Geiger, Johannes Wilhelm (Hans Geiger)yōhänˈəs vĭlˈhĕlm gĪˈgər, 1882–1945, German physicist. Geiger received a doctorate in physics at Erlangen in 1906, then went to Manchester, where he assisted British chemist Ernest Rutherford. They devised an alpha-particle counter that permitted great strides in research on radioactivity. In 1912, Geiger returned to Germany, directing radiation research first at the Physikalisch-Technische Reichsanstalt and later at the universities of Kiel and Tübingen and at the Technische Hochschule, Berlin. In 1928 he participated in the invention of the sensitive, portable radiation counter that bears his name (see Geiger counter).