How does a Geiger tube work and what particles can it detect?

A muon (µ) passes through a Geiger tube producing an electric current.

Image: Wearbeard

A Geiger tube is a chamber filled with an inert gas (such as helium or argon) that has two electrodes between which there is a potential difference of a few hundred volts. The electrodes can be the chamber itself (negative) and a wire running the length of the chamber (positive), both of which are made of metal.

A particle passing through the tube 'collides' with the atoms in the gas and in doing so it may be able to ionise them, i.e. strip electrons from them and transform them into positive ions. The positive ions will then move towards the negative pole and the electrons towards the positive pole, colliding with new atoms and releasing more electrons, which, when they reach the positive electrode, give rise to an impulse of electrical current that can be recorded, indicating the passage of a particle through the tube.

In the detectors, there is also an electronic circuit that takes these current pulses and transforms them so that they can be recorded with their time stamp on a computer.

Geiger tubes are capable of registering the passage of charged particles (electrons, muons, alpha particles, etc.) or photons with sufficient energy to ionise the gas.

It is important to know that Geiger tubes, like all detectors, have a dead time in which they cannot produce a signal even if a particle passes through, since after a discharge in the gas, it needs some time to return to the initial sensitive state. In our tubes, this time is in the order of 190 millionths of a second (0.00019 s).

The same is true for the electronics that process and record the pulses. This means that, if we try to measure events that happen very quickly, the detector will saturate and give measurements that are very poorly adjusted to reality. But in our case, this is not a major problem.