Austrian-born physicist researching nuclear fission.
Frisch studied physics at the University of Vienna, taking a DPhil in 1926. His early research was conducted in Germany, but Nazi racial law led to his dismissal, and he moved to London, where he worked under Blackett on artificial radioactivity, and then to Copenhagen at the invitation of Bohr.
In 1938 he and his aunt Lise Meitner were the first to identify nuclear fission. While they were spending Christmas together in Switzerland, Meitner received a letter from her old partner Hahn describing the discovery of barium in the products of neutron-bombarded uranium. Barium being much lighter than uranium, theoretical physics had no explanation for the observation, but Meitner and Frisch rapidly realised that the uranium nucleus was splitting and Frisch coined the term 'fission' to describe the process. They also realised that, since mass was lost during fission, energy must be released in accordance with Einstein's mass-energy relation (e=mc2), setting the stage for the atomic bomb.
To avoid becoming a German citizen trapped in occupied Denmark, Frisch relocated to Birmingham in 1939, where he worked with Rudolf Peierls on fission reactions. They found that the amount of uranium-235 required to sustain a chain reaction was far less than expected, and they reported to Henry Tizard that a nuclear bomb might be a possibility.
Frisch joined Chadwick in Liverpool in 1940. In 1943 he was naturalised as a British citizen in order to be assigned to the Los Alamos atomic weapons project as part of the British 'mission' headed by Chadwick. Here he did dangerous research into fission. However, when it came to the biggest experiment of them all - the bomb test at Trinity - Frisch was unable to find his dark glasses and had to sit with his back turned to the explosion.
After the war Frisch became head of the nuclear physics division of the Atomic Energy Research Establishment at Harwell, and in 1947 took a professorship at Cambridge, where he remained until his retirement in 1972.