Study of high-pressure xenon gas scintillation drift chambers with wave-shifting fiber and CsI photocathode readouts

We are studying high pressure (20 atmospheres) xenon gas scintillation drift chambers for use in hard x-ray astronomy. These detectors combine the concepts of the gas scintillation proportional counter and the time projection chamber, with the scintillation light read out using waveshifting fibers or plane parallel proportional counters with CsI photocathodes. We have operated both a small technical prototype and a large flight prototype chamber. The CSI photocathodes have consistently given quantum efficiencies near 30% for the detection of xenon scintillation light and plane parallel proportional counters filled with methane have provided gains better than 106. The small GSDC with a CsI readout has a measured energy resolution of 6.0% FWHM at 30 keV, within about a factor of two and a half of the ultimate resolution obtainable in the device. The resolution is currently limited by spread of the incident x-ray beam causing a variable fraction of scintillation light to be observed for each event. We report on the development status of this technology.