A Simplified Method for HPGe Detector Efficiency Calibration Using Certified Reference Materials Containing Natural Radionuclides

Multinuclide calibration sources, consisting of mixtures of gamma-emitting radionuclides, are commonly used for detector efficiency calibration in gamma-ray spectrometry. While they enable fast and accurate calibration, they have certain drawbacks, such as high cost and relatively short usable lifespans. This paper presents a simplified and cost-effective method for the efficiency calibration of cylindrical high-purity germanium (HPGe) detectors, which relies on the use of certified reference materials containing natural radionuclides. The method is based on selected gamma lines from natural radionuclides that are practically unaffected by the true coincidence summing (TCS) effect, enabling reasonably accurate calibration for multiple measurement geometries at energies above 200 keV. The main limitation of the method is its applicability only to energies higher than 200 keV; however, this range is sufficient for most routine environmental measurements. Verification measurements conducted for cylindrical geometry showed that detector efficiency values obtained using the proposed method (with IAEA RGK, RGU, and RGTh certified reference materials) differed by less than approximately 4% from those obtained using a commercial multinuclide calibration source.