Geiger, Hans (1882-1945) was a German physicist who became famous for his work in nuclear physics. He developed the Geiger counter (also called the Geiger-Muller counter), an instrument that detects gamma rays, alpha and beta particles, and other forms of ionizing radiation.

Prospectors use Geiger counters to find uranium, thorium, and other radioactive elements. The instruments are also used in science and industry, chiefly in studies involving radioactive substances called radioisotopes.

Hans Wilhelm Geiger was born in Neustadt, Germany, in 1882. He was the oldest of five children. His father was a professor of philology at the University of Erlangen. Geiger studied physics at the Universities of Munich and Erlangen. He earned a doctorate degree in physics from Erlangen in 1906.

From 1906 to 1912, Geiger worked at the University of Manchester; for most of that time he was a research assistant to Ernest Rutherford, a leading British physicist. Geiger's work on the deflection of alpha particles by thin metal foils led Rutherford to discover his model of atomic structure in 1911.

In 1912, Geiger returned to Germany. He held a series of administrative and teaching posts at leading universities and laboratories, including the Physikalische Technische Reichsanstalt (Berlin), the University of Tübingen, and the Technische Hochschule (Berlin). He was also the editor of Zeitschrift für Physik, a major physics journal, from 1936 through 1944.

In 1920, Geiger married Elisabeth Heffter. The couple had three sons. He served in the German military during World War I (1914-1918) and contributed to Germany's efforts to develop an atomic bomb in World War II (1939-1945). In 1945, he was forced to flee his home and abandon his possessions in Babelsberg, Germany, when that city was occupied by Allied forces. He died several months later in Potsdam, Germany.