EGS4 Monte Carlo simulation of a high-pressure xenon tube detector array

A detector for imaging /sup 99m/Te (140 keV) has been proposed consisting of a close packed array of high-pressure xenon proportional or ionization tubular detectors equipped with a thin entrance window at one end. Such tubes can safely operate to pressures of 60 atmospheres or higher with a very thin aluminum wall of 0.13 mm. However, losses are expected due to interstitial space, photoelectron impingement on the aluminum walls, and Compton interactions with aluminum. Therefore, an EGS4 Monte Carlo simulation was written to determine the 140 keV detection efficiency and energy spectrum produced in such an array of tubes having a fixed outer diameter of 4.8 mm and length of 50 mm. Detector efficiency and energy spectra were simulated at xenon pressures of 40, 50, and 60 atmospheres and for Al wall thicknesses varying from 0.025 to 0.36 mm. At the practical wall thickness of 0.13 mm, efficiency ranges from 47% at 40 atmospheres to 72% at 60 atmospheres and the energy spectra are minimally affected by secondary processes. Thus, high detection efficiency and quality energy spectra are achievable even with losses produced by the aluminum structure. Therefore, with the excellent energy resolution achievable with xenon such a detector can provide a competitive alternative to NaI.