Fermi, Enrico

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FERMI, ENRICO

Enrico Fermi was born on September 29, 1901, and grew up in Rome; his father, Alberto Fermi, was a chief inspector in the Railway Ministry; his mother, Ida de Gattis, was an elementary school teacher. Enrico, his sister, and his brother went to secular schools and were raised as agnostics. A friend of his father lent the young Fermi mathematics books and influenced him to attend the university in Pisa. While an undergraduate, he became Italy's foremost expert on Einstein's theory of general relativity. After Pisa, Fermi received a fellowship for a year in Göttingen. A special professorship in theoretical physics was created for Fermi at the University of Rome in 1927, and at age twenty-six he became the youngest professor in Italy since Galileo. In 1934, he married Laura Capon, who was Jewish. The couple had two children, Nella and Giulio.

Fermi wrote more than 270 articles during his life and made outstanding contributions to most areas of twentieth century physics. At age 24, in January 1926, he wrote the Fermi statistics, one of his

most significant and lasting theoretical contributions. It set forth a method for calculating the behavior and properties of systems that obeyed quantum mechanical rules for two or more electrons. Seven months later, Paul Dirac independently derived the same statistical mechanics. Almost all known elementary particles are called fermions because they obey the rules of Fermi-Dirac statistical mechanics.

In 1933 Fermi successfully constructed a formal theory of the beta-decay of radioactive nuclei. In the radioactive process a neutron changes to a proton by creating an electron and a neutrino. Fermi's theory of beta decay introduced a fourth fundamental force, called the weak interaction, to be added to the previously known three: the gravitational force between masses, the electromagnetic force between electric charges, and the strong force between the particles in nuclei. A new fundamental constant, called the Fermi constant, determines the strength of the weak interaction. In the 1960s the electromagnetic and the weak interactions were combined in a unified theory, and Fermi's weak interaction and well-measured constant have continued to play a major role in particle physics more than half a century later.

After the discovery of the neutron by Chadwick in 1932, Fermi's group in Rome started an experimental program bombarding all available elements with neutrons. Fermi was awarded the Nobel Prize in Physics for the neutron work. He used the trip to Sweden to escape with his family from Italy and Mussolini's anti-Semitic laws. Many people know Fermi as the architect of the atomic age—the scientist who built and controlled the first nuclear chain reaction, the basis for the peaceful uses of nuclear energy. From 1939 until the end of World War II, he played a major role in the U.S. war project that led to the atomic bomb.

After the war, his major interest was in elementary particle physics which includes the properties of the particles, their decays, their production, and their interactions. Measurements are made of what happens in collisions between particles or when particles decay.

Fermi's most extensive particle experiments were studying the interaction of pi mesons and protons. In 1935 Yukawa postulated that pi mesons account for the strong nuclear force that binds nucleons together in short distances. The pi meson is pictured as being emitted by one nucleon and absorbed by another nucleon that binds the two nucleons together. Pi mesons were first observed in cosmic rays. Later, they were found to be produced in the accelerators built in the late 1940s. Fermi and his associates hit protons with beams of negatively or positively charged pi mesons (pi^? or pi⁺) using the synchrocyclotron at the University of Chicago. They measured the angles and energies of particles emitted from the collisions. They found that in some of the collisions between a pi^? and a proton the particles turned into a neutron and an uncharged pion. The combination of a neutron and an uncharged pion constituted the discovery of short-lived baryons; baryons are particles like the neutron and proton with similar or heavier masses, and the masses are conserved in reactions.

During the 1940s and 1950s, Fermi also was active as a theoretical physicist in a variety of fields. In particle physics, Fermi became concerned that some of the twenty-one particles known in 1950 might not really be "elementary particles," that is, structureless particles. He wrote a provocative paper with C. N. Yang entitled "Are Mesons Elementary Particles?"

Fermi was a fabulous teacher and had an enormous influence on several generations of experimental physicists. He tried to impress on students the importance of understanding theory so that, when planning experiments, they could estimate in advance possible results. He enjoyed interacting with students informally and working with them in the laboratory. He put a great deal of effort into preparing classroom and formal lectures. His lecture notes have been widely circulated and some are published.

Fermi's lectures frequently started with simple explanations of an abstract theory, an example of which can be found in his booklet "Elementary Particles" (based on Fermi's 1950 lectures at Yale). Fermi begins his discussion with quantum field theory as a theoretical framework for the interaction of almost all particles. In later chapters, he shows how to obtain quantitative results when calculating a broad variety of phenomena including the range of nuclear forces, the products of the annihilation of an antinucleon with a nucleon, and the decay of weakly interacting particles. In Fermi's "Lectures, on Pions and Nucleons," edited by B. T. Feld and published in Nuovo Cimento in 1955, he explains simple group theory. Group theory provided the classification schemes that became so important in the next decade. Feld's 1969 book Models of Elementary Particles exemplifies Fermi's style of combining theory and quantitative experimental results.

Three of Fermi's graduate students (O. Chamberlain [1959], T. D. Lee [1957], and C. N. Yang [1957]) won Nobel Prizes for their work in elementary particle physics. Fermi died of intestinal cancer in Chicago on November 28, 1954.

Bibliography

Amaldi, E.; Anderson, H. L.; Persico, E.; Rasetti, F. Segrè, E.; Smith, C. S.; and Wattenberg, A., eds. Collected Papers ofEnrico Fermi, Vols. I and II (Chicago University Press, Chicago, IL, 1962).

Fermi, E. Elementary Particles (Yale University Press, New Haven, CT, 1951).

Fermi, E. "Lectures on Pions and Nucleons." Nuovo Cimento Supplemento2 (1955).

Segrè, E. Enrico Fermi Physicist (University of Chicago Press, Chicago, IL, 1940).

Wattenberg, A. "The Fermi School in the United States." European Journal of Physics9 , 88–93 (1988).

Albert Wattenberg

Building Blocks of Matter: A Supplement to the Macmillan Encyclopedia of Physics