Geiger–Müller Counter
An instrument that detects ionising radiation through the avalanche of ionisation it triggers in a low-pressure gas.
Unit
counts/s
In depth
Radiation entering the tube ionises the gas, and a high voltage accelerates the electrons into further ionisation, producing a pulse large enough to count directly. The counter registers events reliably but gives little information about their energy.
Examples in the real world
The familiar clicking survey meter used to check for contamination in a laboratory.