Evaluating the absolute efficiency of the TCS-172 gamma scintillation survey meter for 662 keV and 1250 keV gamma rays emitted from point sources

Abstract

In this study, McGregor’s analytical method was applied to calculate the absolute efficiency of the TCS-172 GSSM equipped with a 1 in. ´ 1 in. NaI(Tl) detector. Calculations were performed for 662 keV and 1250 keV gamma rays emitted from Cs-137 and Co-60 point sources, respectively. The calculated efficiencies were compared with experimental measurements conducted at different source-to-detector distances. The calculated data were fitted over 0.5–5.0 cm and evaluated at the experimental distances. The differences ranged from −7% to 6% for 662 keV and −9% to 6% for 1250 keV, with a maximum absolute difference of 9%. The results showed that the absolute efficiency decreases with increasing distance and is higher at 662 keV than at 1250 keV due to the greater interaction probability of lower-energy gamma rays in NaI(Tl). Good agreement was observed between the calculated and measured efficiencies, confirming the applicability of McGregor’s analytical method to the TCS-172 detector. The proposed approach provides a simple and rapid tool for estimating the absolute efficiency of portable NaI(Tl)-based gamma survey meters.