Geiger counter

Device used for detecting and counting individual particles of radiation. Invented by the German physicist Hans Geiger (1882–1945) and later refined with help from Walther Müller, the device is a gas-filled metal tube with a wire through its axis and a high voltage applied to the wire. As particles enter the tube, they create a large avalanche of ionization in the gas, which then discharges, creating a brief electric pulse. The tube produces the same large output pulse for virtually every charged particle that passes through the gas and so is useful for detecting individual particles. It can therefore indicate lower levels of radiation than is possible with other types of detectors.