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Overview

In the focal plane of the X-ray mirror assembly two redundant position sensitive proportional counters (PSPC) are available. These are multiwire proportional counters with a cathode strip readout scheme for position determination. Both spectral and spatial resolution increase with increasing energy. X-rays penetrate into the counter volume through a polypropylene entrance window additionally coated with carbon and lexan (to decrease UV transmission). A filter wheel with four positions is mounted in front of the detector. The open and closed filter wheel positions are used for ``standard'' observations and for monitoring of particle background; the third position is used for spectral calibrations, while the fourth position contains a boron filter. The insertion of the boron filter into the optical path allows an increase of spectral resolution at lower energies. The full two degree field of view of the XMA can be utilized in conjunction with the PSPC. Table 4.2  gives a tabular summary of the PSPC performance characteristics.

 

Window size 8 cm (diameter) Field of view

Gas mixture 65 percent argon 15 percent methane 20 percent xenon Operating pressure

energy resolution 43 percent at 0.93 keV spatial resolution Entrance window

Support grid transmission 72 percent (on average)