Segrè , Emilio Gino

(1905–1989) Italian–American physicist

Segrè, who was born at Tivoli in Italy, studied at the University of Rome under Enrico Fermi and obtained his doctorate there in 1928. He worked with Fermi until 1936, when he was appointed director of the physics laboratory at Palermo. He was dismissed for political reasons in 1938 and moved to America where he worked at the University of California, Berkeley, from 1938 to 1972, apart from the years 1943–46, which he spent at Los Alamos working on the development of the atom bomb. He became a professor in 1945.

Segrè made a number of significant discoveries in his career. In 1937 he filled one of the gaps in the periodic table at atomic number 43 when he showed that some molybdenum that had been irradiated with deuterium nuclei by Ernest Lawrence contained traces of the new element. As the first completely artificial element they gave it the appropriate name, technetium. Segrè played a part in the detection of element 85, astatine, and also plutonium in 1940.

His main achievement however was the discovery of the antiproton with Owen Chamberlain in 1955, for which they shared the 1959 Nobel Prize for physics. Segrè calculated that producing an antiproton would require about 6 billion electron-volts (Bev), which could be provided by the recently constructed bevatron at the University of California. He therefore went on to bombard copper with protons that had been accelerated to 6 Bev, thus yielding a large number of particles. As only one antiproton was produced to about 40,000 other particles his next problem was to detect this rare event.

This was done by noting that the antiproton would travel much faster than the other particles and at such speeds it would give off Cherenkov radiation in certain media and could thus be detected. The few particles that produced this radiation could more easily be screened to see if any of them possessed the necessary properties. Before long Segrè had identified antiprotons at the rate of about four per hour. The work of the California group was soon confirmed by Italian physicists who began to detect the tracks of antiprotons on photographic plates.