BACKGROUND IN XENON FILLED X-RAY-DETECTORS

Xenon based gas mixtures have been often used in proportional counters for X-ray astronomy in order to achieve a good efficiency in the medi um/high X-ray energy range. Proportional counters flown on past missio ns (i.e. HEAO1 and EXOSAT) filled with Xe-based mixtures have shown a higher residual background (after that all the rejection techniques ha ve been applied) with respect to Ar-based ones, operating in the same energy band and in the same radiation environment. We show, by means o f Monte Carlo simulations, analytical computations and laboratory meas urements, that such difference can be mostly understood in terms of hi gher internal background production and lower pulse discrimination eff iciency in Xe-based gas filling, with respect to Ar-based ones.