Hans Wilhelm Geiger (30.09.1882-24.09.1945) was a German experimental physicist and a member of the Berlin Academy of Sciences (1937). He was born in Neustadt. He graduated from the University of Erlangen (1906). In 1906—12 he worked at the University of Manchester, and in 1912—14 and 1918—24 at the Physico-Technical Institute in Berlin. In 1925 —29 he was professor and director of the Institute of Physics of the University of Kiel, and in 1929 — 36 of the University of Tübingen. From 1936 he was professor at the Technical University in Berlin. His work concerned atomic and nuclear physics and the physics of cosmic rays. In 1908 he measured the charge of the electron and, together with E. Rutherford, invented an instrument for registering (counting) individual charged particles, later (1928) improved by him together with W. Müller (the Geiger — Müller counter). In 1909 — 10, together with E. Marsden, he carried out experiments on the scattering of alpha particles in thin metal films and, using the scintillation method, established that a certain very small number of the particles are scattered through large angles (one particle in 8000 is scattered through an angle greater than 90°). These experiments played a decisive part in E. Rutherford's discovery of the atomic nucleus. Together with J. Nuttall he proposed in 1911 an empirical formula connecting the radioactive decay constant with the energy of the alpha particles (the Geiger — Nuttall law). In 1925, together with W. Bothe, he proved experimentally the validity of the laws of conservation of energy and momentum in an elementary atomic act in the Compton effect.
A member of the Leopoldina Academy (1935). The D. Hughes Medal (1929).