Enrico Fermi (1901–1954)
29 September 1901|
|Died||28 November 1954
Chicago, Illinois, United States
United States (1944–1954)
|Institutions||Scuola Normale Superiore
University of Göttingen
University of Florence
Sapienza University of Rome
University of Chicago
|Alma mater||Scuola Normale Superiore|
|Doctoral advisor||Luigi Puccianti|
|Doctoral students||Edoardo Amaldi
|Other notable students||Jack Steinberger
Chen Ning Yang
|Known for||Controlled nuclear chain reaction,
Theory of beta decay
|Notable awards||Matteucci Medal (1926)
Nobel Prize for Physics (1938)
Hughes Medal (1942)
Medal for Merit (1946)
Franklin Medal (1947)
Rumford Prize (1953)
Enrico Fermi (Italian: [enˈri.ko ˈfeɾ.mi]; 29 September 1901 – 28 November 1954) was an Italian theoretical and experimental physicist, best known for his work on the development of Chicago Pile-1, the first nuclear reactor, and for his contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics. Along with Robert Oppenheimer, he is referred to as "the father of the atomic bomb". He held several patents related to the use of nuclear power, and was awarded the 1938 Nobel Prize in Physics for his work on induced radioactivity and the discovery of transuranic elements. Throughout his life Fermi was widely regarded as one of the very few physicists who excelled both theoretically and experimentally.
Fermi's first major contribution was to statistical mechanics. After Wolfgang Pauli announced his exclusion principle in 1925, Fermi followed with a paper in which he applied the principle to an ideal gas, employing a statistical formulation now known as Fermi–Dirac statistics. Today, particles that obey the exclusion principle are called "Fermions". Later Pauli postulated the existence of an invisible particle with no charge that was emitted at the same time an electron was emitted during beta decay in order to satisfy the law of conservation of energy. Fermi took up this idea, developing a model that incorporated the postulated particle, which Fermi named the "neutrino". His theory, later referred to as Fermi's interaction and still later as the theory of the weak interaction, described one of the four forces of nature. Through experiments inducing radioactivity with recently discovered neutrons, Fermi discovered that slow neutrons were more easily captured than fast ones, and developed a diffusion equation to describe this, which became known as the Fermi age equation. He bombarded thorium and uranium with slow neutrons, and concluded that he had created new elements, for which he was awarded the Nobel Prize, but the new elements were subsequently revealed to be fission products.
Fermi left Italy in 1938 to escape racial laws that affected his Jewish wife Laura, and emigrated to the United States, where he worked on the Manhattan Project during World War II. Fermi led the team that designed and built the Chicago Pile-1, and initiated the first artificial self-sustaining nuclear chain reaction when it went critical on 2 December 1942. He was on hand when the X-10 Graphite Reactor at Oak Ridge, Tennessee, went critical in 1943, and the B Reactor at the Hanford Site went critical in 1944. At Los Alamos he headed F Division, where he worked on the thermonuclear "Super". He was present at the Trinity test on 16 July 1945, where he used one of his Fermi method experiments to estimate the bomb's yield.
After the war, Fermi served on the influential General Advisory Committee of the Atomic Energy Commission, a scientific committee chaired by Robert Oppenheimer which advised the commission on nuclear matters and policy. Following the detonation of RDS-1 in August 1949, the first Soviet fission bomb, he wrote a strongly worded report for the committee, opposing the development of a hydrogen bomb on both moral and technical grounds. He was among the scientists who testified on Oppenheimer's behalf at the Oppenheimer security hearing in 1954 that resulted in denial of Oppenheimer's security clearance. Fermi did important work in particle physics, especially related to pions and muons, and he speculated that cosmic rays arose through material being accelerated by magnetic fields in interstellar space. Many awards, concepts, and institutions are named after Fermi, including the Enrico Fermi Award, the Enrico Fermi Institute, the Fermi National Accelerator Laboratory, the Fermi Gamma-ray Space Telescope, the Enrico Fermi Nuclear Generating Station, and the synthetic element fermium.
Early life 
Enrico Fermi was born in Rome on 29 September 1901, the third child of Alberto Fermi, a Capo Divisione (division head) in the Ministry of Railways, and Ida de Gattis, an elementary school teacher. He had two siblings: a sister, Maria, who was two years older, and a brother, Giulio, who was one year older. The two boys were sent to a rural community to be wet nursed. Enrico rejoined his family in Rome when he was two and a half. While he came from a Roman Catholic family, and was baptized in accord with his grandparents' wishes, the family was not religious, and Fermi was an agnostic throughout his adult life. As a young boy, he shared his interests with his brother Giulio. They built electric motors and played with electrical and mechanical toys. Giulio died during the administration of the anesthesia for an operation on a throat abscess in 1915.
One of Fermi's first sources for the study of physics was a book found at the local market of Campo de' Fiori in Roma. The 900-page book, titled Elementorum physicae mathematicae, written in Latin by Jesuit Father Andrea Caraffa, a professor at the Collegio Romano, covered subjects like mathematics, classical mechanics, astronomy, optics, and acoustics to the extent that they were understood when it was written in 1840. Fermi befriended another scientifically inclined student named Enrico, Enrico Persico, and the two worked together on scientific projects such as building gyroscopes and measuring the Earth's magnetic field. Fermi's interest in physics was further encouraged by his father's colleague Adolfo Amidei, who gave him several books on physics and mathematics, which he read and assimilated quickly.
Scuola Normale Superiore in Pisa 
Fermi graduated from high school in July 1918 and, at Amidei's urging, applied to the Scuola Normale Superiore in Pisa. Having lost one son, his parents were reluctant to let him go away for four years instead of living at home while attending the University of Rome, but in the end they acquiesced. The school provided free lodging for students but candidates had to take a difficult entrance exam, which included an essay. The given theme was "Specific characteristics of Sounds". The 17-year-old Fermi chose to derive and solve the partial differential equation for a vibrating rod, applying Fourier analysis. The examiner, Professor Giuseppe Pittarelli from the University of Rome, interviewed Fermi and concluded that his entry would have been commendable even for a doctoral degree. Fermi achieved first place in the classification of the entrance exam.
During his years at the Scuola Normale Superiore, Fermi teamed up with a fellow student named Franco Rasetti with whom he would indulge in light-hearted pranks and who would later become Fermi's close friend and collaborator. In Pisa, Fermi was advised by the director of the physics laboratory, Luigi Puccianti, who acknowledged that there was little that he could teach Fermi, and frequently asked Fermi to teach him something. Fermi's knowledge of quantum physics reached such a high level that Puccianti asked him to organize seminars on the topic. During this time Fermi learned tensor calculus, a mathematical technique invented by Gregorio Ricci and Tullio Levi-Civita that was needed to demonstrate the principles of general relativity. Fermi initially chose mathematics as his major, but soon switched to physics. He remained largely self-taught, studying general relativity, quantum mechanics, and atomic physics.
In September 1920, Fermi was admitted to the Physics department. There were only three students: Fermi, Rasetti and Nello Carrara. Puccianti let them use the laboratory for whatever they wanted. Fermi then decided that they should research X-ray crystallography, and the three worked to produce a Laue photograph, an X-ray photograph of a crystal. During 1921, his third year at the university, Fermi published his first scientific works in the Italian journal Nuovo Cimento. The first was entitled "On the dynamics of a rigid system of electrical charges in translational motion" (Italian: Sulla dinamica di un sistema rigido di cariche elettriche in moto traslatorio). A sign of things to come was that the mass was expressed as a tensor—usually used to describe something moving and changing in three-dimensional space. The second paper was "On the electrostatics of a uniform gravitational field of electromagnetic charges and on the weight of electromagnetic charges" (Italian: Sull'elettrostatica di un campo gravitazionale uniforme e sul peso delle masse elettromagnetiche). Using general relativity, he showed that a charge has a weight equal to U/c2, where U was the electrostatic energy of the system.
The first paper seemed to point out a contradiction between the electrodynamic theory and the relativistic one concerning the calculation of the electromagnetic masses, as the former predicted a value of 4/3 U/c2. Fermi addressed this the next year in a paper "Concerning a contradiction between electrodynamic and the relativistic theory of electromagnetic mass" in which he showed that the apparent contradiction was a consequence of relativity. This paper was sufficiently well-regarded that it was translated into German, and published in the German scientific journal Physikalische Zeitschrift in 1922. That year, Fermi submitted his article "On the phenomena occurring near a world line" (Italian: Sopra i fenomeni che avvengono in vicinanza di una linea oraria) to the Italian journal I Rendiconti dell'Accademia dei Lincei. In this article he examined the Principle of Equivalence, and introduced the so-called "Fermi coordinates". He proved that when close to the time line, space behaves as if it were a Euclidean space.
Fermi submitted his thesis, "A theorem on probability and some of its applications" (Italian: Un teorema di calcolo delle probabilità ed alcune sue applicazioni), to the Scuola Normale Superiore in July 1922, and received his Laurea at the unusually young age of 21. The thesis was on X-Ray diffraction images. Theoretical physics was not yet considered a discipline in Italy, and the only thesis that would have been accepted was one on experimental physics. For this reason, Italian physicists were slow in embracing the new ideas like relativity coming from Germany. Fortunately for him, Fermi was quite at home in the lab doing experimental work.
While writing the appendix for the Italian edition of the book The Mathematical Theory of Relativity by August Kopff in 1923, Fermi pointed out, for the first time, that hidden inside the famous Einstein equation (E = mc2) was an enormous amount of nuclear potential energy to be exploited. "It does seem possible, at least in the near future", he wrote, "to find a way to release these dreadful amounts of energy—which is all to the good because the first effect of an explosion of such a dreadful amount of energy would be to smash into smithereens the physicist who had the misfortune to find a way to do it."
Fermi decided to travel abroad, and spent a semester studying under Max Born at the University of Göttingen, where he met Werner Heisenberg and Pascual Jordan. Fermi then studied in Leiden with Paul Ehrenfest from September to December 1924 on a fellowship from the Rockefeller Foundation obtained through the intercession of the mathematician Vito Volterra. Here Fermi met Hendrik Lorentz and Albert Einstein, and became good friends with Samuel Goudsmit and Jan Tinbergen. From January 1925 to the autumn of 1926, Fermi taught mathematical physics and theoretical mechanics at the University of Florence, where he teamed up with Rasetti to conduct a series of experiments on the effects of magnetic fields on mercury vapour. He also participated in seminars at the University of Rome, giving lectures on quantum mechanics and solid state physics.
After Wolfgang Pauli announced his exclusion principle in 1925, Fermi followed with a paper "On the quantisation of the perfect monoatomic gas" (Italian: Sulla quantizzazione del gas perfetto monoatomico) in which he applied the principle to an ideal gas. The paper was especially notable for Fermi's statistical formulation, now known as Fermi–Dirac statistics, as it was developed independently soon after by the British physicist Paul Dirac, who also showed how it was related to the Bose–Einstein statistics. Today, particles that obey the exclusion principle are called "Fermions" while those that do not are called "Bosons".
Professor in Rome 
Professorships in Italy were granted by competition (Italian: concorso) for a vacant chair, the applicants being rated on their publications by a committee of professors. Fermi applied for a chair of mathematical physics at the University of Cagliari at Cagliari on Sardina, but was narrowly passed over in favour of Giovanni Giorgi. In 1926, at the age of 24, he applied for a professorship at the University of Rome. This was a new chair, one of the first three in theoretical physics in Italy, that had been created by the Minister of Education at the urging of Professor Orso Mario Corbino, who was the University's professor of experimental physics, the Director of the Institute of Physics, and a member of Benito Mussolini's cabinet. Corbino, who also chaired the selection committee, hoped that the new chair would raise the standard and reputation of physics in Italy. The committee chose Fermi ahead of Enrico Persico and Aldo Pontremoli, and Corbino helped Fermi recruit his team, which was soon joined by notable students such as Edoardo Amaldi, Bruno Pontecorvo, Ettore Majorana and Emilio Segrè, and by Franco Rasetti, whom Fermi had appointed as his assistant. They were soon nicknamed the "Via Panisperna boys" after the street where the Institute of Physics was located.
Fermi married Laura Capon, a science student at the University, on 19 July 1928. They had two children: Nella, born in January 1931, and Giulio, born in February 1936. On 18 March 1929, Fermi was appointed a member of the Royal Academy of Italy by Benito Mussolini, and on 27 April Fermi joined the Fascist Party. He would later come to oppose Fascism, but only a decade later when it affected him personally.
During their time in Rome, Fermi and his group made important contributions to many practical and theoretical aspects of physics. In 1928, he published his "Introduction to Atomic Physics" (Italian: Introduzione alla fisica atomica), which provided Italian university students with an up-to-date and accessible text. Fermi also conducted public lectures and wrote popular articles for scientists and teachers in order to spread knowledge of the new physics as widely as possible. Part of his teaching method was to gather his colleagues and graduate students together at the end of the day and go over a problem, often from his own research. A sign of success was that foreign students now began to come to Italy. The most notable of these was the German physicist Hans Bethe, who came to Rome as a Rockefeller Foundation fellow, and collaborated with Fermi on a 1932 paper "On the Interaction between Two Electrons" (German: Über die Wechselwirkung von Zwei Elektronen).
At this time, physicists were puzzled by beta decay, in which an electron was emitted from the atomic nucleus. To satisfy the law of conservation of energy, Pauli postulated the existence of an invisible particle with no charge that was also emitted at the same time. Fermi took up this idea, which he developed in a tentative paper in 1933, and then a longer paper the next year that incorporated the postulated particle, which Fermi called a "neutrino". His theory, later referred to as Fermi's interaction, and still later as the theory of the weak interaction, described one of the four forces of nature. The neutrino would not be detected until after his death, and his interaction theory showed why it was so difficult to detect. When he submitted his 1934 paper to the British journal Nature, that journal's editor turned it down because it contained speculations which were "too remote from physical reality to be of interest to readers". Thus Fermi saw the theory published in Italian and German before it was published in English.
After his difficult time with beta decay, Fermi decided to switch to experimental physics, using the neutron, which James Chadwick had discovered in 1932. The result would be a burst of more than twenty papers by Fermi and his collaborators. In 1934, Irène Joliot-Curie and Frédéric Joliot bombarded elements with alpha particles and induced radioactivity in them. Fermi suggested to the Via Panisperna boys that they perform the same experiment with neutrons, which would theoretically work better because neutrons had no electric charge, and so would not be deflected. They constructed a neutron source from radium and beryllium and started bombarding elements, starting with hydrogen, and working their way up the periodic table. Nothing registered on their Geiger counter until they reached fluorine and aluminium, which emitted an alpha particle and decayed into calcium.
They also noticed some unexplained effects. The experiment seemed to work better on a wooden table than a marble table top. Fermi decided to try placing some lead in the path of the neutron source, but then, remembering that Joliot-Curie and Chadwick had noted that paraffin wax was more effective than lead at slowing neutrons, he decided to try it instead. The paraffin induced a hundred times as much radioactivity in silver. He guessed that this was due to the hydrogen atoms in the paraffin, and confirmed this by repeating the effect with water. He concluded that slow neutrons were more easily captured than fast ones, and developed a diffusion equation to describe this, which became known as the Fermi age equation.
Fermi's group systematically bombarded elements with slow neutrons. When they reached thorium and uranium, the natural radioactivity of these elements made it hard to determine what was happening, but they concluded that they had created new elements, which they called hesperium and ausonium. At that time, fission was thought to be improbable if not impossible, mostly on theoretical grounds. While people expected elements with higher atomic numbers to form from neutron bombardment of lighter elements, nobody expected neutrons to have enough energy to actually split a heavier atom into two light element fragments, and it was thought still more unlikely that slow neutrons could accomplish such a task. The chemist Ida Noddack did criticise Fermi's work and suggest that some of Fermi's experiments could have produced lighter elements, but was not taken seriously. At the time, Fermi dismissed the possibility on the basis of his calculations. However, he had not taken into account the "pairing energy" that would appear when a nuclide with an odd number of neutrons absorbed an extra neutron.
In 1938, Fermi received the Nobel Prize in Physics at the age of 37 for his "demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons". After Fermi received the Nobel Prize in Stockholm, he, his wife Laura, and their children did not return home to Italy, but rather continued to New York City, where they applied for permanent residency. The decision to move to America and become American citizens was primarily a result of the racial laws promulgated by Mussolini in order to bring Italian Fascism ideologically closer to German National Socialism. The new laws threatened Laura, who was Jewish, and put many of Fermi's research assistants out of work.
Manhattan Project 
Soon after his arrival in New York City on 2 January 1939, Fermi was offered five different chairs, and chose to work at Columbia University, where he had already given summer lectures in 1936. He ultimately became an American citizen in July 1944, the earliest date the law allowed. Soon after his arrival, he received the news that in December 1938, the German chemists Otto Hahn and Fritz Strassmann had detected the element barium after bombarding uranium with neutrons, which Lise Meitner and her nephew Otto Frisch correctly interpreted as the result of nuclear fission. The news of Meitner and Frisch's interpretation of Hahn and Strassmann's discovery crossed the Atlantic with Niels Bohr, who was to lecture at Princeton University. Isidor Isaac Rabi and Willis Lamb, two Columbia University physicists working at Princeton, found out about it and carried it back to Columbia. Rabi said he told Enrico Fermi, but Fermi later gave the credit to Lamb:
I remember very vividly the first month, January, 1939, that I started working at the Pupin Laboratories because things began happening very fast. In that period, Niels Bohr was on a lecture engagement at the Princeton University and I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was the discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of nuclear power.
Bohr soon thereafter went to Columbia to see Fermi. Not finding Fermi in his office, Bohr went down to the cyclotron area and found Herbert L. Anderson. Bohr grabbed him by the shoulder and said: "Young man, let me explain to you about something new and exciting in physics." For Fermi, the news came as a profound embarrassment, as the transuranic elements that he had partly been awarded the Nobel Prize for discovering were likely to turn out to be fission products. He added a footnote to his as yet unpublished Nobel Prize acceptance speech to this effect.
The scientists at Columbia decided that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment. On 25 January 1939, a Columbia team conducted the first nuclear fission experiment in the U.S., in the basement of Pupin Hall. The next day, the Fifth Washington Conference on Theoretical Physics began in Washington, D.C. under the joint auspices of The George Washington University and the Carnegie Institution of Washington. There, the news on nuclear fission was spread even further, which fostered many more experimental demonstrations.
Leó Szilárd obtained 200 kilograms (440 lb) of uranium oxide, allowing Fermi and Anderson to conduct experiments with fission on a much larger scale. Fermi and Szilárd collaborated on a design of a device to achieve a self-sustaining nuclear reaction—a nuclear reactor. Fermi suggested that uranium oxide could be used in the form of blocks. The two agreed that water could not be used as a neutron moderator, and their attention turned to using graphite instead. In the end, Szilárd came up with what proved to be a workable design, a pile of uranium oxide blocks surrounded by graphite bricks. Szilárd, Anderson and Fermi jointly published a paper on "Neutron Production in Uranium", but their work habits and personalities were different, and Fermi had trouble working with Szilárd.
Fermi was the first to warn military leaders about the potential impact of nuclear energy, giving a lecture on the subject at the Navy Department on 18 March 1939. The response fell short of what he had hoped for, although the Navy agreed to provide $1,500 towards further research at Columbia. In August 1939, three Hungarian physicists—Szilárd, Eugene Wigner and Edward Teller—prepared the Einstein–Szilárd letter, which they persuaded Einstein to sign, warning President Franklin D. Roosevelt of the probability that the Nazis were planning to build an atomic bomb. Because of the German invasion of Poland on 1 September, it was October before they could arrange for the letter to be personally delivered. Roosevelt was concerned enough that the S-1 Uranium Committee was assembled. At Teller's request, the committee awarded Columbia University $6,000 for Fermi to buy graphite. Less than a week later, Szilard had to inform the committee that the required graphite would cost $33,000. The money arrived in February 1940, and Fermi used it to build a pile of graphite bricks on the seventh floor of the Pupin laboratory. By August 1941, he had six tons of uranium oxide and thirty tons of graphite blocks, which he used to build a still larger pile in the Schermerhorn Hall at Columbia.
When the S-1 Uranium Committee met on 18 December 1941, the atmosphere had completely changed; because the U.S. was now at war, there was a heightened sense of urgency. While most of the effort thus far had been directed at three different processes for producing enriched uranium, S-1 Uranium Committee member Arthur Compton determined that plutonium was a feasible alternative which could be mass-produced in nuclear reactors by the end of 1944. To achieve this, he decided to concentrate the plutonium work at the University of Chicago. Fermi reluctantly moved, and his team became part of the new Metallurgical Laboratory there.
Given the number of unknown factors involved in creating a self-sustaining nuclear reaction, it seemed inadvisable to do so in a densely populated area. Compton arranged with Colonel Kenneth Nichols, the head of the Army's Manhattan District, for land to be acquired in the Argonne Forest about 20 miles (32 km) from Chicago, and Stone & Webster was contracted to develop the site. However, this work was halted by an industrial dispute. Fermi then persuaded Compton that he could build a reactor in the squash court under Stagg Field at the University of Chicago. Construction of the pile began on 6 November 1942, and Chicago Pile-1 went critical on 2 December.
This experiment was a landmark in the quest for energy, and it was typical of Fermi's approach. Every step was carefully planned, every calculation meticulously done. When the first self-sustained nuclear chain reaction was achieved, Compton made a coded phone call to James B. Conant, the chairman of the National Defense Research Committee.
I picked up the phone and called Conant. He was reached at the President's office at Harvard University. "Jim," I said, "you'll be interested to know that the Italian navigator has just landed in the new world." Then, half apologetically, because I had led the S-l Committee to believe that it would be another week or more before the pile could be completed, I added, "the earth was not as large as he had estimated, and he arrived at the new world sooner than he had expected."
"Is that so," was Conant's excited response. "Were the natives friendly?""Everyone landed safe and happy."
To continue the research where it would not pose a public health hazard, the reactor was disassembled and moved to the Argonne site, where Fermi directed research on reactors and other fundamental sciences, revelling in the myriad of research opportunities that the reactor provided. The lab would become the Argonne National Laboratory on 1 July 1946, the first of the national laboratories established by the Manhattan Project. Fermi was on hand at Oak Ridge to watch the air-cooled X-10 Graphite Reactor go critical on 4 November 1943, allowing the reactor plutonium to be created.
In September 1944, Fermi inserted the first fuel slug into the B Reactor at the Hanford Site. Over the next few days, 838 tubes were loaded, and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the control rods to initiate production. At first all appeared well, but around 03:00, the power level started to drop and by 06:30 the reactor had shut down completely. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor started again, only to shut down once more. The problem was traced to neutron poisoning from xenon-135, which has a half-life of 9.2 hours. As it happened, DuPont had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corners. The scientists had originally considered this overengineering a waste of time and money, but Fermi realized that by loading all 2,004 tubes, the reactor could reach the required power level and efficiently produce plutonium.
In the summer of 1944, Robert Oppenheimer persuaded Fermi to join his Project Y in Los Alamos, New Mexico. Arriving in September, Fermi was appointed an associate director of the laboratory, with broad responsibility for nuclear and theoretical physics, and was placed in charge of F Division, which was named after him. F Division consisted of four branches: the F-1 Super and General Theory under Teller, which was responsible for the development of a thermonuclear "Super"; the F-2 Water Boiler under L. D. P. King, which looked after the "water boiler" research reactor; F-3 Super Experimentation under E. Bretscher; and the F-4 Fission Studies under Anderson. Fermi observed the Trinity test on 16 July 1945, and conducted an experiment using strips of paper to estimate the bomb's yield. He came up with a figure of ten kilotons of TNT; the actual yield was about 18.6 kilotons.
Post-war work 
After the war, Fermi served on the General Advisory Committee of the Atomic Energy Commission, a scientific committee chaired by Robert Oppenheimer that advised the commission on nuclear matters and policy. Following the detonation of the first Soviet fission bomb in August 1949, Fermi, along with Isidor Rabi, wrote a strongly worded report for the committee, opposing the development of a hydrogen bomb on moral and technical grounds. But Fermi also participated in work on the hydrogen bomb at Los Alamos as a consultant and, along with Stanislaw Ulam, calculated that the amount of tritium needed for Teller's model of a thermonuclear weapon would be prohibitive, and a fusion reaction could not be assured to propagate even with this large quantity of tritium. Fermi was among the scientists who testified on Oppenheimer's behalf at the Oppenheimer security hearing in 1954 that resulted in denial of Oppenheimer's security clearance.
In his later years, Fermi continued teaching at the University of Chicago. His PhD students in the post-war period included Owen Chamberlain, Geoffrey Chew, Jerome Friedman, Marvin Goldberger, Tsung-Dao Lee, Arthur Rosenfeld and Sam Treiman. He also conducted important research in particle physics, especially related to pions and muons. In a paper co-authored with Chen Ning Yang, he speculated that pions might actually be composite particles. Fermi wrote a paper "On the Origin of Cosmic Radiation" in which he proposed that cosmic rays arose through material being accelerated by magnetic fields in interstellar space, which led to a difference of opinion with Teller. Fermi examined the issues surrounding magnetic fields in the arms of a spiral galaxy. He also mused about what is now referred to as the "Fermi Paradox": the contradiction between the presumed probability of the existence of extraterrestrial life and the fact that contact has not been made.
Toward the end of his life, Fermi questioned his faith in society at large to make wise choices about nuclear technology. He said:
Some of you may ask, what is the good of working so hard merely to collect a few facts which will bring no pleasure except to a few long-haired professors who love to collect such things and will be of no use to anybody because only few specialists at best will be able to understand them? In answer to such question[s] I may venture a fairly safe prediction. History of science and technology has consistently taught us that scientific advances in basic understanding have sooner or later led to technical and industrial applications that have revolutionized our way of life. It seems to me improbable that this effort to get at the structure of matter should be an exception to this rule. What is less certain, and what we all fervently hope, is that man will soon grow sufficiently adult to make good use of the powers that he acquires over nature.
Impact and legacy 
Fermi received numerous awards in recognition of his achievements, including the Matteucci Medal in 1926, the Nobel Prize for Physics in 1938, the Hughes Medal in 1942, the Franklin Medal in 1947, and the Rumford Prize in 1953. He was awarded the Medal for Merit in 1946 for his contribution to the Manhattan Project. In 1999, Time named Fermi on its list of the top 100 persons of the twentieth century. Fermi was widely regarded as an unusual case of a 20th century physicist who excelled both theoretically and experimentally. The historian of physics, C. P. Snow, wrote that "if Fermi had been born a few years earlier, one could well imagine him discovering Rutherford's atomic nucleus, and then developing Bohr's theory of the hydrogen atom. If this sounds like hyperbole, anything about Fermi is likely to sound like hyperbole"..
Fermi was known as an inspiring teacher, and was noted for his attention to detail, simplicity, and careful preparation of his lectures. Later, his lecture notes were transcribed into books. His papers and notebooks are today in the University of Chicago.
Fermi's ability and success stemmed as much from his appraisal of the art of the possible, as from his innate skill and intelligence. He disliked complicated theories, and while he had great mathematical ability, he would never use it when the job could be done much more simply. He was famous for getting quick and accurate answers to problems that would stump other people. Later on, his method of getting approximate and quick answers through back-of-the-envelope calculations became informally known as the "Fermi method".
Things named after Fermi 
Many things have been named in Fermi's honour. These include the Fermilab particle accelerator and physics lab in Batavia, Illinois, which was renamed in his honour in 1974, and the Fermi Gamma-ray Space Telescope, which was named after him in 2008, in recognition of his work on cosmic rays. Three nuclear reactor installations have been named after him: the Fermi 1 and Fermi 2 nuclear power plants in Newport, Michigan, the Enrico Fermi Nuclear Power Plant at Trino Vercellese in Italy, and the RA-1 Enrico Fermi research reactor in Argentina. A synthetic element isolated from the debris of the 1952 Ivy Mike nuclear test was named fermium, in honour of Fermi's contributions to the scientific community. It follows the element einsteinium, which was discovered with it. Since 1956, the United States Atomic Energy Commission has named its highest honour, the Fermi Award, after him. Recipients of the award include well-known scientists like Otto Hahn, Robert Oppenheimer, Edward Teller and Hans Bethe.
- — (1928). Introduzione alla Fisica Atomica (in Italian). Bologna: N. Zanichelli. OCLC 9653646.
- — (1929). Fisica per i Licei (in Italian). Bologna: N. Zanichelli. OCLC 9653646.
- — (1934). Molecole e cristalli (in Italian). Bologna: N. Zanichelli. OCLC 19918218.
- — (1937). Thermodynamics. New York: Prentice Hall. OCLC 2379038.
- — (1938). Fisica per Istituti Tecnici (in Italian). Bologna: N. Zanichelli.
- —; Amaldi, Edoardo (1938). Fisica per Licei Scientifici (in Italian). Bologna: N. Zanichelli.
- — (1951). Elementary particles. New Haven: Yale University Press. OCLC 362513.
For a full list of his papers, see Bretscher, R.; Cockcroft, J. D. (1955). "Enrico Fermi 1901-1954". Biographical Memoirs of Fellows of the Royal Society 1: 69–78. doi:10.1098.2Frsbm.1955. , pp. 75–78.
- 2206634, Process for the Production of Radioactive Substances, filed October 1935, issued July 1940
- 2524379, Neutron Velocity Selector, filed September 1945, issued October 1950
- 2708656, Neutronic reactor, with Leó Szilárd, filed December 1944, issued May 1955
- 2768134, Testing Material in a Neutronic Reactor, filed August 1945, issued October 1956
- 2780595, Test Exponential Pile, filed May 1944, issued February 1957
- 2798847, Method of Operating a Neutronic Reactor, filed December 1944, issued July 1957
- 2807581, Neutronic Reactor, filed October 1945, issued September 1957
- 2807727, Neutronic Reactor Shield, filed January 1946, issued September 1957
- 2813070, Method of Sustaining a Neutronic Chain Reacting System, filed November 1945, issued November 1957
- 2836554, Air Cooled Neutronic Reactor
- 2837477, Chain Reacting System
- 2852461, Neutronic Reactor
- 2931762, Neutronic Reactor
- 2969307, Method of Testing Thermal Neutron Fissionable Material for Purity, filed November 1945, issued January 1961
- "Enrico Fermi Dead at 53; Architect of Atomic Bomb". New York Times. 29 November 1954. Retrieved 21 January 2013.
- Snow 1981, p. 79.
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