Silicon photodiodes as the VUV photosensor in gas proportional scintillation counters

The application of recently developed VUV silicon photodiodes as a replacem ent for the standard photomultiplier tube (PMT) in a gas proportional scint illation counter (GPSC) is investigated. A photodiode positioned within the gas envelope would result in a GPSC that is more compact, robust, and simp ler to operate. At the 170 nm wavelength of the scintillation light from xe non, UV photodiodes achieve an effective quantum efficiency of 72%, better than the typically 20% figure for PMTs. On the other hand, the lack of ampl ification in the photodiode readout limits the signal-to-noise ratio that c an be achieved. A GPSC based on a silicon photodiode with an active area of 100 mm(2) and no additional amplification stage achieved energy resolution s 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.