Characterization and selection of CZT detector modules for HEX experiment onboard Chandrayaan-1

We present the results of characterization of a large sample of Cadmium Zinc Telluride (CZT) detector modules planned to be used for the HEX (High Energy X-ray spectrometer) experiment onboard India's first mission to the Moon, Chandrayaan-1. We procured forty modules from Orbotech Medical Solutions Ltd. and carried out a detailed characterization of each module at various temperatures and selected final nine detector modules for the flight model of HEX. Here we present the results of the characterization of all modules and the selection procedure for the HEX flight detector modules. These modules show 5–6% energy resolution (at 122 keV, for best 90% of pixels) at room temperature which is improved to ∼4% when these modules are cooled to sub-0 °C temperature. The gain and energy resolution were stable during the long duration tests.