The effect of two-part dead layer thickness on the efficiency curve of a P-TYPE HPGe detector calculated using the Monte Carlo method

Abstract

The full energy peak efficiency (FEPE) of a gamma ray obtained from experimental studies using a high purity germanium detector (HPGe) can be easily reproduced by simulating the experiment in any desired geometry and energy range with Monte Carlo (MC) simulation methods. However, the dead layer (DL) thickness, which is one of the geometric information provided by the manufacturer, changes over time and affects the efficiency calculation, so it must be determined and compared with the initial value for the increases during the life-time of the detector. In this study, the general-purpose MC code PHITS and the special-purpose MC code GESPECOR were used to simulate a p-type HPGe detector and to determine the thickness of the frontal and lateral dead layer. As a result, it was observed that the frontal dead layer thickness increased from 0.7 mm to 1.075 mm, and the lateral dead layer thickness increased from 0.7 mm to 1.7 mm after 7 years of operation of the detector. This increase in dead layer thickness causes both a decrease in the detector's active volume and a decrease in efficiency in the problematic low-energy region.