Basic Principle of Operation
A Geiger counter detects ionizing radiation (such as alpha particles, beta particles, and gamma rays) through a sensor called a Geiger-Müller tube. This tube contains an inert gas, often argon or neon, at a low pressure. When an ionizing particle or photon enters the tube, it collides with the gas atoms, knocking electrons free and ionizing them.
The Avalanche Effect
A high voltage is maintained across the Geiger-Müller tube, with a thin wire anode at the center and the tube's conductive wall acting as the cathode. The free electrons created by ionization are accelerated towards the anode. As they rush towards the anode, they collide with other gas atoms, causing further ionization in a rapid chain reaction known as an 'avalanche effect,' which generates a brief pulse of electrical current.
Signal Processing and Indication
Each electrical pulse generated by an avalanche is amplified by the counter's electronics. This amplified signal is then converted into an audible 'click,' a visible flash of light, or a numerical reading on a display screen. The frequency of the clicks or the numerical value directly corresponds to the intensity of the detected radiation, indicating how many ionizing events are occurring per unit of time.
Key Applications
Geiger counters are essential tools used in various fields for radiation safety, environmental monitoring, and geological surveys to locate radioactive materials. They are also used in educational settings to demonstrate principles of radioactivity and in nuclear medicine to detect radioactive tracers, providing a simple and immediate way to identify the presence of ionizing radiation.