Monte Carlo simulation study on the cause of the formation of the efficiency curve at low energies in germanium detectors

Detector efficiency is a measure of the detectors' ability to detect radiation. It is known that the efficiency values, which are important and affect the activity calculation in germanium detectors, decrease rapidly at low energies. This study focuses on the reasons for this handicap in the low energy region of the efficiency curve. The Monte Carlo simulation was carried out with four setups: germanium only, germanium with a dead layer, germanium with aluminum holders, and finally germanium with a dead layer and aluminum holders. The effect of each setup on the efficiency curve was observed. As a result, it was seen that the main cause of the handicap was the dead layer. For this reason, it was concluded that the current value of the dead layer, which is known to change over time, should be taken into account in detector calibrations or characterizations. •The efficiency of HPGe detectors was questioned by PHITS Monte Carlo code.•The dead layer causes a rapid decrease in efficiency in the low-energy region.•Detector characterization should include a time-varying dead layer.