A computational analysis of intrinsic detection efficiencies of Geiger–Mueller tubes for photons

A new calculation of the intrinsic detection efficiency of the Geiger–Mueller tube (GM tube) for photons is presented. It is found by the calculation that the relation between the efficiency and incident photon energy depends on the cathode materials and thicknesses. For a bare GM tube with the lead cathode of 20 mm in inner diameter, the 0.1 mm thick cathode wall is sensitive in lower photon energies, while 1 mm thick one works sensitively in the higher energy region. On the other hand, the 0.2 mm tube has flat sensitivity over a wide energy region between 0.3 and 3 MeV. For the GM tubes with lead, tin, and copper cathodes whose wall thicknesses are selected as having flat sensitivity, while the efficiency decreases with decreasing atomic number of the wall metal, flat regions extend to lower photon energies. The detection efficiencies of GM tubes with a sheath or a probe (sheathed GM tube) are discussed.