Xenon-neon gas proportional scintillation counters: Experimental and simulation results

When gas proportional scintillation counters (GPSC) are used to detect very low energy x rays, the addition of the light noble gas neon to the usual x enon filling improves the collection of primary electrons that originate ne ar the detector window. However, xenon-neon mixtures have lower electrolumi nescence yields than pure xenon. Increasing the scintillation electric fiel d jeopardizes the energy resolution because of the additional fluctuations introduced by electron multiplication. In this work we investigate the effe ct of a limited amount of charge multiplication on the electroluminescence yield and the energy resolution R of a xenon-neon GPSC using both Monte Car lo simulation and experimental measurements. We consider xenon-neon mixture s with 5%, 10%, 20%, 30%, 40%, 50%, 70%, 90%, and 100% Xe at a total pressu re of 800 Torr. Comparing the experimental and Monte Carlo data for 5.9 keV x rays, we conclude that optimum value of R is reached in a region of weak ionization with a charge gain of less than 2. By extrapolating the experim ental results for R to infinite light yield we obtain the intrinsic energy resolution R-int for 5.9 keV x rays in all mixtures. From these results we can predict Fw values, where F is the relative variance in the number of pr imary electrons (the Fano factor) and w is the mean energy required to prod uce a primary electron. From a comparison between Monte Carlo and experimen tal electroluminescence yields, F and w values are estimated for 5.9 keV x rays in the various mixtures. (C) 1999 American Institute of Physics. [S002 1-8979(99)08509-6].