标准物质对HPGe γ谱仪测定环境放射性核素210Pb和137Cs的影响

为评价不同标准物质效率刻度对环境放射性核素测定准确性的影响，应用具有无源效率刻度（LabSOCS）功能的高纯锗（HPGe）γ谱仪，比较用褐土、黄壤、黄土和紫色土4种土类与供测试土壤栗钙土作为标准物质进行效率刻度获得的210Pb和137Cs比活度之间的差异。选用的5种土类为标准物质对测试土壤中210Pb测定的准确性有显著影响，这是由于标准物质中能够显著影响210Pb测定结果的一组元素Si、Fe和Na，尤其是Fe含量相对于测试土壤存在很大差异（相对差异在94％~166％之间）。不同标准物质对土壤中137Cs测定准确性的影响较小，这是由于不同标准物质中与137Cs比活度显著偏相关（P<0.01）的O和Na含量差异较小（小于10％）。结果表明：标准物质对137Cs测定影响不大，选择与测定样品的化学元素相近的标准物质进行效率刻度，可以提高环境样品中210Pb测定的准确性。

DETERMINATION OF ENVITONMENTAL RADIONUCLIDES 210Pb AND 137Cs USING HPGe γ SPECTROMETRY AS INFLUENCED BY DIFFERENT STANDARD REFERENCE MATERIALS

We compared specific activities of environmental radionuclides 210Pb and 137Cs derived from the target chestnut soil with those from 4 other soil types (cinnamon soil, yellow soil, loess soil and purple soil) as standard reference materials (SRMs) for efficiency calibration. The spectrum of 210Pb and 137Cs in the target soil samples were determined by  HPGe γ-spectrometer and then were converted to the specific activities through the established effective calibration curves using 5 soil types as SRMs. The objective was to investigate the importance of SRMs on analyzing environmental radionuclides. Different SRMs had significant effects on the determination of 210Pb in the target samples. Compared with target soil, specific activity of 210Pb increased by 8％ and 7％ respectively, when using the efficiency curves calibrated with purple soil and cinnamon soil as SRMs. However, specific activity of 210Pb did not increase evidently (less than 2%) when using the yellow soil and loess soil as SRMs. These differences in 210Pb activities, determined with 4 other soil types used as SRMs relative to the target soil, can be attributed to differences in several or a group of chemical elements (Si, Fe and Na) which are significantly partial correlation (from P<0.05 to P<0.01) with 210Pb activities determined. Unlike 210Pb, specific activities of 137Cs had no significant differences between target soil and 4 other soil types used as SRMs. This may attributed to a small differences (<10%) in the chemical elements (O and Na) between the target soil and 4 other soil types although these elements were significantly partial correlation (P<0.01) with 137Cs activities. Our results suggest that the SRMs did not significantly affect 137Cs determination; the SRMs, however, similar to targeted samples should be used in determination of 210Pb in environmental samples to improve analytical precision.