Investigation of the effect of copper contact pin on efficiency in HPGe detectors using Monte Carlo method

The full energy peak efficiency (FEPE) determined by experimental or Monte Carlo (MC) simulation methods is a very important parameter in HPGe detectors. Since FEPE depends on the detector's geometric parameters, the parameters provided by the manufacturer are of great importance in modeling the detector with the MC method. The most important reason for the discrepancy between MC and experimental calculations is the lack of accurate information about the detector's geometric properties. The thickness of the copper contact pin in the middle of the detector hole is not given by the manufacturer. In this study, the effect of copper contact pin thickness on detector efficiency was investigated by using the PHITS 3.24 MC simulation program both at different copper contact pin radii and at different detector-source distances. The efficiency values were calculated for photons in the energy range of 59.5 keV-1408 keV, at 4 different distances, namely 5 cm, 13.25 cm, 15 cm, and 20 cm and for the radii of copper contact pins increased from 1 mm to 3.5 mm at 0.5 mm intervals. According to the results, it has been determined that the presence of copper contact pins causes a change in detector efficiency up to 1.9%, especially in the high energy region, and has no effect on the detector efficiency in the low energy region. In addition, it has been observed that the effect of copper contact pin thickness on detector efficiency is almost independent of the source-detector distance.