A new technique for quick identification of defective region inside γ-ray detector

Department of Nuclear and Atomic Physics Tata Institute of Fundamental Research, Mumbai 400005, India

^* biswajit.das@tifr.res.in

Published online: 21 November 2023

Abstract

The γ-ray detection efficiency of a detector decreases over time due to factors like radiation damage or an increase in the thickness of the inactive dead layer. For large γ-ray detector facilities, it is crucial to assess the health condition and performance of the inner regions of the detector crystals over time. In this study, we have introduced a method using GEANT4 simulation to detect defective regions within thick γ-ray detectors. In the experimental phase, a scanning setup was employed, comprising a single-crystal High Purity Germanium (HPGe) detector and a position-sensitive GAGG:Ce detector for coincidence measurements, using a ²²Na source. The 2D images were reconstructed from the front-face and side-face scans of the single-crystal coaxial HPGe detector, employing an energy gate set at 511 keV. A position gate applied to a specific section of those 2D images allowed for the mapping of γ-ray interactions along a conical path within the HPGe detector. The methodology involved the comparison and analysis of histograms generated from various sector gates, facilitating the identification of the defective region’s position. In the GEANT4 simulation, a defective region was defined within the crystal, and that was effectively represented in the corresponding scanned image, which exhibited reduced efficiency. It’s important to note that this method’s effectiveness is restricted by the absorption profile of the 511 keV γ-ray, limiting its applicability to a depth of approximately 4 cm from the surface of the HPGe crystal. However, this approach can offer a swift and convenient method for inspecting γ-ray detectors, making it a valuable tool for the detector industry.