Improving Spectroscopic Performance of a Coplanar-Anode High-Pressure Xenon Gamma-Ray Spectrometer

High-pressure xenon (HPXe) gas is a desirable radiation detection medium for homeland security applications because of its good inherent room-temperature energy resolution, potential for large, efficient devices, and stability over a broad temperature range. Past work in HPXe has produced large-diameter gridded ionization chambers with energy resolution at 662 keV between 3.5 and 4% FWHM. However, one major limitation of these detectors is resolution degradation due to Frisch grid microphonics. Improved energy resolution using a detector with coplanar anodes as an alternative to a Frisch grid is reported in this submission. It is expected that a coplanar anode design has the potential to provide competitive energy resolution with minimal degradation from microphonics. Experimental data is presented, including an analysis of interaction location effects on the energy spectrum. The HPXe gas is doped with a small amount of H₂ gas to improve charge transport, and the results are compared with Geant simulations.