(b. Rome, Italy, 29 September 1901; d. Chicago, Illinois, 28 November 1954)
His father, Alberto Fermi, was an administrative employee of the Italian railroads; his mother, Ida de Gattis, was a schoolteacher. Fermi received a traditional education in the public schools of Rome, but his scientific formation was due more to the books he read than to personal contacts. It is possible to gather exact information on his readings from an extant notebook, and later in life he mentioned having studied such works as Poisson’s Traité de mécanique, Richardson’s Electron Theory of Matter, Planck’s Vorlesungen über Thermodynamik, and several by Poincaré.
Fermi was fundamentally an agnostic, although he had been baptized a Catholic. In 1928 he married Laura Capon, the daughter of an admiral in the Italian navy. His wife’s family was Jewish and was severely persecuted during the Nazi-Fascist period. Fermi, who enjoyed excellent health until his fatal illness, led a very simple, frugal life with outdoor activities as his main recreations. His unusual physical strength and endurance enabled him to hike, play tennis, ski, and swim; although in none of these sports was he outstanding.
Fermi was a member of a great many academies and scientific societies, including the Accademia dei Lincei, the U.S. National Academy of Sciences, and the Royal Society of London. He received the Nobel Prize in 1938 and the Fermi Prize, named for him, a few days before his death. His prominent part in the development of atomic energy involved him in numerous extrascientific activities that were not particularly attractive to him. He undertook administrative duties conscientiously and ably but without great enthusiasm.
Fermi’s scientific accomplishments were in both theoretical and experimental physics, an unusual feat in the twentieth century, when increasing specialization tends to narrow the field of study. Fermi’s statistics (independently found also by Paul Dirac) and his theory of beta decay were his greatest theoretical contributions. Artificial radioactivity produced by neutron bombardment, slow neutrons, and the realization of a nuclear chain reaction were his greatest experimental achievements. These highlights and his many other results have left their imprint on the most diverse parts of physics.
When Fermi attended school, humanistic literary studies were emphasized: Italian, Latin, and Greek. He was a model student and obtained consistently top marks. But he was primarily self-taught, from a very early age, and he said later that by age ten he had succeeded by concentrated effort in understanding practically unaided why the equation x2 + y2 = r2 represents a circle. His older sister, Maria, and his older brother, Giulio, contributed to this early schooling. In grade school he also exhibited a prodigious memory for poems. In 1915 Giulio died unexpectedly, and the sad event left a deep mark on Enrico. Fortunately he then struck up a friendship with a schoolmate, Enrico Persico, and the two boys’ common scientific interests led to a lifelong friendship. They became the first two professors of theoretical physics in Italy.
A colleague of Fermi’s father, Adolfo Amidei, was perhaps the first adult to recognize Fermi’s unusual talent. He lent him books on mathematics and physics in a pedagogically graduated progression. Fermi himself acquired some secondhand books on mechanics and mathematical physics, mainly Poisson’s Mécanique and A. Caraffa’s Elementa physicae mathematicae (Rome, 1840). By his seventeenth year, while still in high school, he had acquired a thorough knowledge of classical physics, comparable to that of an advanced graduate student in a university. Furthermore, Fermi and Persico had performed many experiments with apparatus they had built themselves, and thus had acquired an excellent grasp of contemporary experimental physics. For example, they determined precisely the value of the acceleration of gravity at Rome, the density of Rome tap water, and the earth’s magnetic field. Fermi was also proficient at building small electric motors.
At Amidei’s suggestion, Fermi competed for a fellowship at the Scuola Normale Superiore in Pisa, where he could acquire an education at no expense to his family. He had to write an assigned essay for the competition, “Distinctive Characters of Sound.” (Fortunately the essay was preserved and after his death was found in the archives of the school.) On the first page is the partial differential equation for vibrating reeds, followed by about twenty pages for its solution through eigenfunctions, the determination of the characteristic frequencies, etc. One can easily imagine the surprise of the examiner who received this essay from a seventeen-year-old boy just out of high school. He was convinced of the candidate’s genius and assured Fermi of that fact when he met him.
From the Scuola Normale Superiore, Fermi wrote regularly to Persico, and the letters give a vivid insight into his life there. He was by no means bashful, and after about a year in Pisa he said that he was the authority on quantum theory and that everybody, including the professors, depended on him to teach them the new physics. At Pisa he became a close friend of Franco Rasetti, another physics student of great ability.
Fermi received his doctorate from the University of Pisa in 1922 and then returned to Rome. At that time he met Orso Mario Corbino, director of the physics laboratory at the University of Rome. Corbino immediately recognized Fermi’s talent and became his lifelong friend and patron. Above all, he saw Fermi as the instrument for one of his fondest aspirations—the rebirth of Italian physics.
To acquire a direct knowledge of modern physics beyond the provincial state of Italian physics, Fermi had to see the world, and to be in touch with foreign scientists. He therefore competed for a foreign fellowship and spent some time at Max Born’s institute at Göttingen and then with Paul Ehrenfest at Leiden. With the latter he struck up a warm friendship, and Ehrenfest greatly encouraged him. He and Arnold Sommerfeld helped to introduce Fermi to other physicists. When the fellowship expired in 1924, Fermi returned to Florence with the post of lecturer. He then competed for a chair of mathematical physics; he did not win although he was supported by Tullio Levi-Civita and Vito Volterra.
Up to this time Fermi’s work had been primarily in general relativity (tensor analysis), where he had developed a theorem of permanent value: that in the vicinity of a world line, space can always be approximated by a pseudo-Euclidean metric (FP no. 3 in Collected Papers). In statistical mechanics he had written subtle papers on the ergodic hypothesis (FP no. 11) and on quantum theory. Here he had developed an original form of analyzing collisions of charged particles. He developed the field produced by the charged particle by the Fourier integral and used the information from optical processes to determine the result of the collision (FP no. 23). This method was later refined and better justified on the basis of quantum mechanics and is generally known as the Weizsäcker-Williams method. Other studies on the entropy constant of a perfect gas are historically important as preparation for things to come. An experiment done with Rasetti, who was also in Florence, on the depolarization of resonance light in an alternating magnetic field was the subject of Fermi’s first important experimental paper (FP no. 28). This experiment was the first of a series that, in subsequent years, was to become extremely important in the hands of other physicists.
In 1925 Wolfgang Pauli discovered the exclusion principle, which in the language of the old quantum theory prevents more than one electron from occupying an orbit completely defined by its quantum numbers. This principle had far-reaching consequences in statistical mechanics for a particulate gas when its temperature and density are such that the cube of the de Broglie wavelength is large compared with the total volume divided by the number of particles in the formula N/V ≫ (2πkmT)3/2h–3. Peculiar phenomena, comprised under the technical name of “degeneracy,” then appear: for instance, the specific heat of the gas vanishes. The problems of gas degeneracy had been known for many years. Bose and Einstein had shown in 1924 that they could be solved by a modification of classical statistical mechanics (Bose-Einstein statistics). Bose-Einstein statistics are applicable to light quanta and account for Planck’s radiation formula. But Bose-Einstein statistics are not applicable to particles obeying Pauli’s principle, for which one needs the new type of statistics discovered by Fermi early in 1926 (FP no. 30). Dirac independently found the same result a few months later and connected it to the new quantum mechanics. Fermi statistics, which are applicable to electrons, protons, neutrons, and all particles of half integral spin, have a pervading importance in atomic and nuclear physics and in solid-state theory. The importance of Fermi statistics was immediately appreciated by physicists and established Fermi as a leader in the international community of theoreticians, as was obvious at the International Conference in Physics held at Como in 1927.
In 1927, mainly through the efforts of Corbino, a chair in theoretical physics, the first such in Italy, was established at the University of Rome. In the competition for the position Fermi placed first and Persico second. Fermi then came to Rome, to the Physics Institute in Via Panisperna, to join Corbino. He had friends there among the mathematicians also, and he was soon joined by Rasetti.
They strove to establish a modern school of physics in Rome. The first task was to recruit students suitable for advanced training and capable of later becoming independent scientists. The first was Emilio Segrè, who was then an engineering student but who had always had a strong interest in physics. When he became acquainted with Rasetti and Fermi through mutual friends, he enthusiastically joined the group as an advanced student. Segrè informed his schoolmate and friend Ettore Majorana of the new opportunity and introduced him to Fermi and Rasetti. Majorana soon (1928) transferred from engineering to physics. Edoardo Amaldi was recruited directly from undergraduate work in physics. Later they were joined by many others. Some came as temporary visitors: Giulio Racah, later rector of the University of Jerusalem and known mainly for his studies on the Racah coefficients and atomic spectra; Giovanni Gentile, Jr., later professor of theoretical physics at Milan; Gilberto Bernardini, later an experimental physicist and director of the Scuola Normale Superiore; and Bruno Rossi, who was a pioneer in the study of cosmic rays. Others joined them as students or fellows: Bruno Pontecorvo; Ugo Fano, later professor of theoretical physics at the University of Chicago; Eugenio Fubini; Renato Einaudi, later professor of mechanics at the University of Turin; and Leo Pincherle, later professor of physics at London University. Gian Carlo Wick came at a later date as an assistant professor. The activity in Rome helped to reanimate several other centers, including Florence (Rossi, Bernardini, Giuseppe Occhialini, Racah) and Turin (Gleb, Wataghin, Wick), and brought about a notable rebirth of physics in Italy.
Fermi’s next important study was the application of his statistics to an atomic model. This had been anticipated, however, by L. H. Thomas, who was working independently. The Thomas-Fermi atom gives very good approximations in a great number of problems. The fundamental idea was to compute the density of the electronic cloud around the nucleus as an atmosphere of a totally degenerate gas of electrons attracted by the nucleus. Fermi made numerous applications of his method to X-ray spectroscopy, to the periodic system of the elements, to optical spectroscopy, and later to ions. This work required a considerable amount of numerical calculation, which he performed with a primitive desk calculator. Many of these results were summarized in a paper he read at the University of Leipzig in 1928 (FP no. 49). Other studies in atomic and molecular physics followed.
Another important group of papers which were devoted to the reformulation of quantum electrodynamics made this important subject accessible to many physicists (FP no. 67). Dirac had written a fundamental but difficult paper on the subject. Fermi, after reading the paper, decided to obtain the same results by more familiar methods. He developed by Fourier analysis the electromagnetic field which obeys Maxwell’s equations, and he quantized the single harmonic components as oscillators. He thus wrote the Hamiltonian of the free field, giving a Hamiltonian form to Maxwell’s theory. To this Hamiltonian, he added the Hamiltonian of an atom and a term representing the interaction between atom and radiation. The complete system was then treated by perturbation theory.
Corbino did not miss any occasion to extol Fermi’s work, and early official recognition followed. Mussolini named Fermi to the newly created Accademia d’Italia. He was the only physicist so honored, and this singular recognition was also accompanied by a substantial stipend. He was subsequently elected to the Accademia dei Lincei, at an unusually young age. In spite of some grumbling by older professors, it became clear to the academic world and to the cultivated public that Fermi was indeed the leading Italian physicist. His economic position became comfortable although not affluent.
At this time quantum mechanics had reached its full development; nonrelativistic problems, at least in principle, were soluble except for mathematical difficulties. In this sense atomic physics was showing signs of exhaustion, and one could expect the next really important advances to be in the study of the nucleus. Realizing this, Fermi decided to switch to nuclear physics. He initially investigated the theory of the hyperfine structure of the spectral lines and the nuclear magnetic momenta (FP no. 57), a suitable subject for making the transition from atomic to nuclear physics.
The development of experimental physics at Rome presented greater problems than had theoretical physics. In the latter Fermi was a leader of worldwide reputation at the peak of his powers; no substantial amount of money was needed; and it was relatively easy to attract young people from Italy and from abroad. Indeed, very early promising physicists destined to leave their mark in science came to Rome. Besides the Italians mentioned earlier, several foreign physicists studied there, among them Hans Bethe, Edward Teller, Rudolf Peierls, Fritz London, Felix Bloch, George Placzek, and Homi Bhabha. The state of experimental physics was different. Rasetti was the senior man, and although he had outstanding ability he was no Fermi. The only techniques known locally were spectroscopic, and therefore the equipment available was predominantly spectroscopic. Shops were poor and money was scarce. In this situation, with the object of widening the techniques available and ultimately turning to nuclear physics, Rasetti, Amaldi, and Segre spent periods of about a year in the laboratories of Lise Meitner, Peter Debye, and Otto Stern, respectively, learning various experimental techniques.
In Rome, about 1929, Rasetti and Fermi began experiments on nuclear subjects. In the meantime the great discoveries of the early 1930’s, the portents of the impending revolution in nuclear physics, were being made: positron, neutron, deuterium, and artificial acceleration. The Solvay Conference of 1933 was devoted to the nucleus, and shortly thereafter Fermi developed the theory of beta decay, based on the hypothesis of the neutrino formulated for the first time in 1930 by Wolfgang Pauli. Beta decay—the spontaneous emission of electrons by nuclei—presented major theoretical difficulties. Apparently, energy and momentum were not conserved. There were also other difficulties with angular momentum and the statistics of the nuclei. Pauli sought a way out of the apparent paradoxes by postulating the simultaneous emission of the electron and of a practically undetectable particle, later named “neutrino” by Fermi. There remained the task of giving substance to this hypothesis and of showing that it could account quantitatively for the observed facts.
An entirely new type of force had to be postulated, the so-called weak interaction. This new force, together with gravity, electromagnetism, and the strong interaction which binds the particles of the nucleus, constitutes the family of forces presently known in physics. They should account for the whole universe. Weak interactions occur between all particles and are thus unlike electromagnetic or strong interactions, which are restricted to certain particles. The first manifestation of the weak interaction to be treated in detail was the beta decay. The treatment was accomplished by applying second quantization and destruction and creation operators for fermions and by adopting (or better, guessing) a Hamiltonian for weak interactions on the basis of formal criteria, such as relativistic invariance, linearity, and absence of derivatives. Of the five possible choices which satisfied the formal requirements, Fermi treated the vector interaction in detail, mainly because of its analogy with electromagnetism.
In his paper on beta decay, Fermi also introduced a new fundamental constant of nature, the Fermi constant, G, which plays a role analogous to that of the charge of the electron in electromagnetism. This constant has been experimentally determined from the energy available in beta decay and the mean life of the decaying substance. Its value is 1.415 × 10–49 erg cm3. To clarify its significance we point out that the electromagnetic interaction is of the order of 1012 times stronger than the weak interaction. More precisely, the dimensionless number e2/ℏc = 1/137 is to be compared with G2(ℏc)–2(ℏ/mc)–4 ∼ 5.10–14, where m is the mass of the pion. The famous paper in which Fermi developed this theory had far-reaching consequences for the future development of nuclear and particle physics (FP no. 80). For instance, it served as an inspiration to Hideki Yukawa in his theory of the nuclear forces. It is probably the most important theoretical paper written by Fermi.
Soon thereafter Frédéric Joliet and Irène Joliot-Curie discovered artificial radioactivity—the creation of radioactive isotopes of stable nuclei by alpha particle bombardment. The Joliots’ discovery provided the occasion for experimental activity which Fermi continued for the rest of his life. Fermi reasoned that neutrons should be more effective than alpha particles in producing radioactive elements because they are not repelled by the nuclear charge and thus have a much greater probability of entering the target nuclei.
Acting on this idea, Fermi bombarded several elements of increasing atomic numbers with neutrons. He hoped to find an artificial radioactivity produced by the neutrons. His first success was with fluorine. The neutron source was a small ampul containing beryllium metal and radon gas. The detecting apparatus consisted of rather primitive Geiger–Müller counters. Immediately thereafter Fermi, with the help of Amaldi, D’Agostino, Rasetti, and Segrè, carried out a systematic investigation of the behavior of elements throughout the periodic table. In most cases they performed chemical analysis to identify the chemical element that was the carrier of the activity. In the first survey, out of sixty-three elements investigated, thirty-seven showed an easily detectable activity. The nuclear reactions of (n, α), (n, p), and (n, γ) were then identified, and all available elements, including uranium and thorium, were irradiated. In uranium and thorium the investigators found several forms of activity after bombardment but did not recognize fission. Fermi and his collaborators, having proved that no radioactive isotopes were formed between lead and uranium, put forward the natural hypothesis that the activity was due to transuranic elements. These studies, which were continued by Otto Hahn, Lise Meitner, Irène Joliot Curie, Frédéric Joliot, and Savitch, culminated in 1938 in the discovery of fission by Hahn and Fritz Strassmann.
In October 1935 Fermi and his collaborators, now including Pontecorvo, observed that neutrons passed through substances containing hydrogen have increased efficiency for producing artificial radioactivity. Fermi interpreted this effect as due to the slowing down of the neutrons by elastic collisions with hydrogen atoms. Thus slow neutrons were discovered. The study of slow neutrons was to form the main object of Fermi’s work for several years thereafter. Among other things, Fermi and his collaborators showed that the neutrons reached thermal energy and that neutrons of a few electron volts of energy could show sharp peaks (resonances) in the curve of the collision and absorption cross section, versus neutron energy. Fermi then developed a mathematical theory of the slowing down of neutrons, and he tested it experimentally in considerable detail. This work lasted until about 1936. All the neutron work, which cost approximately a thousand American dollars, was supported by the Consiglio Nazionale delle Ricerche of Italy. The tremendous experimental activity of the years 1934–1938 brought a considerable change in the working habits at the Rome Institute. Because of the lack of time, it became impossible for Fermi to follow all the developments in physics as he had done before. He was forced to curtail the extracurricular teaching of promising young men, nor could he spare time for foreign visitors, who practically stopped coming.
The Ethiopian War marked the beginning of the decline of the work at the Institute, and the death of Corbino on 23 January 1937 brought further serious complications. The deteriorating political situation also materially hampered the work, and finally the Fascist racial laws of 1938 directly affected Fermi’s wife. The foregoing problems and his deep, although mute, resentment against injustice were the final arguments that convinced Fermi to leave Fascist Italy. He passed the word to Columbia University, where he had been previously, that he was willing to accept a position there. In December 1938 he received the Nobel Prize in Stockholm. He then proceeded directly from there to New York. He was not to return to Italy until 1949.
Fermi had barely settled himself at Columbia when Bohr brought to the United States the news of the discovery of fission. This discovery made a tremendous impression on all physicists. Fermi and others immediately saw the possibility of the emission of secondary neutrons and perhaps of a chain reaction; he started at once to experiment in this direction.
In the early period at Columbia, Fermi was helped by H. L. Anderson, a graduate student who later took his Ph.D. under Fermi and remained a close collaborator and friend to the end of Fermi’s life. The young physicist Walter Zinn was also associated with Fermi for an extended period. Leo Szilard was independently pursuing similar studies, and there were active interchanges of ideas and even some collaboration with other Columbia and Princeton University groups during early research on the chain reaction.
The first problem was to investigate whether on the fission of uranium secondary neutrons were in fact emitted—as was expected because the fragments have excess neutrons for their stability. If such did occur, it might be possible to use these neutrons to produce further fission, and under favorable circumstances one could obtain a chain reaction. To make this possible it is necessary to use the fission neutrons economically, i.e., to employ the neutrons to produce other fissions and not to lose them in parasitic captures by uranium, by other materials used as a moderator to slow down the neutrons, or by escape from the body of the reactor. If one uses natural uranium and a graphite moderator with unseparated isotopes, the margin by which one can obtain a chain reaction is very small and utmost care is needed in husbanding the neutrons. It soon became apparent that more than two neutrons were emitted per fission. This is a necessary but not sufficient condition for a chain reaction. But the number, now known to be about 2.5, is small enough to create an extremely difficult technical problem.
Of the two isotopes contained in natural uranium, only the isotope of mass 235, present in one part out of 140, is fissionable by slow neutrons and the cross section is large at low energy. On the other hand, most of the fission neutrons are unable to produce fission in the abundant isotope uranium 238, but if they are slowed down they are easily captured by U235 and produce fission. Neutrons must therefore be slowed down, but in the collisions that reduce the energy of the neutrons there is always a fraction of neutrons which are captured without producing fission. The moderator must thus be carefully chosen. Hydrogen, the first obvious choice, captures too many neutrons, and deuterium was unavailable in sufficient quantities. So for practical purposes the only suitable, and available, substance in 1939 was graphite, and several physicists independently suggested its use. In a long series of measurements of great ingenuity, Fermi and his collaborators studied the purity of the materials (impurities were often important neutron capturers) and the best configuration in which to assemble them. In order to analyze the problems facing him, Fermi needed a great amount of quantitative information on cross sections, delayed neutrons, branching ratios of the fission reactions, and nuclear properties of several nuclei to be used in a future reactor. This information was not available. He then proceeded to collect it with the help of many collaborators. Other independent groups were of course working on the same problems, but exchange of information was limited by self-imposed secrecy.
The potential overwhelming practical importance of this work was clear to physicists, and Fermi, together with George B. Pegram, chairman of the physics department at Columbia and a close personal friend, tried to alert the U.S. government to the implications of the recent discoveries. A small subsidy for further research was obtained from the U.S. Navy, and the studies that were to culminate in the atomic bomb were initiated. At the beginning the staff and equipment were completely inadequate. Perhaps Fermi thought he might be able to repeat, on a somewhat larger scale, work similar to the neutron research in Rome. He certainly did not realize, as very few scientists did, the project’s colossal requirements of manpower and means for its successful completion. Fermi was always reluctant to take administrative responsibilities and he concentrated his efforts on the scientific side, leaving to others the staggering problems of organization and procurement. As an expert of exceptional ability and great authority, he naturally helped; but his activity was directed primarily to the scientific aspects of the problems. It must also be remembered that his position—first as an alien, and later, after the United States entered World War II, as an enemy alien—rendered his situation difficult.
Fermi concentrated his efforts on obtaining a chain reaction using ordinary uranium of normal isotopic composition. As soon as it was established that of the two isotopes present in natural uranium, only U235 is fissionable by slow neutrons, it became apparent that if one could obtain pure U235 or even enrich the mixture in U235, the making of a reactor or possibly even of an atom bomb would be comparatively easy. Still, the isotope separation was such a staggering task that it discouraged most physicists. By the end of the war even this task had been mastered, and isotope separation was soon a normal industrial operation.
In 1939 and 1940, however, isotope separation was very uncertain and other avenues had to be explored. In December 1940, Fermi and Segrè discussed another possibility: the use of the still undiscovered element 94 (plutonium) of mass 239 (Pu239). This substance promised to undergo slow neutron fission and thus to be a replacement for U235. If it could be produced by neutron capture of U238 in a naturaluranium reactor, followed by two beta emissions, one could separate it chemically and obtain a pure isotope with, it was hoped, a large slow-neutron cross section. Similar ideas had independently occurred in England and Germany. J. W. Kennedy, Glenn Seaborg, Segrè, and Arthur Wahl undertook the preparation and measurement of the nuclear properties of Pu239, using the Berkeley cyclotron. The favorable results of these experiments (January–April 1941) added impetus to the chain-reaction project because it opened another avenue for the realization of a nuclear bomb. By December 1941, the whole world was engulfed in war, and military applications were paramount. The United States developed, under government supervision, an immense organization, which evolved according to the technical necessities and led to the establishment of the Manhattan Engineer District (MED). The purpose of the MED was to make an atomic bomb in time to influence the course of the war. The history of this development is admirably recounted in the Smyth report. Fermi had a technically prominent part in the whole project. His work at Columbia was still on a small scale, but in 1942 he transferred to Chicago, where it was expanded. It culminated on 2 December 1942 with the first controlled nuclear chain reaction at Stagg Field at the University of Chicago.
The industrial and military developments of the release of nuclear energy, which are of immense importance, will not be treated here. The nuclear reactor, however, is also a scientific instrument of great capabilities, and these were immediately manifest to Fermi. Even during the war, under the extreme pressure of the times, he took advantage of these capabilities to begin research on neutron diffraction, neutron reflection and polarization, measurements of scattering lengths, etc. These investigations, developed later by other physicists, opened up whole new areas of a science sometimes called neutronology, i.e., application of neutronic methods to solid state and various other branches of physics.
When his work at Chicago was finished, Fermi went to Los Alamos, New Mexico, where the Los Alamos Laboratory of the Manhattan Engineer District, under the direction of J. R. Oppenheimer, had the assignment of assembling an atomic bomb. Fermi spent most of the period from September 1944 to early 1946 at Los Alamos, where he served as a general consultant. He also collaborated in the building of a small chain reactor using enriched uranium in U235 and heavy water. Fermi actively participated in the first test of the atomic bomb in the desert near Alamogordo, New Mexico, on 16 July 1945.
Following the successful test of the bomb, he was appointed by President Truman to the interim committee charged with advising the president on the use of the bomb and on many fundamental policies concerning atomic energy.
In 1946 the University of Chicago created the Institute for Nuclear Studies and offered a professorship to Fermi. The Institute was promising in its financing and organization; and Fermi, although very influential in its direction, would be spared administrative duties. The offer proved attractive to Fermi, and early in 1946 he and his family left Los Alamos for Chicago. He remained at the University of Chicago for the rest of his life.
The new institute had Samuel K. Allison as director and a faculty in which the new generation of physicists who had been active in the Manhattan Project was strongly represented: Herbert Anderson, Maria Goeppert Mayer, Edward Teller, and Harold C. Urey were among the first members. At Chicago, Fermi rapidly formed a school of graduate students whom he instructed personally, in a fashion reminiscent of his earlier days in Rome. Among those who later distinguished themselves as physicists were Richard L. Garwin, Murray Gell-Mann, Geoffrey Chew, Owen Chamberlain, Marvin L. Goldberger, Leona Marshall, Darragh E. Nagle, T. D. Lee, and C. N. Yang. Chicago thus became an extremely active center in many different areas of physics.
Fermi himself had concluded, at the end of the war, that nuclear physics was reaching a stage of maturity and that the future fundamental developments would be in the study of elementary particles. He thus prepared himself for this new field by learning as much as possible of the theory and by fostering the building of suitable accelerators with which to perform experiments. We have a hint of his effort to assimilate the theory in his Silliman lectures at Yale in the spring of 1950, which were published as Elementary Particles (New Haven, 1951). He systematically organized a great number of calculations on all subjects, numerical data, important reprints, etc., which he called the “artificial memory.” This material was a daily working tool for him and substituted for books, which he scarcely used any more. It also helped his memory, which, although still excellent, was not as amazing as in his early youth and could not cope with the avalanche of new results.
During the postwar Chicago years, Fermi traveled a good deal, particularly to research centers, where he could meet young, active physicists. He repeatedly visited the Brookhaven National Laboratory, the Radiation Laboratory in Berkeley, the Los Alamos Laboratory, and many universities. He was welcomed everywhere, especially by the younger men who profited from these contacts with him and, in turn, helped Fermi to preserve his youthful spirit. He attended all the Rochester conferences on high-energy physics and taught in several summer schools. In 1949 he revisited Italy, where he was very well received by his former colleagues and by the new generation of physicists who had heard of him as an almost legendary figure.
As soon as the Chicago cyclotron was ready for operation, Fermi again started experimental work on pion-nucleon scattering. (He had coined the word “pion” to indicate pi-mesons.) He found experimentally the resonance in the isotopic spin 3/2, ordinary spin 3/2 state, which had been predicted by Keith Bruckner. The investigation became a major one. With H. L. Anderson and others, Fermi worked out the details up to an energy of about 400 MeV lab of the nucleon-pion interaction. The methods and techniques employed, including the extensive use of computers, were for many years models for the subsequent host of investigators of particle resonances.
In addition to this experimental activity, Fermi did theoretical work on the origin of cosmic rays, devising a mechanism of acceleration by which each proton tends to equipartition of energy with a whole galaxy. These ideas had an important influence on the subsequent studies on cosmic rays. He also developed a statistical method for treating high-energy collision phenomena and multiple production of particles. This method has also received wide and useful applications.
In 1954 Fermi’s health began to deteriorate, but with great will power he carried on almost as usual. He spent the summer in Europe, where he taught at summer schools in Italy and France, but on his return to Chicago in September he was hospitalized. An exploratory operation revealed an incurable stomach cancer. Fully aware of the seriousness of his illness and his impending death, he nevertheless maintained his remarkable equanimity and self-control. He died in November and was buried in Chicago.
It is too early to give a historically valid assessment of Fermi’s place in the history of physics. He was the only physicist in the twentieth century who excelled in both theory and experiment, and he was one of the most versatile. His greatest accomplishments are (chronologically) the statistics of particles obeying the exclusion principle, the application of these statistics to the Thomas-Fermi atom, the recasting of quantum electrodynamics, the theory of beta decay, the experimental study of artificial radioactivity produced by neutron bombardment and the connected discovery of slow neutrons and their phenomenology, the experimental realization of a nuclear chain reaction, and the experimental study of pion-nucleon collision. In addition there are Fermi’s innumerable, apparently isolated contributions to atomic, molecular, nuclear, and particle physics, cosmic rays, relativity, etc., many of which initiated whole new chapters of physics.
Fermi’s Collected Papers, E. Segrè, E. Amaldi, H. L. Anderson, E. Persico, F. Rasetti, C. S. Smith, and A. Wattenberg, eds., 2 vols. (Chicago, 1962–1965), contains most of Fermi’s papers and a complete bibliography, a biographical introduction by E. Segrè, introductions to the various papers by members of the editorial committee, a chronology of Fermi’s life, and subsidiary material.
Secondary literature includes Laura Fermi, Atoms in the Family (Chicago, 1954), a biography by Fermi’s wife emphasizing the human aspects of their life; Emilio Segrè, Enrico Fermi, Physicist (Chicago, 1970), a scientific biography; and H. D. Smyth, Atomic Energy for Military Purposes (Princeton, 1945), which gives an excellent account of the history of the development of atomic energy up to 1945.
See also R. G. Hewlett and O. E. Anderson, Jr., The New World (University Park, Pa., 1962); R. G. Hewlett and F. Duncan, Atomic Shield (University Park, Pa., 1969); and Review of Modern Physics, 27 (1955), 249–275, which contains the memorial symposium in honor of Fermi held at Washington, D.C. (Apr. 1955).
Born September 29, 1901
Died November 30, 1954
Nobel Prize–winning physicist
"It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge."
E nrico Fermi had a long and illustrious career as a physicist. By the age of twenty-five, he had won international recognition for devising a new statistical method for describing atomic particles. After winning the Nobel Prize for Physics in 1938, Fermi and his family immigrated to the United States to avoid growing political oppression in Italy. Immediately after his arrival in America, Fermi was swept up into what President Harry S. Truman (1884–1972) would later describe as "the battle of the laboratories." World War II (1939–45) was underway and scientists in Nazi Germany and the United States were racing to harness atomic power. Fermi was the first scientist to create an atomic chain reaction, which provided a new source of energy and made it possible to build the atom bomb.
Asking questions shows intelligence
Enrico Fermi was born in Rome, Italy, in 1901. His father, Alberto, was a government official with the Italian state railway system and later with the Ministry of Communication. His mother, Ida de Gattis, was a school teacher. Fermi had two siblings, a brother, Giulio, and sister, Maria. Giulio died when Enrico was fourteen, an event that was traumatic for Fermi. The boys had been very close. While grieving, Fermi went into a bookshop one day, bought two volumes on elementary physics, and read through them. Later, he told his sister Maria that he had not even noticed they were written in Latin. Fermi's frequent questions about sophisticated topics in mathematics caught the attention of Adolfo Amidei, a family friend, who guided Fermi's studies. Fermi was an extraordinary student in mathematics and physics. He graduated from secondary school a year early. At the age of twenty-one, Fermi earned a doctorate from the University of Pisa.
Fermi published several scientific papers by the time he graduated from college. He received a fellowship, or a special scholarship, to study in Germany for two years with famous physicists. Fermi knew how to speak German. Fermi already knew how to speak French and Italian, but Amidei had encouraged him to learn German because many advances were being made and written about by German physicists of the period.
Fermi returned to Italy in 1924 and became a professor at the University of Florence. He soon earned an international reputation for what became called Fermi-Dirac statistics. Both he and English physicist P. A. M. Dirac (1902–1984), working independently, were successful in using equations to describe the behavior of heated, subatomic particles. Physicists today use the term "fermions" to identify atomic particles obeying Fermi-Dirac statistics.
Fermi moved to the University of Rome in 1927 to become head of the school's first department of theoretical physics. (Unlike experimental physics, in which experiments can be conducted and results precisely measured, theoretical physics is based on applying theories to explain what cannot be seen, like atomic particles, or what cannot be tested, like the universe.) Fermi formed a group of scholars who worked together on experiments and theories. They published nearly one hundred scientific papers during Fermi's years in Rome, from 1927 to 1938.
In July 1928, Fermi married Laura Capon, the daughter of an Italian admiral. They would have two children.
Fermi became increasingly interested in experimental research in the 1930s. He began focusing on the nucleus of atoms. Following the discovery of artificial radioactivity in 1934, he showed that radioactivity can be made to occur in almost every element. Radioactivity is the energy released when the nucleus of an atom breaks down. It happens naturally in some elements, but it was not until the 1930s that scientists learned how humans could create radioactivity. Fermi formulated a theory of beta decay that was extremely valuable in understanding how an atom functions and predicting how an atom reacts to different kinds of stimuli, like heat. Beta decay is a process through which a neutron in an atomic nucleus breaks apart into a proton and an electron.
While Fermi was making these advances in science, the political and social situation in Italy was becoming dangerous. The country was ruled by a dictator, Benito Mussolini (1883–1945), whose government was exerting control over every aspect of life in Italy and threatening other nations with war. Italy aligned with Germany, another nation that was threatening its neighbors. Germany was controlled by the National Socialist (Nazi) Party of Adolf Hitler (1889–1945). Like Nazi Germany, Italy began imposing laws against certain racial and ethnic groups.
The political situation in Italy affected Fermi's life in two ways: his work life and his family life. The work of scientists in Italy was being increasingly monitored and controlled by government officials. Outside the laboratory, Fermi's family was in danger because Fermi's wife, Laura, was Jewish, and therefore subject to increasingly discriminatory laws and threats from Mussolini's government. The Fermis knew they would have to leave Italy.
In 1938, Fermi was awarded the Nobel Prize in Physics. The prestigious award is given annually, and ceremonies are held in Stockholm, Sweden. The Fermi family traveled to Sweden, attended the ceremonies, and then boarded a ship to the United States. Fermi, who enjoyed using humor in his remarks, would later say that the move was made because he wanted to establish the American branch of the Fermi family.
As Fermi began working in the physics department at Columbia University in New York in 1939, news broke that German physicists were finding success with nuclear fission, the ability to split the nucleus of an atom. Nuclear fission makes it possible to create a chain reaction (one split atom after another in high-speed sequence) that can release enormous amounts of energy. Fermi began working with colleagues at Columbia on experiments in the fission of uranium, a highly radioactive element.
Meanwhile, famous scientists, including Albert Einstein (1879–1955; see entry in volume 1), joined to write a letter to U.S. president Franklin D. Roosevelt (1882–1945; served 1933–45) on the importance of nuclear research, which could lead to the creation of a devastating new weapon. They warned that such research was already well underway in Nazi Germany and would pose a grave threat if expansion-minded Nazi Germany were to have such a weapon. In September 1939, Germany invaded Poland, which started World War II. In the United States, a top-secret study on nuclear fission, called the Manhattan Project, was established in 1941.
The surprise attack by Japanese airplanes on Pearl Harbor in Hawaii on December 7, 1941, brought the United States into World War II. Japan was an ally of Germany. Fermi was among several key physicists who were transferred to work at the University of Chicago in Illinois, where all efforts on the Manhattan Project were brought together. Secretly, the scientists worked in a specially constructed laboratory beneath athletic fields. Their job was to create nuclear fission.
On December 2, 1942, Fermi was the first scientist to be successful in creating an atomic chain reaction. This was key to releasing explosive energy and the building of an atom bomb—which would be the most powerful weapon ever created up to that time. A coded phrase was used to communicate to project and government officials, including President Roosevelt, that it was Fermi who created the first self-sustaining chain reaction controlled by humans. That now famous coded phrase read, "The Italian Navigator has landed in the New World."
For the next two years, Fermi conducted further research on nuclear fission at the Argonne National Laboratory outside of Chicago. On July 11, 1944, the Fermi family became naturalized citizens of the United States.
The battle of the laboratories
Fermi moved briefly to Hanford, Washington, where he assisted in the design and construction of a plant where plutonium, a radioactive chemical element, would be processed for use in atomic weapons. In September 1944, he joined a group of renowned scientists in Los Alamos, New Mexico, where the final assembly of the first nuclear weapons was to occur. Fermi was in charge of a division charged with solving special problems that arose during construction of the bomb.
The Manhattan Project was so secret that President Roosevelt's vice president, Harry S. Truman (1884–1972), was not informed about it. Truman learned that atomic bombs were being constructed only after he assumed the office of president, after Roosevelt died on April 12, 1945.
The first atomic bomb was detonated at a test site in Alamogordo, New Mexico, on July 16, 1945. Fermi was there, and as always his mind was busy. At the time of the explosion, he was conducting an experiment by dropping bits of paper to estimate the force of the blast. Although miles away from the explosion, he wanted to observe how the paper was affected by the bomb's explosive power. Instead of just falling to the ground—as they had before the blast—they moved backwards and landed behind him. Fermi was able to measure that distance and determine the amount of energy released.
J. Robert Oppenheimer, the physicist who headed the Manhattan Project, wrote that Enrico Fermi was not a philosopher. He had, according to Oppenheimer, a "passion for clarity. He was simply unable to let things be foggy. Since they always are, this kept him pretty active."
Following the successful creation of the bomb, President Truman debated whether or not to use the powerful new weapon, of which only a few people were aware. Germany had already surrendered, but war between Japan and the United States was ongoing, with no clear end in sight. Truman's secretary of war, Henry Stimson (1867–1950), sought input from a group of scientists working at Los Alamos called the "Interim Committee" (An interim is the time between
one action and another; in this case, the interim was the time between testing the bomb and using it for military purposes.) After deep soul-searching, Fermi and physicists Arthur H. Compton (1892–1962), J. Robert Oppenheimer (1904–1967), and Ernest O. Lawrence (1901–1958) concluded that a technical demonstration of the bomb was not likely to persuade Japan to end the war. The physicists found no acceptable alternative to military use as a way to demonstrate the power of the bomb.
An atom bomb was dropped on Hiroshima, Japan, on the morning of August 6, 1945. Japanese strongholds in Manchuria, China, were invaded by the Soviet Union, an ally of the United States in World War II, on August 8. A second atom bomb was detonated over the Japanese city of Nagasaki on August 9, 1945. Following these devastating events, Japan announced its surrender on August 14, 1945, and the surrender became official on September 2, 1945.
Sixteen hours after the bombing of Hiroshima, President Truman made a radio speech to inform Americans about the explosion. He noted that Nazi Germany had been "working feverishly to find a way to add atomic energy to the other engines of war with which they hoped to enslave the world." Speaking of what scientists had accomplished in America by being first to harness atomic power, Truman stated, "The battle of the laboratories held fateful risks for us as well as the battles of the air, land and sea, and we have won the battle of the laboratories as we have won the other battles."
After World War II ended, Fermi became a professor at the University of Chicago Institute for Nuclear Studies and served on the general advisory committee of the newly created Atomic Energy Commission. He was elected to the National Academy of Sciences in 1945.
Against the Hydrogren Bomb
Fermi helped unleash the power of atomic energy and assisted in the creation of the atom bomb. However, he was against creating an even more powerful weapon, the hydrogen bomb, a few years later. After a meeting in 1949 of the Atomic Energy Commission, on which he served on the advisory board, Fermi and fellow scientist Isidor Rabi (1898–1988) authored an opinion that was included in a report of the meeting. They stated: "It is clear that such a weapon cannot be justified on any ethical ground…. The fact that no limits exist to the destructiveness of this weapon makes its very existence and the knowledge of its construction a danger to humanity as a whole. It is necessarily an evil thing considered in any light." Nevertheless, the United States and the Soviet Union both developed the weapon and were successful testing it during the 1950s.
Fermi remained in Chicago for most of the rest of his life. He was a popular lecturer and taught courses at the University of Michigan and Stanford University. In addition to receiving many honorary degrees from universities, Fermi was awarded the Civilian Medal of Merit (from the U.S. Congress) in 1946 for his work on the Manhattan Project and the Franklin Medal from the Franklin Institute (a distinguished science institute) in 1947.
Fermi had many accomplishments as a physicist. In his honor, physicists named a newly discovered element "fermium" and a form of nuclear measurement, the femtometer, was also referred to as a "fermi." He was elected president of the American Physical Society in 1953. When not involved in studies and experiments, Fermi enjoyed walks, mountain hikes, and winter sports.
Fermi began to experience health problems in 1954. Exploratory surgery showed that he had stomach cancer. He continued his research almost to the day he died, November 30, 1954. He was buried in Chicago. Shortly after his death, the Enrico Fermi Award was established by the U.S. Atomic Energy Commission, and Fermi was honored as the first recipient for his life's work.
For More Information
Cooper, Dan. "Enrico Fermi, and the Revolutions of Modern Physics." In Oxford Portraits in Science. Oxford: Oxford University Press, 1995.
Fermi, Laura. Atoms in the Family: My Life with Enrico Fermi. Chicago: University of Chicago Press, 1954.
Segrè, Emilio. Enrico Fermi: Physicist. Chicago: University of Chicago Press, 1970. Reprint, 1995.
Stux, Erica. Enrico Fermi: Trailblazer in Nuclear Physics. Berkeley Heights, NJ: Enslow, 2004.
American Experience: The Race for the Superbomb.http://www.pbs.org/wgbh/amex/bomb/index.html (accessed on March 12, 2004).
Rhodes, Richard. The Time 100: The Most Important People of the Century.http://www.time.com/time/time100/scientist/profile/fermi03.html (accessed on March 12, 2004).
The Italian-American physicist Enrico Fermi (1901-1954) discovered "Fermi statistics," described beta decay, established the properties of slow neutrons, and constructed the first atomic pile.
In Enrico Fermi, the theorist and experimentalist were combined in a supremely intimate, complementary, and creative way. He possessed an almost uncanny physical intuition which, together with his personal simplicity, made him universally admired and respected.
Fermi was born on Sept. 29, 1901, in Rome, the third child of an official in the Ministry of Railroads. At about the age of 10 his interest in mathematics and physics awakened. A perceptive colleague of his father's, the engineer A. Amidei, recognized Fermi's truly exceptional intellectual qualities and guided his mathematical and physical studies between ages 13 and 17.
By the time Fermi received his doctorate from the University of Pisa in 1922, he had written several papers on relativistic electrodynamics, using the methods of Albert Einstein's general theory. Fermi received a fellowship to study at the University of Göttingen. In spite of the fact that he attacked problems of interest to the Göttingen physicists, his 8 months there were not very satisfactory. In 1924, on George E. Uhlenbeck's urging, Fermi went to study at the University of Leiden with Uhlenbeck's teacher, Paul Ehrenfest. Several years later, when Uhlenbeck was at the University of Michigan, he arranged for Fermi to spend the summers of 1930, 1933, and 1935 at Michigan's Summer School for Theoretical Physics.
Late in 1924, after leaving Leiden, Fermi went to the University of Florence, where he taught mathematical physics and theoretical mechanics. In 1926 he published his first major discovery, namely, the quantum statistics now universally known as Fermi-Dirac statistics. The particles obeying these statistics are now known as fermions.
Fermi's discovery did not stem basically from the concurrently emerging quantum theory, as might be expected, but rather from his own studies in statistical mechanics. These studies began as early as 1923 but were frustrated because a key concept, Wolfgang Pauli's exclusion principle, was still missing. Fermi saw immediately that all particles (fermions) obeying Pauli's exclusion principle would behave in a definite way, quantum-mechanically and statistically speaking. Fermi's discovery led to an understanding of certain important features of gas theory, of how electrons in metals conduct electricity, of why electrons do not contribute to the specific heats of substances, and of many other phenomena. It also undergirded Fermi's widely used 1927 statistical model of the atom, an approximate model in which the atom is envisioned as a statistical assemblage of electrons.
Theory of Beta Decay
The years between 1926 and 1938 constituted Fermi's "golden age." He accepted the chair of theoretical physics at the University of Rome in 1926 and only 3 years later became one of the first 30 members (and sole physicist) to be elected to the Royal Academy of Italy. In 1928 he married Laura Capon; they had a son and a daughter.
Fermi made significant contributions to a wide variety of problems in atomic, molecular, and nuclear spectroscopy; in particle scattering theory; in atomic and nuclear structure; and in quantum electrodynamics. His most celebrated theoretical work of this period was his 1933 theory of nuclear beta decay, a theory that nicely supplemented the theory of nuclear alpha decay of George Gamow, R. W. Gurney, and Edward U. Condon.
In beta decay a negatively charged particle (beta particle), known to be identical to an electron, is emitted from the nucleus of an atom, thereby increasing the atomic number of the nucleus by one unit. Fermi worked out in a short time an elegant theory of beta decay based on the idea that a neutron in the nucleus is transformed (decays) into three particles: a proton, an electron (beta particle), and a neutrino. Actually, the neutrino—an elusive, massless, chargeless particle—was not detected experimentally until the 1950s.
In the late 1920s Fermi decided to attack experimental problems in nuclear physics rather than continue his ongoing spectroscopic researches. By mixing beryllium powder with some radon gas, he had a source of neutrons with which to experiment and determine whether neutrons could induce radioactivity. He constructed a crude Geiger-counter detector and, methodically, he started bombarding hydrogen, then went on to elements of higher atomic number. All results were negative until he bombarded fluorium and detected a weak radioactivity. This key date in neutron physics was March 21, 1934.
With high excitement Fermi and his coworkers continued. By summer 1934 they had bombarded many substances, discovering, for example, that neutrons can liberate protons as well as alpha particles. In addition, they had detected a slight radioactivity when bombarding uranium, and they attempted, without success, to understand why aluminum, when bombarded with neutrons, could not decide, in effect, which of two different nuclear reactions to undergo.
Their next discovery was a milestone. They found that the level of radioactivity induced in a substance was increased if a paraffin filter was placed in the beam of neutrons irradiating the substance. Fermi's hypothesis for this miracle, which he immediately confirmed, was that in passing through the paraffin, a compound containing a large amount of hydrogen, the neutrons had their velocity much reduced by collisions with the hydrogen nuclei; and these very slow neutrons—contrary to all expectations—induced a much higher radioactivity in substances than did fast neutrons. Furthermore, the old aluminum mystery had been solved: slow neutrons produce one kind of reaction, fast neutrons another. The discovery of the remarkable properties of slow neutrons was the key discovery in neutron physics.
By 1937 Fermi's wife and their children became directly affected by the racial laws in Fascist Italy. In December 1938 the Fermi family went to Stockholm for the presentation of the Nobel Prize in physics to Fermi. He and his family then left for the United States, arriving in New York on Jan. 2, 1939, where Fermi accepted a position at Columbia University.
With the assistance of Herbert L. Anderson, Fermi produced a beam of neutrons with the Columbia cyclotron, thus verifying the fission of uranium. Then he quantitatively explored the conditions governing its production. He and his coworkers also proved, using a minute sample, that the fissionable isotope of uranium is U235. By mid-1939 there was clear evidence that a self-sustaining chain reaction might be realizable. Furthermore, the stupendous military importance of nuclear fission had become clear. By July 1941 Arthur H. Compton, chairman of a special committee of the National Academy of Sciences, could report the possibility not only of a uranium bomb but also of a plutonium bomb.
Fermi was asked to assume the huge responsibility of directing the construction of the first atomic pile. He, and other key physicists, moved to the University of Chicago in the spring of 1942; by early October their researches had progressed to the point where Fermi was confident he knew how to construct the pile, and the project (the "Manhattan Project") was under way. Construction of the pile began in mid-November 1942, and on December 2 Fermi directed the operation of the first self-sustaining chain reaction created by man. The actual length of time it was operated on that historic day was 40 minutes; its maximum power was 1/2 watt, enough to activate a penlight. It was the opening of a new age, the Atomic Age.
Fermi's experiment was far more than an experiment in pure research. Huge national laboratories were constructed, one of which, Los Alamos, had immediate responsibility for the construction of the nuclear bomb. Its director was J. Robert Oppenheimer. In September 1944 he brought Fermi from Chicago primarily to have him on hand during the last, critical stages in the construction of the bomb. By early 1945 the project had proceeded to the point where the greatest amount of new information could be obtained only by actually exploding the fearsome weapon. The test, which bore the code name "Project Trinity," was successfully carried out on July 16, 1945, in the desert near Alamogordo in southern New Mexico.
On Dec. 31, 1945, Fermi became Charles H. Swift distinguished service professor of physics and a member of the newly established Institute (now the Enrico Fermi Institute) for Nuclear Studies at the University of Chicago. This was the beginning of a period during which his reading and range of interests—always confined largely to physics— contracted considerably. For a few years he continued working in the fields of nuclear and neutron physics. In 1949 he demonstrated theoretically that the extremely high cosmic-ray energies can be accounted for by the accelerations imparted to them by vast interstellar magnetic fields. At about the same time his interest shifted away from nuclear physics to high-energy (particle) physics. In a number of his researches he used the Chicago synchrocyclotron to explore pi-meson interactions in an effort to discover the means by which the nucleus is held together in a stable configuration.
Fermi died in Chicago on Nov. 29, 1954.
The best existing guides to Fermi's scientific work are Emilio Segrè's Enrico Fermi, Physicist and his "Biographical Introduction" and various physicists' "Notes" in The Collected Papers of Enrico Fermi, edited by Segre' and others (2 vols., 1962-1965). Personal aspects of Fermi's life are recounted in the delightful work by his wife, Laura Fermi, Atoms in the Family: My Life with Enrico Fermi (1954) and Illustrious Immigrants: The Intellectual Migration from Europe, 1930-41 (1968). See also Niels H. de V. Heathcote, Nobel Prize Winners in Physics, 1901-1950 (1954); the obituary notices of Fermi by E. Bretscher and John D. Cockcroft in the Royal Society of London, Biographical Memoirs of Fellows of the Royal Society, vol. 1 (1955), and by Samuel K. Allison in the National Academy of Sciences of the United States, Biographical Memoirs, vol. 30 (1957); Pierre de Latil, Enrico Fermi: The Man and His Theories (trans. 1965); and Nobel Foundation, Nobel Lectures, Including Presentation Speeches and Laureates' Biographies, 1922-1941 (1965). □
The Italian American physicist (specialist in the relationship between matter and energy) Enrico Fermi developed the first nuclear (using atomic energy) chain reaction, which helped lead to the creation of the atomic bomb.
Enrico Fermi was born on September 29, 1901, in Rome, Italy, the third child of Alberto and Ida de Gattis Fermi. His father was an inspector in the Ministry of Railroads, and his mother was a schoolteacher. At about the age of ten his interest in mathematics and physics awakened. A friend of his father's, the engineer Adolfo Amidei, recognized Fermi's intellectual abilities and guided his mathematical and physical studies by loaning him books during his teenage years.
By the time Fermi received his doctorate degree from the University of Pisa, in Italy, in 1922, he had already written several papers on electrodynamics (a branch of physics dealing with the relationships between electric currents and magnets). Fermi went on to study at the University of Göttingen in Germany for eight months. In 1924, Fermi went to study at the University of Leiden, in Holland.
Late in 1924, after leaving Leiden, Fermi went to the University of Florence, Italy, where he taught mathematical physics and theories of mechanics (the study of forces and their effect on matter). In 1926 he published his first major discovery, what became known as Fermi-Dirac statistics. He had come up with a way to determine the properties and behavior of certain particles that obey (conform to) Wolfgang Pauli's exclusion principle. (Pauli's principle holds that no two particles have the same position and the same velocity, or speed.) These obeying particles are now known as fermions.
Fermi's discovery came directly from his own studies. These studies began in 1923 but ran into problems because Pauli's idea was not then known. Fermi saw immediately that all particles (fermions) obeying Pauli's not-yet-proposed exclusion principle would behave in a certain way. This discovery led to an understanding of certain features of gas theory and of how metals conduct electricity, among other things. It also became the foundation of Fermi's widely used 1927 model of the atom.
Theory of beta decay
The years between 1926 and 1938 are considered Fermi's "golden age." He accepted the chair of theoretical physics (existing in theory only) at the University of Rome in 1926 and three years later became one of the first thirty members (and only physicist) to be elected to the Royal Academy of Italy. In 1928 he married Laura Capon; they had two children.
Fermi's most famous work of this period was his 1933 theory of nuclear beta decay. In beta decay a particle (beta particle), known to be identical to an electron in that it is said to have a "negative" electric charge, is given off from the nucleus (core) of an atom. This increases the atomic number (the number of protons, or particles with "positive" electric charges, minus the number of electrons) of the nucleus by one unit. Fermi worked out a detailed theory of beta decay based on the idea that a neutron (a particle with no electric charge) in the nucleus "decays," or changes, into three particles: a proton, an electron (beta particle), and a neutrino. Actually, the neutrino (a particle without mass or electric charge) was not found in experiments until the 1950s.
In the late 1920s Fermi came up with a source of neutrons with which to experiment and determine whether neutrons could cause radioactivity (a process by which the atoms of an element give off particles of matter and harmful rays of energy). Fermi constructed a machine similar to a Geiger counter (a device for measuring radioactivity) and started bombarding different elements with neutrons. He had no success until he detected a weak radioactivity while subjecting fluorium to the treatment. This key date was March 21, 1934. By summer 1934 Fermi and his coworkers had tested many substances and detected a slight radioactivity in some.
Fermi and his team then found that the level of radioactivity created in a substance was increased if a filter made of paraffin (a waxy substance) was placed in the path of the neutrons bombarding the substance. Fermi's idea was that in passing through the paraffin (a compound containing a large amount of hydrogen), the speed of the neutrons was reduced by contact with the hydrogen atoms, and these very slow neutrons caused a much higher radioactivity in substances than fast neutrons did. Slow neutrons produce one kind of reaction, fast neutrons another. The discovery of the properties of slow neutrons was the key discovery in neutron physics.
By 1937 Fermi's wife and their children became concerned by the changing political atmosphere in Italy. In December 1938 the Fermi family went to Stockholm, Sweden, for the presentation of the Nobel Prize in physics to Fermi. He and his family then left for the United States, arriving in New York in January 1939, where Fermi accepted a position at Columbia University.
With the assistance of fellow physicist Herbert L. Anderson, Fermi produced a beam of neutrons at Columbia, with which he proved that the fission (the splitting of an atom into two roughly equal parts) of uranium was possible. By mid-1939 there was evidence that a man-made nuclear chain reaction might be possible. (The goal was to get at least one of the neutrons released in a fission reaction to cause another fission, with the process repeating over and over. This would lead to the release of a large amount of energy very quickly.) The military became very interested, and Fermi was asked to direct the research on the idea. He and other physicists moved to the University of Chicago in early 1942; by October, Fermi was confident that he knew how to get the job done, and the project (the "Manhattan Project") was under way. Construction began in November, and on December 2 Fermi directed the operation of the first self-sustaining chain reaction created by man. It lasted forty minutes and created power equal to one-half watt, enough to activate a penlight. It was the opening of the Atomic Age.
As a result of Fermi's experiment, huge national laboratories were constructed, one of which, Los Alamos, had immediate responsibility for the construction of the nuclear bomb. In September 1944 Fermi was brought in from Chicago for the final important stages in the construction of the bomb. By early 1945 the project had proceeded to the point where it was time to explode the deadly weapon. The test, which had the code name "Project Trinity," was successfully carried out in July 1945, in the desert in southern New Mexico.
In December 1945 Fermi became professor of physics and a member of the Institute for Nuclear Studies (now the Enrico Fermi Institute) at the University of Chicago. During this period his reading and range of interests decreased considerably. For a few years he continued to work in nuclear physics. Around 1949 his interest shifted to high-energy (particle) physics. Enrico Fermi died in Chicago, Illinois, on November 29, 1954.
For More Information
Fermi, Laura. Atoms in the Family: My Life with Enrico Fermi. Chicago: University of Chicago Press, 1954.
Fermi, Laura. Illustrious Immigrants: The Intellectual Migration from Europe, 1930–41. Chicago: University of Chicago Press, 1968.
Segrè, Emilio, ed. The Collected Papers of Enrico Fermi. 2 vols. Chicago: University of Chicago Press, 1962–1965.
Segrè, Emilio. Enrico Fermi: Physicist. Chicago: University of Chicago Press, 1970.
Enrico Fermi was born on September 29, 1901, and grew up in Rome; his father, Alberto Fermi, was a chief inspector in the Railway Ministry; his mother, Ida de Gattis, was an elementary school teacher. Enrico, his sister, and his brother went to secular schools and were raised as agnostics. A friend of his father lent the young Fermi mathematics books and influenced him to attend the university in Pisa. While an undergraduate, he became Italy's foremost expert on Einstein's theory of general relativity. After Pisa, Fermi received a fellowship for a year in Göttingen. A special professorship in theoretical physics was created for Fermi at the University of Rome in 1927, and at age twenty-six he became the youngest professor in Italy since Galileo. In 1934, he married Laura Capon, who was Jewish. The couple had two children, Nella and Giulio.
Fermi wrote more than 270 articles during his life and made outstanding contributions to most areas of twentieth century physics. At age 24, in January 1926, he wrote the Fermi statistics, one of his
most significant and lasting theoretical contributions. It set forth a method for calculating the behavior and properties of systems that obeyed quantum mechanical rules for two or more electrons. Seven months later, Paul Dirac independently derived the same statistical mechanics. Almost all known elementary particles are called fermions because they obey the rules of Fermi-Dirac statistical mechanics.
In 1933 Fermi successfully constructed a formal theory of the beta-decay of radioactive nuclei. In the radioactive process a neutron changes to a proton by creating an electron and a neutrino. Fermi's theory of beta decay introduced a fourth fundamental force, called the weak interaction, to be added to the previously known three: the gravitational force between masses, the electromagnetic force between electric charges, and the strong force between the particles in nuclei. A new fundamental constant, called the Fermi constant, determines the strength of the weak interaction. In the 1960s the electromagnetic and the weak interactions were combined in a unified theory, and Fermi's weak interaction and well-measured constant have continued to play a major role in particle physics more than half a century later.
After the discovery of the neutron by Chadwick in 1932, Fermi's group in Rome started an experimental program bombarding all available elements with neutrons. Fermi was awarded the Nobel Prize in Physics for the neutron work. He used the trip to Sweden to escape with his family from Italy and Mussolini's anti-Semitic laws. Many people know Fermi as the architect of the atomic age—the scientist who built and controlled the first nuclear chain reaction, the basis for the peaceful uses of nuclear energy. From 1939 until the end of World War II, he played a major role in the U.S. war project that led to the atomic bomb.
After the war, his major interest was in elementary particle physics which includes the properties of the particles, their decays, their production, and their interactions. Measurements are made of what happens in collisions between particles or when particles decay.
Fermi's most extensive particle experiments were studying the interaction of pi mesons and protons. In 1935 Yukawa postulated that pi mesons account for the strong nuclear force that binds nucleons together in short distances. The pi meson is pictured as being emitted by one nucleon and absorbed by another nucleon that binds the two nucleons together. Pi mesons were first observed in cosmic rays. Later, they were found to be produced in the accelerators built in the late 1940s. Fermi and his associates hit protons with beams of negatively or positively charged pi mesons (pi− or pi+) using the synchrocyclotron at the University of Chicago. They measured the angles and energies of particles emitted from the collisions. They found that in some of the collisions between a pi− and a proton the particles turned into a neutron and an uncharged pion. The combination of a neutron and an uncharged pion constituted the discovery of short-lived baryons; baryons are particles like the neutron and proton with similar or heavier masses, and the masses are conserved in reactions.
During the 1940s and 1950s, Fermi also was active as a theoretical physicist in a variety of fields. In particle physics, Fermi became concerned that some of the twenty-one particles known in 1950 might not really be "elementary particles," that is, structureless particles. He wrote a provocative paper with C. N. Yang entitled "Are Mesons Elementary Particles?"
Fermi was a fabulous teacher and had an enormous influence on several generations of experimental physicists. He tried to impress on students the importance of understanding theory so that, when planning experiments, they could estimate in advance possible results. He enjoyed interacting with students informally and working with them in the laboratory. He put a great deal of effort into preparing classroom and formal lectures. His lecture notes have been widely circulated and some are published.
Fermi's lectures frequently started with simple explanations of an abstract theory, an example of which can be found in his booklet "Elementary Particles" (based on Fermi's 1950 lectures at Yale). Fermi begins his discussion with quantum field theory as a theoretical framework for the interaction of almost all particles. In later chapters, he shows how to obtain quantitative results when calculating a broad variety of phenomena including the range of nuclear forces, the products of the annihilation of an antinucleon with a nucleon, and the decay of weakly interacting particles. In Fermi's "Lectures, on Pions and Nucleons," edited by B. T. Feld and published in Nuovo Cimento in 1955, he explains simple group theory. Group theory provided the classification schemes that became so important in the next decade. Feld's 1969 book Models of Elementary Particles exemplifies Fermi's style of combining theory and quantitative experimental results.
Three of Fermi's graduate students (O. Chamberlain , T. D. Lee , and C. N. Yang ) won Nobel Prizes for their work in elementary particle physics. Fermi died of intestinal cancer in Chicago on November 28, 1954.
Amaldi, E.; Anderson, H. L.; Persico, E.; Rasetti, F. Segrè, E.; Smith, C. S.; and Wattenberg, A., eds. Collected Papers ofEnrico Fermi, Vols. I and II (Chicago University Press, Chicago, IL, 1962).
Fermi, E. "Lectures on Pions and Nucleons." Nuovo Cimento Supplemento2 (1955).
Segrè, E. Enrico Fermi Physicist (University of Chicago Press, Chicago, IL, 1940).
Wattenberg, A. "The Fermi School in the United States." European Journal of Physics9 , 88–93 (1988).
Enrico Fermi was born in Rome, the son of Italy's chief railroad inspector (Alberto Fermi) and a schoolteacher (Ida de Gattis). While he was attending Ginnasio Liceo Umberto I, an associate of his father recognized Fermi's talents in physics and mathematics and encouraged him to master several challenging scientific treatises. At the University of Pisa and the Scuola (1918–1922), Fermi published two papers on relativistic electrodynamics and one on general relativity. He completed doctoral theses at each institution. After holding several short-term positions, Fermi attracted the attention of Italian senator and chemist Orso M. Corbino, who helped establish for Fermi the country's first chair of theoretical physics at the University of
Rome. In 1928 Fermi married Laura Capon, and the couple had two children.
As a chair at the University of Rome, Fermi did much of his most important work between 1927 and 1938. Along with the English physicist Paul Dirac but independently, he developed quantum-mechanical statistics that measure particles of half-integer spin (now known as fermions); between 1929 and 1932 he reformulated more simply and elegantly Dirac's then recent work on quantum electronics. In 1933–1934, he published a theory of β -decay that included what became known as the Fermi interaction, Fermi interactions, and the Fermi coupling constant. He also theorized and named the neutrino ("little neutral one"), originally hypothesized by Wolfgang Pauli but not detected experimentally until 1956.
After 1933 Fermi turned increasingly to experimental physics. Inspired by recent work in which artificial radioactive substances were produced by α -particle bombardment, Fermi and several collaborators used neutron bombardment to create several "transuranic" elements heavier than uranium, including plutonium. This work, and his finding that slow neutrons produce nuclear reactions more efficiently than fast ones, earned Fermi wide acclaim and the 1938 Nobel Prize in physics. After accepting the prize in Sweden, Fermi and his Jewish wife immigrated to the United States to escape the Nazis.
After replicating the German fusion of the uranium atom in early 1939, Fermi was recruited to join the secret U.S. atomic bomb project, the Manhattan Project . He initially worked at the project's metallurgical laboratory at the University of Chicago, where he was chief designer of an atomic pile that achieved a sustained nuclear reaction on December 2, 1942. Throughout the war he worked on reactor design and fissionable fuel production at several project facilities.
Fermi became a naturalized U.S. citizen on July 11, 1944. Short in stature and barrel-like, he retained a thick Italian accent and refreshingly unassuming manner throughout his life. Although he supported the atomic bombing of Japan, after the war, as a member of the powerful General Advisory Committee of the Atomic Energy Commission, he opposed the development of a hydrogen bomb. Fermi moved into new areas of research, including cosmic rays (the "Fermi mechanism" modeled their acceleration) and elementary particle physics. In addition to the Nobel Prize, Fermi was honored with many other distinguished awards, including the Presidential Medal of Merit (1946), the Franklin Medal (1947), the Max Planck Medal (1954), and the Fermi Award (1954). The latter, as well as the Fermi National Accelerator Laboratory in Batavia, Illinois, were named in his honor.
see also Nuclear Chemistry; Pauli, Wolfgang.
David B. Sicilia
Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon & Schuster.
Segrè, Emilio (1970). Enrico Fermi: Physicist. Chicago: University of Chicago Press.
Enrico Fermi discovered a way to induce artificial radiation in heavy elements by shooting neutrons into their atomic nuclei. Using this technique he produced the first transuranium elements; that is, heavy elements that appear after uranium in the periodic table. For these accomplishments, Fermi was awarded the Nobel Prize in Physics in 1938. He was also instrumental in the design and construction of the world's first nuclear reactor at the University of Chicago. December 2, 1942, when a self-sustaining chain reaction was first achieved there, is often considered to be the beginning of the Atomic Age.
Fermi was born on September 29, 1901, in Rome, the son of railroad employee Alberto Fermi and his wife, Ida de Gattis. A precocious student, Fermi had decided to become a physicist before he had graduated from high school. He received his doctorate in physics at the University of Pisa in 1922. After postdoctoral studies with Max Born (1882-1970) at Göttingen and Paul Ehrenfest (1880-1933) in Leiden, he lectured in mathematics at the University of Florence. There, he published his first important theoretical papers. By the age of 25, he had obtained a professorship at the University of Rome and begun his experimental work. Fermi married Laura Capon in 1928. Their daughter Nella was born in 1931, and their son Giulio followed in 1936.
In 1934, the French physicists Frédéric (1900-1958) and Irène Joliot-Curie (1897-1956) had first produced artificial radioactivity by bombarding atoms with helium nuclei, or alpha particles. However, this technique ran into difficulties with heavy elements, which had many positively charged protons in their nucleus to repel the positively charged alpha particles. The newly discovered neutron, with no charge at all, seemed to Fermi to be a good projectile to throw at these heavy atoms. The neutrons were even more effective when slowed down by collisions with the atoms in hydrogen-rich materials such as water or paraffin.
Fermi began announcing transuranium elements in 1934. It was not until 1939, after Otto Hahn (1879-1968) and Fritz Strassmann (1902-1980) had performed the same experiment, that Lise Meitner (1878-1968) and her nephew Otto Frisch (1904-1979) realized that Fermi had also been the first to split the atom. "We did not have enough imagination," he later wrote. Meitner realized that nuclear fission was accompanied by the release of enormous amounts of energy, in accordance with the famous equation of Albert Einstein (1879-1955), E = mc2.
While Fermi had been working on his neutron bombardment experiments, he and his wife, who was Jewish, had grown increasingly concerned about the Fascist regime in Italy. Having received permission to leave the country to pick up Fermi's Nobel Prize in Sweden in 1938, the family fled to the United States. After three years at Columbia University, he went on to the University of Chicago.
Fermi was alarmed by the possibility of Hitler's Germany harnessing the massive destructive power of nuclear fission. With this in mind, he helped compose a letter signed by several eminent physicists and delivered to President Roosevelt by Einstein, urging him to establish what came to be called the Manhattan Project. Fermi's role was to develop the nuclear reactor, or "atomic pile" as he called it. The reactor was built in an unused squash court at the University of Chicago and went into operation in 1942. Fermi became an American citizen in 1944. He continued with the Manhattan Project in Los Alamos, New Mexico, where the first atomic bomb was tested on July 16, 1945. A few weeks later, bombs were dropped on Hiroshima and Nagasaki.
After the war, Fermi returned to the University of Chicago. His later research concentrated on nuclear particles, especially mesons. A meson is a packet of energy, or quantum, corresponding to the strong force that holds the nucleus together, just as the photon is a quantum of light. Fermi died in Chicago on November 28, 1954.
SHERRI CHASIN CALVO
[See also Atomic Scientists; Nuclear Weapons.]
Emilio Segre , Enrico Fermi: Physicist, 1970.
Laura Fermi , Atoms in the Family: My Life with Enrico Fermi, 1971.
Peter J. McNelis