Geiger-Muller Tube

[Can detect: Alpha, Beta and Gamma]

The tube contains argon gas at low pressure.
The end of the tube is sealed by a mica ‘window’ thin enough to allow alpha particles to pass into the tube as well as beta and gamma radiation.
When a charged particle or gamma-radiation enters the tube, the argon gas becomes ionized. This triggers a whole avalanche of ions between the electrodes.
For a brief moment, the gas conducts and a pulse of current flows in the circuit.
The circuit includes either a scaler or a ratemeter. A scaler counts the pulses and shows the total on a display.
A ratemeter indicates the number of pulses or counts per second. The complete apparatus is often called a Geiger counter.