Born Sept. 30, 1882, in Neustadt; died Sept. 24, 1945, in Potsdam. German physicist. Studied at the Universities of Erlangen, Munich, and Manchester. Taught at the University of Manchester from 1907 to 1912. Became a professor at the University of Kiel in 1925, at the University of Tubingen in 1929, and at the University of Berlin in 1936.

In 1908, Geiger determined the charge of the electron and, together with E. Rutherford, invented a device that made possible the counting of individual charged microscopic particles. The counter was subsequently improved by Geiger and the German physicist W. Müller and came to be called the Geiger-Müller counter. In 1911-12, together with the English physicist J. M. Nuttall, Geiger proposed an empirical formula linking the decay constant and the energy of alpha particles. Together with W. Bothe, he confirmed the correctness of the laws of conservation of energy and momentum during single collision events of elementary particles. Together with the English physicist Marsden, Geiger studied the scattering of alpha particles in thin metallic plates, experimentally confirming Rutherford’s formula.