Silicon photodiodes as the VUV photosensor in gas proportional scintillation counters

The application of recently developed VUV silicon photodiodes as a replacement for the standard photomultiplier tube (PMT) in a gas proportional scintillation counter (GPSC) is investigated. A photodiode positioned within the gas envelope would result in a GPSC that is more compact, robust, and simpler to operate. At the 170 nm wavelength of the scintillation light from xenon, UV photodiodes achieve an effective quantum efficiency of 72%, better than the typically 20% figure for PMTs. On the other hand, the lack of amplification in the photodiode readout limits the signal-to-noise ratio that can be achieved. A GPSC based on a silicon photodiode with an active area of 100 mm/sup 2/ and no additional amplification stage achieved energy resolutions of 20.5, 14.5 and 13.4% for 5.9, 22.1, and 59.6 keV X-rays, respectively. Signal noise in the low energy limit extends up to approximately 3 keV.