Bothe, Walthar

Born Jan. 8, 1891, in Oranienburg, near Berlin; died Feb. 8, 1957, in Heidelberg. German physicist (Federal Republic of Germany).

Bothe graduated from the University of Berlin (1914). He was a student of M. Planck. He became professor at the universities of Berlin (1929), Giessen (1930), and Heidelberg (1932–34, 1946). Beginning in 1934 he was director of an institute of physics (Kaiser Wilhelm Institute). He devised a coincidence method that has been widely used in atomic physics. In 1925, Bothe and H. Geiger proved that the law of the conservation of energy is obeyed during the scattering of hard gamma rays onto electrons. In 1929 he applied the coincidence method to the study of cosmic rays (in collaboration with W. Kolhörster). He was awarded the Nobel Prize in 1954 for his work on cosmic rays. In 1930, in collaboration with H. Becker, Bothe discovered that upon irradiation of polonium, beryllium, and certain other light elements with alpha particles, an extremely penetrating radiation is produced which, as J. Chadwick showed (1932), consists of neutrons. In 1937, Bothe and W. Gentner were the first to observe the transformation of heavy nuclei under the effects of hard gamma radiation.