Geiger - Müller counter

This device was invented by the German physicist Hans Wilhelm Geiger in 1913 and it was perfected by Walther Müller in 1928. It is used to detect and measure radioactivity. It is made of a metallic cylinder that contains a rarefied gas and a collector to which is applied a high potential difference. When an ionising particle crosses the tube, it produces a brief electrical shock that is amplified and indicated by the device.