In gamma-ray spectrometry, the full energy peak efficiency can be determined by experimental, or by Monte Carlo (MC) simulation methods. In experimental methods, reference standard materials including a large number of gamma emitters or mixed gamma emitters in different geometries are requested to determine the efficiency curves. Besides, simulation by MC methods has advantages of modelling any geometries and energy range of interest. However, by simulation it is not easy to determine the efficiency curves due to the lack of information supplied from manufacturers. In this work, it is focused on the effect of dead layer thickness and other geometric parameters of detector crystal on the efficiency of the detector. The general-purpose MC code PHITS and specific-purpose MC code GESPECOR are used to simulate the detector. The experiments are performed by single gamma point sources at a 12.5 cm distance from the end cap of the detector. The results showed that the physical parameters of the detector are different from those provided by the manufacturer. After 15 years of operation of the detector, it is observed that the dead layer thickness increased from 0.7 mm to 1.29 mm. It causes a decrease in the efficiency by a reduction in the active volume of the detector. In addition, it is showed that the round shape of the front edge and bullet shape of the inner hole of the detector crystal have an undeniable effect on efficiency of detector especially for low energy photons. The study shows that the PHITS MC simulation program can be successfully used in obtaining efficiency calibration of HPGe detectors and determining the dead layer thickness.

在伽马射线光谱法中，全能量峰值效率可以通过实验或蒙特卡罗 (MC) 模拟方法确定。在实验方法中，需要使用包含大量不同几何形状的伽马发射器或混合伽马发射器的参考标准材料来确定效率曲线。此外，通过 MC 方法进行的模拟具有对任何感兴趣的几何形状和能量范围进行建模的优点。然而，由于缺乏制造商提供的信息，通过模拟很难确定效率曲线。在这项工作中，重点研究了探测器晶体的死层厚度和其他几何参数对探测器效率的影响。通用 MC 代码 PHITS 和专用 MC 代码 GESPECOR 用于模拟检测器。实验由距探测器端盖 12.5 cm 的单伽马点源进行。结果表明，检测器的物理参数与制造商提供的不同。探测器运行 15 年后，观察到死层厚度从 0.7 毫米增加到 1.29 毫米。它通过减少检测器的有效体积而导致效率降低。此外，研究表明，探测器晶体前缘的圆形和内孔的子弹形状对探测器的效率有着不可否认的影响，尤其是对于低能光子。研究表明，PHITS MC仿真程序可以成功地用于获得HPGe探测器的效率校准和确定死层厚度。