New Developments in Gas-Filled Image Intensifier Detectors for X and Gamma Rays

In spark operation, with short-circuit electronics having a triggering delay of ⩽ 40 ns and yielding a peak current of 15 amperes, the detector, which is filled with xenon (720Torr) and diethylamine (40 Torr) has a counting plateau equal to 4% of the mean operating voltage. The electronic short-circuit is more effective when diethylamine replaces methylal. It is shown that this vapour produces a delay in the triggering of the spark. The life is improved. Study of electron avalanches has shown that, in the case of detection of X-rays of a mean energy of 27 keV, the number of carriers which they contain may reach 108 and that the probability is then less than 10-4 for triggering sparks. These avalanches also make it possible to obtain completely proportional amplitude spectra of excellent resolution (9% for 27 keV). When the detector is used in avalanche operation, the light emitted by the latter enables an image of the X-ray emitting source to be recorded. The quantity of light emitted can be increased by increasing the number of carriers in the avalanche but at the risk of creating a spark. This risk is eliminated by a short-circuit system similar to that operating for spark conditions but with a triggering threshold corresponding to about 105 electrons. The possibility of using this detector for recording X-ray diffraction patterns on biological molecules is discussed.