The Environmental Background in Gas-Filled Detectors for X Ray Astronomy

We present the results of a detailed study of the environmental background in gas-filled detectors for X-ray astronomy. A compilation of in-flight raw background count rates is presented. A number of possible components have been quantitatively assessed for several detectors, and are able to account for the observed background rate within -10%, also providing the observed majority of extended ionisation tracks. The energy spectrum of the raw background has been analysed, making it possible it estimate the spectrum for any detector. We also present the results of a similar analysis of the residual background which escapes the best extended track rejection systems. It is thus possible to optimise a detector design with respect to the environmental background.