Physics – 5.2.1 Detection of radioactivity | e-Consult

A Geiger-Müller tube is a type of radiation detector used to detect the presence of ionising radiation. It consists of a gas-filled tube with a central wire running through it, maintained at a high voltage. The tube has a metal casing which acts as the cathode and the central wire acts as the anode.

Principle of Operation:

• When ionising radiation (alpha, beta, or gamma) enters the tube, it ionises the gas atoms within the tube. This creates positive ions and free electrons.
• The high voltage potential difference between the anode and cathode creates a strong electric field.
• The free electrons are accelerated towards the anode, and the positive ions are accelerated towards the cathode.
• As the electrons accelerate, they collide with other gas atoms, causing further ionisation – this is a chain reaction.
• This chain reaction results in a sudden surge of electrons reaching the anode, producing a measurable electrical pulse.
• The size of the pulse is independent of the energy of the incoming radiation; it only indicates the presence of radiation.
• After the pulse, the gas is quenched to stop further discharge, usually by a halogen gas.

The counter then registers each pulse as a count, providing a measure of the radiation intensity.