Hans Geiger, German physicist and academic, co-invented the Geiger counter (born 1882)

Johannes Wilhelm Geiger was a German nuclear physicist. He is known as the inventor of the Geiger counter, a device used to detect ionizing radiation, and for carrying out the Rutherford scattering experiments, which led to the discovery of the atomic nucleus. He also performed the Bothe–Geiger coincidence experiment, which confirmed the conservation of energy in light-particle interactions.

A Geiger counter is an electronic instrument for detecting and measuring ionizing radiation with the use of a Geiger–Müller tube. It is widely used in applications such as radiation dosimetry, radiological protection, experimental physics and the nuclear industry.