A large area gas proportional scintillation counter with a ring-shaped anode for x- and gamma-ray spectroscopy

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Abstract
Gas Proportional Scintillation Counters (GPSCs) are noble gas detectors in which the primary ionization charge generated by radiation interactions is amplified via electroluminescence (EL) in the gas. Under an external electric field, the primary ionization electrons drift into a region where the field exceeds the gas scintillation threshold. Compared to charge amplification via electron avalanches, EL amplification provides higher gain with improved signal-to-noise ratio, no space charge effects, and better immunity to radiofrequency noise and electrical discharges. GPSCs have been used in applications such as x-ray fluorescence analysis and x- and γ-ray astrophysics. Their high resistance to radiation damage, wide operational temperature range, simple yet flexible design, and large detection area capability are notable advantages. However, the solid angle subtended by the photosensor varies with the EL emission position, causing the detected signal to depend on the radiation interaction location. This limits the size of the detector's radiation window relative to the photosensor. To overcome these limitations, we recently proposed a novel and simple GPSC design that ensures a constant solid angle across the scintillation region. In this configuration, a single annular anode electrode, centered on the photosensor axis, defines a localized scintillation region near its surface. As a result, the entire region maintains a fixed solid angle with respect to the photosensor, making the EL signal independent of the interaction position. This design enables a large window-to-photosensor size ratio while maintaining uniform response. Previously, we developed a comprehensive simulation tool incorporating radiation absorption, electron drift, EL emission and light detection, which was validated against an annular-anode GPSC prototype. In this work, we use this simulation tool to explore the optimal geometrical parameters of the annular anode GPSC, aiming to balance energy resolution and the different parameters, mamely the detector window-to-photosensor radius ratio.

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