Testing and Characterization of Detection Plane Elements of the XGIS Instrument on Board the THESEUS Mission

This paper presents the procedures employed for experimental functional and performance characterization of a 2 × 2 pixel prototype detection system tailored specifically for the X and Gamma-ray Imaging Spectrometer (XGIS) instrument onboard the THESEUS mission. The XGIS system comprises of two coded masked wide field cameras integrated with monolithic SDDs (Silicon Drift Detectors) and CsI:Tl (Thallium doped-Cesium Iodide) scintillators, contributing to its broad X and 𝛾 -ray detection range. Given the space instrumentation complexity, thorough requirement qualification and testing procedures are essential. This work focuses on working principle, the testing setup utilized, and observed performance for the small scale four-pixel XGIS prototype. Furthermore, the alignment of light output performance of the four-pixel SDD and scintillator prototype detection system with the XGIS instrument requirements is emphasized.