A Geiger counter is an instrument designed to detect ionizing radiation by measuring the electrical charge generated from ionization events.

The operation of a Geiger counter relies on its ability to sense the electrical charge created when ionizing radiation interacts with the gas in its detection tube. When ionizing radiation passes through a gas-filled tube, it ionizes the gas atoms, resulting in the formation of positively charged ions and negatively charged electrons. The electrons are drawn towards a positively charged electrode, while the positively charged ions are attracted to a negatively charged electrode. This movement generates a pulse of electrical current, which the Geiger counter can detect.

The most prevalent type of Geiger counter utilizes a tube filled with low-pressure gas, such as helium, neon, or argon. Typically, this tube is constructed from metal and features a thin wire running along its center. As ionizing radiation traverses the tube, it ionizes the gas atoms, producing a detectable pulse of electrical current that travels to the wire. This pulse is subsequently amplified and counted by the Geiger counter.

Geiger counters find widespread application in radiation safety, particularly in environments like nuclear power plants, hospitals, and laboratories. They are also popular among hobbyists and enthusiasts who use them to identify natural sources of radiation, such as radon gas and cosmic rays. However, it is essential to recognize that Geiger counters have certain limitations; they are not capable of detecting all types of radiation, particularly non-ionizing radiation.