Geiger counter

A Geiger counter detects ionizing radiation by measuring electrical pulses produced in a Geiger–Müller tube. It can register individual events but usually cannot identify the radiation’s energy or type.

Geiger–Müller tube: A gas-filled detector tube in which ionizing radiation triggers an electrical discharge. Radiation initiates the discharge that produces each pulse counted by the instrument.
Ionizing radiation: Radiation with enough energy to remove electrons from atoms or molecules. The counter responds to ionization caused by this broad class of radiation.
Radiation survey meter: A portable instrument that measures radiation levels or contamination in an area. Many survey meters use Geiger–Müller tubes to find elevated radiation.
Ionization chamber: A gas-filled detector that measures charge collected from ion pairs without relying on a Geiger discharge. It measures radiation intensity with a response suited to dose-rate measurements rather than individual clicks.
Townsend avalanche: The multiplication of free electrons in a gas by impact ionization under an electric field. It amplifies the initial ionization into a detectable discharge in the tube.
Gas ionization: The formation of ions and free electrons when gas atoms or molecules lose or gain electrons. Ionization inside the tube supplies the charged particles that initiate its pulse.
Radiation protection: Practices and systems that limit harmful exposure to ionizing radiation. Counters help locate sources and check whether protective procedures are working.
Proportional counter: A gas-filled radiation detector whose pulse size varies with the ionization produced by an event. Its pulse information can distinguish event energies, unlike the nearly uniform pulses of a Geiger tube.
Quenching gas: A gas additive that suppresses repeated discharges in a gas-filled radiation detector. It helps end each discharge so the tube can register another event.
Radioactivity: The spontaneous transformation of unstable atomic nuclei, accompanied by particle or electromagnetic radiation. Radioactive sources are common producers of the emissions counted by the instrument.

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