Enrico Fermi

Nuclear Physicist

• Born: September 29, 1901
• Birthplace: Rome, Italy
• Died: November 28, 1954
• Place of death: Chicago, Illinois

Italian-born American physicist

Fermi’s experiments utilizing neutron bombardment led to the production of the first controlled chain reaction, critical to the development of the atomic bomb by the United States.

Areas of achievement Physics, mathematics

Early Life

Enrico Fermi (ayn-REE-koh FEHR-mee) was born to Alberto Fermi, an administrator in the Italian railroad system, and Ida de Gattis, an elementary school teacher. Enrico learned to read and write at an early age, probably instructed by his older brother and sister. At six years of age, Enrico entered public school and soon displayed a talent for mathematics. By the age of ten, the young boy, by this time exhibiting a remarkable memory, entered a school that emphasized Latin, Greek, French, history, mathematics, natural history, and physics, courses that would prepare him for entrance into the university. Enrico led his class in scholarship and, in his spare time, studied science and built electrical motors and toys.

In 1918, after receiving his diploma from the liceo (high school) and winning on a competitive examination, Fermi was admitted as a fellow in the Scuola Normale Superiore, a college of the University of Pisa. The young scholar earned his doctorate, graduating magna cum laude in 1922 at age twenty-one, and obtained a postdoctoral fellowship to study physics under Max Born in Göttingen in 1923. During the academic year of 1923-1924, Fermi held a temporary position at the University of Rome as an instructor of mathematics. In September, 1924, Fermi began a three-month fellowship at the University of Leiden. He then accepted a nontenured position as incaricato (instructor) at the University of Florence, teaching mechanics and mathematics.

Fermi’s physical appearance at this time, according to his future wife, was not as impressive as his mental abilities. His rounded shoulders, short legs he was five feet six inches tall thin lips, a neck thrust forward when he walked, and a dark complexion were in sharp contrast to his gray-blue, close-set, cheerful eyes. Vital and energetic, he particularly enjoyed skiing and hiking.

Life’s Work

In November, 1926, Fermi won the concorso (competition) for a new chair in theoretical physics at the University of Rome, a result, in part, of the publication of his paper “On the Quantization of the Perfect Monoatomic Gas.” This paper calculated the behavior properties (“Fermi’s statistics”) of an ideal gas composed of particles of half integral spin (electrons, protons, and so on).

In 1928, Fermi published a book on modern physics for upper-level university students, Introduzione alla fisical atomica. During this period as professor at the university, he successfully recruited talented students to study physics with him and other faculty members. On July 19, 1928, the young physicist married Laura Capon in Rome. Two children were born of the union, Nella in 1931 and Giulio in 1936. In 1929, Fermi was appointed as the youngest member of the Royal Academy of Italy with a government salary as part of the honor, and in the summer of 1930, he was invited to teach theoretical physics at the University of Michigan, Ann Arbor, lecturing on the quantum theory of radiation.

In 1933, Fermi wrote a famous paper on the explanation of beta decay. After the announcement of Frédéric Joliot and Irène Joliot-Curie in Paris that alpha particle bombardment of aluminum produced artificial radioactivity, the Italian physicist experimented with neutrons as the bombarding source. He was able to produce artificial radioactivity in fluorine in March, 1934, using a radon-plus-beryllium source of neutrons. Seven months later, in October, 1934, Fermi discovered a principle of nuclear physics that was to have far-reaching effects on the future of science. Placing a piece of paraffin in front of a neutron source, he observed increased radioactivity in the silver target. He surmised that the paraffin showed the neutron “bullets” and increased the neutron-proton collision cross section. This allowed the silver nuclei to capture the slow neutron, eject a proton, and become temporarily radioactive. Fermi and his coexperimenters, Bruno Pontecorvo, Edoardo Amaldi, Franco Rasetti, and Emilio Segre, also noted that water produced almost the same slowing-down effect as paraffin. The theory was proposed that neutrons lose energy in repeated collisions with hydrogen nuclei. Anticipating possible commercial applications, the scientists took out an Italian patent on this neutron-bombardment process of producing radioactive substances in October, 1935.

Fermi’s reputation in scientific circles in the United States grew, and in the summer of 1936, he was invited to give a course on thermodynamics at Columbia University in New York. On previous teaching trips in 1933 and 1935, Fermi was impressed by the freedom and kindness of the American people. This appreciation had prompted him earlier to consider moving to the United States to escape the dictatorship of the regime of Benito Mussolini in Italy. Although Fermi had little interest in politics, he did understand that free and open scientific investigation was more desirable than that practiced under the dictates of an oppressive government. In 1938, Italy, influenced by the anti-Semitism sweeping Germany at that time, passed laws against persons of Jewish ancestry. Since Fermi’s wife was Jewish, he decided to leave Italy. He accepted a teaching position at Columbia and obtained an immigration visa in November, 1938. The next month, Fermi was awarded the Nobel Prize in Physics for his work with slow neutrons, and on December 24, 1938, the Fermi family left Europe for the United States. (Fermi became a U.S. citizen in July, 1944.)

Events in nuclear physics were developing rapidly in late 1938. On December 22, 1938, Otto Hahn and Fritz Strassmann in Germany published the results of their experiments on the neutron bombardment of uranium. They had discovered radioactive barium among the products of that bombardment. In January, 1939, Otto Frisch and Lise Meitner theorized that the presence of radioactive barium indicated the fission (splitting) of the uranium nucleus into two nuclei of approximately equal size, barium and krypton. Fermi then surmised that if enough excess neutrons were released in the fission process, and if enough uranium atoms were present, a chain reaction, with the release of enormous amounts of energy, might result.

In early 1939 at Columbia, Fermi exchanged experimental information with two Hungarian emigrant scientists, Leo Szilard and Edward Teller. In August, 1939, Albert Einstein, the most famous physicist in the world, informed President Franklin D. Roosevelt by letter that the work of Fermi and Szilard demonstrated the possibility that a powerful bomb might be constructed, utilizing the nuclear chain-reaction principle. Roosevelt formed a Committee on Uranium to keep him apprised of the progress of the experimentation.

In the spring of 1940, Fermi and others discovered the use of graphite as a moderator in slowing down neutrons. This principle would be vital in future chain-reaction experiments involving a nuclear reactor (“pile”). Fermi also observed that lumping natural uranium would permit the start of a chain reaction without the need of isotope separation a process that, given the technology of the time, seemed to be an almost impossible task.

By the summer of 1940, scientists at the University of California identified the product of the fission of natural uranium 238 as neptunium 239. Neptunium decays and produces plutonium 239, which fissions when bombarded with slow neutrons. If a chain reaction utilizing uranium 238 could be sustained, then enough fissionable plutonium 239 could be obtained for use in the manufacture of an atomic bomb.

During 1941, Fermi experimented with a small atomic pile at Columbia University. He showed that a self-sustaining nuclear chain reaction could be achieved if the proper amount of uranium was placed in a graphite pile. By the spring of 1942, Arthur Holly Compton, professor of physics at the University of Chicago, had been placed in charge of all work pertaining to the chain reaction. Compton brought physicists to Chicago to coordinate the experimental effort under the code name “Metallurgical Laboratory.” Fermi supervised the construction of a large pile under the stands of the university’s football stadium beginning in October, 1942. On December 2, 1942, cadmium control rods were slowly withdrawn; a twenty-eight-minute, self-sustaining chain reaction occurred, producing one-half watt of energy. This was the first nuclear reactor to produce energy that would eventually be used for peaceful purposes. Several months later, a second pile (one hundred kilowatts) was built at the Argonne Laboratory outside Chicago. This success led to the construction, with Fermi’s consultation, of the large water-cooled, natural uranium-fueled, plutonium-production reactor at Hanford, Washington, in 1944.

Near Los Alamos, New Mexico, in an isolated mesa area, a new laboratory was constructed for the purpose of building an atomic bomb. The best minds in nuclear physics were brought to Los Alamos or consulted regarding the bomb construction. The first experiments began in July, 1943, under the direction of J. Robert Oppenheimer of the University of California, Berkeley. Fermi was still conducting work in Chicago and traveling to Oak Ridge, Tennessee, the site of a plant that produced uranium 235, a fissionable isotope that would be used in the manufacture of yet another bomb. He came to Los Alamos in August, 1944, and was appointed as an associate director of the laboratory by Oppenheimer. During this period, Edward Teller was working on the hydrogen bomb under Fermi’s direction.

By July, 1945, enough reactor-produced plutonium had been delivered to Los Alamos to allow for the production of the first atomic bomb. The testing of this weapon occurred on July 16, 1945, at Alamogordo, New Mexico. Fermi was responsible for measuring the energy levels produced by the explosion and for collecting sand and soil samples to be analyzed for radioactivity.

The first atomic bomb was dropped on Hiroshima, Japan, on August 6, 1945, and the war ended shortly thereafter. In January, 1946, Fermi returned to Chicago as Distinguished-Service Professor of Physics at the Institute of Nuclear Studies, and in that year, he and four other scientists were awarded the Congressional Medal of Merit by President Harry S. Truman for their work in developing the bomb. For the next eight years, Fermi continued his experiments in high-energy physics. During this period, he also served on the General Advisory Committee of the Atomic Energy Commission and on other advisory bodies in need of his scientific knowledge and counsel. In April, 1954, Fermi testified at the security risk hearing of Oppenheimer, whose loyalty to the United States had been questioned because he had opposed the program for developing the hydrogen bomb. (Fermi himself, as well as other influential scientists, including Einstein, had opposed the development of this thermonuclear weapon on ethical grounds.) At the hearing, Fermi pointed out Oppenheimer’s service to the United States and suggested that there should be no question of Oppenheimer’s loyalty.

By the summer of 1954, Fermi’s health was deteriorating. An undiagnosed illness that later proved to be cancer drained his energy. He died in Chicago on November 28, 1954, at the age of fifty-three.

Significance

Fermi epitomized the popular image of the scientist, the diligent experimenter in lab coat surrounded by the apparatus of discovery, yet he was much more. He was a talented mathematician and theorist who was able, if necessary, to build analytical instruments with his own hands. His keen mind searched for simple alternatives to problems that others thought impossible. He was an immigrant to the United States, imbued with a spirit of gratitude and loyalty to his new country. He was a devoted husband and father. Although he helped develop the atomic bomb as a weapon of war, a weapon that he hoped would not be used on a civilian population, his name is primarily associated with the controlled chain reaction that is the basis of the peaceful use of atomic energy in nuclear power plants. Fermi the immigrant, like so many immigrants to America before him, brought to this nation a new knowledge, a new prestige, influence in world politics, and the basis of a new power. Fermi has entrusted future generations with the responsible use of that power.

Further Reading

Amaldi, Edoardo. “Personal Notes on Neutron Work in Rome in the Thirties and Post-War European Collaboration in High-Energy Physics.” In Proceedings of the International School of Physics: “Enrico Fermi,” edited by C. Weiner. New York: Academic Press, 1977. Technical account of the experimental techniques and early research on the properties of the neutron by Fermi’s Rome-based team, during the year 1934-1935. Excellent photographs of the early handmade apparatus used as neutron sources.

Cooper, Dan. Enrico Fermi and the Revolution in Modern Physics. New York: Oxford University Press, 1999. Traces Fermi’s life and scientific experiments, including an understandable explanation of quantum physics and sidebars to illustrate the scientific principles of Fermi’s work.

Dardo, Mauro. Nobel Laureates and Twentieth-Century Physics. New York: Cambridge University Press, 2004. Chronicles major developments in physics since 1901, the year the first Nobel Prize in Physics was awarded. Includes information about the work of Fermi and other prize winners.

Fermi, Laura. Atoms in the Family: My Life with Enrico Fermi. Chicago: University of Chicago Press, 1954. This biography, written by Fermi’s wife, provides a personal portrait of the scientist as husband and father. The first three chapters deal with the period before 1924, the year Enrico and Laura met.

Jaffe, Bernard. “Enrico Fermi.” In Men of Science in America. New York: Simon & Schuster, 1958. Brief but informative account of Fermi’s work before and after he came to the United States as well as descriptions of the work of other physicists leading up to the development of the atomic bomb. Particularly useful diagrams illustrating the theory of nuclear fission.

Jones, Vincent C. Manhattan: The Army and the Atomic Bomb. Washington, D.C.: Center of Military History, U.S. Army, 1985. A well-documented account of the history of the development of the atomic bomb. Describes the collaboration between American science and industry under the direction of the U.S. Army.

Latil, Pierre de. Enrico Fermi: The Man and His Theories. Translated by Len Ortzen. New York: Paul S. Ericksson, 1966. Readable biography of Fermi’s life with simplified explanations of complex nuclear theories. Useful as an introduction to the scientific methods of the physicist.

Libby, Leona Marshall. The Uranium People. New York: Crane, Russak, 1979. Fascinating account of the production of the first controlled chain reaction for the manufacture of plutonium and the use of plutonium in bomb construction; the author was the only woman scientist on the project. Includes photographs of the people who were involved in the work and diagrams of the first nuclear reactor at the University of Chicago and the plutonium-production reactor in Hanford, Washington.

Segrè, Emilio. Enrico Fermi: Physicist. Chicago: University of Chicago Press, 1970. A well-documented, concise historical narrative written by Fermi’s lifelong friend and colleague. Particular emphasis is given to the scientific background and to theories developed by Fermi.

Webb, Stephen. If the Universe Is Teeming with Aliens . . . Where Is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. New York: Copernicus Books, 2002. In 1950, Fermi was wondering why, if there is life on other planets, no one has been able to find it. “Where is everybody?,” he asked, setting forth what has since been called the Fermi paradox of extraterrestrial life. This book searches for answers to his question.