加速器质谱法测定环境和生物样品中的^(129)I

Determination of ^(129)I Levels in Chinese Biological and Environmental Specimens by Accelerator Mass Spectrometry

建立了环境和生物样品中的129I的分析方法,采用碱式灰化、萃取反萃、沉淀等步骤对环境和生物样品中的碘进行预浓集,用131I[NaI]为放射性示踪剂优化各分步的制备条件,运用加速器质谱法测定了北京地区松针和干草、青岛地区海藻和海水中的129I/127I。用超热中子活化法测定样品中的稳定碘(即127I)含量。上述松针、干草、海藻和海水样品中的129I/127I分别为8.11×10-9、5.97×10-9、1.70×10-10和6.05×10-10;相应的129I浓度分别为3.22×10-15、1.24×10-14、1.27×10-14g/g干重和2.30×10-14g/L。与文献报道值相比,我国与国外同类地区相当甚至更低,比法国和英国乏核燃料后处理厂附近环境中的129I低2～3个数量级,表明我国这些非核设施影响地区的129I处于当今全球环境的本底放射性沉降水平。

Preconcentration procedures including alkaline wet ashing, extraction-back extraction and precipitation have been established for the separation and purification of iodine-129 in the biological and environmental specimens. The ratios of 129I/ 127I in the specimens of pine needles and dry grass collected from Beijing area, and seaweed and seawater from Qingdao area of China have been determined by using the preconcentration procedures with accelerator mass spectrometry (AMS). The recovery in each step of the preconcentration procedures has been studied using 131I [NaI] as a tracer for optimizing the sample preparation conditions. The concentrations of stable iodine ( 127I) in the above samples were analyzed by epithermal neutron activation analysis. With the necessary correlation on the amount of added carrier and yields, the ratios of 129I/ 127I of 8.11×10 -9, 5.97×10 -9, 1.70×10 -10 and 6.05×10 -10, and the corresponding values of 129I concentration of 3.22×10 -15, 1.24×10 -14, 1.27×10 -14 g/g dry weight and 2.30×10 -14 g/L were determined for the samples of pine needles, dry grass, seaweed and seawater, respectively. It was found that the 129I levels in the two areas, which were not directly influenced by nuclear facilities, were similar to or even lower than those of the reported values for the same kind areas of the world. They are 2~3 orders of magnitude lower than those for the areas near the spent nuclear fuel reprocessing facilities in France and united kingdom. In addition, they are still 1~2 orders of magnitude higher than those of samples collected in the prenuclear age, showing the impact of anthropogenic nuclear activities. The results indicate that the 129I level in these areas of China is within the global fallout background level.