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BIOGRAPHIES OF GREAT SCIENTISTS
Fermi Enrico. Biography of a scientist
Directory / Biographies of great scientists
“The great Italian physicist Enrico Fermi,” wrote Bruno Pontecorvo, “occupies a special place among modern scientists: in our time, when a narrow specialization in scientific research has become typical, it is difficult to point to an equally universal physicist who was Fermi. One could even say that the appearance in the scientific arena of the XNUMXth century, a person who has made such an enormous contribution to the development of theoretical physics, and experimental physics, and astronomy, and technical physics, is a phenomenon rather unique than rare. Enrico Fermi was born on September 29, 1901 in Rome. He was the youngest of three children of a railroad employee, Alberto Fermi, and née Ida de Gattis, a teacher. Even as a child, Enrico showed great aptitude for mathematics and physics. His outstanding knowledge in these sciences, acquired mainly as a result of self-education, allowed him to receive a scholarship in 1918 and enter the Higher Normal School at the University of Pisa. Then, under the patronage of Senator Corbino, Associate Professor of the Physics Institute of the University of Rome, Enrico received a temporary position as a teacher of mathematics for chemists at the University of Rome. In 1923 he received a business trip to Germany, to Göttingen, to Max Born. Fermi does not feel very confident, and only the great moral support of Ehrenfest, with whom he was in Leiden from September to December 1924, helped him to believe in his vocation as a physicist. Upon returning to Italy, Fermi worked from January 1925 until the autumn of 1926 at the University of Florence. Here he receives his first degree of "free associate professor" and, most importantly, creates his famous work on quantum statistics. In December 1926 he took up the post of professor in the newly established chair of theoretical physics at the University of Rome. Here he organized a team of young physicists: Rasetti, Amaldi, Segre, Pontecorvo and others, who made up the Italian school of modern physics. When the first chair of theoretical physics was established at the University of Rome in 1927, Fermi, who managed to gain international prestige, was elected its head. In 1928, Fermi married Laura Capon, who belonged to a well-known Jewish family in Rome. The Fermi couple had a son and a daughter. Here, in the capital of Italy, Fermi rallied several eminent scientists around him and founded the country's first school of modern physics. In international scientific circles, it began to be called the Fermi group. Two years later, Fermi was appointed by Benito Mussolini to the honorary position of a member of the newly created Royal Academy of Italy. In the 1932s, it was generally accepted that an atom contains two types of charged particles: negative electrons, which revolve around the nucleus of positive protons. Physicists were interested in whether the nucleus could contain a particle devoid of an electric charge. Experiments to detect an electrically neutral particle culminated in XNUMX when James Chadwick discovered the neutron, which physicists, especially Werner Heisenberg, almost immediately recognized as the nuclear partner of the proton. In 1934, Frédéric Joliot and Irene Joliot-Curie discovered artificial radioactivity. By bombarding the nuclei of boron and aluminum with alpha particles, they created new radioactive isotopes of known elements for the first time. This discovery caused a wide resonance, and in a short time a number of new radioactive isotopes were obtained. However, if the atoms are bombarded with charged particles, then in order to overcome the electrical repulsion, the charged particles must be accelerated on powerful and expensive accelerators. Incident electrons are repelled by atomic electrons, and protons and alpha particles are repelled by the nucleus in the same way as electric charges of the same name are repelled. Fermi appreciated the significance of the neutron as a powerful means of initiating nuclear reactions. Since the neutron has no electric charge, there is no need for accelerators. In the spring of 1934, Fermi began to irradiate elements with neutrons. It was unexpected and bold. “I remember,” O. Frisch wrote, “that my reaction and the reaction of many others were skeptical: the Fermi experiment seemed pointless, because there were much fewer neutrons than alpha particles.” In the first communication, dated March 25, 1934, Fermi reported that by bombarding aluminum and fluorine, he obtained sodium and nitrogen isotopes that emit electrons (and not positrons, as in Joliot-Curie). The method of neutron bombardment proved to be very effective, and Fermi wrote that this high fission efficiency "completely compensates for the weakness of existing neutron sources in comparison with sources of alpha particles and protons." He managed to activate 47 of the sixty-eight elements studied by this method. Encouraged by success, he, in collaboration with F. Razetti and O. d'Agostino, undertook neutron bombardment of heavy elements: thorium and uranium. "Experiments have shown that both elements, previously purified from the usual active impurities, can be strongly activated when bombarded with neutrons." By bombarding uranium, the ninety-second element, the heaviest naturally occurring element, they produced a complex mixture of isotopes. Chemical analysis did not detect in it either uranium isotopes or isotopes of the neighboring element (moreover, the results of the analysis excluded the presence of all elements with numbers from 86 to 91). The suspicion arose that the experimenters had succeeded in obtaining a new artificial element with atomic number 93 for the first time. To Fermi's displeasure, the director of the laboratory, Orso Corbino, announced the successful synthesis of the ninety-third element without waiting for the control tests. In reality, Fermi failed to obtain it. But he, without knowing it, caused the fission of uranium, splitting the heavy nucleus into two or more fragments and other fragments. Uranium fission was discovered in 1938 by Otto Hahn, Lise Meitner and Fritz Strassmann. Rutherford followed Fermi's experiments with great interest. As early as April 23, 1934, he wrote to him: "Your results are very interesting, and there is no doubt that in the future we will be able to obtain more information about the actual mechanism of these transformations." On October 22, 1934, Fermi made a fundamental discovery. By placing a paraffin wedge between the neutron source and the activated silver cylinder, Fermi noticed that the wedge did not decrease the neutron activity, but slightly increased it. Fermi concluded that this effect was apparently due to the presence of hydrogen in the paraffin, and decided to test how a large number of hydrogen-containing elements would affect the splitting activity. Having carried out the experiment first with paraffin, then with water, Fermi stated an increase in activity hundreds of times. Fermi's experiments revealed the enormous efficiency of slow neutrons. But, in addition to remarkable experimental results, in the same year Fermi achieved remarkable theoretical achievements. Already in the December issue of 1933, his preliminary thoughts on beta decay were published in an Italian scientific journal. Early in 1934, his classic paper "On the Theory of Beta Rays" was published. The author's summary of the article reads: "A quantitative theory of beta decay based on the existence of neutrinos is proposed, while the emission of electrons and neutrinos is considered by analogy with the emission of a light quantum by an excited atom in radiation theory. Formulas are derived from the lifetime of the nucleus and for the form of the continuous spectrum of beta- rays; the obtained formulas are compared with experiment". Fermi in this theory gave life to the neutrino hypothesis and the proton-neutron model of the nucleus, also accepting the isotonic spin hypothesis proposed by Heisenberg for this model. Based on the ideas expressed by Fermi, Hideki Yukawa predicted in 1935 the existence of a new elementary particle, now known as the pi-meson, or pion. Commenting on Fermi's theory, F. Razetti wrote: "The theory he built on this basis turned out to be able to withstand almost unchanged two and a half decades of the revolutionary development of nuclear physics. One might notice that a physical theory is rarely born in such a final form." Meanwhile, in Italy, the fascist dictatorship of Mussolini was gaining more and more strength. In 1935, Italian aggression against Ethiopia led to economic sanctions by members of the League of Nations, and in 1936 Italy formed an alliance with Nazi Germany. The Fermi group at the University of Rome began to disintegrate. Following the passage of anti-Semitic civil laws by the Italian government in September 1938, Fermi and his Jewish wife decided to emigrate to the United States. Accepting an invitation from Columbia University to take up the position of professor of physics, Fermi informed the Italian authorities that he was leaving for America for six months. In 1938, Fermi was awarded the Nobel Prize in Physics. The decision of the Nobel Committee stated that the prize was awarded to Fermi "for evidence of the existence of new radioactive elements obtained by irradiation with neutrons, and the discovery of nuclear reactions caused by slow neutrons." "Along with Fermi's outstanding discoveries, his skill as an experimenter, amazing ingenuity and intuition ... made it possible to shed new light on the structure of the nucleus and open up new horizons for the future development of atomic research," said Hans Pleyel of the Royal Swedish Academy of Sciences, introducing the laureate. During an awards ceremony held in December 1938 in Stockholm, Fermi shook hands with the King of Sweden, instead of saluting him with a fascist salute, for which he was attacked in the Italian press. Immediately after the celebrations, Fermi went overseas. Upon arrival in the United States, Fermi, like all immigrants of that time, had to pass an intelligence test. A Nobel laureate was asked to add 15 and 27 and divide 29 by 2. Shortly after the Fermi family landed in New York, Niels Bohr arrived in the United States from Copenhagen to spend several months at the Princeton Institute for Basic Research. Bohr reported the discovery by Hahn, Meitner and Strassmann of the fission of uranium by bombarding it with neutrons. Many physicists began to discuss the possibility of a chain reaction. In order to carry out a chain reaction, Fermi set about planning experiments that would make it possible to determine whether such a reaction was possible and whether it was controllable. In negotiations with the Navy in 1939, Fermi first mentioned the possibility of creating an atomic weapon based on a chain reaction with a powerful release of energy. He received federal funding to continue his research. In the course of his work, Fermi and the Italian physicist Emilio Segre, his former student, established the possibility of using the then-undiscovered element plutonium as an "explosive" for an atomic bomb. Although plutonium, an element with a mass number of 239, was not yet known, both scientists were convinced that such an element must be fissile and could be produced in a uranium reactor by capturing a neutron with uranium-238. In 1942, when the Manhattan Project was created in the United States to work on the creation of an atomic bomb, the responsibility for researching the chain reaction and obtaining plutonium was assigned to Fermi, who had the status of a "foreign subject of a hostile power" from a legal point of view. The following year, research was transferred from Columbia to the University of Chicago, where Fermi, as chairman of the Theoretical Aspects Subsection of the Uranium Committee, supervised the construction of the world's first nuclear reactor, which was being built on a squash court under the stands of the university's Stagg Field football stadium. The erected reactor was called a "heap" in technical jargon, since it was built from bars of graphite (pure carbon), which were supposed to restrain the speed of the chain reaction (slow down neutrons). Uranium and uranium oxide were placed between graphite bars. On December 2, 1942, neutron-absorbing cadmium control rods were slowly extended to start the world's first self-sustaining chain reaction. "It was clear," John Cockcroft later wrote, "that Fermi had opened the door to the atomic age." Somewhat later, Fermi was appointed head of the department of modern physics in a new laboratory created under the direction of Robert Oppenheimer to create an atomic bomb in the highly classified Los Alamos, New Mexico. Fermi and his family became citizens of the United States in July 1944, and they moved to Los Alamos the following month. Fermi witnessed the first atomic bomb explosion on July 16, 1945, near Alamogordo, New Mexico. In August 1945, atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki. At the end of the war, Fermi returned to the University of Chicago to take up the post of professor of physics and become a member of the newly created Institute for Nuclear Research at the University of Chicago. Fermi was an excellent teacher and was famous as an unsurpassed lecturer. Among his graduate students are Murray Gell-Mann, Yang Zhenning, Li Zhengdao, and Owen Chamberlain. After completing the construction of the cyclotron (particle accelerator) in Chicago in 1945, Fermi began experiments to study the interaction between the recently discovered pi-mesons and neutrons. Fermi also belongs to the theoretical explanation of the origin of cosmic rays and the source of their high energy. A man of outstanding intellect and boundless energy, Fermi was fond of mountaineering, winter sports and tennis. He died of stomach cancer at his home in Chicago shortly after he turned fifty-three on November 28, 1954. The next year, the new, hundredth element was named fermium in his honor. Author: Samin D.K.
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