Walther Bothe (8.1.1891 - 8.02.1957) was a German physicist and one of the pioneers of nuclear physics. He was born in Oranienburg. He graduated from the University of Berlin (1912). In 1920-30 he worked at that university, in 1930 — 34 he was professor and director of the Institute of Physics of the university in Giessen, and from 1934 professor and director of the Institute of Physics of the University of Heidelberg.
His research concerned atomic and nuclear physics, the physics of cosmic rays, accelerator technology and neutron physics. He studied the scattering of alpha and beta rays and worked out a statistical theory of multiple scattering through small angles. In 1924 he developed the coincidence method, which came into wide use and led to many discoveries (Nobel Prize, 1954). In 1925, studying with H. Geiger the scattering of hard gamma rays by electrons (the Compton effect), he was the first to prove experimentally the validity of the laws of conservation of energy and momentum for each single act of scattering. In 1929, with W. Kolhörster, he was the first to apply the coincidence method to the study of cosmic rays and established that cosmic radiation contains charged particles capable of passing through a considerable thickness of absorbing matter. In 1930 Bothe, together with H. Becker, irradiating a number of elements with alpha particles, in particular beryllium, found an unknown radiation, which they took to be hard gamma rays. The correct interpretation of the “beryllium radiation” was given by the English physicist J. Chadwick, who showed that it is a stream of new particles — neutrons. In 1937 Bothe, together with W. Gentner, observed the nuclear photoeffect in heavy nuclei (from lithium to bismuth), caused by hard gamma quanta with an energy of 12—17 MeV. Together with his colleagues he built a Van de Graaff accelerator and a cyclotron in Heidelberg (1943). He proposed (1935) a notation for the equations of nuclear reactions.
He founded a school of physicists (1953).