Yuanzineng kexue jishu (Oct 2023)
Simulation of Small-amplitude Pulse Counting Loss Correction in Gas Radioactivity Measurement Based on Geant4
Abstract
In the absolute measurement method of nuclide radioactivity by the internal gas proportional counter, the reasonable correction of the small pulse counting loss is the key to accurately obtain the measurement results. During the activity measurement of radionuclides, counting loss from low-energy β-ray and wall effects can generally be corrected by extrapolating the energy deposition spectrum, changing the working gas pressure, and using Monte Carlo simulations or theoretical calculations. Considering the decay type and energy of radioactive gas nuclides, the influence of the low-energy β-ray and the wall effect counting loss on the activity measurement results is also different. To this end, three typical radioactive gas nuclides 37Ar, 3H and 85Kr were used to study the cause of counting loss based on the Geant4 simulation. According to the simulated particle decay characteristics and energy ranges, the physical process package FTFP_ BERT built in Geant4 was selected. The results show that the counting loss of small pulse in the activity measurement of 37Ar mainly comes from the wall effect generated by X-ray. Within the given gas pressure of 60-300 kPa, the simulated wall effect correction factors are 1063-1021, and the counting loss of the wall effect can be completely corrected by extrapolating the pressure and detection efficiency. The decay energy of β-ray generated by 3H is very low, and there is no obvious wall effect. The small pulse counting loss mainly comes from the low-energy β-ray contribution with the energy below the counting threshold, which can be corrected by extrapolating the β energy spectrum at a lower counting threshold (below 1 keV). For 85Kr nuclide, the small pulse count loss is mainly due to the wall effect of high-energy β-ray, and it can’t be completely corrected only by the extrapolation correction of β energy spectrum. In addition, the wall effect correction factors were also simulated in this paper. Below the threshold 1 keV at the pressure of 60-300 kPa, the results are 1017-1005, and the correction factors decrease as the counting threshold decrease.
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