A Geiger counter measures ionizing radiation. Geiger counters can used to detect alpha and beta but not gamma radiation or neutrons. Due to the fact that the density of the gas is so low, it is unlikely that a gamma photon will interact with the gas in a GM tube, hence the GM tube is very insensitive to gamma rays. A much better device for detecting gamma rays is a sodium iodide scintillation counter . The window on the scintillation counter is too thick to allow beta particles to enter the detector. It is vital that the correct detector is chosen for the radiation which is to be tested for.
The sensor is a Geiger-Müller tube, a gas-filled tube that briefly conducts electricity when a particle or photon of radiation briefly makes the gas conductive. The instrument amplifies this signal and displays it to the user, either as a current measurement (needle, lamp) or an audible click (one click for each single particle).
Hans Geiger developed the Geiger counter in 1908 together with Ernest Rutherford. This counter was only capable of detecting alpha particles. In 1928 Geiger and Walther Müller (a PhD student of Geiger) improved the counter so that it could detect all kinds of ionizing radiation. The current version of the Geiger counter is called the halogen counter. It was invented in 1947 by Sidney H. Liebson (Phys. Rev. 72, 602–608 (1947)). It has superseded the earlier Geiger counter because of its much longer life and lower operating voltage.
The Geiger-Müller tube is one form of a class of radiation detectors called gaseous detectors or simply gas detectors. Although useful, cheap and robust, a counter using a GM tube can only detect the presence and intensity of radiation.
Gas detectors with the ability (due to their construction, gas filling, and associated electronics) to both detect radiation and determine particle energy levels are called proportional counters. Some proportional counters can detect the position and/or angle of the incident radiation as well. Some of these have many internal wires and electrodes and are called multi-wire proportional counters or simply MWPCs, and have been used extensively in nuclear physics/medicine, particle physics, astronomy and in industry.
Other devices detecting radiation include: ionisation detectors, dosimeters, photomultiplier, semiconductor diode detectors and variants including CCDs, microchannel plates, scintillation counters, solid-state track detectors, cloud chambers, bubble chambers, spark chambers, neutron detectors and microcalorimeters.
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