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Enrico Fermi
Father of Nuclear Physics
Dr Subodh Mahanti


“Enrico Fermi was the greatest Italian scientist of modern times and was highly creative both as a theoretical and experimental physicist.”

The Cambridge Dictionary of Scientists, 2002

“Having one’s name permanently attached to an important physical concept or unit bestows a kind of immortality. It is hard to imagine any discussion of modern physics in which Fermi’s name does not come up at least once, in terms of such as fermion, Fermi gas, Fermi momentum, Fermi temperature, Fermi surface, Fermi coupling, Fermi transition, and Fermi length. Still, because Fermi died so young—and so long ago—he has become, for the current generation of physicists, a somewhat mystical figure.”

Valentine L. Telegdi

“Fermi devoted a great deal of his time to the graduate students…his teaching was exemplary, minutely prepared, clear, with emphasis on simplicity and understanding of the basic ideas, rather than generalities and complications…We would knock at his office door, and if free, he would take us in, and then he would be ours until the question was resolved.”

Jack Steinberger

“Fermi had the widest scope of all the founders of quantum physics. As a theorist, he contributed decisively to quantum mechanics (Fermi-Dirac statistics) and nuclear physics (theory of beta decay). As an experimentalist, he introduced the technique of neutron bombardment to study artificial radioactivity, opening the way to the discovery of nuclear fission.”

Arturo Russo

Enrico Fermi is regarded as father of nuclear physics. In the history of modern physics there is none who matched the versatility of Fermi. His contributions in pure theoretical physics and concrete experimental work were equally great. He could design and build, with his own hands, astonishingly useful experimental tools. He developed the mathematical statistics required to describe a large class of sub-atomic particles. He discovered neutron-induced radioactivity.In 1938, Fermi was awarded Nobel Prize in physics “for his identification of new radioactive elements produced by neutron bombardment and for his discovery of nuclear reaction effected by slow neutrons.” In 1942 Fermi constructed the first nuclear reactor. He directed the first controlled chain reaction involving nuclear fission. Fermi was a great teacher and through the influence of his eminent students, in Italy and the US, Fermi effectively revolutionized the training of physicists. Fermi established a famous school (The Rome School) of nuclear physics in Rome. In Chicago also he established a vibrating school. Fermi was a central figure in the Manhattan project to build the first atomic bomb. The element with atomic number 100, discovered one year after his death, was named Fermium (Fm) in Fermi’s honour.

Fermi was born on September 29, 1901 in Rome. His father Alberto Fermi was a railroad engineer and his mother Ida de Gattis was a school teacher. He was the youngest of three children of his parents. Fermi learned to read and write from his mother. He studied at the local high schools. Fermi as a child displayed unusual mathematical ability and prodigious memory. His school records were excellent. Fermi was much influenced by a colleague of his father, Adolfo Amidei, who lent him books on mathematics. At the age of 17, Fermi entered the highly selective Reale Scuola Normale Superiore, an Italian advanced study and research institution. It was Amidei who advised Fermi to go for this elit institution. The institution was established by Napoleon in 1810 as a branch of the Ecole Normale Superieure of Paris. It was associated with the University of Pisa.

Fermi obtained his PhD at the age of 21 from the University of Pisa. His PhD thesis was on his research on X-rays. After his PhD he made a short visit to Rome and then left for Germany with the Fellowship from the Italian Ministry of Public Instruction to study at the University of Gottingen under Max Born. From Germany he went to Leiden in the Netherlands, where he worked with P. Ehrenfest (1880-1933). After returning in Italy in 1924, Fermi joined the University of Florence, where he lectured on mathematical physics and mechanics.

In 1926, Fermi started to study statistical mechanics of particles that obey Pauli exclusion principle, such as electrons. Fermi was the first to apply Pauli exclusion principle to systems of multiple electrons not attached to atoms.The result was the so-called Fermi-Dirac Statistics, as Dirac also obtained the same conclusion.

In 1927 Fermi was appointed Professor of Theoretical Physics at the University of Rome, the post he held for 12 years. At the time of his appointment he was just 25 years old. He became the youngest full professor in Italy. He also became the first person to occupy a chair in theoretical physics. This was no mean achievement for a person of Fermi’s age particularly considering the traditional and bureaucratic nature of the Italian Universities in those days. It was true that Fermi had established his reputation by publishing 30 substantial research papers. But perhaps this was not the only reason for Pauli’s success in climbing the ladder of Italian science. Fermi was patronized by Orso Mario Corbino, the most distinguished Italian physicist of his time and also a senator. Corbino was all for modernizing Italian physics and thought that Fermi, in spite of his youth, was ideal man to advance his ideas. With Corbino’s support Fermi organized his group of young experimental and theoretical physicists. The group, which later came to be called as the Rome School, included Edoardo Amaldi, Franco Rasetti, Bruno Pontecorvo, Emilio Segre, Oscar D’Agostino and Ettore Majorana. The Rome school changed the landscape of Italian physics, and indeed world physics.

Fermi and his group followed up the then-new phenomenon artificial radioactivity. In 1934, Irene and Frederic Joliot-Curie had announced the production of artificial radioactive isotopes by the bombardment of boron and aluminium with helium nuclei or alpha particles. Fermi realized that neutron discovered by James Chadwick in 1932 would be a better candidate than alpha particle for creating new radio isotopes. Though neutron is less massive but because of its neutrality it could overcome the positive charge of a target nucleus. In 1934 Fermi found that neutrons slowed down in passing through light elements and if neutrons are suitably retarded they become extremely effective in carrying out nuclear transmutation. Actually Fermi had stumbled on the slow neutrons. Fermi without any advance warning, or conscious prior reasoning took some odd piece of paraffin and placed it in front of the incident neutrons. As the result of the collisions with the light hydrocarbon molecules the neutrons slowed down and as they slowed down they remained in the vicinity of the target nucleus sufficiently long to increase their absorption.

In the summer of 1938, the fascist government of Mussolini introduced racial laws modeled after the notorious German Nurenberg laws. Under the provision of these laws scientists and scholars of Jewish origin working in Italian universities were to be dismissed. Fermi was affected because his wife Laura was a Jewish. He was also publicly accused by fascist extremists of “having transformed the physics institute into a synagogue.” Fermi and his family decided to leave Italy. They went to America.

Before emigrating to America in January 1939, Fermi had already visited the America several times. In 1933, he had taught a course in quantum electrodynamics at the University of Michigan. His celebrated article “Reviews of Modern Physics” was based on this course. In 1936, he was a visiting professor at Columbia University, where he taught a course on thermodynamics. Lloyd Motz edited Fermi’s lecture notes into book form and which is still in use. During his visit to Columbia University in 1936, George Pegram, the Chairman of the Physics Department, offered him a permanent appointment at the Columbia University. However, at that time Fermi did not feel the urgency of leaving Italy.

Fermi was a great teacher. Commenting on Fermi’s understanding of theoretical physics, the German born American physicist, Hans Bethe (1906-2005) wrote: “My greatest impression of Fermi’s method of teaching in theoretical physics was its simplicity. He was able to analyse into its essential point every problem, however complicated it seemed to be. He stripped it of mathematical complications and of unnecessary formalism. In this way, often in half an hour or less, he could solve the essential physical problem involved….His approach was pragmatic….He was master of achieving important results with a minimum of effort and mathematical apparatus.”

The Italian born American physicist Emilio Segre (1905-1989) wrote: “The speed at which it was possible to train a young physicist at the ‘Fermi school’ was incredible. Naturally a good deal of the success was due to the immense enthusiasm that had been aroused in the young people—never by exhortations or ‘sermons’ but by the eloquence of example. After having spent time in the institute in Via Panisperna, one became completely absorbed in physics.”

To know personal attributes of Fermi let us quote Valentine Telegdi, who was associated with Fermi in Chicago in the early 1950s. Telegdi wrote: “It was not easy to know Fermi intimately, in the sense of understanding his deeper motivations. Professionally, he was always accessible, but he stayed aloof on the personal level. When I knew him at Chicago, he did not seem to develop bonds of friendship with colleagues at the university. Herb Anderson and Leona Marshall were perhaps the only exceptions. Fermi avoided gossip and rarely expressed his opinions, high or low, about the practices of others. All this gave him an air of modesty that belied his full awareness of his own capabilities.
Fermi rarely made mistakes when he was talking about physics. A public mistake was a painful experience for him. The story is told that once, when writing on the blackboard in front of a class, he realized that he had gotten a certain factor wrong. He faced the audience to make some interesting remarks and, at the same time—without interrupting his delivery—he wiped out the wrong formula with his left elbow. Another story tells of a student who pointed out that Fermi had written a ‘c’ in the numerator rather than in the denominator where it belonged. ‘Who told you’, responded the great teacher, ‘that I use ‘c’ and not ‘1/c’ for the velocity of light?’

Fermi had very regular working habits and a frugal lifestyle. He usually came to work before 8 AM, either walking or biking when weather permitted. He had already been working for several hours at home. He was totally secure in his own physics talent and almost never displayed jealousy of another scientist. The only exception was Einstein. More than one, Fermi expressed annoyance at the attention Einstein received from the press.”

Fermi jointly with Leo Szilard and Eugene Wigner, drafted an important letter for Einstein to send to President Roosevelt explaining the dangerous military potentialities offered by nuclear fission and warning him that Germany might develop these weapons. The letter itself has become important part of history. This letter played an important role in initiating American efforts that finally produced the nuclear reactor and the fission bomb. On December 06, 1941, President Roosevelt authorized the organization of the secret project, named as “Manhattan Project”. The programme, the final aim was to produce the atomic bomb, included work on chain reaction, research to develop ways of producing plutonium-239 and to find methods of obtaining enriched uranium-235. The first step of the project was to try to create a chain reaction. A fission chain reaction experiment was first performed at Columbia University under the leadership of Fermi. The project was then transferred to Chicago. But Fermi was not involved with this initiative. Fermi being an émigré Italian was considered enemy alien and he was confined to New York. Fermi’s mail was subject to censorship. But then the situation was changed in 1942 when President Roosevelt declared that Italians would no longer be considered enemy aliens. Fermi was allowed to join other scientists working in the project for the atomic bomb. However, his letters were still censored.

At Chicago, Fermi and his team, succeeded in constructing the world’s first nuclear reactor. On December 02, 1942, the reactor went critical. An account of the historic event was given in this way. “The clicks [of the counter] came more and more rapidly, and after a while they began to merge into a roar, the counter couldn’t follow any more. That was the moment to switch to the chart recorder. Everyone watched in the sudden silence the mounting deflection of the recorder’s pen. It was an awesome silence. Everyone realized the significance of that switch; we were in the high intensity regime. Again and again, the scale of the recorder had to be changed to accommodate the neutron intensity which was increasing more and more rapidly. Suddenly Fermi raised his hand. ‘The pile has gone critical’, he announced. No one present had any doubt about it.”

Arthur Compton informed the managing committee by saying “the Italian navigator has just landed in the new world and that the natives were friendly.’’

After completing the chain reaction Fermi continued to work on the project. In the preparation of the testing of the first atomic bomb named, Trinity, Fermi’s role was instrumental. Segre wrote: “This was one of those occasions when Fermi’s dominion over all physics, one of his most startling characteristics, came into its own. The problems involved in the Trinity test ranged from hydrodynamics to nuclear physics, from optics to thermodynamics, from geophysics to nuclear chemistry. Often they were closely interrelated, and to solve one it was necessary to understand all the others. Even though the purpose was grim and terrifying, it was one of the greatest physics experiments of all time. Fermi completely immersed himself in the task. At the time of the test he was one of the very few persons (or perhaps the only one) who understood all the technical ramifications of the activities at Alamogordo.”
In 1952, Fermi was elected President of the American Physical Society. On November 16, 1954, President Eisenhower presented the Atomic Energy Commission’s special award for his lifetime of accomplishments in physics and in particular for the development of atomic energy.
Fermi died on November 28, 1954 in Chicago, just after his fifty-third birthday. He was survived by his wife Laura and their two children.


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