) in the courtyard of Rome University's Physics Institute in Via Panisperna, 1934. From left to right:
Oscar D'Agostino,
Emilio Segrè,
Edoardo Amaldi,
Franco Rasetti and Fermi Professorships in Italy were granted by competition ('''') for a vacant chair, the applicants being rated on their publications by a committee of professors. Fermi applied for a chair of mathematical physics at the
University of Cagliari on
Sardinia but was narrowly passed over in favour of
Giovanni Giorgi. In 1926, at the age of 24, he applied for a professorship at the Sapienza University of Rome. This was a new chair, one of the first three in theoretical physics in Italy, that had been created by the Minister of Education at the urging of professor
Orso Mario Corbino, who was the university's professor of experimental physics, the director of the Institute of Physics, and a member of
Benito Mussolini's cabinet. Corbino, who also chaired the selection committee, hoped that the new chair would raise the standard and reputation of physics in Italy. The committee chose Fermi ahead of Enrico Persico and
Aldo Pontremoli, and Corbino helped Fermi recruit his team, which was soon joined by notable students such as
Edoardo Amaldi,
Bruno Pontecorvo,
Ettore Majorana and
Emilio Segrè, and by Franco Rasetti, whom Fermi had appointed as his assistant. They soon were nicknamed the "
Via Panisperna boys" after the street where the Institute of Physics was located. Fermi married
Laura Capon, a science student at the university, on 19 July 1928. They had two children: Nella, born in January 1931, and Giulio, born in February 1936. On 18 March 1929, Fermi was appointed a member of the
Royal Academy of Italy by Mussolini, and on 27 April he joined the
Fascist Party. He later opposed Fascism when the 1938
racial laws were promulgated by Mussolini in order to bring Italian Fascism ideologically closer to German
Nazism. These laws threatened Laura, who was Jewish, and put many of Fermi's research assistants out of work. During their time in Rome, Fermi and his group made important contributions to many practical and theoretical aspects of physics. In 1928, he published his
Introduction to Atomic Physics (''''), which provided Italian university students with an up-to-date and accessible text. Fermi also conducted public lectures and wrote popular articles for scientists and teachers in order to spread knowledge of the new physics as widely as possible. Part of his teaching method was to gather his colleagues and graduate students together at the end of the day and go over a problem, often from his own research. A sign of success was that foreign students now began to come to Italy. The most notable of these was the German physicist
Hans Bethe, who came to Rome as a Rockefeller Foundation fellow, and collaborated with Fermi on a 1932 paper "On the Interaction between Two Electrons" (). At this time, physicists were puzzled by
beta decay, in which an
electron was emitted from the
atomic nucleus. To satisfy the law of
conservation of energy, Pauli postulated the existence of an invisible particle with no charge and little or no mass that was also emitted at the same time. Fermi took up this idea, which he developed in a tentative paper in 1933, and then a longer paper the next year that incorporated the postulated particle, which Fermi called a "
neutrino". His theory, later referred to as
Fermi's interaction, and still later as the theory of the
weak interaction, described one of the four
fundamental forces of nature. The neutrino was detected after his death, and his interaction theory showed why it was so difficult to detect. When he submitted his paper to the British journal
Nature, that journal's editor turned it down because it contained speculations which were "too remote from physical reality to be of interest to readers". According to Fermi's biographer David N. Schwartz, it is at least strange that Fermi seriously requested publication from the journal, since at that time
Nature only published short notes on articles of this kind, and was not suitable for the publication of even a new physical theory. More suitable, if anything, would have been the
Proceedings of the Royal Society of London. He agrees with some scholars' hypothesis, according to which the rejection of the British magazine convinced his young colleagues (some of them Jews and leftists) to give up the boycott of German scientific magazines, after
Hitler came to power in January 1933. Thus Fermi saw the theory published in Italian and German before it was published in English. In the introduction to the 1968 English translation, physicist Fred L. Wilson noted that: In January 1934,
Irène Joliot-Curie and
Frédéric Joliot announced that they had bombarded elements with
alpha particles and induced
radioactivity in them. By March, Fermi's assistant
Gian-Carlo Wick had provided a theoretical explanation using Fermi's theory of beta decay. Fermi decided to switch to experimental physics, using the
neutron, which
James Chadwick had discovered in 1932. In March 1934, Fermi wanted to see if he could induce radioactivity with Rasetti's
polonium-
beryllium neutron source. Neutrons had no electric charge, and so would not be deflected by the positively charged nucleus. This meant that they needed much less energy to penetrate the nucleus than charged particles, and so would not require a
particle accelerator, which the Via Panisperna boys did not have. (left) and
Emilio Segrè in
academic dress Fermi had the idea to resort to replacing the polonium-beryllium neutron source with a
radon-beryllium one, which he created by filling a glass bulb with beryllium powder, evacuating the air, and then adding 50 m
Ci of radon gas, supplied by . This created a much stronger neutron source, the effectiveness of which declined with the 3.8-day
half-life of radon. He knew that this source would also emit
gamma rays, but, on the basis of his theory, he believed that this would not affect the results of the experiment. He started by bombarding
platinum, an element with a high
atomic number that was readily available, without success. He turned to
aluminium, which emitted an alpha particle and produced
sodium, which then decayed into
magnesium by beta particle emission. He tried
lead, without success, and then
fluorine in the form of
calcium fluoride, which emitted an alpha particle and produced
nitrogen, decaying into
oxygen by beta particle emission. In all, he induced radioactivity in 22 different elements. Fermi rapidly reported the discovery of neutron-induced radioactivity in the Italian journal
La Ricerca Scientifica on 25 March 1934. The natural radioactivity of
thorium and
uranium made it hard to determine what was happening when these elements were bombarded with neutrons but, after correctly eliminating the presence of elements lighter than uranium but heavier than lead, Fermi concluded that they had created new elements, which he called
ausenium and hesperium. The chemist
Ida Noddack suggested that some of the experiments could have produced lighter elements than lead rather than new, heavier elements. Her suggestion was not taken seriously at the time because her team had not carried out any experiments with uranium or built the theoretical basis for this possibility. At that time, fission was thought to be improbable if not impossible on theoretical grounds. While physicists expected elements with higher atomic numbers to form from neutron bombardment of lighter elements, nobody expected neutrons to have enough energy to split a heavier atom into two light element fragments in the manner that Noddack suggested. . A
neutron decays into a
proton, and an
electron is emitted. In order for the total energy in the system to remain the same, Pauli and Fermi postulated that a
neutrino (\bar{\nu}_e) was also emitted. The Via Panisperna boys also noticed some unexplained effects. The experiment seemed to work better on a wooden table than on a marble tabletop. Fermi remembered that Joliot-Curie and Chadwick had noted that
paraffin wax was effective at slowing neutrons, so he decided to try that. When neutrons were passed through paraffin wax, they induced a hundred times as much radioactivity in
silver compared with when it was bombarded without the paraffin. Fermi guessed that this was due to the hydrogen atoms in the paraffin. Those in wood similarly explained the difference between the wooden and the marble tabletops. This was confirmed by repeating the effect with water. He concluded that collisions with hydrogen atoms slowed the neutrons. The lower the atomic number of the nucleus it collides with, the more energy a neutron loses per collision, and therefore the fewer collisions that are required to slow a neutron down by a given amount. Fermi realised that this induced more radioactivity because
slow neutrons were more easily
captured than fast ones. He developed a
diffusion equation to describe this, which became known as the
Fermi age equation. In 1938, Fermi received the
Nobel Prize in Physics at the age of 37 for his "demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of
nuclear reactions brought about by slow neutrons". After Fermi received the prize in Stockholm, he did not return home to Italy but rather continued to New York City with his family in December 1938, where they applied for permanent residency. The decision to move to America and become US citizens was due primarily to the racial laws in Italy. == Manhattan Project ==