An X-ray detector consisting of a chamber filled with a noble (i.e. unreactive) gas such as argon or xenon. Ionization of the gas by X-ray photons produces an avalanche of electrons. Atoms of gas excited by the avalanche emit an ultraviolet photon, producing a flash whose intensity is proportional to the energy of the X-ray. This technique gives an improved energy resolution compared with a conventional proportional counter.
Subjects: Astronomy and Astrophysics.