Geiger, Hans (Johannes) Wilhelm (1882–1945), and Müller \ˈmue-lər\ , Walther (flourished 1928), German physicists. Geiger did significant research on atomic theory, radioactivity, and cosmic rays. He developed a number of techniques and instruments for the detection and counting of individual charged particles. With the British physicist Ernest Rutherford (1871–1937), he developed in 1908 the first radiation counter, an instrument that counted alpha particles. With the help of Müller he introduced an improved version of the Geiger counter in 1928. The Geiger-Müller counter marked the introduction of modern electrical devices into radiation research.