How does a Geiger counter detect radioactive decay?

A Geiger counter detects radioactive decay by measuring ionising radiation such as alpha, beta particles and gamma rays.

A Geiger counter, also known as a Geiger-Müller counter, is a type of particle detector that measures ionising radiation. It was named after Hans Geiger, a German physicist who co-invented the device, and Walther Müller, who collaborated with him. The device is widely used in applications such as radiation dosimetry, radiological protection, experimental physics, and the nuclear industry.

The Geiger counter operates based on the principle of ionisation. It consists of a Geiger-Müller tube, which is a gas-filled tube that conducts electricity when it is struck by a high-energy particle or photon. The tube is filled with an inert gas such as helium, neon, or argon at low pressure, plus a small amount of a "quenching" gas (typically alcohol or halogen) to prevent spurious pulsing.

When ionising radiation passes through the tube, it ionises the gas inside, causing an avalanche of ion pairs to be created. This ionisation process results in a brief pulse of current, which is detected and amplified by the counter's electronics. Each pulse corresponds to one particle or photon of radiation, so by counting the pulses, the device can measure the amount of radiation in a given area.

The Geiger counter is sensitive to all types of ionising radiation, but it cannot distinguish between them. Therefore, it cannot tell the difference between alpha particles, beta particles, gamma rays, or other types of radiation. However, by using different types of detectors or by applying different voltages, it is possible to make the device more sensitive to certain types of radiation.

In summary, a Geiger counter detects radioactive decay by measuring the ionising radiation that is emitted. It does this by using a gas-filled tube that conducts electricity when struck by a high-energy particle or photon. The resulting pulses of current are counted and amplified, providing a measure of the amount of radiation in the area.