Ionization counters are used to measure radioactive emissions as these emissions ionize a gas. All of these counters follow a general mechanism in which the ionization of a gas produces free electrons and gaseous cations. These cations are attracted to electrodes which then conduct a current to a recording device.
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Today, the most widely used ionization counter is the Geiger-Müller counter, which detects and measures alpha, beta, and gamma radiation. It is composed of a tube full of a mixture of argon and methane. The tube itself is the cathode, and a thin wire running through the center of the tube is the anode. The radioactive sample to be tested emits radiation that enters the tube through a small window, which then strikes argon atoms, producing free electrons that are accelerated to the thin wire anode. While these electrons move towards the anode, they collide with other argon atoms, releasing even more electrons, in what is called the avalanche effect. The electrons create a current that is amplified and received at a recording device. This recording device can appear as a meter reading, a clicking sound, or both.
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