Italian-born American physicist who was one of the chief architects of the nuclear age. He developed the mathematical statistics required to clarify a large class of subatomic phenomena, discovered neutron-induced radioactivity, and directed the first controlled chain reaction involving nuclear fission. He was awarded the 1938 Nobel Prize for Physics, and the Enrico Fermi Award of the U.S. Department of Energy is given in his honour.
Education and early career
In 1926 his paper on the behaviour of a perfect, hypothetical gas impressed the physics department of the University of Rome, which invited him to become a full professor of theoretical physics. Within a short time, Fermi brought together a new group of physicists, all of them in their early 20s. In 1926 he developed a statistical method for predicting the characteristics of electrons according to Pauli's exclusion principle, which suggests that there cannot be more than one subatomic particle that can be described in the same way. In 1928 he married Laura Capon, by whom he had two children, Nella in 1931 and Giulio in 1936. The Royal Academy of Italy recognized his work in 1929 by electing him to membership as the youngest member in its distinguished ranks.
This theoretical work at the University of Rome was of first-rate importance, but new discoveries soon prompted Fermi to turn his attention to experimental physics. In 1932 the existence of an electrically neutral particle, called the neutron, was discovered by Sir James Chadwick at Cambridge University. In 1934 Frederic and Irene Joliot-Curie in France were the first to produce artificial radioactivity by bombarding elements with alpha particles, which are emitted as positively charged helium nuclei from polonium. Impressed by this work, Fermi conceived the idea of inducing artificial radioactivity by another method: using neutrons obtained from radioactive beryllium but reducing their speed by passing them through paraffin, he found the slow neutrons were especially effective in producing emission of radioactive particles. He successfully used this method on a series of elements. When he used uranium of atomic weight 92 as the target of slow-neutron bombardment, however, he obtained puzzling radioactive substances that could not be identified.
Fermi's colleagues were inclined to believe that he had actually made a new, "transuranic" element of atomic number 93; that is, during bombardment, the nucleus of uranium had captured a neutron, thus increasing its atomic weight. Fermi did not make this claim, for he was not certain what had occurred; indeed, he was unaware that he was on the edge of a world-shaking discovery. As he modestly observed years later, "We did not have enough imagination to think that a different process of disintegration might occur in uranium than in any other element. Moreover, we did not know enough chemistry to separate the products from one another." One of his assistants commented that "God, for His own inscrutable ends, made everyone blind to the phenomenon of atomic fission."
Late in 1938 Fermi was named a Nobel laureate in physics "for his identification of new radioactive elements produced by neutron bombardment and for his discovery of nuclear reaction effected by slow neutrons." He was given permission by the Fascist government of Mussolini to travel to Sweden to receive the award. As they had already secretly planned, Fermi and his wife and family left Italy, never to return, for they had no respect for Fascism.
Meanwhile, in 1938, three German scientists had repeated some of Fermi's early experiments. After bombarding uranium with slow neutrons, Otto Hahn, Lise Meitner, and Fritz Strassmann made a careful chemical analysis of the products formed. On Jan. 6, 1939, they reported that the uranium atom had been split into several parts. Meitner, a mathematical physicist, slipped secretly out of Germany to Stockholm, where, together with her nephew, Otto Frisch, she explained this new phenomenon as a splitting of the nucleus of the uranium atom into barium, krypton, and smaller amounts of other disintegration products. They sent a letter to the science journal Nature, which printed their report on Jan. 16, 1939.
Meitner realized that this nuclear fission was accompanied by the release of stupendous amounts of energy by the conversion of some of the mass of uranium into energy in accordance with Einstein's mass-energy equation, that energy (E) is equal to the product of mass (m) times the speed of light squared (c2), commonly written E = mc2.
Having satisfied the residence requirements, the Fermis had become American citizens in 1944. In 1946 he became Distinguished-Service Professor for Nuclear Studies at the University of Chicago and also received the Congressional Medal of Merit. At the Metallurgical Laboratory of the University of Chicago, Fermi continued his studies of the basic properties of nuclear particles, with particular emphasis on mesons, which are the quantized form of the force that holds the nucleus together. He also was a consultant in the construction of the synchrocyclotron, a large particle accelerator at the University of Chicago. In 1950 he was elected a foreign member of the Royal Society of London.
Fermi made highly original contributions to theoretical physics, particularly to the mathematics of subatomic particles. Moreover, his experimental work in neutron-induced radioactivity led to the first successful demonstration of atomic fission, the basic principle of both nuclear power and the atomic bomb. The atomic pile in 1942 at the University of Chicago released for the first time a controlled flow of energy from a source other than the Sun; it was the forerunner of the modern nuclear reactor, which releases the basic binding energy of matter for peaceful purposes. Element number 100 was named for him, and the Enrico Fermi Award was established in his honour. He was the first recipient of this award of $25,000 in 1954.
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