(1901-1954) Italian/American Theoretician and Experimentalist, Particle Theorist, Nuclear Physicist
Enrico Fermi was the last great physicist to wear the double hat of theorist and experimentalist before the explosion of knowledge after 1900 forced physicists to specialize. His early research in using slow neutrons to produce new radioactive elements won him a Nobel Prize in physics in 1938. His theory of radioactivity, known as beta decay, introduced the last of the four basic forces known in nature: gravity, electromagnetism, and, operating within the nucleus of the atom, the strong force and Fermi’s weak force. His most famous achievement was the creation of the first known chain reaction in a nuclear reactor, which led to both the atomic bomb and the production of nuclear power for peaceful purposes.
Enrico Fermi developed the theory of radioactivity known as beta decay, which is based on a weak force acting within the nucleus of the atom. He also created the first known chain reaction in a nuclear reactor.
Enrico Fermi was born in Rome on September 19, 1901, the youngest of the three children of Alberto Fermi, an administrator with the Italian national railroad, and Ida de Gattis. He discovered physics at age 14, when, stunned by the death of his older brother, he took refuge in reading from cover to cover two old volumes of elementary physics that he had chanced to find. He was a prodigy in secondary school, composing an essay for university admission that was deemed worthy of a doctoral examination. In 1918, he entered the elite Reale Scuola Normale Superior, associated with the University of Pisa. Fermi received his Ph.D. four years later, at age 21, for a thesis on X rays. His subsequent postdoctoral study at Gottingen University, where he worked under max born among such leaders of the quantum revolution as wolfgang pauli and werner heisenberg, was perhaps the only time in his career when his own talents were eclipsed.
In 1924, Fermi accepted a position as lecturer in mathematics at the University of Florence. There he published a paper on the behavior of perfect gases, which spurred the physics department at the University of Rome to make him an offer; Fermi accepted, becoming a full professor of theoretical physics at age 25. Intent on reviving Italian physics, he set about attracting the best young minds to Rome.
He soon developed a statistical method for predicting the characteristics of electrons according to Pauli’s exclusion principle, which states that no two subatomic particles can be described with the same quantum numbers. Fermi-Dirac statistics, as they came to be known, continue to be useful in nuclear and solid state physics, for example, to determine the distribution of electrons at different energy levels. Particles with half-integer spins, such as the electron, that obey Fermi-Dirac statistics, were later named fermions.
Fermi gained national recognition for his 1928 book Introduction to Atomic Physics, the first textbook on modern physics to appear in Italy, and the following year became the youngest member of the prestigious Royal Academy of Italy.
In the 1930s he engaged in experimental work that yielded some of his most important results and earned him an international reputation. In 1930, Pauli had proposed that the emission of an electron in beta decay is accompanied by the production of an unknown particle. Pauli’s particle had neither charge nor mass; as a result, it had never been detected. In 1934, Fermi experimentally confirmed Pauli’s hypothesis and dubbed the new particle the neutrino. That same year Frederik and Irene Joliot-Curie discovered artificial radioactivity, using alpha particle bombardment. Learning of their work, Fermi began producing new radioactive isotopes by neutron bombardment. He found that a block of paraffin wax or a jacket of water around the neutron source produced slow, or “thermal,” neutrons, which are more effective in producing such elements. This work garnered him the 1938 Nobel Prize in physics.
Receiving the Nobel Prize proved to be more than an honor for Fermi; it saved his life. In 1928, he had married a Jewish woman, Laura, with whom he had two children. As Italian anti-Semitism grew during the 1930s, under Benito Mussolini’s fascist regime, the Fermis’ life became increasingly precarious. Taking the opportunity to leave Italy for the Nobel Prize ceremonies, they emigrated to the United States.
Their new home was in New York, where Fermi received a position at Columbia University. Together with two eminent Hungarian emigres, Leo Szilard and eugene paul wigner, Fermi wrote a famous letter to Franklin Delano Roosevelt, warning him of the danger of Hitler’s scientists’ applying the principle of the nuclear chain reaction to the production of an atomic bomb. Roosevelt acted on the warning, and Fermi and Szilard soon found themselves working on the development of a nuclear reactor at Columbia.
Continuing his work on the fission of uranium induced by neutrons, Fermi constructed an elegantly simple machine that he called an “atomic pile.” It had a moderator consisting of a pile of purified graphite blocks, to slow the neutrons, with holes drilled in them to take rods of enriched uranium. Other neutron-absorbing rods of cadmium, called control rods, could be lowered into or withdrawn from the pile to limit the number of slow neutrons available to initiate the fission of uranium.
In 1941, when the Manhattan Project consolidated its operations at the University of Chicago, Fermi and his team moved there and began building a nuclear reactor on the university’s squash court. On December 2, 1942, the control rods were withdrawn for the first time and the reactor began to work, powered by the first self-sustaining nuclear chain reaction. It was the forerunner of the modern nuclear reactor, which releases the basic binding energy of matter.
Fermi moved to Los Alamos, New Mexico, and, with arthur holly compton, led the team that constructed an atomic bomb, which used the same nuclear reaction process, but now without control mechanisms. This bomb produced a nuclear explosion in July 1945 at Alam-ogordo Air Base, New Mexico. Fermi used a simple experiment to estimate its explosive yield: he dropped scraps of paper both before the explosion and afterward, when the blast wind arrived, and compared their displacement. A few weeks later atom bombs were dropped on Hiroshima and Nagasaki, in Japan.
After the war Fermi, who had become a U.S. citizen in 1944, returned to the University of Chicago as Distinguished-Service Professor of Nuclear Studies. There he continued his research on the basic properties of nuclear particles, focusing on mesons, which are the quantized form of the force that holds the nucleus together. He also played a key role in the construction of the university’s synchrocyclotron particle accelerator.
In 1949, he argued against U.S. development of the hydrogen bomb, calling it “a weapon, which in practical effect is almost one of genocide.” The warning went unheeded. Fermi died prematurely in Chicago of stomach cancer on November 28, 1954, but his name and his achievements have been honored in many ways: element number 100, discovered in 1955, was named fermium. The Fermi is a unit of length used in atomic and nuclear physics, and the Fermi level is the energy level in a solid at which a quantum state would be equally likely to be empty or to contain an electron. Finally, the highly prestigious Fermi Award, which he himself received shortly before his death, was established in his honor.
