An ellipsoidal grid gas proportional scintillation counter

Abstract

Gas Proportional Scintillation Counters using curved grids for solid angle and reflection compensation have been described in the recent literature. They allow large radiation windows with diameters of 25 mm keeping at the same time the good energy resolutions characteristic of those X-ray detectors. However, the grids used have a spherical curvature, which does not correspond to the optimal curvature. In the present work we have calculated by computer simulation an improved shape for the curved grid. This shape can be well fitted to an ellipsoid of revolution, with a large eccentricity. A detector was designed with such an ellipsoidal grid and a radiation window 40 mm in diameter, filled with pure xenon at 927 Torr coupled to an EMI D676QB VUV photomultiplier tube having a 2'' diameter window. For the experiments envisaged, detection of solar X-rays in the 20-80 keV energy range, a 7 cm thick drift region was used, leading to efficiencies from 80% to 20%, respectively. Such a thick drift region reduces the performance mainly for soft X-rays. For 22 keV X-rays the energy resolution obtained, for a broad X-ray beam entering the full 40 mm diameter detector window, is 6.0%. Results are presented showing the variation of the energy resolution with the window diameter and a performance, for ellipsoidal grids superior to that for spherical grids. A discussion of the results obtained is presented.