PROPORTIONAL-COUNTERS FOR THE STELLAR X-RAY POLARIMETER WITH A WEDGE AND STRIP CATHODE PATTERN READOUT SYSTEM

We describe the design and performances of the four imaging proportion al counters for the flight model of the Stellar X-ray Polarimeter (SXR P) to be flown on the Spectrum X-Gamma Satellite at the focus of the S ODART X-ray telescope. The SXRP will measure the linear polarization f rom celestial sources in an energy band between 2 and 15 keV. We descr ibe the design and the performance of the X-ray detectors with particu lar care to the design philosophy for a space-borne focal plane polari meter. Pie demonstrate;he use of a wedge and strip pattern as a cathod e which provides the desired position resolution in the whole energy b and with moderate power consumption and only three preamplifiers per d etector. The design, manufacturing techniques, and the performance of the wedge and strip position readout are described. Measurement of the background produced by impact of high-energy protons on different spe cies of the material used to build the detector are presented. Also, t he effect of high ionization charge density produced by end-of-range h igh-Z particles has been measured and the results are discussed. (C) 1 998 Elsevier Science B.V. All rights reserved.