Efficiency Determination of a BEGe Detector for Complex Environmental Geometries: Experimental Measurements, LabSOCS Modelling, and MCNP Simulations

Abstract

High-purity germanium detectors are widely used in gamma-ray spectrometry. Due to their excellent energy resolution, the measurement of naturally occurring radiation material (NORM) and application to environmental samples requires accurate knowledge of the full-energy-peak efficiency over a broad energy range. In order to extract the accurate source activity values. Direct experimental calibration at high energies, such as the 2614keV line from 208Tl, is often not feasible due to the absence of suitable reference sources and the complex geometry of real samples. This work investigates the determination of absolute detection efficiencies for a Broad Energy Germanium (BEGe) detector using three comple mentary approaches: experimental calibration, Monte Carlo simulation with MCNP, and semi-empirical modelling with LabSOCS. Efficiency data were collected with the BEGe detector using standard radionuclide sources (57Co, 137Cs, 60Co, 88Y) in point and Marinelli geometries. These measurements were compared with effi ciency curves generated by LabSOCS and MCNP under identical conditions. Simulations were then extended to complex geometries, including environmental soil and geological core samples, where direct calibration was not possible. The results demonstrate that LabSOCS provides efficiency predictions in reasonable agreement with experiment within 10–20% for most energies above 300 keV, while MCNP simulations require careful refinement of detector and source geometry to converge with both LabSOCS and experimental data. The study concludes that validation at intermediate source-to-detector distances (5–10 cm) is essen tial for ensuring model reliability. Once validated, the combined use of LabSOCS and MCNP allows the extrapolation of efficiencies to the 2614keV gamma line of 208Tl and supports accurate activity determinations in environmental samples with complex geometries.