The original detection principle was realized in 1908 at the University of Manchester,[3] but it was not until the development of the Geiger–Müller tube in 1928 that the Geiger counter could be produced as a practical instrument.

[5] A Geiger counter consists of a Geiger–Müller tube (the sensing element which detects the radiation) and the processing electronics, which display the result.

The Geiger–Müller tube is filled with an inert gas such as helium, neon, or argon at low pressure, to which a high voltage is applied.

The ionization is considerably amplified within the tube by the Townsend discharge effect to produce an easily measured detection pulse, which is fed to the processing and display electronics.

This large pulse from the tube makes the Geiger counter relatively cheap to manufacture, as the subsequent electronics are greatly simplified.

The purpose of this is to allow the user to concentrate on manipulation of the instrument while retaining auditory feedback on the radiation rate.

For α-particles and low energy β-particles, the "end-window" type of a Geiger–Müller tube has to be used, as these particles have a limited range and are easily stopped by a solid material.

The "pancake" Geiger–Müller tube is a variant of the end-window probe, but designed with a larger detection area to make checking quicker.

Although the tube walls have a greater stopping power than a thin end-window, they still allow these more energetic particles to reach the fill gas.

[8] Those instrument types are manufactured with much larger detector areas, which means that checking for surface contamination is quicker than with a Geiger counter.

At very low energies (less than 25 keV), direct gas ionisation dominates, and a steel tube attenuates the incident photons.

The tube, which can contain the fill gas boron trifluoride or helium-3, is surrounded by a plastic moderator that reduces neutron energies prior to capture.

This can easily be achieved because the casing usually has little attenuation, and is employed in ambient gamma measurements where distance from the source of radiation is not a significant factor.

A pancake probe (for alpha/beta) is generally used to increase the area of detection in two-piece instruments whilst being relatively light weight.

In the United Kingdom the National Radiological Protection Board issued a user guidance note on selecting the best portable instrument type for the radiation measurement application concerned.

[13] Halogen compounds have superseded the organic quench gases because of their much longer life and lower operating voltages; typically 400-900 volts.