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Assessment of the inactive dead layer thickness of old high-purity germanium detector: A study by Monte Carlo simulations and experimental verification

High-purity germanium (HPGe) detectors are commonly used for high-resolution gamma spectrometry. A HPGe detector considered for this study was in continuous operation for the past 15 years in our laboratory. The performance of the detector system has been monitored periodically using energy and efficiency calibration data. It is observed from the experimental efficiency calibration that there is a reduction in absolute efficiency of the detector for practical geometries after long period of operation. The main reason for this reduction in efficiency is due to increase in inactive Ge dead layer thickness of the detector. A study has been carried out using Monte Carlo techniques to assess the dead layer thickness of the detector after 15 years of operation and compared with the value quoted by the manufacturer while procuring the system and find out how much the dead layer thickness of the detector has varied from the manufactured value. The study shows that dead layer thickness has increased from 0.5 to 1.028 mm.