Establishment of HPGe detector efficiency for point source including true coincidence correction

Abstract

Due to the variation of the activity levels of various samples in γ-ray spectroscopy, the source-to-detector distance is not fixed at a constant value. This means that the measurements of the absolute detector efficiency must be carried out for each geometrical arrangement used in γ-ray measurements, which is difficult and non-feasible. This work established a method to calibrate an HPGe detector using only one precise efficiency curve obtained experimentally at a reference source-to-detector distance and a simple computer program to extract the resulting efficiency curves at other distances. The validity of the computed efficiencies for various detector geometries was checked against published calculation and simulation results. The disagreements were <1% for the calculations and <2.7% in the case of simulation results except for one case with a 9% discrepancy. The results obtained with this method were also checked against efficiency curves measured experimentally at different source-to-detector distances using 10% and 50% p-type HPGe detectors with single and multi γ-ray emitters. The results of this method are in good agreement with that carried out by single γ-ray emitters. The disagreement was <2.2% and 4.7% for the 50% and 10% HPGe, respectively. The experimental results with multi γ-ray radionuclides were found to disagree with those obtained using the established method at small source-to-detector distances. A computer program was used to estimate the γ–γ true coincidence correction factor to eliminate this disagreement. For multi γ-ray emitters the disagreement after true coincidence correction was found to be <10% and <6% at small source-to-detector distances for the 50% and 10% HPGe, respectively. The maximum values were <3% and <5% at large distances (⩾11.5 cm) in the case of the 50% and 10% HPGe, respectively.