Reflective and semi-transparent CsI-photocathodes in microstrip plate gas chamber photosensors for gas proportional scintillation counters: a comparative study

We report the results of a comparative study of a Xe proportional scintillation counter instrumented with photosensors based on a microstrip plate. The photosensor is isolated from the gas proportional scintillation counter by a quartz window and is operated in P-10 gas at atmospheric pressure. The CsI-photocathode is operated either in the reflective or semi-transparent mode. In the reflective mode, the CsI-photocathode is deposited directly on the microstrip plate. Gain fluctuations due to a geometric factor, which degrade the energy resolution, are observed. In the semi-transparent mode the CsI-photocathode is deposited onto the surface of the quartz window resulting in two potential improvements: an increase in the number of photoelectrons produced in the photocathode and a reduction of geometry-related effects. Both modes of operation will be evaluated and their performance characteristics determined.