EFFECT OF GRID MISALIGNMENT ON THE UNIFORMITY OF RESPONSE OF GAS PROPORTIONAL SCINTILLATION-COUNTERS

In the present work we revisit the simplifying assumptions of an earli er theoretical treatment on the effects of grid misalignment on the pe rformance of a planar gas proportional scintillation counter (GPSC). W e present new experimental and computational results to establish the dependence of the effects of misalignment in terms of the reduced elec tric field in the scintillation region, the finite size of the electro n cloud, and the solid angle subtended by the photosensor. It is shown that solid angle effects will offset to some degree the effects of gr id misalignment in an optimized detector. For the reduced fields norma lly used in the scintillation region of an optimized GPSC (5 V cm(-1)t orr(-1)), misalignments as large as 3% have less than a 2% effect on p ulse-amplitude variations. This effect is less than the statistical fl uctuations in the number of primary electrons nominally produced in th e absorption of x-rays in the 1- to 6-keV energy region. For reduced f ields closer to the scintillation threshold (1 V cm(-1)torr(-1)), 15% variations in pulse amplitudes are possible, although it is unlikely t hat a GPSC would be operated under such unfavorable conditions.