A Geiger Counter is an instrument for detecting and measuring ionising radiation. The display shows the "counts" - the number of ionising events detected, and the device has a "clicks" setting, so the instruments produces audible clicks representing the number of ionisation events detected. 

It detects ionising radiation, such as alpha particles, beta particles, and gamma rays, using the ionisation effect produced in a Geiger–Müller tube, hence its name. 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 tube briefly conducts electrical charge when high energy particles or gamma radiation make the gas conductive by ionisation. The ionisation 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.

We will provide you with two natural occurring radioactive samples in the loan kit, (both are low levels of radiation):

• Lo-salt: This is a salt with 66% less sodium than usual, where the sodium has been replaced with potassium. 0.01% of potassium in nature is potassium-40, which is radioactive. This won't be picked up by the Geiger counter, but will produce a spectrum with the Kromek detector.

• Rock Mineral Sample: The kit will contain a radioactive rock mineral sample that has been set in resin.

These two radioactive samples can be used with both the Kromek Detector and the Geiger Counter to look at the number of ionising events detected, as well as to produce a gamma ray spectrum.