环境样品中超痕量129I与99Tc及其形态的加速器质谱分析方法和应用研究

Human nuclear activities have released large amount of long-lived radionuclides iodine-129 (129I) and technetium-99 (99Tc) to the environment. Because of high fission yields, long half-life, strong beta radiotoxicity, high mobility and volatility, concentrations and species of 129I and 99Tc have been always receiving great attention in nuclear waste disposal and nuclear safety monitoring. However, extremely low-level of the two radionuclides in the environment is hard to be measured, which is the main reason that rare data are available in the investigation of environmental radioactivity in China, in particular the level of 129I in the atmosphere and 99Tc in all kinds of environmental media. This study aim to mainly develop highly efficient trapping technique of gaseous iodine in atmosphere, removal of 99Ru isobar interference of 99Tc, target source preparation of 99Tc, and finally establish highly sensitive analytical method of accelerator mass spectrometry (AMS) for measurement of ultra-low level of 129I and 99Tc and their species in environmental samples. Using AMS detection, extraction of iodide and technetium fluoride negative ions, crucial AMS instrumental parameters, separation and purification of radionuclides, as well as conditions of speciation separation will be carefully optimized to achieve the best analytical performance. This study will firstly conduct measurement of 99Tc in environmental samples using a small (3 MV) AMS instrument in combination with chemical treatment. These established methods will be mainly applied on determination of 129I and 99Tc in air, soil and sediment, aiming to investigate the levels and the species distribution, at the service of the nuclear waste disposal, environmental radioactivity investigation and environmental tracing applications.

人类核活动向环境中释放了大量的长寿命放射性核素129I和99Tc，由于其裂变产额高、寿命长、易迁移等特点，其总浓度及其在环境中的赋存形态，一直以来在核废物处置和核环境安全监测中都受到极大的关注。环境中129I和99Tc的浓度极低，测量难度大，在我国的环境放射性调查中一直缺失相关的数据报道。本课题拟对大气气态碘的采集和分离技术，99Tc的干扰核素99Ru的去除，99Tc的靶源制备等关键技术难题进行研究，基于碘负离子和锝的氟化物负离子提取，优化AMS的关键仪器参数、样品化学分离纯化条件等，建立超痕量129I和99Tc及其形态的加速器质谱分析方法。本申请将首次在小型化AMS（3MV）上进行实际样品的99Tc分析。方法将用于分析大气中的129I及其形态、土壤和沉积物中的129I和99Tc及其形态，初步获得129I和99Tc的环境水平及其形态分布信息，为核废料处置和环境示踪研究提供科学依据。

随着我国核工业的快速发展，公众对核与辐射安全关注度持续提升。碘-129和锝-99因其裂变差额较高、寿命长、易溶于水、流动性强等特点，成为核设施退役、核废物管理、环境中放射性核素的安全评估等工作中的关键核素。建立环境129I和99Tc及其形态的高灵敏度分析方法，有助于高放废物处置中129I和99Tc的传输迁移行为、放射生态影响，重建核事故中短寿命放射性碘的的水平和分布，评估其辐射危害，为核应急决策提供科学依据，进行环境示踪应用研究。.在方法学研究方面，本项目成功建立了用于颗粒物129I分析的大体积采样系统，初步建立了大气碘-129的串级采样系统; 通过选择不同载气，深入研究探讨了大气129I水平对超低129I水平样品的流程空白的影响程度，有效降低了分析检出限；建立的方法不仅可以将分析效率至少提高三倍，也使获得高分辨率的大气碘同位素变化研究成为可能；项目采集并分析了200余个气溶胶样品中的129I水平；采集并部分分析了10组大气碘形态样品，包括颗粒结合态碘、气态无机碘和气态有机碘。通过详细优化99Tc-AMS测量中的实验参数，如基体元素、 99Tc剥离价态、辅助介质等，初步探索了小型3 MV加速器质谱仪对99Tc的测量性能。.在核环境安全监测和环境示踪应用研究方面，项目分析了我国季风城市（西安）的大气气溶胶中129I水平的时间变化特征及其影响因素，首次建立了我国第一条大气129I本底曲线，为我国核环境安全应急准备提供了重要科学依据；利用菲律宾沉积物获得了60年129I的时间序列，详细阐明了人类核活动对低纬度地区的影响程度，充分表明了129I的长距离全球传输过程。同时研究了2017年9月的朝鲜核武器试验期间我国内陆大气中发现的高129I水平，研究表明与朝鲜核事故无关。监测我国某铀矿区及其周边地表环境的岩石和土壤中129I，结果表明该铀矿区的采矿活动未对周边环境的129I水平造成影响。