Geiger counter
Definition and meaning of Geiger counter in chemistry.
A Geiger counter is an instrument that detects and measures ionizing radiation by counting electrical pulses produced when radiation ionizes gas inside a sealed tube.
In more detail
The device's core component, the Geiger-Müller tube, is a cylinder filled with a low-pressure inert gas (often argon) held at high voltage between a central wire anode and the tube wall as cathode. An incoming alpha or beta particle, or gamma photon, ionizes gas atoms, and the freed electrons accelerate toward the wire, triggering a cascading avalanche of further ionizations that produces a detectable current pulse. Each pulse registers as one "count," typically reported as counts per minute (cpm) or counts per second, and is often converted into an audible click through a speaker. Because every pulse has roughly the same size regardless of the radiation's energy, a Geiger counter reports the rate of radioactive decay events rather than the energy or type of radiation.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Also known as | Geiger-Müller counter |
| Invented by | Hans Geiger and Walther Müller, 1928 |
| Typical output | Counts per minute (cpm) or counts per second |
Holding a Geiger counter near a sample of cesium-137 causes the click rate to rise sharply as the tube detects gamma photons emitted during its radioactive decay, and the rate falls again as the instrument is moved farther away.
Frequently asked questions
Can a Geiger counter tell alpha, beta, and gamma radiation apart?
Only partially. A thin mica end-window lets fast-moving alpha and beta particles enter and be counted, while a bare metal-walled tube mainly registers penetrating gamma rays; distinguishing the types precisely requires shielding experiments or a different detector.
Does a Geiger counter measure radiation dose to a person?
Not directly. It measures the rate of ionization events (count rate), which must be converted using calibration factors to estimate dose equivalent; dedicated dosimeters are used for accurate dose measurement.