Large-window gas proportional scintillation counter with photosensor compensation

New methods are presented that allow the design of non-focused gas proportional scintillation counters (GPSC) with window areas that approximate the photomultiplier window area. These methods are alternatives to a previously reported technique that uses a non-uniform electric field produced by a curved grid to compensate for the radial decrease of the scintillation light collected in the photosensor due to solid angle and reflection effects. The present work reverts to a uniform electric field and compensation is achieved with a mask with a radially-decreasing density of opaque dots that are deposited onto the window of the photosensor. The variation in the density of opaque dots is calculated to produce radially-independent light collection in the photosensor. An implementation of this new design is presented for a 52-mm-diameter photomultiplier tube with a 46-mm-effective diameter. The variation in pulse amplitude as a function of radial position was observed to be reduced from 18% to only 3.5% over the area contained within the central 19 mm radius. For a 38-mm-diameter window, the energy resolution for 5.9 keV X-rays was improved from 18% to 10% with the addition of the compensating mask