Emilio Segre

Emilio Segre was an Italian-American physicist whose Manhattan Project measurements of plutonium's behavior shaped the design of the first nuclear weapons and, with it, the handling of nuclear fuel more broadly. Leading a group at Los Alamos, Segre found that reactor-bred plutonium contained enough of the isotope plutonium-240 to undergo spontaneous fission at a rate too high for the simple gun-type detonation design already built for the uranium bomb, a finding that forced the laboratory to develop the more complex implosion design used in the plutonium weapon instead. Segre had trained under Enrico Fermi in Rome before immigrating to the United States, and he later shared the 1959 Nobel Prize in Physics for a separate postwar discovery, the antiproton.