Analysis of background variations in low-background γ-ray spectrometer with lead shielding

Objective To study the variation in net count rates of natural radionuclides in background of gamma-ray spectrometer, so as to provide a scientific basis for reducing the effect of background fluctuations on sample measurement. Methods The unscheduled background spectrum obtained using two high-purity gamma-ray spectrometers during 2013-2017 were collected, and then the net count rates of 210Pb, 234Th, 212Pb, 214Pb, 208Tl, 214Bi, 228Ac and 40K were calculated and analyzed by aid of statistical method. Results There was a significant difference in the net count rates of 210Pb, 234Th, 212Pb, 214Pb, 208Tl, 214Bi, 228Ac and 40K in the background spectrum of gamma-ray spectrometer, and the net count rates of 214Pb, 214Bi and 40K was significantly higher than those of 210Pb, 234Th, 212Pb, 208Tl and 228Ac. There were no significant differences in the net count rates of these eight natural radionuclides from 2013 to 2017, respectively (P>0.05). However, the coefficients of variation in the net count rates for 214Pb and 214Bi were both greater than 50%. Conclusions When the activity concentration of natural radionuclides is determined in a sample by gamma-ray spectrometer, it is critical to subtract the background spectrum obtained recently to ensure the accuracy of the measurement, especially for the low activity concentration of natural radionuclide to be measured. Key words: Low-background gamma-ray spectrometer; Lead shielding; Natural radionuclides