Editing Geiger counter (section)

===Gamma and X-ray detection===
Geiger counters are widely used to detect [[gamma radiation]] and [[X-rays]], collectively known as [[photons]], and for this the windowless tube is used. However, detection efficiency is low compared to alpha and beta particles.
The article on the [[Geiger–Müller tube]] carries a more detailed account of the techniques used to detect photon radiation. For high energy photons, the tube relies on the interaction of the radiation with the tube wall, usually a material with a high [[atomic number]] such as [[stainless steel]] of 1–2&nbsp;mm thickness, to produce free electrons within the tube wall, due to the [[photoelectric effect]]. If these migrate out of the tube wall, they enter and ionize the fill gas.<ref name="knoll" />

This effect increases the detection efficiency because the low-pressure gas in the tube has poorer interaction with higher energy photons than a steel tube. However, as photon energies decrease to low levels, there is greater gas interaction, and the contribution of direct gas interaction increases. At very low energies (less than 25 [[kiloelectronvolt|keV]]), direct gas ionisation dominates, and a steel tube attenuates the incident photons. Consequently, at these energies, a typical tube design is a long tube with a thin wall which has a larger gas volume, to give an increased chance of direct interaction of a particle with the fill gas.<ref name="cent" />

Above these low energy levels, there is a considerable variance in response to different photon energies of the same intensity, and a steel-walled tube employs what is known as "energy compensation" in the form of filter rings around the naked tube, which attempts to compensate for these variations over a large energy range.<ref name="cent" /> A steel-walled Geiger–Müller tube is about 1% efficient over a wide range of energies.<ref name="cent">’’Geiger Muller Tubes; issue 1’’ published by Centronics Ltd, UK.</ref>