An ellipsoidal grid gas proportional scintillation counter

Gas proportional scintillation counters using curved grids for solid angle and reflection compensation have been described in the recent literature. T hey allow large radiation windows with diameters of 25 mm keeping at the sa me time the good energy resolutions characteristic of those X-ray detectors . However, the grids used have a spherical curvature, which does not corres pond to the optimal curvature. In the present work we have calculated by co mputer simulation an improved shape for the curved grid. This shape can be well fitted to an ellipsoid of revolution, with a large eccentricity. A det ector 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 tubs having a 2 " diameter window. For the experiments envisaged, detection of solar X-rays in the 20-80 keV energy range, a 7cm thick drift region was used, leading to efficiencies from 80% to 20%, respe ctively. 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 ar e presented showing the variation of the energy resolution with the window diameter and a performance, for ellipsoidal grids superior to that for sphe rical grids. A discussion of the results obtained is presented. (C) 1999 El sevier Science B.V. All rights reserved.