过筛粒径及平衡时间对γ能谱仪测量土壤中放射性核素的影响

目的 研究土壤样品过筛粒径和平衡时间对测量放射性核素的影响，提高γ能谱仪测量土壤样品中放射性核素比活度的准确性。方法 将采集的土壤样品干燥后分成4份，分别经过2.0 mm、1.0 mm、0.5mm 和0.25 mm过筛粒径处理后装入样品盒中密封，然后分别在密封0、4、8、12、16、21、25 和 29 d后，使用高纯锗γ能谱仪测量土壤中²²⁶Ra、²¹⁰Pb、²²⁸Ra、⁴⁰K和¹³⁷Cs的比活度并进行比较。结果 不同平衡时间间隔测量的土壤样品中²²⁶Ra、²¹⁰Pb和²²⁸Ra比活度的变异系数范围为0.9% ～ 4.3%，不同过筛粒径土壤样品中²²⁶Ra、²¹⁰Pb、²²⁸Ra、⁴⁰K和¹³⁷Cs的比活度的变异系数范围为3.7% ～ 14.1%。结论 用γ能谱仪测量土壤中放射性核素的比活度时，须考虑过筛粒径对测量结果的影响，且其影响程度高于平衡时间。研究结果在提高利用γ能谱仪准确测量土壤样品中放射性核素比活度方面具有重要意义。

Effects of sieved particle size and equilibration time on the measurement of radionuclides in soil by gamma-ray spectrometer

Objective The effect of sieved particle size and equilibration time of soil samples on the measurement of radionuclides was studied to improve the accuracy of the specific activity of radionuclides in soil samples measured by gamma spectrometer.Methods The collected soil samples were dried and divided into four parts. After sieved with width of the mesh 2.0 mm, 1.0 mm, 0.5 mm and 0.25 mm respectively, they were filled into sample containers and sealed. The activity concentrations of ²²⁶Ra, ²¹⁰Pb, ²²⁸Ra, ⁴⁰K and ¹³⁷Cs in different sieved soil samples were then measured at the sealed interval of 0, 4, 8, 12, 16, 21, 25 and 29 days by HPGe gamma-ray spectrometry respectively.Results The coefficients of variation ofthe specific activities of ²²⁶Ra, ²¹⁰Pb, and ²²⁸Ra in soil samples measured at different equilibration intervals range from 0.9% to 4.3%. The coefficients of variation of the specific activities of ²²⁶Ra, ²¹⁰Pb, ²²⁸Ra, ⁴⁰K and ¹³⁷Cs in soil samples with different sieved particle sizes range from 3.7% to 14.1%.Conclusion When the specific activities of radionuclides are determined by gamma-ray spectrometer, the effect of the sieved particle size on the measurement result must be considered, and its impact is higher than the equilibration time. This study is very useful for improving the accuracy of the determination of radionuclides in soil sample using gamma-ray spectrometer.