The Geiger counter, named after one of the men who invented it, is a device used to find out how much radioactivity is present in a substance or an area. It works somewhat the way a neon light works.
In a neon light, an electrical current excites gas molecules inside the glass tube, causing them to glow. Like the neon light, a Geiger counter consists of a gas-filled tube, with two pieces of metal inside it.
Radiation consists of particles traveling at high speeds and energy waves, and together, these excite the gas molecules inside the Geiger counter’s tube when they pass through it.
The excited gas molecules set up an electrical current between the two pieces of metal inside the tube. The metal is attached to an amplifier and a meter, which increase and read the current. The strength of the current shows the strength of the radiation. The current also sets off the clicking sounds the Geiger counter makes when it finds radioactivity.
Since a Geiger counter reads only radioactivity, it cannot be used to find metals such as gold or silver, which aren’t radioactive. It can be used, though, to find uranium.