Departures of note

Bruno Pontecorvo, a nuclear physicist and early assistant of Enrico Fermi, defected to the Soviet Union in 1950, abruptly leaving a holiday in Italy with his wife and three sons. He had been working at the British Atomic Energy Research Establishment at Harwell, where he was involved in reactor design and had access to sensitive materials. His disappearance caused concern among Western intelligence services, and he was suspected of being a Soviet spy, though he never confirmed or denied this. In the Soviet Union, he was welcomed with honors and continued his research at the Joint Institute for Nuclear Research in Dubna, focusing on theoretical studies of high-energy particles and neutrinos.

Born in 1913 in Marina di Pisa to a wealthy Jewish-Italian family, Pontecorvo studied physics at the University of Rome under Fermi, becoming the youngest of the Via Panisperna boys. In 1934, he participated in Fermi's experiment on slow neutrons, which led to the discovery of nuclear fission. He moved to Paris in 1936 to work with Irène and Frédéric Joliot-Curie, and during this period, influenced by his cousin, he joined the Italian Communist Party. When the German Army approached Paris in 1940, he fled on a bicycle with his brother and others, eventually making his way to the United States. In Tulsa, Oklahoma, he applied nuclear physics to oil prospecting, creating a neutron source that could differentiate minerals, a technique later used for well logging.

In 1943, Pontecorvo joined the British Tube Alloys team in Canada, working on the design of nuclear reactors at Chalk River Laboratories. He was present when the ZEEP reactor went critical in 1945, the first reactor outside the United States, and later worked on the NRX reactor. After the war, he moved to Britain in 1949, but his career was interrupted by his defection. In the Soviet Union, he proposed using chlorine to detect neutrinos and, in a 1959 paper, argued that electron neutrinos and muon neutrinos were different particles. He also proposed the phenomenon of neutrino oscillation to explain the solar neutrino problem, where fewer neutrinos were detected than predicted. This was confirmed by the Super-Kamiokande experiment in 1998, and he predicted that supernovae would produce intense neutrino bursts, confirmed in 1987 with Supernova SN1987A.

Pontecorvo died in Dubna on 24 September 1993, afflicted by Parkinson's disease. In accordance with his wishes, half of his ashes were buried in the Protestant Cemetery in Rome, and the other half in Dubna. In 1995, the Pontecorvo Prize was instituted by the Joint Institute for Nuclear Research in recognition of his scientific merits, awarded annually for significant investigations in elementary particle physics.