Name an instrument used to detect radioactivity - Leaving Cert Physics - Question (i) - 2008

The principle of operation of the GM tube is based on ionization. When ionizing radiation passes through the gas inside the tube, it ionizes the gas molecules, creating positive ions and free electrons. This creates ion-pairs. The resulting free electrons are attracted to a positively charged electrode, resulting in an electric current. This current is then amplified and can be counted, giving a measure of the radioactivity.