A SIMPLE METHOD TO IMPROVE THE SPATIAL UNIFORMITY OF VENETIAN-BLIND PHOTOMULTIPLIER TUBES

An improvement in the uniformity of venetian-blind photomultiplier tub es has been achieved by reducing the voltage difference between the fi rst and second dynodes. The method has been applied to a gas proportio nal scintillation counter (GPSC) instrumented with a venetian-blind ph otomultiplier (PMT). When exposed to a 20-mm collimated 5.9-keV x-ray beam, an overall improvement in energy resolution for the GPSC/PMT com bination from 20% to 11.5% was achieved. An alternative method that re duces the photocathode-to-first-dynode voltage was less effective and resulted in a severe degradation of detector energy resolution.