Hans Geiger invented his eponymous counter for measuring radioactivity in 1911. Radioactivity is the emission of radiation by certain elements, which results from the unstable nuclei of an element’s atoms or a nuclear reaction. Humans cannot detect radioactivity through their senses alone. As a result, Geiger’s invention has become indispensable in a variety of scientific and medical settings, from detecting cosmic rays to determining the presence of radon in home basements.
Geiger was born in Germany in September 1882 and studied physics at the University of Munich and the University of Erlangen. After earning his doctorate in 1906, he moved to England, where he worked with Nobel Prize-winning chemist Ernest Rutherford at his laboratory at the University of Manchester.
Rutherford and his Manchester colleagues were performing breakthrough research in the field of radiation. Geiger worked with J.M. Nuttal to establish the Geiger-Nuttall rule. That rule showed a linear relationship between the logarithm of the range of alpha-particles and the radioactive time constant. Geiger assisted Rutherford in his research on the structure of the atom, which would show that each atom contains a nucleus occupying a small volume at its center.
Geiger’s work with Rutherford led him to develop a measuring device for counting how many alpha particles and other forms of ionizing radiation were being emitted in their experiments. His early approach was tedious and imprecise: he used gold foil and a screen to detect moving particles, which would flash when they hit the foil. Geiger spent countless hours in a dark room counting these flashes.
He began work on a machine that would relieve him from this strain. In 1911, these efforts produced the first Geiger counter. The early Geiger counter was a sealed metal tube filled with gas. The tube served as the device’s primary electrode, and a thin wire inserted in the middle of the tube was the counter’s secondary electrode. When electrical current was applied, it traveled through the gas from one electrode to the other.
The gas filling the Geiger counter was sensitive to radiation. When the counter was near a radioactive substance, the gas ionized. The ionized gas particles carried the electrical current in a complete circuit. As each particle passed through the circuit, an electronic mechanism made audible “clicks” by amplifying the circuit. In addition to counting the number of particles, it measured the rate of their ionization using a pointer and scale.
Geiger returned to Germany in 1914. Following the First World War, he worked at radiation laboratories at a number of German universities. In 1928, he and physicist Walther Müller developed an improved counter of radioactivity, later known as the Geiger-Müller counter, which was more sensitive, durable, and reliable than the 1911 design