Egon Bretscher

Egon Bretscher (1901–1973) was a Swiss-born British physicist.

Born near Zurich, Switzerland and educated at the ETH there, Bretscher gained a PhD degree in organic chemistry at Edinburgh in 1926. He returned to Zurich as privat docent to Peter Debye, later moving in 1936 to work in Rutherford’s laboratory at the Cavendish in Cambridge as a Rockefeller Scholar. Here he switched to research in nuclear physics, proposing (with Norman Feather) in 1940 that the 239 isotope of element 94 could be produced from the common isotope of uranium-238 by neutron capture and that, like U-235, this should be able to sustain a nuclear chain reaction.

A similar conclusion was independently arrived at by Edwin McMillan and Philip Abelson at Berkeley Radiation Laboratory. In addition, he devised theoretical chemical procedures for purifying this unknown element away from the parent uranium; this element was named Plutonium by Nicholas Kemmer. In 1944 he became a part of the British Mission to the Manhattan Project in Los Alamos, New Mexico led by James Chadwick, where he made the first measurements on the energy released in fusion processes.

His contributions up to 1945 are discussed by Margaret Gowing in her "Britain and Atomic Energy, 1935-1945", published in 1964. During his time in Los Alamos, he took many Kodachrome slides which appear to constitute a unique coloured record of that research site. His pictures, which are now held by the Churchill Archives Centre, include photographs of Enrico Fermi, Edward Teller and the Trinity site in New Mexico after the first atomic bomb was detonated, showing the surface light brown sand turned to a green-blue glass.

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