超低水平环境236U的加速器质谱分析及环境示踪研究

Uranium-236 (236U) is an important long-lived anthropogenic radionuclide in the environment, and has great potential on environmental tracing applications. However, determination of 236U can be only performed in a few laboratories in the world. This study aims to combine high-efficiency radiochemical separation and high-sensitivity accelerator mass spectrometry (AMS) measurement and establish a method for determination of low-level 236U in environmental samples (e.g. seawater, soil, sediment, etc.). Two main challenges lie in development of a uranium target preparation method for high ionization efficiency of uranium and AMS detection technique of ultra-low level of 236U in microgram level of uranium target. Water masses interaction and current circulation in marine system is key driving factors of global and regional climate change, as well as dispersion of marine pollutant. Coupling to hydrological and environmental data, a 236U-129I dual tracing model will be established by utilizing the different source terms of high conservative anthropogenic 236U and 129I in the ocean. Seawater samples collected in the China East Sea will be analyzed for 236U and 129I, to obtain the characteristic atomic ratios of 236U/129I in each water mass, to investigate the interaction of water masses and movement pattern, and to explore diffusion kinetic mechanisms of marine pollutants, serving to scientific prediction of diffusion and dynamic distribution of radioactive substance and soluble contaminants. Remediation of uranium-contaminated soil is vital for environmental remediation. Surface and depth-profile soil samples collected from Northwest China will be analyzed for 236U for investigation of sources, distribution and migration of 236U, to explore the association of anthropogenic uranium contaminants with soil and its migration mechanism, serving to remediation of uranium-contaminated soil.

铀-236是重要长寿命人工放射性核素，在环境示踪领域具有极大的应用潜力。本工作拟通过研发高离子化效率靶源制备技术和微克量铀靶中超微量236U的加速器质谱测量技术，建立海水、土壤等环境样品中超低水平236U的准确测定方法。洋流循环是气候变化以及海洋污染物扩散的关键驱动因子，利用海洋中高溶解性的人工236U和129I的来源差异特性，结合水文数据，建立海洋236U-129I双示踪技术。通过测定我国海域海水中236U和129I浓度，获得不同水团的特征236U/129I比值，研究我国海域的水团相互作用和运动模式，探索污染物在海洋中的扩散动力学机制，服务于放射性物质和可溶性污染物在海洋中的扩散和动态分布的科学预测。铀污染土壤修复是环境修复的一个重要挑战。分析我国不同环境表层和剖面土壤中236U，研究其分布、来源和迁移规律，探索人工铀污染在土壤中的结合和迁移机制，服务于铀污染土壤的修复。

铀-236是重要长寿命人工放射性核素，研究其在不同环境介质中的迁移扩散行为，不仅能服务于放射性物质和可溶性污染物在海洋中的扩散和动态分布的科学预测，还能服务于铀污染土壤的修复。然而受限于当前国内外对低水平环境样品中236U分析测定技术水平，铀-236在环境示踪领域的应用缺乏深入、系统的研究。本项目开发了土壤和沉积物中超低水平铀的分离纯化技术，以及超痕量236U的ICP-MS/MS准确测量技术，建立了土壤、沉积物样品中痕量236U的高灵敏分析方法，实现236U/238U原子比值低至1E-11的环境样品中236U的准确测定；系统研究了塞米帕拉金斯克核试验场附近及其下风向我国北方地区土壤样品中236U水平分布、来源及其环境中的迁移传输规律；同时创建了海水样品中铀的预浓集分离技术，改进了低铀含量样品中超微量236U的加速器质谱分析方法，建立了大体积海水样品中痕量236U和129I的同时分析方法，获得了我国南海海域表层海水中236U和129I浓度水平分布，建立了海洋环境中236U-129I的双示踪技术，并初步用于探索研究我国海域各水团的相互作用和洋流循环。