Emilio Segrè was born into a prosperous Jewish family in Tivoli on 30th January 1905. The son of a paper mill owner, he had a happy childhood and was taught by his cousins, who helped him to develop a fair command of German and English. In 1917, he moved with his family to Rome, where he finished his studies. He initially enrolled, as was the norm at the time, in engineering where he was able to forge links with two other promising students, Ettore Majorana and Edoardo Amaldi.
His meeting with Franco Rasetti, who was then an assistant at the Institute of Physics in Florence, was fundamental to his career. Through Rasetti, Segrè got to know the then 27-year-old Enrico Fermi, who had just been appointed extraordinary professor of theoretical physics at the University of Rome. In 1927 Segrè went with the two young professors to the Volta International Congress in Como where, in the wake of the recent fundamental developments in quantum mechanics, some of the great names in physics were gathering. Segrè attended the seminars of Werner Heisenberg, Wolfgang Pauli, Max Planck, Niels Bohr and many others. On his return to Rome, he decided to switch to a degree course in physics. He graduated with Fermi in July 1928. After completing his compulsory military service, Segrè returned to the Via Panisperna Laboratories, which in the meantime had already been enriched by the presence of Edoardo Amaldi and the more discontinuous and unusual presence of Ettore Majorana. In 1930 he began to study the separation of spectral lines, known as the Zeeman effect, in certain metals; he was then invited by Peter Zeeman himself to complete his work in Amsterdam. He then obtained a scholarship from the Rockefeller Foundation and on Fermi’s advice went to Hamburg to study with Otto Stern.
In 1932 he was appointed Fermi’s assistant in Rome, a post he held until 1935, when he won the competition for professorships and moved to the University of Palermo. During these years he participated assiduously, as did the whole group, in research on slow neutrons. In 1936, he went to the University of California, Berkeley (USA), where he met, among others, Robert Oppenheimer and Ernest Lawrence. The promulgation of racial laws in Italy forced him to seek refuge in the United States, where he settled permanently at the University of California, Berkeley.
In 1943, he was called to Los Alamos to work on the Manhattan Project. Together with his Los Alamos team, he succeeded in measuring the spontaneous fission rate of plutonium. But the best period in Emilio Segrè’s career came after the war, when he returned to Berkeley as Professor of Physics and group leader at the Radiation Laboratory. He was joined by two key members of the Los Alamos team, Owen Chamberlain and Clyde Wiegand, who participated in the 1955 discovery of the antiproton. The research carried out thanks to a new instrument introduced at that time, the Bevatron, enabled the detection of antiprotons soon after the start of the studies. The tests, in fact, had confirmed the discovery of a negatively charged particle with the same mass as the proton. Thanks to this discovery Chamberlain and Segrè won the Nobel Prize for Physics in 1959. Segrè himself later recounted that, when he went to receive the prize, he wore a tailcoat borrowed from a colleague: the same waistcoat had already been worn in Stockholm in 1951 by Edwin McMillan to receive the Nobel Prize for Chemistry. The year after Segrè’s award, Donald Glaser won the Nobel Prize for Physics in 1960, and in his speech, he said:
“Your Majesty, besides me take a good look at this waistcoat, because it is the third time you have seen it!”
After winning the Nobel Prize, Segrè became increasingly involved in travelling to hold seminars. He retired in 1972 but continued his work as a writer and populariser of science, which kept him busy for a long time. He is credited with one of the most important biographies of Fermi, as well as one written by his wife Laura. Throughout his life, he maintained a great curiosity about developments in physics and often went in search of colleagues who could explain to him the meanings behind the new research findings. He died on 22 April 1989 in Lafayette, California, and his remains were brought back to Tivoli.
During his experiments with neutrons, Fermi realised that he needed the help of a chemist. Fermi asked Nicola Parravano, director of the Institute of Chemistry at the University of Rome, to give him the name of a good chemist who could help Rasetti during these experiments. That good chemist was called Oscar D’Agostino. It was 1933 when Fermi called him to the Institute in Via Panisperna. Thanks to the combined efforts of D’Agostino and Rasetti, the Rome Institute found itself in possession, within a very short time, of a quantity of radium D second only to that produced by the Institut du Radium in Paris. It was precisely to the Institut du Radium that D’Agostino was directed at the suggestion of Corbino and Rasetti, in the early months of 1934, thanks to a study grant he had been awarded in November of the previous year by the CNR. In Paris he was able to deepen his knowledge of radioactivity through the lectures given by Marie Curie and Irène and Frédéric Joliot-Curie, who had obtained the first artificial radioactive elements at the beginning of 1934. A few months later, towards the end of March, D’Agostino returned to Rome for the Easter holidays, and Fermi decided to involve him in research into neutron-induced radioactivity. The aim was to bombard all 92 naturally occurring elements in a very short time, and D’Agostino played a key role, separating and characterising a large number of artificial radioisotopes. As usual, Fermi would say:
“In the course of the work, the problem of manipulating and preparing natural radioactive substances also frequently arose. In all these researches I have always been able to appreciate D’Agostino’s skill and industriousness, as well as his aptitude for rapidly orienting himself in the face of new problems.”
In 1935 the Roman nucleus began to disintegrate, especially with Segrè’s departure for Palermo where he had won the competition for professorships, D’Agostino also left, and in March 1938 he was awarded a professorship in general chemistry. After a few years at the CNR, he returned permanently to the Istituto Superiore di Sanità, where he was involved in radiotherapy research, particularly on the use of radioactive isotopes in chemical and biological research. Edoardo Amaldi, regarding his own attempts to rebuild a research group in 1939, wrote:
“At that time I made several attempts to convince Oscar D’Agostino to return to work in radiochemistry, as he had successfully done from spring 1934 to June 1935. Both the fission of uranium and the use of new radioactive isotopes as tracers were areas of extraordinary scientific interest. His collaboration with our group, using the facility at the Istituto Superiore di Sanità, could have borne considerable fruit, but his interests had shifted to other fields and all my efforts were in vain despite the fact that he too was greatly impressed by the discovery of fission”.
Bruno Pontecorvo was born in August 1913 in the small village of Marina di Pisa into a Jewish family that was endowed with an almost natural predisposition for genius: Guido, the older brother, was to become an internationally renowned geneticist, while Gillo, the younger, chose a career in film, directing successful films such as “The Battle of Algiers”. From an early age, the germ of shyness settled in him, leading to the hypothesis that his parents considered him to be their ‘best but most limited son, as shown by his eyes, good but not intelligent’. After finishing high school in Pisa, he decided to study physics; his brother Guido supported his decision but forced him to move to Rome because Enrico Fermi and Franco Rasetti were there to examine him. Bruno passed the oral interview with flying colours, but Fermi made a less than benign comment:
“Physics is one thing, but unfortunately today physicists are divided into two categories: theorists and experimenters. If a theoretician does not have extraordinary abilities, his work is meaningless. As for experimental physics, here there is the possibility of useful work even for an individual of average ability.”
Pontecorvo, perhaps, took this as a warning and immediately threw himself into experimental physics, although he went on to become a great physicist, both theoretical and experimental. He graduated at the age of 20, with top marks, and thus officially joined the group of boys from Via Panisperna, under the nickname “The Puppy”. Together with Amaldi, Pontecorvo became involved in the discovery of neutron-induced radioactivity: the two began to study what conditions were favourable for obtaining reproducible results, and Pontecorvo immediately observed that wooden tables had “miraculous properties”: If elements were irradiated on those tables, rather than on marble tables, an increase in radioactivity was observed. This was the first step towards the great discovery the properties of slow neutrons, which was to culminate in Fermi being awarded the Nobel Prize for his all-Italian work in 1938. Unfortunately, in the famous photo that immortalises the “Ragazzi di Via Panisperna”, Pontecorvo is not present, but he specified that he was missing because it was he who was taking the photo! In 1936, Pontecorvo won a scholarship for a six-month stay at the prestigious Institut du Radium, run by Frédéric and Irène Joliot-Curie: His stay in Paris left a deep mark on him, not only scientifically but also culturally and politically, as he found himself in an openly left-wing environment.
Pontecorvo remained in France until June 1940 when, unable to return to Italy following the promulgation of racial laws, he had to flee a Paris besieged by the Nazis and finally reached the United States. With the help of his old friend Emilio Segrè and his mentor Fermi, he was offered a job with an oil company in Tulsa, Oklahoma. There, based on the neutron-slowing technique he had learned in Rome, he developed an ingenious technique for detecting possible oil wells, the so-called neutron coring, which was one of the first (if not the first) application of the discovery made by the “Ragazzi di Via Panisperna”. In 1942, the arms race began in the USA, with the famous Manhattan Project for the construction of the atomic bomb, a project in which Pontecorvo did not take part. In 1943, however, Pontecorvo was called to a Canadian laboratory to coordinate the construction of a heavy-water nuclear reactor, which was also of military interest. The reactor went into operation in July 1947 and became the main supplier of radioactive isotopes for medical use for many years.
The Canadian period was an inexhaustible source of inspiration for Pontecorvo: he came up with some brilliant insights into elementary particle physics, developing a radiochemical method for capturing solar neutrinos. The technique was not perfect, but it laid the foundations for the experiment performed in the 1960s to definitively observe and estimate the number of solar neutrinos. After the Conversi–Pancini–Piccioni experiment, which identified a new particle, about two hundred times heavier than the electron, the muon, Pontecorvo hypothesized that the capture of the muon by an atomic nucleus would lead to the emission of an electron and, at least, two other neutrino particles (in complete analogy to what Fermi described in his theory of beta decay). Pontecorvo thus discovered that Fermi’s theory had a much more general character. He also hypothesised that these two neutrinos were of different natures, eventually establishing himself as one of the world’s leading experts on neutrino physics.
In the summer of 1950, after a short stay in Italy, Bruno Pontecorvo’s entire family disappeared. After they had made a tortuous journey to the Soviet Union. To cross the border, Bruno hid in the boot of a car. For five years, the West had no news of the Italian physicist, and it was only five years later that his statement appeared in Pravda, the press organ of the Soviet Communist Party. After years of close surveillance and mistrust by the Soviet government, Pontecorvo was finally accepted. From then on, he would be recognised by the name Bruno Maksimovič Pontecorvo, in accordance with the Soviet tradition of using the patronymic. In the meantime, he had moved to Dubna, the famous atomic city located 120 km north of Moscow, where an important institute for nuclear research had sprung up in those years, housing one of the world’s largest particle accelerators, a synchrocyclotron. His reputation as a former student of Fermi’s, combined with his genius, preceded him, and all his colleagues were enthusiastic about starting to work with him. Here he was put in charge of the Experimental Physics Division of the Laboratory of Nuclear Problems, where some of his most outstanding ideas began to take shape. In 1959 he published a paper in which he hypothesised the existence of three types of neutrinos. This work laid the foundations for high-energy neutrino physics. Unfortunately, the Dubna accelerator could not reach energies high enough to prove his hypothesis. It was not until the 1970s that American physicists experimentally confirmed the Italian physicist’s theory.
Between 1957 and 1967 Pontecorvo worked on the theory of leptonic mixing. A remarkable and important consequence of this theory is that neutrinos have mass. This fact was first verified for solar neutrinos in 1968 and was only definitively confirmed in 2010 by experiments carried out at the Gran Sasso National Institute of Nuclear Physics Laboratories. It was not until 1978 that Pontecorvo returned to Italy, on the occasion of Edoardo Amaldi’s 70th birthday. The first symptoms of Parkinson’s disease had already appeared, but it never deprived him of mental lucidity. He died in Dubna on 24 September 1993. His brilliant insights and methods of investigation led to the awarding of four Nobel Prizes in the world of physics.