Geiger counters are used to detect ionizing radiation, usually beta particles and gamma rays, but certain models can detect alpha particles. An inert gas-filled tube (usually helium, neon or argon with halogens added) briefly conducts electricity when a particle or photon of radiation makes the gas conductive. The tube amplifies this conduction by a cascade effect and outputs a current pulse, which is then often displayed by a needle or lamp and/or audible clicks.