Geiger counter

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Any of a number of devices used for detecting nuclear radiation and measuring its intensity by counting the number of ionizing particles produced (see radioactivity). It detects the momentary current that passes between electrodes (anode and cathode) in a suitable gas (such as argon) when radiation causes the ionization of the gas. The electrodes are connected to electronic devices that enable the number of particles passing to be measured. The increased frequency of measured particles indicates the intensity of radiation. The device is named after the German physicist Hans Geiger.

The becquerel (Bq) is the unit used to measure radioactive decay. The number of particles emitted in one second by a radioactive source is known as the activity (or disintegration): 1 Bq = 1 disintegration per second.

The Geiger–Müller, Geiger–Klemperer, and Rutherford–Geiger counters are all devices often referred to loosely as Geiger counters.