HIGH-PRESSURE XENON PROPORTIONAL COUNTER UP TO 10 ATM

The characteristics of a conventional cylindrical geometry proportional counter filled with high pressure xenon gas up to 10 atm were investigated for use as a detector in hard X-ray astronomy. With a 2% methane gas mixture the energy resolutions at 10 atm were 9.8% and 7.3% for 22 and 60 keV X-rays, respectively. The corresponding resolutions at 1 atm were 7.7% and 5.1%. From calculations of the Townsend ionization coefficient it is shown that proportional counters at high pressure operate at weaker reduced electric field than low pressure counters. It is suggested that this is the fundamental reason for the degradation of resolution observed with increasing pressure.