Gas Mixtures
This can be such as helium, neon or argon (usually neon), in some cases in a Penning mixture, and an organic vapor or a halogen gas. The halogen G-M tube was invented by Sidney H. Liebson in 1947. The discharge mechanism takes advantage of a metastable state of the inert gas atom to more-readily ionize a halogen molecule, enabling the tube to operate at much lower voltages, typically 400–600 volts instead of 900–1200 volts. This type of G-M tube is therefore by far the most common form now. It has a longer life than tubes quenched with organic compounds, because the halogen ions can recombine while the organic vapor is gradually destroyed by the discharge process (giving the latter a life of around 108 events).
Read more about this topic: Geiger–Müller Tube
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