Basic characteristics of X-ray polarimeter using Microstrip Gas Proportional Counter

We have been developing an X-ray polarimeter employing MSGC (MicroStrip Gas Proportional Counter) in the energy range from 20 keV to 40 keV. Primary electron clouds produced by photoelectric absorption spread to the direction of the electric vector of incident polarized X-rays. It is possible to obtain the information on the polarization vector of incident X-rays by counting the number of anode strips with the signal due to electron cloud. We considered a wiring for the MS-plate anodes grouped by an appropriate spacing as a simple signal readout system for MSGC. To optimize the spacing, the extent of electron cloud spreading was experimentally investigated and was simulated with the computer simulation code modified EGS4. Moreover, an optimum pitch between anode strips was simulated for polarized X-rays incoming to MS-plate. For the X-rays in the energy range from 20 keV to 40 keV, the optimum spacing and pitch are 20 mm and 0.2 mm for the grouping and for the anode strips, respectively