The application of the curved-grid technique in a gas proportional scintillation counter with a small-diameter photo-multiplier tube

The curved-grid technique was developed to maintain the superior performance of large-area gas proportional scintillation counters (GPSCs) without resorting to complex and bulky focusing systems or large photomultiplier tubes (PMTs) for applications in energy-dispersive X-ray fluorescence analysis. The technique is a simple method to compensate for the variation in solid angle viewed by the PMT as a function of the radial distance from the cylindrical axis of the detector. The feasibility of the technique is demonstrated in a GPSC, by measuring the energy resolution as a function of entrance window diameter. With a properly shaped curved grid, no degradation in detector energy resolution is observed even when the effective detector sensitive area is increased approximately six-fold. The maximum ratio of detector entrance window to PMT diameter achieved thus far is approximately 0.75.