X-ray proportional gas detectors are used in X-ray diffraction and X-ray fluorescence and emission analysis. The amplitude of the electrical pulses produced by these detectors is directly proportional to the energy of the incident X-rays. In most instances, the energy of the incident photons will be utilized completely in producing photo-ionization in the outermost shells of the detector atoms. If the energy of these photons is greater than the absorption edge of the atoms in the detector, a certain fraction of them will produce photo-ionization of an inner shell. This in turn results in the production of a characteristic X-ray. If this characteristic X-ray is absorbed by the detector, then the original X-ray may still be considered to have deposited the whole of its energy within the detector. In this case the amplitude of the detector output pulse will be the same as if the original X-ray photon had been absorbed entirely by photo-ionization of the outer shells. Because of the relatively low absorption of a detector for its own characteristic radiation, there is a significant probability that the detector characteristic X-ray will escape from the detector without producing further photo-ionization.