The geiger counter (also known as the geiger-muller tube) is an instrument which detects radiation, it is a form of ionization counter. The detector within consists of a gas-filled tube utilising two electrodes, through which are passed large voltages. One of these electrodes is actually the tube, while the other is a fine wire inside. When either radiation or a charged particle enters the detector it ionizes the gas. These gas ions then become electrically conducting and the resulting current passes between the two electrodes. The route of current is displayed by the twitch of a needle, a pulse of light, or a clicking sound in earphones. The indication produced is dependent on the type of geiger counter equipment being used. One of the great advantages of the geiger counter is that it is extremely sensitive, so much so, it can detect the course of a single atomic particle.
