Study on the detection efficiencies of liquid 99Tcm, 131I, and 18F in a well-type NaI(Tl) gamma spectrometer

To assess the detection efficiencies of liquid radioisotopes in a well-type NaI(Tl) gamma spectrometer, focusing on the short-lived isotopes 99 Tc m , 131 I, and 18 F. The detection efficiencies of liquid 99 Tc m , 131 I, and 18 F in a well-type NaI(Tl) gamma spectrometer were systematically investigated through calibration experiments and Monte Carlo simulations, and accounting for the coincidence-summing effect. The results indicated that the detection efficiencies of 99 Tc m , 131 I and 18 F varied from 64.4% to 72.3%, 34.8% to 43.1% and 27.3% to 28.5% for different sample volumes ranging from 15 mL to 80 mL, respectively. The simulated detection efficiencies were highly consistent with the experimental results, with a largest relative deviation of 5% for the 3 radionuclides and 4 different sample volumes. The consistent results between the calibration experiments and Monte Carlo simulations reveal that this measuring device possesses high detection efficiencies of 99 Tc m , 131 I and 18 F, making it suitable for measuring low-level activity radioactive liquids, such as radioactive waste liquids to be discharged.