The effect of grid misalignment on the uniformity of response of gas proportional scintillation counters

Abstract

In the present work we revisit the simplifying assumptions of an earlier theoretical treatment on the effects of grid misalignment on the performance of a planar gas proportional scintillation counter (GPSC). We present new experimental and computational results to establish the dependence of the effects of misalignment in terms of the reduced electric field in the scintillation region, the finite size of the electron cloud, and the solid angle subtended by the photosensor. It is shown that solid angle effects will offset to some degree the effects of grid misalignment in an optimized detector. For the reduced fields normally used in the scintillation region of an optimized GPSC (5 V cm -1 torr-1), misalignments as large as 3% have less than a 2% effect on pulse-amplitude variations. This effect is less than the statistical fluctuations in the number of primary electrons nominally produced in the absorption of X-rays in the 1- to 6-keV energy region. For reduced fields closer to the scintillation threshold (1 Vcm -1 torr-1), 15% variations in pulse amplitudes are possible, although it is unlikely that a GPSC would be operated under such unfavorable conditions