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Radiation detectors: Geiger Muller counter

We continue talking about radiation detectors and in this case we want to explain what the Geiger Muller counter is, the most popular tool for detecting radioactivity. If you want to know what it is and what kind of detector it is, read on!

Geiger Muller detector

As we explained in our article about the types of radiation detectors, we can make different classifications of detectors, among which we find the gaseous ionisation equipment.

In these, the radiation, when passing through a gas, ionises it. Gaseous ionisation detectors use the ionic current collected in a known volume of gas. This gas is chosen according to the characteristics of the radiation and the mode of operation of the detector.

The Geiger-Muller counter is such a radiation detector: it contains a gas which ionises as the radiation passes through so that it counts the number of particles or photons regardless of their nature or energy.

They have the ability to measure alpha, beta and gamma radiation.

They have an electrode in the centre of the chamber and are configured so that there is an electrical voltage between the electrode and the metal wall of the chamber.

Geiger Muller counter operation

Its operation is based on the principle of the Geiger Müller tube, invented in 1913 by Hans Wilhelm Geiger and later improved by Walther Müller.

When the radiation hits the gas molecules in the tube, it separates the electrons from the atoms, a process known as ionisation. The electron is attracted by the effective charge of the anode and the rest of the atom (a positively charged ion) is thrown towards the wall of the tube. The electron then travels through the wires that form the electrical circuit and recombines with the ion. Part of the Geiger counter is a device that measures this electron flow.

Thus, after positive electron-ion pairs are created in the ionisation of the gas produced by the radiation, they are displaced towards two electrodes where a potential difference is established a priori.

Their operation can be summarised as follows:

– Gas-filled detectors (such as Geiger counters and ion chambers) are filled with a gas to which an electrical voltage is applied.

– As the radiation interacts with the gas it causes ionisations, and this small signal is amplified by the electrical voltage. The amplification ratio is voltage dependent.

– Ion chambers have the possibility to measure the difference in radiation energy, which is why they are especially suitable for measuring radiation dose rates.

Differences to other detectors

In a Geiger counter, the voltage is so high that the whole gas chamber is ionised, which gives a very high sensitivity to incoming radiation. In other detectors (so-called ion chamber and proportional counters) the voltage is lower and the gas amplification ratio is also lower; only a few gas atoms are ionised in these detectors.

If you are interested in radiation detection, we encourage you to check other articles in our blog.

At Helgeson we have years of experience in the field. We will be pleased to help you. If you need specialised advice, guidance or have any questions, please contact us.

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