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Hans Albrecht Bethe


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German-born US physicist, who discovered the source of energy in the sun and the stars. He was awarded the 1967 Nobel Prize for Physics.

The son of a university professor, Bethe was educated at the University of Munich, where he obtained his PhD under the supervision of Arnold Sommerfeld in 1928. He taught initially at the University of Tübingen but as a Jew was dismissed in 1933. He abandoned Germany and after two years in Britain accepted in 1935 the post of professor of physics at Cornell University, a post he retained until his retirement in 1975.

Bethe established his reputation with a series of papers, known as Bethe's Bible (1936–37), in which he reviewed the current state of nuclear physics. In the following year he went on to explain how the stars were able to produce prodigious amounts of energy for vast periods of time. Bethe proposed a cyclic nuclear reaction in which, starting with carbon-12, four protons fuse to form two helium nuclei, leaving the original carbon-12 to enter into the reaction once more. The small mass loss accounted for the energy released. It was for this work that Bethe was awarded his Nobel Prize. Bethe also collaborated with Ralph Alpher and George Gamow on their well-known paper (1948) concerning the origin of the elements of the universe.

During World War II Bethe worked on the military application of nuclear fission. He was appointed head of the theoretical division at Los Alamos in 1943. Later, when his old colleague and director J. R. Oppenheimer was under investigation by the security authorities, Bethe gave evidence in his favour. In the 1960s he spoke out for the test-ban treaty and in the 1970s he argued strongly that nuclear power was essentially safe and the only real alternative to fossil fuels.

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