用于铀微粒年龄测量的铀钍氧化物混合微粒SIMS测量研究

放射性材料的年龄信息是一项重要的溯源指纹特征，铀微粒年龄测量研究对于核取证技术应用具有重要意义。本工作通过使用二次离子质谱（SIMS）、电感耦合等离子体质谱（ICP-MS）测量自制单分散铀钍氧化物混合微粒获得了单个微米级微粒中铀钍比值的相对灵敏度因子（RSF_Th/U），结合扫描电子显微镜（SEM）等常规分析技术，确定了最佳测量条件，探索了微米级铀钍混合微粒的SIMS测量方法。测量结果表明，对于粒径为2~3 μm的混合微粒，不同微粒间²³²Th/²³⁸U比值的相对标准偏差小于3%(n=12)，平均RSF_Th/U为1.259±0.032。通过测量年龄已知的铀同位素固体标准物质CRM970对RSF_Th/U进行了验证。结果表明，对于粒径为5~10 μm的CRM970铀粉末样品，年龄测量结果准确，相对标准偏差为3%(n=16)。该方法受干扰信号影响较小，测量结果稳定，可用于微米级铀微粒年龄的测量。

SIMS Measurement of Mixed Particle of Uranium and Thorium Oxide for Age Dating of Uranium Particle

The age of radioactive materials is an important traceable fingerprint feature. The study of uranium particle age measurement is of great significance for the application of nuclear forensics technology. The age analysis of uranium particles is one of the most advanced research contents in environmental sample analysis technology in the field of nuclear safeguards. The age of uranium particles refers to the last separation and purification time of uranium. By collecting and measuring the age of wiping samples from the internal or surrounding environment of nuclear facilities, the key information of the occurrence time of corresponding nuclear activities can be obtained, and then whether there is a default production activities can be determined. The principle of particles age measurement is the same as bulk samples, its age is calculated by measuring the atomic ratio of uranium and its decay daughters. The age of uranium particles is usually analyzed by measuring the ratio of ²³⁴U and ²³⁰Th. In this work, based on the preparation of monodisperse micron-sized mixed particles of uranium and thorium oxide, the thorium uranium ratios in self-made monodisperse mixed particles of uranium and thorium oxide and the uranium and thorium mixed solution were measured by secondary ion mass spectrometer (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS). The relative sensitivity factor (RSF_Th/U) of uranium thorium ratio in a single micron particle was calculated. Combined with scanning electron microscope (SEM) and micromanipulator, the influence of sample preparation process on the measurement results is successfully reduced, the optimal measurement conditions are determined, and the SIMS measurement method of micron mixed particles of uranium and thorium oxide is explored. The results of mixed particles of uranium and thorium oxide measured by SIMS show that for mixed particles with a diameter of 2-3 μm, the relative standard deviation (RSD) of the ratio of ²³²Th/²³⁸U between different particles is less than 3%(n=12), and the average RSF_Th/U is 1.259±0.032. RSF_Th/U was verified by measuring CRM970 uranium powder standard material with a known age. The results show that for CRM970 uranium powder samples with a diameter of 5-10 μm, the age measurement results are accurate, and the RSD is 3%(n=16). The results show that the SIMS measurement method of mixed particles established in this work is less affected by interference signals and the measurement results are stable. It can be used to measure the age of micron uranium particles.