| Summary: | The performance for X-ray spectrometry of argon-xenon gas proportional scintillation counters (GPSCs) using a CsI-coated microstrip plate in direct contact with the scintillation gas as a vacuum ultraviolet photosensor is investigated for different argon-xenon mixtures. The GPSC/microstrip gas chamber hybrid detectors filled with argon-xenon mixtures present superior performance when compared to those with pure argon and pure xenon fillings. For these mixtures, the signal amplification due to the scintillation processes and the detector energy resolution may achieve values of 15-18 and 11-10%, respectively. The best energy resolutions can be achieved for mixtures with a broad range of xenon concentration, 20-70% Xe, and for lower reduced electric fields in the scintillation region as the xenon concentration is reduced. As in pure argon or pure xenon gas-filling, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the microstrip plate anodes. The best energy resolutions are achieved for positive feedback gains of about 1.1
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