Geiger counter

A Geiger counter detects ionising radiation that human senses cannot perceive. During the visit, the guide explains how the instrument works and how to read its measurements. The demonstration also covers the difference between a counter and a spectrometer. Both instruments are used to study radiation, but they provide different information.

A typical counter detects radiation using a gas-filled tube. Radiation causes ionisation inside it, creating charged particles. The electronics register the resulting pulses. A display can show their number, while a counter with its speaker switched on produces characteristic clicks. The counter records events but does not determine the precise energy of the radiation it detects. A spectrometer can provide that analysis.

The instrument can also register events away from an exhibit because natural background radiation is present in the environment. Its sources include rocks and cosmic radiation. A single click therefore does not mean that uranium ore has been found. A reading needs to be considered against the usual background at that location. During the demonstration, notice the difference between detecting radiation and identifying its source: a simple counter cannot independently identify the substance responsible for the reading.