Feasibility study of tRAYcy-based efficiency calibration and transfer methods for HPGe gamma-ray spectrometry

This study evaluated the feasibility of using the Monte Carlo-based tRAYcy software for efficiency calibration and efficiency transfer in high-purity germanium (HPGe) gamma-ray spectrometry. Detection efficiencies were simulated employing both tRAYcy and MCNP6 for two Marinelli beaker geometries, 450 and 1000 mL, and were compared with experimental measurements obtained from certified multi-nuclide reference sources. Efficiencies simulated with tRAYcy showed good agreement with those generated using MCNP6, with average absolute relative differences of 5.3% and 7.3% for the 450 mL and 1000 mL geometries, respectively. Detector-parameter optimization within tRAYcy further improved agreement with experimental data, reducing the average absolute relative differences from initial values of approximately 12% to 5.2% and 5.7 % for the 450 mL and 1000 mL geometries, respectively. The efficiency transfer method estimated the efficiency of a target geometry by scaling an experimentally calibrated reference efficiency using the ratio of simulated efficiencies between two geometries. In this study, the 450 mL geometry served as the reference for deriving the 1000 mL efficiency. The transferred efficiencies obtained with tRAYcy agreed with direct experimental measurements, with an average absolute relative differences of 0.80%. Validation using proficiency test samples showed that the activity concentrations derived using the tRAYcy-based efficiency transfer agreed with the certified reference values within approximately 6.5%, except for ¹⁵²Eu. A zeta-score (ζ) evaluation showed acceptable agreement (|ζ| ≤ 2) for most radionuclides, whereas ¹⁵²Eu exhibited values marginally exceeding 2. These results indicate that tRAYcy is a practical tool for routine efficiency calibration and transfer in HPGe gamma-ray spectrometry.