Enrico Fermi (1901-1954)
Enrico Fermi was a titan of twentieth-century physics. Adept in both theory and experiment, the Italian-born American outlined the statistical laws that govern the behavior of particles that abide by the Pauli exclusion principle and developed a theoretical model of the atom when he was only in his mid-twenties. He went on to incorporate the neutral particle (lightheartedly hailed by Fermi as the neutrino, or “little neutral one”) hypothesized by Wolfgang Pauli into a quantitative theory of beta decay, as well as to demonstrate that bombardment of elements with neutrons can generate artificial radioactivity and that slow neutrons produce much stronger nuclear reactions. These latter discoveries paved the way for the invention of nuclear reactors and the atomic bomb.
The son of a national railroad administrator and an elementary school teacher, Fermi was born in Rome on September 29, 1901. He showed early promise in mathematics and physics, gaining the attention of a family friend who was an engineer. The friend helped direct the young Fermi’s education, exposing him to advanced mathematical and scientific works, suggesting he learn German so that he could follow the latest advances in physics, and encouraging him to apply to the Scuola Normale Superiore of the University of Pisa. Based on the strength of an essay he wrote on the mathematic and physical aspects of sound, Fermi gained entrance into the prestigious school for gifted students. At the unusually young age of 21, he received his Ph.D. from there.
Fermi traveled overseas for postgraduate study. He spent time in Germany at the University of Göttingen, where he met many of the scientists doing pioneering work on quantum mechanics. Fermi then traveled on a Rockefeller Fellowship to the University of Leiden in the Netherlands. There he worked under Paul Ehrenfest, whose interest in statistics and quantum mechanics encouraged the development of Fermi’s own interests in those areas. In 1926, not long after Fermi returned to Italy, he discovered the quantum statistical laws that bear his name. They are commonly referred to as Fermi-Dirac statistics because they were independently determined by Paul Dirac at about the same time Fermi made his discovery. The particles that Fermi-Dirac statistics apply to are termed fermions. Unlike bosons, which abide by Bose-Einstein statistics, two fermions cannot occupy exactly the same quantum state. Protons, electrons and neutrons are just a few of the particle types that are fermions.
Fermi carried out his statistical work at the University of Florence, where he had joined the faculty as a lecturer of mathematics. The research established his reputation as a brilliant young physicist and helped him win the chair of the theoretical physics department at the University of Rome in 1927. Fermi soon began building up the nascent department and enticed many promising physics students to Rome. He developed his statistical model of the atom this same year. Because of the analogous, independent description of the atomic model made by L. H. Thomas, it is referred to today as the Thomas-Fermi model.
His professional life advancing quickly, Fermi made an important personal change in 1928, when he married Laura Capon. By her, he would have two daughters. Years later, due to Laura’s Jewish heritage, the family’s well-being was threatened by the fascist government of Mussolini. Their opportunity for escape came in 1938, when Fermi was awarded the Nobel Prize in Physics. After traveling to Sweden for the ceremony, the family immigrated to the United States.
The prize stemmed from Fermi’s work on neutron irradiation that led to the discovery of new radioactive elements and his related research on the nuclear reactions facilitated by slow neutrons. In 1934, Frédéric Joliot and Irène Joliot-Curie had announced that they had generated artificial radioactivity via the bombardment of elements with alpha particles. Their success inspired Fermi to attempt to produce radioactivity through neutron bombardment. His experiments proved even more successful than he could have hoped when a change in the filter he used resulted in a slowing of the neutrons. Much to Fermi’s surprise, the slow neutrons were extremely effective in the production of nuclear reactions.
Fermi used his revised neutron bombardment technique in the study of many elements. Through this method he first achieved atomic fission. At the time, Fermi was not sure what to make of the experimental results he achieved when he bombarded uranium with slow neutrons. But a short time later the analysis of a group of scientists in Berlin proved it was fission. By the time Fermi landed in New York, word had leaked from Germany about the discovery. As a result, Fermi found himself in an atomic arms race: Once it was realized that atomic fission was possible, it was quickly recognized that a chain reaction was also possible. If such a reaction was produced, astounding amounts of energy could be released in the form of a bomb.
In the U.S. Fermi accepted a post at Columbia University, but soon transfered to the University of Chicago to work on the Manhattan Project. He also spent time during the war years in Los Alamos, New Mexico, and was present at the first test detonation of the atomic bomb there. He became an American citizen in 1944. After the war ended, Fermi settled in Chicago to teach at the Institute for Nuclear Studies of the University of Chicago. He was a professor there until he died of stomach cancer in 1954. Even after his diagnosis, he continued working. Much of his later research focused on high-energy physics and the origin of cosmic rays.