A gas-filled X-ray detector in which the electric potential is high enough for the gain to reach a value in the range from 10E2 to 10E5. Each electron produced by the initial photo-ionization causes one avalanche. Since the number of avalanche events is proportional to the energy of the incident photons, the charge collected by the anode is proportional to the X-ray photon energy.
PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1754 (https://doi.org/10.1351/pac199567101745)