Geiger counters are used to detect radiation usually gamma and beta radiation, but certain models can also detect alpha radiation. The sensor is a Geiger-Müller tube, an inert gas-filled tube (usually helium, neon or argon with halogens added) that briefly conducts electricity when a particle or photon of radiation temporarily makes the gas conductive.
The Geiger counter, also known as the Geiger Muller Counter, is an instrument used to detect and measure the intensity of radiation, such as beta particles and cosmic rays. The device, which takes its name from the German physicists Hans Geiger and Wilhelm Muller, may be used as a laboratory instrument, in mineral exploration, as a thickness gauge for continuous sheet materials, and as a stock level gauge in blast furnaces. It is also employed in diagnostic medical work.
The heart of the Geiger counter is the ionization tube which may be metal, or glass with a metalized interior, and a central conductor maintained at a high positive potential with respect to the outer onclosure. The tube may contain air, argon, or other gas at or below atmospheric pressure. When the tube is exposed to nuclear radiation the gas is ionized. Negative ions or electrons are attracted to the center conductor, and positive ions are attracted to the negative enclosure. If the voltage on the tube is in the Geiger range (800-1,500 volt), each ionizing event will cause an electron avalanche (gas amplification) and will result in a large output pulse. This pulse may be received audibly in headphones or recorded electronically through counting devices.