Determination of detection efficiency curves of HPGe detectors on radioactivity measurement of volume samples

An efficiency calibration method has been developed to measure radioactivity of volume samples with HPGe detectors. The method has two main procedures. One is a point-source calibration at a representative point near the detector. The position of the representative point is determined by Monte Carlo simulations. The other is correction for absorption by a sample matrix and a sample container. This paper presents application of the method for obtaining efficiency curves for volume samples in the energy range from 22 to 1836 keV. In addition to the standard volume sources of cement and water matrices, measurement was made with some kinds of environmental samples that are often used in environmental monitoring for radiation control works. The composition of the environmental sample was determined by elemental analysis. For these samples, measured absorption correction factors were compared with those by the Monte Carlo simulations. As a result, detection efficiency curves were obtained with good accuracy for variety types of volume samples.