样品厚度对实验室无源效率刻度技术测定~(137)Cs和~(210)Pb的影响

为评价样品厚度对实验室无源效率刻度(LabSOCS)测定环境放射性核素的影响,用LabSOCS技术对不同黄土样品厚度进行了模拟计算和实际测定对比。模拟计算的137Cs和210Pb的探测效率均随样品厚度呈对数函数关系下降(P0.001),当样品厚度从5 mm增至80 mm时,对137Cs和210Pb的探测效率分别减少68%和83%。样品厚度对LabSOCS技术测定137Cs和210Pb比活度的影响均不明显,但对137Cs的分析误差有明显的影响,对210Pb分析误差的影响较小,15 mm是影响LabSOCS技术测定137Cs和210Pb分析误差的临界样品厚度。这一结论对于提高LabSOCS技术测定土壤样品中137Cs和210Pb的分析精度具有指导意义。

Effect of Sample Thickness on Determination of ~(137)Cs and ~(210)Pb Using LabSOCS

In order to evaluate the extent of different sample thickness affecting the measurement of ¹³⁷Cs and ²¹⁰Pb in loess soil, a comparison between simulative calculation on detecting efficiency and actual measurements was conducted through using the Laboratory Sourceless Object Calibration Software (LabSOCS). An increase in the sample thickness results in a decline of the detection efficiency on ¹³⁷Cs and ²¹⁰Pb as shown a logarithm function (P<0.001). An increase in the sample thickness from 5 mm to 80 mm results in 68% and 83% reduction of the detection efficiency for ¹³⁷Cs and ²¹⁰Pb, respectively. The specific activities of ¹³⁷Cs and ²¹⁰Pb in samples determined through the LabSOCS do not change evidently with thickness, suggesting that the LabSOCS can eliminate or correct the effect on detection efficiency resulting from changes in sample thickness. The sample thickness, however, has a significant effect on the analysis precision of ¹³⁷Cs compared with a slight effect for ²¹⁰Pb. A 15 mm sample thickness can be considered as a critical thickness for significantly affecting the analysis precision of LabSOCS. This conclusion is of importance in improving the analytical precision of ¹³⁷Cs and ²¹⁰Pb in soil samples.