Hans Geiger was a German physicist who invented the Geiger counter, a device for detecting alpha particles and ionizing radiations. The Geiger counter can locate a speeding alpha particle within 1 centimeter in space and within one-hundred-millionth of a second.
Because it was developed while working with Walther Müller, the Geiger counter is sometimes referred to as the Geiger–Müller counter. It was used to confirm the existence of packets of energy. Before collaborating with Müller, Geiger built an earlier version of a particle counter and used it to identify alpha particles in the nucleus of a helium atom. Throughout his career, Geiger investigated many areas of nuclear physics, including cosmic rays, nuclear fission and artificial radioactivity.