON G. “Striking gold in science: Fermi’s group and the recapture of Italy’s place inphysics”. Minerva, 12 (1974), 159-98.23. LATTES C.M.G. “My work in meson physics with nuclear emulsions”. In BROWN andHODDESON, Birth (1983), 307-10.24. MARSHAK R.E. “Particle physics in rapid transition: 1947-1952”. In BROWN andHODDESON, Birth (1983), 376-401.25. PICCIONI O. “The observation of the leptonic nature of the ‘mesotron’ by Conversi,Pancini, and Piccioni”. In BROWN and HODDESON, Birth (1983), 222-41.26. RHODES R. The making of the atomic bomb. New York: Simon and Schuster, 1986.27. ROSSI B. Cosmic rays. A dramatic and authoritative account. London: George Allen andUnwin, 1964.28. SEGRÈ E. Enrico Fermi, physicist. Chicago: University of Chicago Press, 1970.29. SEGRÈ E. A mind always in motion. The autobiography of Emilio Segrè. Berkeley: Universityof California Press, 1993.30. SMITH A.K. A peril and a hope. The scientists’ movement in America 1945-47. Chicago:University of Chicago Press, 1965.359

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEJohn L. HeilbronJohn.L. Heilbron, formerly professor of history and the vice chancellor at theUniversity of California, Berkeley, is now senior research fellow at WorcesterCollege and at the Museum for the History of Science, Oxford. His generalsubject of research is the history of the physical sciences and their institutionsfrom the Renaissance into the 20 th century. His work most relevant to the FermiConference,Lawrence and his Laboratory, a history of the Lawrence BerkeleyLaboratory, vol. 1(Berkeley, 1989), was written in collaboration with RobertSeidel. It includes much information about the development of nuclear physicsin Europe and the US in the 1930s as well as a local history of the Berkeleyaccelerators. His recent book, The sun in the church: Cathedrals as solarobservatories (Harvard, 1999), describes the contributions to astronomy andcalendrics made by observers at meridian lines installed in a few majorchurches, all but one of them in Italy, during the 17 th and 18 th centuries, andthe operation of the censorship of books on cosmology after the condemnationof Galileo. His latest work is the Oxford companion to the history of modernscience (Oxford, 2003), of which he was the general editor.360

Leon LedermanThe Beginnings of Pion and Muon PhysicsMy talk will review the birth and early evolution of High Energy Physics (ParticlePhysics) as it emerged from the series of post world war II accelerators. This willtouch, in a detailed way, the work of Fermi at Chicago in the decade of the1950’s. Fermi, in Chicago with a spectacular group of students, was a primemover in opening this field. The major physics concerns of the day were theproperties of pions and muons. The scattering of pions by protons gave physicsa glimpse of the strong force whereas muons and their related neutrinos were theentry to high energy weak forces. My own work at Columbia and research atBerkeley, Rochester, Liverpool, etc. are relevant to that seminal epoch at thebeginning of a new field.La nascita della fisica dei pioni e dei muoniLa mia relazione verterà sulla nascita e l’evoluzione iniziale della fisica delle alteenergie (fisica delle particelle) derivante dalla serie di acceleratori costruiti dopola seconda guerra mondiale, analizzando dettagliatamente il lavoro svolto daFermi a Chicago all’inizio degli anni 50. A Chicago Fermi, con un gruppospettacolare di studenti, fu un pioniere in questo campo. I principali temi distudio dell’epoca erano le proprietà dei pioni e dei muoni. Lo scattering deipioni per mezzo dei protoni aprì alla fisica uno squarcio sulla forza nucleareforte, dove i muoni ed i relativi neutrini rappresentavano la strada verso le forzenucleari deboli.Il mio lavoro alla Columbia University e la mia ricerca alla Berkeley University, aRochester, a Liverpool ecc. riguardano quell’epoca determinante che segnal’inizio di un nuovo settore di ricerca.361

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIsend this note instead of attending this meeting because of the disruptionsto all of our lives by the tragic events of September 11 th . I had been lookingforward to coming to Rome, celebrating Enrico Fermi’s centennial andseeing many old friends. The scientific community, which so reveres Fermi’scontributions, both in science but also in style, must now maintain our faithin rationality, which is threatened on all sides. It is my personal belief that wemust understand and act wisely on the root causes of terrorism. But now letme make a few remarks relevant to the Centennial.My assignment, for the Fermi Centennial, was to discuss the early periodof pion and muon physics. I was among the first post-WWII graduate studentsto get a Ph.D. at Columbia University’s NEVIS Cyclotron Laboratory.The date was 1951. My thesis was on the lifetime of the pion and the massof the muon. My advisor was visiting Professor Gilberto Bernardini.Through Gilberto, I met Fermi several times. Our involvement with pionswas essentially simultaneous; Fermi’s Chicago Period included a new collectionof awesome students that Fermi seemed to attract. It was quintessentialFermi, with an almost seamless mix of theory and experiment. I recall beingdelighted that the great Fermi was working on the same things as I. NEVIScame on line a few years before Chicago. John Tinlot and I had discoveredhow to get beams of pions out of the accelerator, focused by the fringingfield of the cyclotron magnet. We had “hot and cold” pion beams! OurBerkeley competitors were not so lucky. Our negative beams went out to~150 MeV, but positive pions (obtained from backwards emission in protontargetcollisions) died at about 60 MeV. We worked on lifetimes of pions, onscattering of pions from a carbon plate in a Wilson Chamber, on the mass ofthe muon and the properties of the neutrino. Fermi’s group concentrated onpion-proton scattering. I still recall the excitement of Fermi’s “RochesterConference” presentation of his negative pion scattering. The cross sectionwas large, definitively establishing the strong interaction of pions after somedisturbing cosmic ray results.When Fermi’s group turned to positive pions, the results were even morespectacular. The cross section rose dramatically. When it was last seen, it wasat about 135 MeV, heading steeply upward. The suspicion was a resonancebut it took several years to establish the “3-3” resonance, although Fermi, onthe basis of a glance at a paper written by Keith Bruekner, predicted thefamous ratio of the three pion-proton cross sections (pi plus to pi plus; piminus to pi zero and pi minus to pi minus) as 9:2:1.Fermi led in the reduction of the data via a phase shift analysis. Again, it362

Leon LedermanTHE BEGINNINGS OF PION AND MUON PHYSICSwas only after Fermi’s death that the correct phase shifts were established andthe isospin 3/2, angular momentum 3/2 resonance firmly established.I will never forget the first Rochester Conference in 1950. I was the onlygraduate student present and found myself standing next to Enrico on thelunch line. Desperate to show my deep knowledge, I asked him:“Professor, what do you think of the evidence for the V-zero-two which wejust heard?”He looked at me and gave a response that became famous:“Young man, if I could remember the names of these particles, I wouldhave been a botanist”.We were in a new field which emerged from the fields of cosmic rays andnuclear physics. The beginnings in the accelerators of Chicago, Berkeley andColumbia are the clear progenitors of a field that has led to our currentunderstanding of the Standard Model of Fundamental Particles and its essentialcoupling to the astrophysics of the origins and evolution of the universe.It is clear that Enrico Fermi’s personal leadership, his scientific style and hisinfluence on students was a major force in the establishment of physics in theUnited States.My personal contact with Fermi in visits to Chicago, in RochesterConferences, in his early summer visit to Brookhaven just months before hisillness, was a seminal experience. I was later honored to become Director ofthe Fermi National Accelerator Lab (Fermilab) and to receive the EnricoFermi Medal at the hands of President Bill Clinton in 1993. I now send mywarmest greetings to the Centennial assembly convinced that the pursuit ofour efforts to understand the world, and to insist that this knowledge beapplied compassionately, is the highest form of tribute to the memory ofEnrico Fermi.Leon LedermanInternationally renowned high-energy physicist, is Director Emeritus of FermiNational Accelerator Laboratory in Batavia, Illinois and holds an appointmentas Pritzker Professor of Science at Illinois Institute of Technology, Chicago. Dr.Lederman served as Chairman of the State of Illinois Governor’s ScienceAdvisory Committee. He is a founder of and Resident Scholar at the IllinoisMathematics and Science Academy, a 3-year residential public high schoolfor the gifted. Dr. Lederman was the Director of Fermi National AcceleratorLaboratory from June 1, 1979 to June 30, 1989. He is a founder andChairman of the Teachers Academy for Mathematics and Science, active in363

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEthe professional development of primary school teachers in Chicago. In1990 he was elected President of the American Association for theAdvancement of Science, the largest scientific organization in the US. He isa member of the National Academy of Science and has received numerousawards, including the National Medal of Science (1965), the Elliot CressonMedal of the Franklin Institute (1976), the Wolf Prize in Physics (1982), theNobel Prize in Physics (1988) and the Enrico Fermi Prize given by PresidentClinton in 1993. He served as a founding member of the High EnergyPhysics Advisory Panel of the United States Department of Energy and theInternational Committee for Future Accelerators. Lederman chairs theCommittee on Capacity Building in Science of the Paris-based InternationalCouncil of Scientific364

Luciano MaianiPerspectives in High Energy Particle PhysicsFermi was much interested in high energy physics at the end of his life: we recallhere the main lines of his thought in order to show the continuity of thedevelopment of this extremely important frontier of knowledge since his time. Theimportance of high energies is stressed as far as some unpredictableimprovements in the last 50 years both in the instruments (colliders andcomputers) and in the theory (symmetries and new particles). LHC at CERN istherefore a natural achievement in Fermi’s legacy.Prospettive della fisica delle alte energieFermi fu estremamente interessato alla fisica delle alte energie nell’ultima partedella sua vita. Vogliamo qui ricordare e tracciare le linee principali del suopensiero, tanto da evidenziare la continuità di sviluppo di questa frontiera cosìrilevante della conoscenza.L’importanza della fisica delle alte energie è evidenziata dagli imprevedibilimiglioramenti sia nella strumentazione (computer e Collider) sia nella teoria(simmetria e nuove particelle) degli ultimi cinquant’anni.L’LHC del CERN rappresenta dunque una conseguenza logica dell’ereditàfermiana.365

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEIntroduction: a Fermi’s legacyIn January 1954, E. Fermi gave a talk entitled “What Can We Learn WithHigh Energy Accelerators?” at the American Physical Society. He was thenleaving the APS Chair, which he had taken during 1953. The University ofChicago Library has short personal notes that Fermi wrote for the talk as wellas the slides of the figures.It was indeed a crucial moment in particle physics. 1 The discovery of manynew particles in cosmic rays had opened a new world and stimulated thedevelopment of particle accelerators. Big projects were starting in the US,the URSS and Europe, where CERN was being created just for this purpose.At that time, Fermi was fully engaged in particle physics. On the experimentalside, he was studying the π-N cross sections at the ChicagoSynchrocyclotron, finding the first indications of the 3/2-3/2 resonance andthe confirmation of the isotopic spin symmetry in π-N interactions. On thetheoretical side, Fermi was impressed by the wealth of new particles that werebeing discovered in the high-energy cosmic ray interactions. Not all these particlescould really be elementary! Together with C. N. Yang, he had developed,in 1949, a model of the π mesons as bound states of a nucleon-antinucleonpair, the precursor of the quark model of mesons and baryons, whichwas going to be discovered by Gell-Mann and Zweig some twelve years later.What to do with high-energy accelerators? Fermi underlines the difficulty oflooking into a “very, very cloudy crystal ball”. He mentions the observation ofantinucleons, the puzzle of the long lifetime of strange particles (high angularmomentum barrier, or associated production, which he qualifies as “at presentmore probable”), the need for precision measurements. But also the possibilityof “a lucky break, or theoretical leap, or more probably a combination of hardwork, ingenuity and a little bit of good luck”. All that and much more did infact happen from the 1950s until now in High-Energy Particle Physics. Progressis exemplified in Figure 1, by the chart of what are now considered to be theelementary constituents of matter, the three generations of quarks and leptons.The forces acting on quarks and leptons are described by a coherent theoreticalframework, usually referred to as the Standard Theory (see box). Theyencompass the familiar electromagnetic forces acting between charged particles,the weak forces responsible, among other processes, of the beta decayof nuclei, and the strong forces that bind quarks into nucleons (proton and1 See M. JACOB and L. MAIANI “L’eredità di Enrico Fermi nella fisica delle particelle”, in Conoscere Fermi,edited by C. BERNARDINI and L. BONOLIS, SIF, ed. Compositori, Bologna 2001.366

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICS1.0E+121.0E+101.0E+081.0E+061.0E+041.0E+021.0E+001.0E–021.0E–04eVdirect limitsto ν-masses1st generation 2nd generation 3rd generation1 2 3ν-massesfrom oscillationsnu-directnu-oscillup-Quarksd-Quarksch-LeptonsFigure 1The mass spectrum of quarksand leptons (ascending powersof eV). Upper bounds toneutrino masses are takenfrom beta decay spectra;estimates of ν µ and ν τ massesare from solar and atmosphericneutrino oscillationsneutron) and nucleons into nuclei. To those forces, one has to add thoseassociated with the, still hypothetical, Higgs field, which are responsible forthe arising of particle masses, as discussed below.In the Standard Theory, the Electromagnetic and weak forces are unifiedin a simple scheme and all the three forces are determined by the sameprinciple: the invariance under transformations which may vary arbitrarilyfrom point to point (in jargon, a gauge symmetry). This similarity is astrong hint that it may be possible to discover a more unified scheme whichencompasses all forces, including the Higgs and, most important, the gravitationalforces. New dynamical concepts and new symmetries will be certainlyrequired to accomplish this very ambitious further step in our knowledgeof Nature.CollidersTo illustrate the potential of particle accelerators, Fermi considered in hisseminar a proton accelerator running on a maximum circle around the Earth.With a magnetic field of 2 Tesla, this gives an energy E Max = 5 10 15 eV. It isthe energy of the cosmic rays around the ‘knee’, the most energetic cosmicrays that can be accelerated by the galactic magnetic clouds, according toFermi’s ideas developed in the very same years.By extrapolating from the plots of energy or cost vs. time of the nuclear367

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1. Normal Matter (Galaxies, stars, us,…)QUARKSLEPTONS(M. Gell-Mann, G. Zweig, 1962)uv(ed)( e)2. Analogous structures at higher energyc(1974) v µ (1962)( s ) ( µ )t(1994) v τ (2000)( b(1977) ) ( τ(1976) )3. ForcesElectromagnetic → PHOTON (A. Einstein, 1905)Weak → W, Z (CERN, 1982)Nuclear → GLUONS (not seen in isolation)Gravitational → GRAVITON (not yet observed)Mass Generation → HIGGS BOSON (not yet observed)Particles of the Standard Theory. The year of the first experimental observation isindicated next to each particle, but for the “classical” ones (the electron, the muon,the nuclear beta decay neutrino and the three quarks of Gell-Mann and Zweig).installations of the time, Fermi concluded that this energy could be reachedin the year 1994, at a cost of about 170 billion US dollars.The key to high energy and relatively low cost (very low indeed, comparedto Fermi’s extrapolation) has been, of course, technological innovation,above all the invention of “colliders”, structures which are capable to accelerateand store two beams of particles, then made to collide head-on at a few,fixed points. The discovery has made possible a gigantic leap forward in theenergy available for the collision, the energy in the center of mass, which inturns determines the discovery potential of the machine. 2The first electron–positron collider was realized in Italy, at the FrascatiNational Laboratories (AdA, 1962) by Bruno Touschek and collaborators.2For relativistic particles, the c.o.m. energy in the fixed target mode is √2E beam M target , while for two symmetricallycolliding beams is √4E beam E beam ≈ 2E beam . Thus the available energy increases much faster(1) (2)with E beam in the second case. Colliders, on the other hand, pose enormous technological challenges toachieve sufficiently high density of beam packets and to store them for enough time, so as to have anappreciable number of collisions.368

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSProton–proton (ISR, CERN, 1971), proton–antiproton (Sp p – S, CERN,1981) and electron-proton (HERA, DESY, 1992) colliders followed.Transforming back to the fixed-target energy, the Tevatron (protonantiprotoncollider, 2 TeV in the c.o.m.) reached 2 10 15 eV in 1987. LEP(electron-positron, 200 GeV in the c.o.m.) and HERA (electron-proton,300 GeV in the c.o.m.) have explored about the same energy range withprobes unthinkable at Fermi’s time. The Large Hadron Collider (LHC, proton-protoncollider with 14 TeV in the c.o.m.) will reach 1 10 17 eV in 2006,20 times E Max , at an all-out cost of about $5 billion.If the VLHC which is being considered today at the Fermi National Laboratoryor the Eloisatron proposed by INFN will be realized, with a center-of-mass energyof 200 TeV and corresponding to fixed-target energy around 2 ⋅ 10 19 eV,mankind will have been able to produce collisions at an energy equivalent to thatof the highest-energy cosmic rays that can originate from nearby galaxies. 3Symmetry in Particle PhysicsOn the theoretical side, symmetry has been a crucial concept to investigatethe role of the new particles.In plain language, symmetry implies well-balanced proportions (from theGreek words σψµ, ‘with’, and µετροσ, ‘measure’). Symmetric objects havegrace and beauty. The most beautiful vistas, whether faces or buildings, arethe most symmetric, the most perfect. What is more important for us, thenatural balance of symmetry leads to predictability. We can guess a hiddenpart of a figure, if we know the symmetry, which supervises its design.Symmetry is demanding. The slightest fault, and the symmetry is no longerfaithful. The picture in Figure 2 (Pala della Misericordia) looks left right symmetricat first sight, but this is not exact. The Madonna has an asymmetricbelt’s knot; the praying figures are not symmetrical. Most important, the figureis illuminated from one side. The fully symmetric picture looks more flat,static and hieratic, the real Madonna is human and closer to us.In the Madonna del Parto (Figure 3), the angels are almost left right symmetric,but the different colours of their dresses give movement to the wholepicture. And, of course, the Madonna in the centre is now “breaking the symmetry”,with the wonderful curve associated to her maternity. We still do not3 i.e. those below the GZK cut-off due to the onset of π-meson production in the scattering of cosmicray protons off the microwave cosmic background photons.369

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFigure 2Pala della Misericordia. The real picture is shown (left) together with the artificially reconstructedpicture “predicted” by left-right symmetry, from the right half of the figureknow why symmetry is relevant to physics, but predictability is the key of itssuccess. To describe fully the complexity of the world, however, some of themost beautiful symmetries have to be broken. Figure 4 shows with a fewexamples the power of symmetry and the need for symmetry to be broken.Can we break a local symmetry?Piero della Francesca could introduce variations at will in his symmetry pattern.But, is this possible in Nature? Is it possible at all to violate the symmetry?And if so, are there limitations?There is only a numerable infinity of discrete symmetries (the “crystallographicgroups”). Similarly, we can classify by numerable series the continuousgroups. It would be relatively easy for God to assign a symmetry to theworld! Symmetry breaking, instead, belongs to the realm of unpredictability,fantasy and chaos (is this why the Madonnas and angels of Piero are so fas-370

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSFigure 3N PIsopic Spin (SU2)Deviations0 +1from symm.Mc 2 0.9396 0.9383 input0.14%π + π 0 π –+1 0 –1photonMc 2 0.1396 0.1350 0.1396 M(π 0 ) = M(π + ) ??3.3%N PEightfold Way (SU3)0 +1Σ – Σ 0 /∆ 0 Σ +–1 0.0 +1Ξ – Ξ 0All equal masses? ? 30%Mc 2Mc 2–10photon00W + Z 0 W –+1 –1 080.419 91.188 80.419Mass (photon) = 0Mass (W, Z) = 0 !!!!La Madonna del Parto. The angels areleft-right symmetric to great extent,except for the colours of their dresses,but the Madonna breaks the symmetryquite dramaticallyThe “gaugesymmetry”of fundamentalforces is brokenFigure 4Symmetry in particlephysics: predictions vs.reality. Top: predictions ofthe approximate globalsymmetries in ParticlePhysics. Bottom: localsymmetry predicts equalmasses for the photonand for the intermediatebosons, in flagrantcontradiction with reality371

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEcinating?). In mathematical terms, symmetry can be broken in infinitelymany continuous ways.Seen in this context, the issue belongs to the wider philosophical questionof the uniqueness of the fundamental laws of physics. Is there only one consistentset of laws and therefore only one consistent Universe? Or can we putarbitrary parameters in the basic laws such that there may exist, or at least wecan “imagine”, different, equally consistent Universes, distinguished by theactual values of these parameters (masses, electric charges, Newton constant)?We have made limited but interesting progress on these fascinating questions.First, we have to distinguish between symmetries where the same transformation(say, a rotation) is applied at all points of space and time, the so-called“global symmetries”, and symmetries where laws are invariant under transformations,which can be chosen differently from point to point in space andtime. The latter are called “local”, or “gauge”, symmetries.There is essentially no restriction to violate any global symmetry. However,more important is the second case, which includes the Einstein Theory ofgravity and the theories introduced by Yang and Mills in 1954 (the so-called“gauge theories”), known today to accurately describe the interactions offundamental particles.In these cases, introducing symmetry violations in the basic laws (technically,adding non-symmetric terms in the Action) leads to mathematicalinconsistency.There are quite a number of qualifications to append to this very bluntstatement, but I think my theoretical colleagues would agree that it describescorrectly the situation: no Piero della Francesca has the freedom to “deform”even slightly the Yang Mills or Einstein basic laws.But then, how are we going to account for the asymmetries observed inNature, namely the unequal masses of photons, W and Z particles, or themasses of quarks and leptons, which also should vanish in the symmetricworld? The solution is simple and fascinating.A field pervades all space and affects the way particles move. Whilst the basiclaws are exactly symmetric, the very presence of this field violates the symmetry,in that the field itself “distinguishes” different particles related by symmetry.By their interaction with this background field, W and Z acquire a mass butthe photon remains mass-less, leptons and quarks acquire different masses.In this picture, the “vacuum”, the state where “there is nothing”, is notempty at all. Rather, it is like the surface of a perfectly calm lake: there seemsto be nothing because it is everywhere equal to itself. In collisions, waves can372

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSFigure 5ALEPH: candidate event for e + +e – → Z+ H, followed by Z → hadrons (jets 1 and 2) and H → b+b – (thedotted lines indicate the path of neutral unstable particles which decay in jets 3 and 4 and are identifiedas beauty particles); the decay into a beauty particle pair is the theoretically preferred decay mode of theHiggs boson and is used to select events which should contain this particle with higher probabilitybe produced on the surface of the lake, some of which correspond to a newparticle: the Higgs boson. The Higgs boson is needed for the mathematicalstructure of the theory to agree with what we see in Nature, but the wholepicture gives a description of vacuum which may lead us to a new vision ofthe Universe, in particular of the primordial Universe (inflation, chaoticUniverse).Higgs HuntingI would not go so far as to call the Higgs Boson the “God particle” 4 , butit is clear that the observation of this particle is crucial, to give solid foundationto our theory of Elementary Particles and to validate the more advancedviews on the primordial Universe. This justifies the excitement that has pervadedthe world of physics (not only!) when some tantalizing evidence of aHiggs boson was seen, last summer, in the ALEPH experiment at CERN.The definitive analysis of the LEP data still shows some evidence of a Higgsboson, but the degree of confidence that the events seen are not due to a sta-4 L. LEDERMAN with D. TERESI, The God particle, Dell Publishing, New York, 1993.373

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEtistical fluctuation is smaller than what was indicated by the preliminaryanalyses made at the end of the year 2000.This dry scientific statement has recently given rise to a curious debate on ascientific journal, following a rather unrefined interpretation of the LEP dataanalysis given by its scientific editor, which reads 5 : “No sign of the Higgs boson.The legendary particle that physicists thought explained why matter has massprobably does not exist. So say researchers who have spent a year analysing datafrom LEP accelerator at the CERN nuclear physics lab near Geneva”.The ensuing discussion has made clear 6 the importance of continuing thesearch with the TeVatron, at the Fermi National Laboratory in the US, andlater with the LHC. 7 In one year running, the LHC will be able to clarify definitelythe issue of the Higgs boson, not only in the energy range indicatedby the LEP events but also in all the wider energy range compatible with thepresent theory of particle interactions.More symmetry at High EnergyThe fundamental particles that we see in Nature feature different values oftheir intrinsic angular momentum, spin. Quarks and leptons, the constituentsof matter, carry 1/2 unit of spin, the Higgs boson and the particles thatmediate the different forces carry integer values of the spin. Spin equal tozero for the Higgs boson, spin equal to one for the intermediaries of thestrong, electromagnetic and weak forces, and spin two for the elementaryquantum of gravity, the graviton.In a truly unified scheme, all these particles should be related to each otherby some symmetry, which then has necessarily to transform into one anotherparticles with different spin, unlikely any other of the known symmetrytransformations.5 New Scientist, 5 Dec. 2001.6 Edward Witten, Princeton New Jersey: “One question is whether the Higgs boson exists; the answer isalmost certainly yes…”. MICHAEL CHANOWITZ, Lawrence Berkeley National Laboratory: “I would argueeven more strongly that the precision data does not support the standard model prediction of the mass ofthe Higgs boson, based on my recent analysis of the data (Physics Review Letters, vol 87, p 23802). The standardmodel may well be “dead” but the Higgs boson can survive, accompanied by other – as yet unknown– new physics. Until the nature of this new physics is known, we cannot predict the mass of the Higgsboson”. JOHN ELLIS, CERN: “Those measurements suggest strongly that the particle weighs less than about200 gigaelectronvolts (GeV). Direct searches for the Higgs boson at LEP tell us that it must weigh morethan about 114 GeV, leaving plenty of space for it to exist… You quote John Swain as being prepared to betlarge amounts of money that the Higgs boson will not be found: many of us particle physicists are each preparedto bet £100 against him. Let us see how much money he is prepared to put where his mouth is!”.7 See finally the article by G. KANE and E. WITTEN, New Scientist, 30 March 2002.374

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSmass1TeV00 1/2 1 3/2 2spinFigure 6The spectrum of particles of different spin in SUSY theories. The lowest level is filled by the particles ofthe Standard Theory (Higgs boson, quarks and leptons, vector bosons and the gravitons, with spin 0,1/2, 1 and 2, respectively). Each of these particles has a SUSY partner with a spin differing by 1/2unit and a mass of the order of 1 TeV. At present, we have only experimental lower limits to the massesof SUSY partners, of the order of some 100 GeV, obtained from the non-observation of any suchparticle at LEP, the Tevatron and HeraFor some time it was believed that such a symmetry would be so restrictivethat it would not be compatible with any possible interaction among particles,a clear absurdity. In the 70s, in Russia and at CERN 8 a completely newkind of symmetry, able to transform particles with spin differing by 1/2 unit 9was discovered and shown to be compatible with the usual laws of QuantumTheory and Relativity. The new concept was so remarkable that it wasdubbed Supersymmetry (later SUSY for brevity), to distinguish it from normalsymmetries, and the properties of quantum field theories enjoying sucha symmetry have been systematically studied since then. It was also foundthat theories with local Supersymmetry must necessarily encompass gravity,which shows that this concept provides the natural bridge between particleforces and gravity.Two new aspects have been brought into this matter during the 80’s. Thefirst one is a stability condition on the Higgs boson mass that requires thatthe supersymmetry partners of the known particles have to appear in a massrange of the order of 1 TeV (1 TeV = 1000 GeV). This is very attractiveindeed. While there is little doubt that Supersymmetry must apply in the real8By D.V. Volkov and V.P. Akulov and by J. Wess and B. Zumino, respectively.9As a consequence, the generators of Supersymmetry obey anti-commutation relations, unlike the generatorsof a usual symmetry; it is precisely this anti-commuting property that allows super symmetry toescape the no-go theorem alluded to before (due to S. Coleman and J. Mandula theorem) and permitsrelativistic, supersymmetric field theories with non vanishing interaction.375

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEworld, because of unification with gravity, the particles characteristic of thissymmetry could be so heavy as to escape being produced at the energiesreachable with particle accelerators.The second element has been the observation of large quantities of nonradiating(dark) matter in the Universe. The dark matter makes large massivehalos around Galaxies and it accounts for the largest fraction of the matter inthe Universe. The dark matter is “seen” by its gravitational effects, but itseems very unlikely that it is made by usual atoms, nuclei etc. Rather, it couldbe made by heavy, electrically neutral particles, which have only a very weakinteraction with the normal matter or with the electromagnetic field and thatare remnants of the Big Bang. The SUSY partners of the Higgs boson or ofthe vector bosons could be ideal candidates as constituents of the dark matter,and again a mass scale of 1 TeV would be consistent with the dark mattercosmological properties and distribution.The arguments just mentioned indicate that SUSY particles may form mostof the Universe’s mass and appear in a range accessible to the accelerators ofthe next generation. In particular, the LHC should cover most of the energyrange where such particles are predicted to appear. The search for signalsassociated with the SUSY partners of quarks, leptons and gluons is an essentialpart of today’s high-energy frontier.How many dimensions?In the ‘30s, P. Kaluza and O. Klein, in an attempt to write a unified theoryof electromagnetism and gravity, made the hypothesis that our physical spacehas one more additional dimension. If the subspace corresponding to theadditional dimension is “curved” upon itself, with radius R, waves of wavelengthlarger than 2πR could not be fitted into it, therefore ordinary lightwould not propagate in the additional dimension and we would not perceiveit. Similarly, if R were much smaller than the typical wavelengths of our electronsand nuclei, according to the wave mechanics of De Broglie andSchrödinger, normal matter would be prevented to move into the new dimension.Only very energetic particles, with momentum p>>h/(2πR), with h thePlanck constant, would be able to “feel” a space with more than 3 dimensions.For a long time, the Kaluza Klein (KK) idea has remained an intriguing butunwarranted hypothesis. The situation changed when it was found that the“string theories”, the best available candidate theory for unifying gravity withquantum mechanics, do require a high dimensional space to be mathemati-376

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICScaly consistent. All of a sudden, we learn that the KK idea is not only possible,but it is in fact required.Only waves of wavelength such that λ= (2πR)/n, with integer n, can propagatein the additional dimension, corresponding to a momentum 10 p 5 =n h/(2πR). Amass-less particle in the full 5-dimensional space-time would have a momentum,which satisfies the Einstein null condition (p → represents the usual threedimensionalmomentum):E 2 →– (p) 2– (p 5 ) 2 = E 2 →– (p) 2– (n –––h2πR )2 = 0that is:E 2 →– (p) 2= (n –––h2πR )2 ≡ (M n ) 2This result means that each mass less particle in normal space, like the photon,the graviton, etc, is accompanied by a “KK tower” of massive companions,with mass M n (n = 1, 2 etc.) which are called its KK excitations. KK particlesare stable if the extra component of momentum is conserved (as it happensfor the usual momentum). These particles must be rather heavy on particlemass scale (say more than a few hundred GeV) and therefore R must berather small, since otherwise we would have seen their effects, in particularthere would be a lot of such particles as remnants of the Big Bang.In high-energy collisions, if energy were enough, we would start producingthe low-lying excitations. As energy, and n, increases we would be sending wavepackets of smaller and smaller wavelength in the new dimension, and we wouldexplore it with finer and finer resolution. While particles are turning around thecurved dimension, our macroscopic detectors would see energy and electriccharge disappearing into nothing and coming back (periodically) from nothing.Together with the observation of the typical spectrum of KK excitations of massM n , the lack of energy and charge conservation in our three-dimensional spacewould be a most unique sign of the existence of new dimensions.Recently, the issue of additional dimensions has taken a dramatic turn withthe realisation that in most string theories, particles associated with normalmatter (electrons, quarks, photons, gluons, etc.) are confined to a threedimensionalsurface in multidimensional space, called a p-brane. In the simplestversion of such theories 11 gravity only can extend to the full space. Inthis case, there is no need for a microscopic radius of curvature to avoid us10We consider a space-time with one time-like and four space-like dimensions; the additional curveddimension is labelled as the fifth dimension.377

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE1/MFigure 7In certain string theories, normal particlesare dynamically confined to a p-brane (represented as a grey slab inthe figure 13 ) while gravity canpropagate in the full space. Theextra dimension could even bemacroscopically large. Deviationsfrom the Newton’s law, the gravitationalpull between two bodies at distancer decreases proportionally to1/r 2 , are expected for values of r ofthe order of or smaller than the radiusof the extra dimension, R. The presentexperimental tests of theNewton’s law do not exclude thispossibility for R of the order of amicron, or smallere +x 1 x 5Ge –2πRgoing in the new dimensions, confinement to the p-brane assures it. Theonly limit to the radius arises from the fact that the Newton law we observewith macroscopic bodies (force inversely proportional to the square of thedistance) is itself indicative of a three-dimensional space. But we havechecked Newton’s law only down to distances of millimetres or, more recently,microns. 12 This leaves open the issue of a macroscopic KK radius R!Gravity in the full multidimensional space would be still characterized by aconstant of the dimension of a mass, but if the radius is large, this constantcould be of the order of 1 TeV, thus eliminating the disparity of scalebetween the W mass (about 0.1 TeV) and the mass which characterizes gravityin three dimensions, the so-called Planck mass of order 10 16 TeV.If this picture were true, the mass of KK excitations of the graviton wouldbe way smaller than in the other case. Also they would not be stable, sincethe p-brane can absorb any momentum in the additional dimensions. In fact,one could ask if reactions like:e + + e - →γ+(KKtower – of – gravitons)11 N. ARKANI-HAMED, S. DIMOPOULOS and G. R. DVALI, Phys. Lett. B 429, 263 (1998).12C. D. HOYLE et al., Feb. 2001.13L. HALL, ICHEP2000, Osaka.378

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSare already occurring at LEP. If one can produce excitations of the gravitonup to very high order, a large cross-section would result. This process wouldthen produce a typical distortion at low energy of the photon spectrum inthe reaction:e + + e - →γ+(unobserved – particles)with respect to what predicted by the Standard Theory. No distortionshave been observed so far at LEP.The LHC would push further the limit on the additional dimension (orobserve it!) with the study of reactions like:P+P → gluon + (unobserved – particles)The Large Hadron ColliderStarted in 1996, the construction of the Large Hadron Collider proceeds atfull speed at CERN. The LHC is a proton-proton or ion-ion collider to behoused in the 27 km underground circular tunnel nearby Geneva, where theLEP collider has been operating until the end of the year 2000. The design energyof each proton beam is 7 TeV, corresponding to the design magnetic field of8.1 Tesla in the super-conducting dipoles that keep the protons in circular orbitsinside the tunnel. Oppositely circulating beams cross in eight fixed pointsaround the circumference, four of which are reserved for the experiments.Protons are packed in very dense bunches which are stacked in the orbit at intervalsof about 7.5 m in space (25 ns in time) from each other. Very high designluminosity is foreseen, of 10 34 cm -2 sec -1 . At this luminosity, there are about 30elementary proton-proton collisions at each bunch crossing and correspondinglya very high flux of secondary particles bunched with a 40 MHz frequency.The limited transverse size of the tunnel and the need of very high magneticfield have required an innovative and compact design for the accelerator.Each dipole has two parallel apertures, which house the vacuum pipes.Coils are designed so that the magnetic field is oriented in opposite directionsin the two apertures. Therefore, two independent proton beams canrun in opposite directions inside the same dipoles.A current of 12 kA is circulating in super-conducting cables, kept at 1.8 °Kby super-fluid Helium. Cables are made of Ti-Nb filaments, imbedded intoa copper matrix.In turn, the super-fluid Helium is distributed by a cryogenic line, whichruns in parallel to the dipoles.379

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEOne problem of high-energy, high-field cryogenic machines is synchrotronradiation. Increasing with the fourth power of energy, synchrotron radiationin the LHC deposits about 0.2 W/m. In cryogenic machines, this power isexpensive to carry away, due to the low temperature of the walls where it isto be dissipated (thermal capacity goes like the fourth power of the absolutetemperature). For this reason, in the LHC, there is an inner beam screenkept at about 19 K (gaseous helium cooling), considerably higher than the1.8 K temperature of the cold mass of the dipoles.There are in all 1236 dipoles. Alternating with the dipoles, super-conductingquadrupoles complete the main magnetic structure of the LHC. Thebasic cell of the structure is 120 m long (with 6 dipoles and 2 quadrupoles).Figure 9 shows an artist’s view of the LHC.Figure 8In high-energy cryogenic protonmachines, the power deposited bysynchrotron radiation is difficult toremove because of the lowtemperature of the dipoles, 1.8 °K.In the LHC the heat is depositedon the an inner tube, which is keptat 19 °K by gaseous heliumcoolant circulating in the smalltubes visible on both sides of theinner tubeFigure 9Artist’s view of the LHC. Dipolesin blue, quadrupoles in white.The cryoline is not visible, exceptfor the grey tube shaped at rightangles, which feeds the superfluid He in the cryostats of themagnets380

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSFigure 10A view of String2 in the SM18 Hallof CERN (September 2001)A half-cell of the LHC (called String2) is at present operating at CERN,with dipoles and quadrupoles of the final design, to test the properties of thevery complex magnetic system. Figure 10 shows a picture of String2 in theSM18 Hall of CERN. String2 has been powered for the first time on Sept.27, 2001, when it has reached successfully the 12 kA current, correspondingto the nominal magnetic field (and energy) of the LHC.At the moment of writing (April 2002) the R&D and prototyping phase iscompleted. The main industrial contracts (cables, dipole assembly, cryogenicline) have been adjudicated and signed; industrial production and installationhave started. It will be quite a remarkable enterprise. For one the productionof super conducting cable for the LHC amounts to little less than 30% of theworld production.The excavation of the two big halls for the general-purpose experiments,ATLAS and CMS, is well advanced, after several problems, in particular forthe CMS cavern.The caverns will be handed over to the experimental collaborations in April2003 (ATLAS) and July 2004 (CMS).A new schedule for the commissioning of the LHC has been recentlydefined, which foresees the super-conducting dipoles completed in mid 2006381

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFigure 11The vault of the ATLAS cavern(September 2001). The concretevault is suspended with cables, toallow for the excavation of thelower part of the cavern, down tosome 30 m below the ground levelshown in the picture. The ATLAScavern is the biggest in the worldto be excavated in the type of rock(molasse) present below CERNand the first physics in 2007. The schedule is based on the contractual datesfor the main items.In 2001, the LHC has gone through a mid-project review of the cost tocompletion. The review indicates some 20% global extra cost for the machinehardware and installation and for the preparation of the experimental halls.A discussion is going on between the Council and CERN Management tocompensate for the extra costs, which envisages a plan for savings, the reductionof non-LHC activities and consequent budget reallocation to the LHCand the prolongation of the period of payments up to the year 2010.Experiments at the LHCThe effective energy in proton-proton collisions is directly related to theenergy carried by the proton constituents, quarks and gluons. In turn, theconstituent density decreases as its energy approaches the proton full energy.The collision probability itself, in addition, decreases with constituent energy.Thus the energy range that can be explored with a proton-proton collideris considerably limited with respect to the nominal beam energy. However,with a given beam energy and a given running time it is still possible toobserve the interactions of the harder constituents, provided we have enoughproton collisions per unit time, i.e. a sufficiently high luminosity. Luminositycan be traded for energy. At a given beam energy, as luminosity goes up theinteractions of the harder constituents become more and more visible andthe machine potential for discovery goes up.This concept is particularly important for the LHC, which had to fit in theexisting LEP circular tunnel, of a radius of about 4 km. With the magnetic382

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSfield also limited by the available technology to 8-9 Tesla, the luminosityhandle has been vital to extend the discovery potential of the machine wellinside the TeV region, where signals of new physics are expected.From the start, the LHC has aimed at values of luminosity one order ofmagnitude larger than what could be considered as “normal” for protonmachines, and what detectors of the time could stand. To design detectorscapable to face the luminosity challenge, a large R&D program and importantconceptual developments have been required. Key issues have been radiationhardness and capability to handle the enormous flux of information, whichgoes through the detectors (the products of 30 high-energy collisions repeatingat 40 MHz frequency). The programme has produced very innovativedetectors, now in the phase of industrial production, and is essentially over.Four experiments are foreseen at the LHC. Two general-purpose detectors,ATLAS and CMS, to search for the Higgs boson, signals of super-symmetricparticles and what ever else may be found at high energy.Figure 12Artist’s view of the four LHC detectors383

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEFigure 13Left: the ATLAS End-Capcryostat during construction.Right: parts of theCMS detector beingassembled at CERNA smaller size detector, ALICE, is designed to study the high-energy heavyion collisions. At these energies, the collision is supposed to produce a newstate of nuclear matter, the quark-gluon plasma, where quarks and gluons arenot confined inside hadrons as it happens at low temperature. Hints of thenew phase have been observed at CERN, with the SPS, and similar collisions,at higher energy with respect to the SPS but still lower than those of theLHC, are being studied at the Relativistic Heavy Ion Collider, RHIC, inBrookhaven. Finally, a fourth detector, LHC-b, is optimised for the study ofCP violation in decays of particles containing the b quark, extending andcompleting the studies which are being done at present with the so-called B-factories, in the US and in Japan.The LHC experiments will have to deal with enormous quantity of data.The amount of information that will come out of the collisions is the orderof the information carried by 300 million simultaneous phone calls, theinformation accumulated in one year will be in the order of some 10 15 bytes.Analysing and storing this information will require technologies which arestill in development.Another problem is the distribution of the information to the global collaboration,which build and will operate the detectors. A new infrastructureis needed, to make available the data and the applications to analyse them tothe single users diffused around the globe. Because of the similarity with thepower grid, which distributes the electrical power to a diffused population ofusers, this new infrastructure has been named the “Computing and Data Grid”(see Figure 14). The Grid concept will find application in many fields other384

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSFigure 14Schematic representation of the Grid. The analogy with the distribution of energyin the power grid is emphasizedthan particle physics. 14 The development of the LHC Data Grid is raising aconsiderable interest in other scientific disciplines and in industry.ConclusionsMany of the problems that Fermi could enumerate in the fifties have beensolved by the Standard Theory, notably the composite nature of the hadronicparticles (proton, mesons and so on) and the common origin of the weakand electromagnetic forces. The next generation of accelerators should shedlight on the new problems that the Standard Theory leaves unsolved.There are many fascinating discoveries waiting for us in the High EnergyFrontier. They range from what we could define as “normal business” – findingthe Higgs boson or discovering low-energy SUSY – to “new world”, likefinding that there are extra dimensions in our space-time.The High Energy frontier does not exhaust particle physics. We certainlyneed to understand better the physics of flavour, that is neutrinos and the ori-14The Grid: blueprint for a new computing infrastructure, I. FOSTER and C. KESSELMAN editors, MorganKaufmann Publishers Inc., San Francisco, California, 1999.385

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEgin of matter antimatter symmetry violation.Developing new tools for particle acceleration is still the key to affordablehigh-energy. More than ever, we need to support research in the field of particleaccelerators, in big laboratories like CERN, but also, and most importantly,in our Universities.As for strategy, a consensus is emerging on the roadmap to High-EnergyPhysics. First, and most important, the LHC has to be completed as soon aspossible and exploited. The LHC is supposed to give us the much-neededindication of what is the solution to the problem of particle masses (theHiggs boson?) and of the hierarchy of mass scales (SUSY?). The completeexploration of the sub-TeV region, particularly in the lepton sector, requiresin addition a high luminosity, e + e - Linear Collider in the class which is nowarriving to technological maturity (either based on super-conducting cavitiesas in the TESLA project at DESY, Germany, or on warm cavity technologyof the NLC at SLAC, US, and of the JLC at KEK, Japan).The next step would be a Multi-TeV accelerator, something for which wedo not have the appropriate technologies, yet. The most advanced study todayrefers to the two-beam accelerating principle for electrons developed atCERN (the Compact LInear Collider project, CLIC), capable to producefield gradients in excess of 150 MeV/m (i.e. 3 TeV over 20 km!). A VeryLarge Hadron Collider, a proton-proton collider with 200 TeV c.o.m. energyhas been considered in Europe (the Eloisatron project) and is studied atthe Fermi National Laboratory, in the US. Proposals and studies of a µ + µ - colliderare being entertained in US and, to a minor extent, in Europe but arestill in their infancy.On the flavour physics side, the violation of matter-antimatter symmetry,now studied with the so-called B factories at SLAC and KEK, will be continuedwith the LHC.A long baseline neutrino beam exists in Japan (K2K, from KEK to theKamioka underground laboratory) others are being built in CERN (fromCERN to Gran Sasso, in Italy) and the Fermi National Laboratory (fromFNAL to the Soudan mine). Studies for the production of very intense neutrinobeams (Neutrino-factory) are being carried out in the US and inEurope, to produce a new generation of long-baseline neutrino beams, suchthat could be detected in underground laboratories placed at distances ofsome thousand kilometres. Similar developments are being considered inJapan, in connection with the construction of a very intense proton source,the Japan Hadron Facility.386

Luciano MaianiPERSPECTIVES IN HIGHT ENERGY PARTICLE PHYSICSCan we realise the ambitious plans I have just described, in a reasonabletime, say 15 to 20 years? Can we afford them? It is becoming more and moreclear that new mechanisms for international collaboration are needed, carryingfurther what has been done for the LHC. Better efficiency is needed indecision-making, now left to separate negotiations inside each region(Europe, US, Japan) and to difficult approaches between different regions.Also, mechanisms must be found to follow the user distribution, in order tokeep in the picture the young generations, which are formed in theUniversities.To realize the full programme, a transition to a new global organisationmay be necessary, similar to the transition that Europe underwent fifty yearsago, from National Laboratories to CERN. The wide discussion, which hasstarted in the last years, gives reasons to believe that a solution may be nottoo far.Luciano MaianiLuciano Maiani was born in Rome in 1941. He obtained his degree inphysics in 1964 and started working as a researcher at the Istituto Superioredella Sanità in 1964. He collaborated with Prof. R. Gatto’s group in the fieldof Teorethical Physics at the University of Florence. He became post-doctoralfellow at the Lyman Laboratory of Physics, Harvard, in 1969, visitingProfessor at the Ecole Normale Supérieur in Paris in 1977 and at CERN inGeneva in 1979.He has been Professor of Theoretical Physics at the University of Rome “LaSapienza” since 1976, was President of the INFN from 1993 to 1998, andis presently Director General of CERN, the European Organization forNuclear Research located in Geneve.Luciano Maiani is author of over 100 scientific publications on the theory ofelementary particles. His most important achievement, reached with the collaborationof Gashow and Iliopolous, is the theoretical prediction of“charmed particles”, that has been crucial to the formulation of the unified theoryof Electroweak Interactions.He is member of the Accademia dei Lincei and the Accademia Nazionaledelle Scienze, also called XL.He was awarded the Honorary Degree by the University of Aix-Marseille, St.Petersburg’s and the Slovak Academy of Science. He was given theMatteucci medal by the Accademia Nazionale delle Scienze, also called XL,and the J.J Sakurai prize by the American Physical Society.387

Chen Ning YangEnrico Fermi389

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEThey that have power to hurt and will do none,That do not do the thing they most do show,Who, moving others, are themselves as stone,Unmoved, cold, and to temptation slow;They rightly do inherit heaven’s graces,And husband nature’s riches from expense;They are the lords and owners of their faces,Others but stewards of their excellence. 1Enrico Fermi was, of all the great physicists of the 20 th century, among themost respected and admired. He was respected and admired because of hiscontributions to both theoretical and experimental physics, because of hisleadership in discovering for mankind a powerful new source of energy, andabove all, because of his personal character. He was always reliable and trustworthy.He had both of his feet on the ground all the time. He had greatstrength, but never threw his weight around. He did not play to the gallery.He did not practise one-up-manship. He exemplified, I always believe, theperfect Confucian gentleman.Fermi’s earliest interests in physics seem to be in general relativity. Startingfrom around 1923 he began to think deeply about the “Gibbs paradox” andthe “absolute entropy constant” in statistical mechanics. Then, as Segrè laterwrote, 2As soon as he read Pauli’s article on the exclusion principle, he realizedthat he now possessed all the elements for a theory of the ideal gas whichwould satisfy the Nernst principle at the absolute zero, give the correctSackur-Tetrode formula for the absolute entropy in the limit for low densityand high temperature, and be free of the various arbitrary assumptionsthat it had been necessary to introduce in statistical mechanics in order toderive a correct entropy value.This research led to his first monumental work, and to the “Fermi distribution”,“Fermi sphere”, “Fermi liquid”, “Fermions”, etc.It was characteristic of Fermi’s style in research that he should follow thisabstract contribution with an application to the heavy atom, leading to whatis now known as the Thomas-Fermi method. The differential equationinvolved in this method was solved by Fermi:1 Shakespeare’s Sonnets, No. 94.2 E. SEGRÈ, in Collected Papers of Enrico Fermi (1962, Univ. of Chicago Press), p. 178.390

Chen Ning YangENRICO FERMINumerically with a small and primitive hand calculator. This numericalwork took him probably a week. E. Majorana who was a lightning-fastcalculator and a very skeptical man decided to check the numerical work.He did this by transforming the equation into a Riccati equation and solvingthe latter numerically. The result agreed exactly with the one obtainedby Fermi. 3Fermi’s love of the use of computers, small and large, which we graduatestudents at Chicago observed and admired, began evidently early in hiscareer and lasted throughout his later life.Fermi’s next major contribution was in quantum electrodynamics, wherehe succeeded in eliminating the longitudinal field to arrive at the Coulombinteraction. Fermi was very proud of this work, as his students at theUniversity of Chicago in the years 1946-1954 knew. (But it seems today thatfew theorists under the age of 65 know about this contribution of Fermi’s).It again was characteristic of Fermi’s style that in this work he saw throughcomplicated formalisms to arrive at the basics, in this case a collection of harmonicoscillators, and to proceed to solve a simple Schrödinger-like equation.The work was first presented in April 1929 in Paris and later at thefamous Summer School at Ann Arbor in the summer of 1930. G. Uhlenbecktold me in the late 1950’s that before this work of Fermi, nobody reallyunderstood the quantum theory of radiation, and that this work had establishedFermi as among the few top field theorists in the world.I shall skip describing his beautiful contribution in 1930 to the theory ofhyperfine structure, and come to the theory of β-decay. According to Segrè,Fermi had considered, throughout his life, that this theory was his mostimportant contribution to theoretical physics. I had read Segrè’s remarks inthis regard, but was puzzled. One day in the 1970’s, I had the following conversationwith Eugene Wigner in the cafeteria of Rockefeller University:Y: What do you think was Fermi’s most important contribution to theoreticalphysics?W: β-decay theory.Y: How could that be? It is being replaced by more fundamental ideas.Of course it was a very important contribution which had sustained thewhole field for some forty years: Fermi had characteristically swept whatwas unknowable at that time under the rug, and focused on what can be3 F. RASETTI, in Collected Papers of Enrico Fermi (1962, Univ. of Chicago Press), p. 277.391

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEcalculated. It was beautiful and agreed with experiment. But it was notpermanent. In contrast the Fermi distribution is permanent.W: No, no, you do not understand the impact it produced at the time. VonNeumann and I had been thinking about β-decay for a long time, as dideverybody else. We simply did not know how to create an electron in anucleus.Y: Fermi knew how to do that by using a second quantized ψ?W: Yes.Y: But it was you and Jordan who had first invented the second quantized ψ.W: Yes, yes. But we never dreamed that it could be used in real physics.I shall not go into Fermi’s later contributions. Nor into his relations withstudents which I had written about before. 4 I shall only add a couple of storiesabout Fermi.One of Fermi’s assistants at Los Alamos during the war was Joan Hinton,who became a graduate student at the University of Chicago after the war.When I began working in late 1946 for Sam Allison, she was a fellow graduatestudent in the same laboratory. In the spring of 1948 she went to Chinaand married her boy friend Sid Engst and settled down in China permanentlyto do agricultural work. (Hers was a very interesting story that should be writtendown. I hope she will do it soon). In the summer of 1971 during my firstvisit to the New China, half a year before Nixon, I accidentally met her in ahostel in Da-zhai, then a model agricultural commune in the County of Xi-Yang. Surprised and delighted, we reminisced about the Chicago days: how Iwas awkward in the laboratory, how I almost accidentally electrocuted her,how I had taught her a few sentences of Chinese, how I had borrowed a carand had driven her to the La Salle station to embark on her long trip to China,etc., etc. She asked me whether I remember the farewell party that the Fermishad given her before she left. I did. Did I remember the camera that they hadgiven her that evening? No, I did not. After a pause, she said she had felt, afew days before that farewell party, that she should tell Fermi about her planto go to the communist controlled area of China. So she did. And what didFermi say? “He did not object. For that I am eternally grateful”. I consideredthis such an important statement 5 that after coming back to Stony Brook, Icalled Mrs. Fermi in Chicago and reported to her my whole encounter with4 C.N. YANG, in Collected Papers of Enrico Fermi (1962, Univ. of Chicago Press), p. 673.5 Joan Hinton went to China in the spring of 1948, before the Chinese communists’ victory over ChiangKai-Shek, and two years before the Korean War. If she had planned to go to China after the beginningof the Korean War, I am sure the US Government would not have allowed her to go.392

Chen Ning YangENRICO FERMIJoan in Da-zhai. A few years later, Joan visited Chicago herself and had theopportunity to visit with Mrs. Fermi and her daughter, Nella Fermi.I shall end this article by quoting from page 48 of my Selected Papers (1983):Fermi was deeply respected by all, as a physicist and as a person. The qualityabout him that commands respect is, I believe, solidity. There wasnothing about him that did not radiate this fundamental strength of character.One day in the early 1950’s, J. R. Oppenheimer, who was theChairman of the important General Advisory Committee (GAC) of theAtomic Energy Commission (AEC), told me that he had tried to persuadeFermi to stay on the GAC when Fermi’s term was up. Fermi was reluctant.He pressed, and finally Fermi said, “You know, I don’t always trustmy opinions about these political matters”.Chen Ning YangChen Ning Yang, son of a mathematician, was born in 1922 in Hofei(Anhwei). Upon graduating from college, in 1946, he was awarded a scholarshipto the University of Chicago, where he worked initially with Fermi andTeller. In 1949 he and Fermi co-authored an article in which they discussedthe possibility that pions were particles composed of one nucleon and oneantinucleon. When physicists began to discover strange particles, Fermi’sand Yang’s idea was taken up by Shoichi Sakata, whose work contributedto the development of the idea of quarks by M. Gell-Mann and G. Zweig.In 1949 Mr. Yang joined the Institute for Advanced Studies at Princeton, andin 1955 became a professor. In 1966 he was appointed head of thedepartment of theoretical physics at the State University of New York at StonyBrook.In 1954, in collaboration with R. L. Mills, Mr. Yang tried to explain interactionamong nucleons by the request for local gauge invariance under theSU(2) isospin group. The attempt failed in this specific case but opened theway to the formulation of the theory of electroweak interactions by S.Glashow, A. Salam and S. Weinberg.Given the difficulties encountered in interpreting certain mesonic decay phenomena,in 1956 Mr. Yang, in collaboration with Tsung Dao Lee, advancedthe theory that symmetry through spatial reflections might be violated in weakinteractions. The two scientists suggested possible experimental controls independentof this hypothesis, which was demonstrated in 1957 by the Chinesephysicist Chien Shung Wu.That same year, Lee and Yang were awarded the Nobel Prize.393

Giorgio SalviniConcluding Remarks395

PROCEEDINGS OF THE INTERNATIONAL CONFERENCEWe are at the end of these days dedicated to Enrico Fermi. It has beenan immersion in that first half of our recently past century, and a furtherinvitation to mediate those origins which determined a new progress ofour knowledge, and new questions on the future of men.Looking from the high levels that we reached due to the contributes ofFermi and his great coevals, Heisenberg, Pauli, Jordan, Dirac, Wigner, wehave seen the consequences to day of their work. The new vision of physicsapparead so dazzling to some scientists that they thought that the extremepossible limits of our scientific knowledge had been reached. We know to daythat those genii rather opened the door of a new world which we still haveto explore, in its many dimensions of space and time, in the relation betweengravity and other forces, in the properties of order, chaos and complex systems.A new world which we only scratched until now.It is a merit of these great scientists not only to have given the leadingideas, but also having shown the precise methods to resolve an immensenumber of specific problems, and to get preliminary but clear conclusion.Are they superb mountain guides of existing mountains, or they also inventedand opened new peaks and valleys? I am not able to reply to this question.Historians shall have still to work on the documents left to us from EnricoFermi. We know that his print on the politics of this time is not the mainmark of his intense life, but still it is very important for uman history. In factwe can see in Enrico Fermi also the greatest direct link between sciences andother human activities. T. Regge wrote, in 1992 (Fermi symposium, p. 216):“Our responsability in healing the rift between Science and Society isimmense, our failure to do so will place a heavy burden on future generations,and threaten life on that starship called Earth which looks smallerby the day”.The life of Fermi was too short. But every day of him was important andsignificant, and controlled by a calm intense curiosity for the facts of nature,and the results from the laboratory.He was constently a great subtle teacher, in Rome, in Los Alamos, inChicago. Let me recall what Valentino Telegdi said of Fermi as a teacher inChicago, where he was one of his best students and collaborators.“No single individual in this century has contributed so much to physics,through theory as well as axperiments, as did Enrico Fermi. Still, in thisspeaker opinion, his greatest contribution in the Chicago period lays in histeaching. Through his students and their teachings, the Fermi spirit is stillalive to day” (Quoted Fermi Symposium, p. 71).396

Giorgio SalviniCONCLUDING REMARKSMany of those who remembered him in this room during these days didjoin to the admiration for the capacity of Fermi to illuminate the mind of thiscolleagues and listeners. We had the privilege of listen the comments of personswho spent days with him as their students and coworkers:Leon Lederman, whom I knew since when he was a student of GilbertoBernardini in Illinois, wrote:“It is clear that Enrico Fermi’s personal leadership, his scientific style andhis influences on students was a major force in the establishment ofphysics in the United States”.Chen Ning Yang wrote:“Enrico Fermi was, of all the great physicist of the 20 th century, amongthe most respected and admired. He was always reliable and trustworthy.He exemplified, I always believe, the perfect Confucian gentleman”.Let me make a final comment on Enrico Fermi, and our destiny. The characterof Enrico Fermi may also be an example to us. His life developedthrough political difficulties and dangers and he had take in short time decisionsof fundamental importance for him, his country, his family. He succededto make his choices with calm and a strong determination, and alwaysworrying for the destiny of the others, students, coworkers, colleagues.We cannot foresee the future of human kind, and we know that also Fermiwas thoughtful and uncertain about it. Our future shall depend on us, ideas,schools, capacity to understand and help each other. It will depart from ourwork to day, and develop on unpredictable ways. But we have the responsabilityto prepare for it the best starting line.This conferences dedicated to Enrico Fermi, came at the right moment inthese difficult times, as an invitation to ponder our future.397

Report on the Celebration for the Centenaryof Enrico Fermi’s BirthCarlo Bernardini, Rocco CapassoBy decree of 11 June 1999, the Minister for Cultural Properties andActivities, responding to a request dated 5 March 1998 from the ItalianSociety for the Progress of Science, gave the National Committee “the taskof promoting, preparing and implementing events suitable to celebrate thecentenary of the birth of Enrico Fermi”.The National Committee for the Celebrations of the Birth of Enrico Fermi(1901-2001) was made up of the Minister for Cultural Properties andActivities; the Foreign Minister; the Education Minister; the Minister ofUniversities and Scientific and Technological Research; the Industry Minister;the President of the Latium Region; the President of the Tuscany Region; thePresident of the Province of Rome; the President of the Province of Pisa; theMayor of Rome; the Mayor of Pisa; the Rector of “La Sapienza” Universityof Rome; the Rector of the University of Pisa; the Director of the PisaSuperior Normal School; the Director-General of the Central Office forBibliographic Properties, Cultural Institutions and Publishing; the DirectorGeneral of the Central Office for Archaeological, Architectural, Artistic andHistorical Properties; the Director General of the Central Office for ArchivalProperties; the Foreign Ministry’s Director General for Cultural Relations;the Education Ministry’s Director General for Cultural Exchange; thePresident of the Italian Society for the Progress of Science “called” of the XL;the President of the National Lincei Academy; the President of the NationalAcademy of Science; the President of the Pontifical Academy of Science; thePresident of the National Research Council; the President of ENEA; thePresident of the National Institute for Nuclear Physics; the President of RAI(the Italian state broadcaster); the President of the National ElectrotechnicalIndustry Association; the President of the Italian Encyclopedia Institute; thePresident of the Italian Physics Institute; the President of the Italian NuclearAssociation; Professors Luigi Amerio, Franco Bassani, Enrico Bellone, CarloBernardini, Fabio Bevilacqua, Gianni Bonera, Rocco Capasso, GianfrancoChiarotti, Renato Cialdea, Umberto Colombo, Maurizio Cumo, LuigiDadda, Michelangelo De Maria, Alberto Gigli Berzolari, Giulio Giorello,399

Giuseppe Giuliani, Giorgio Israel, Salvatore Lorusso, Luciano Maiani,Carmine Marinucci, Franco Prattico, Alessandro Pascolini, Renato AngeloRicci, Carlo Rubbia, Giorgio Rumi, Giorgio Salvini, Fabio Sebastiani andRoberto Vergara Caffarelli.At its first meeting, on October 19, 1999, the National Committee electedCarlo Bernardini as its chairman and Rocco Capasso as secretary-treasurer.As proposed by the chairman, Mr. Bernardini, the committee voted to set upan executive board composed of Franco Bassani, Carlo Bernardini, RoccoCapasso, Renato Cialdea, Maurizio Cumo, Michelangelo De Maria, GiorgioIsrael, Salvatore Lorusso, Carmine Marinucci, Alessandro Pascolini, RenatoAngelo Ricci, Giorgio Salvini, Fabio Sebastiani and Roberto Vergara Caffarelli.The National Committee for the Celebrations of the Birth of Enrico Fermiorganized a series of projects with high cultural content, including a booktitled Conoscere Fermi (All About Fermi), an international conference, anexhibition, a CD-ROM, a Web site, a documentary film, an historical marker,a postage stamp and the volumes on the subject of “Enrico Fermi”.Book “Conoscere Fermi”The book (17.5x24.5 cm, 385 pp., 48 ill., 24 b&w photos) was producedby the editorial staff of the Italian Physics Society with funding from theEducation Ministry.The texts, intended to be considered for use in teaching physics to highschool seniors, were written by twenty eminent physicists.News conference (28 Sept. 2001)The National Committee held a news conference on September 28, 2001,to present the programme of events. On this occasion the Italian media wereable to talk with the illustrious guests, in particular with some of EnricoFermi’s direct descendants. The guests included A. Agnew, G. Holton, J.Orear, Giulio Fermi’s wife and children, Nella Fermi’s daughter, and theNational Committee’s president and secretary-treasurer.Exhibition “Enrico Fermi and Universe of Physics”(29 Sept. - 5 Nov. 2001)The exhibition and the international conference were both held in Rome,at the Dioscuri Theatre exhibition and conference complex operated by theCultural Properties Ministry’s Directorate-General for BibliographicProperties and Cultural Institutions.400

Visitors at the Exhibition “Enrico Fermi and the Universe of Physics”The exhibition was opened by the President of the Republic on September29, 2001, the centenary of Fermi’s birth, and ran through November 5. Theopening ceremony was attended by leading representatives of Italian scienceand culture (including Giorgio Salvini; Edoardo Visentini, president of theNational Lincei Academy; Carlo Rubbia, president of ENEA; Enzo Iarocci,president of the Italian Institute for Nuclear Physics; and Francesco Sicilia,Director-General for Bibliographic Properties and Cultural Institutions) andmany of Fermi’s relatives, some of whom live in the United States.The exhibition was designed for the general public, in particular highschool students. It described Fermi’s life and work in Italy and America, ahuman experience that paralleled and helped determine the history of the20 th century. Enrico Fermi made an enormous contribution to the rebirth ofscience in Italy, and left a cultural heritage that is still bearing fruit throughthe work of his students.To help young students understand the various apects of Fermi’s contributionsto physics and modern technology, the exhibition was organised alongan historical path divided into seven phases (reflecting the architectural structureof the Dioscuri complex) centring on the principal events in the great401

scientist’s life: the days of a young genius, on the brink of fame, an Italianschool of science, refuge in America, a new era begins, Fermi’s legacy in Italyand the world, his last message.On display were original scientific instruments from Rome University’smuseum, Fermi’s notebooks from the Domus Galileana in Pisa, letters fromthe University of Rome’s Amaldi Archive, Fermi’s essay for admission to thePisa Normal School, books used by Fermi as a student and books he wrote,a fraction of the moderator from the first atomic pile, and scientific instrumentsused today by researchers in fields opened by Fermi. Besides photographicmaterials, the exhibition contained six areas for viewing documentson film from the historical archives of Italy’s Istituto Luce, RAI-TV, and theArgonne, Los Alamos and Oak Ridge laboratories in the United States, plusa multimedia station, to give visitors a better grasp of the most importantmoments in Fermi’s life and work.The exhibition’s original design enabled the materials to be shown to theirbest advantage, combining objects, texts, images and video inserts in a unitarypresentation. An important contribution to its effectiveness was provided bythe constant presence of university physics students, who gave visitors the benefitof personal contact and adapted the viewing paths to their specific interests.The opening of the International Conference “Enrico Fermi and the Universe of Physics”402

International Conference “Enrico Fermi and the Universe of Physics”(29 Sept. - 2 Oct. 2001)Documentary film on the Fermi exhibitionThis film (37′), coordinated by Alessandro Pascolini, organised as a visit tothe exhibition, is of extraordinary topical interest. Perfectly up-to-date andinterwoven with interviews and brilliantly structured inserts, it is a model ofeffective and innovative scientific communication and popularisation.CD-ROMThe CD-ROM was planned by the National Committee, co-ordinated byMichelangelo De Maria, created by UNICITY and produced by CASPUR atthe end of the Fermi celebrations. Its main purpose was to “reconstructEnrico Fermi’s life and work in the larger institutional, political, scientific andtechnological context of an era of enormous historical and social upheavals”.The CD-ROM is a multimedia “gateway” by which to enter Fermi’s life asa man and a scientist against the background of his historical period. The filmsegments, animations, photographs and original documents that interpretand recount Fermi’s life up to the time of his move to the United Statesoccupy more than an hour’s time and constitute a significant account of thescientist and his times. It contains over 500 photos and documents, many ofthem not easy to come by, that describe various aspects of Fermi’s scientifictraining, development and research.The CD-ROM also shows Fermi receiving the Nobel Prize, his Chicagoperiod, the construction of the first atomic pile, and the historic event onDecember 2, 1942. It includes accounts by A. H. Compton, L. Marshall andL. Szilard (in English, with Italian translations available), and illustratesFermi’s 1954 lectures at Varenna and his last speech. On the CD, Fermi liveson in the memory of Laura Fermi, Edoardo Amaldi, Emilio Segrè and otherfriends and colleagues who describe the man they knew.This wealth of original documents, animations and graphics is compoundedby over 400 pages of historical texts written for the CD-ROM.The Physics Glossary, with around a hundred entries, enables non-specialistusers to approach the world of modern nuclear and particle physics.The Biographies section presents, with texts and photos, around a hundredscientists to whom it seemed appropriate to call the attention of contemporaryItalian culture.In sum, the CD offers a new way of understanding 20 th century history,403

a new way to study its facts, events, politics, culture, science and society.Under an agreement between CASPUR and the Italian magazine Le Scienze,the CD-ROM was distributed with the magazine’s March 2002 issue andkept available at newsstands through September 2002, and can be orderedby mail for a period of three years. This means that as of October 2002,CASPUR, in agreement with the E. Fermi National Committee, can distributethe CD to schools, universities, libraries, etc.Web siteThe Web site went on line at www.enricofermi.it even before the exhibitionopened at the Dioscuri complex. Besides containing many of this exhibition’smaterials (including the entire text of the book Conoscere Fermi, which canthus be acquired by <strong>download</strong>ing), it includes those presented at the oneorganised by the Ministry of Universities and Research in the spring of 2001on “One Thousand Years of Science in Italy”.Historical markerIn agreement with Rome city councillor Giovanni Borgna’s press office, anhistorical marker was unveiled at Via Gaeta 19 on September 28, 2001. Inaddition to local authorities and representatives of the National Committee,the ceremony was attended by Sarah Fermi, Daniel and Rachel Fermi, JayOrear and Harold Agnew. The event was reported in various newspapers,including Corriere della Sera and La Nazione.Postage stampThe Italian Post Office issued a commemorative stamp in 3.5 millioncopies. Enrico Fermi is shown in the left foreground, the atomic pile on theright, and in the background a backboard on which appear Fermi’s handwritingand signature. The name ENRICO FERMI, the dates “1901-1954”,the word “ITALY” and the denomination “800 – w 0,41” complete thestamp. On the issue date, the Rome Philatelic Office placed on sale a postcardreproducing the commemorative stamp, priced at 1000 lire plus thestamp’s face value.VolumesBesides this volume, the National Committee has also sponsored the Fermicentenary celebrations organized by SIF (Italian Society of Physics) andICRA (International Center for Relativistic Astrophysics), with the engage-404

ment of partly financing both a special edition of the “Nuovo Cimento B”by SIF – containing most of the papers on Fermi – and the volume “Fermiand Astrophysics” by ICRA, to be published and diffused worldwide by theWorld Scientifics of Singapore.In the opinion of the Committee, the organisers and a large part of themedia (press, radio, TV and the Internet), the events to date have indeedhelped bring back to Italy the extraordinary figure of one of the greatestphysicists of all time. Public interest seems clearly destined to increase, in partthanks to the publication of this volume of Proceedings, edited by ENEA andthe Italian Society for the Progress of Science, which constitutes an extraordinaryreference source for scholars.The community of physicists, research institutes and scholars now has theimportant task of keeping alive the memory and the example of this great scientist,at once a theoretical and an experimental physicist, an engineer and amathematician. In a way, this many-sided nature of Fermi’s was absolutelyunique on the world scene, and one may well wonder how the precociousstudent came to attain such heights. Much is known of his studies, but it isnot yet clear what price the young man of 18 paid, in terms of commitmentand sacrifice, to be able to outstrip all his teachers and win the universitychair of theoretical physics at barely 25. Those of us who organised the celebrationscan only be thankful for the opportunity provided by the Ministryof Cultural Properties and Activities to render this service to our country’sculture.On behalf of the executive board and the National Committee, in concludingthis note we wish to thank the Ministry for its funding and supportof the program carried out to honour Enrico Fermi.405

Edito dall’ENEARelazioni Esterne – Unità ComunicazioneLungotevere Thaon di Revel, 76 – 00196 Romawww.enea.itEdizione del volume a cura di Laura Falera, Giuliano Ghisu e Diana SavelliProgetto grafico e stampa: Litografia Fabiano snc – Canelli (Asti)Finito di stampare nel mese di maggio 2003

download - Enea

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?