A High Resolution Sealied Xenon Filled Position Sensitive Proportional Counter

Xenon filled imaging proportional counters enable X-ray Astronomy images to be obtained at higher energies than with Argon filled counters. Such a counter filled with Xenon/Methane (90/10) at 2 atmospheres pressure has been built. It has a sensitive area 9 cm × 9 cm and a FWHM position resolution of 360 microns. A very low noise readout system using pulse amplitude ratio, and a Graded Density Cathode, which has no resistive element, enables intrinsic counter resolution to be measured. Resolution appears to be limited by secondary avalanche effects rather than by diffusion, and is improved by use of faster pulse shaping if signal to noise in the electronic readout allows.