Krachler Michael, Varga Zsolt, Nicholl Adrian, Mayer Klaus
European Commission, Joint Research Centre (JRC), Karlsruhe, Germany.
Anal Chim Acta X. 2019 Apr 30;2:100018. doi: 10.1016/j.acax.2019.100018. eCollection 2019 Jul.
Validated analytical measurement protocols for the fast and accurate determination of the uranium (U) isotopic composition (U, U, U, U) of solid nuclear materials were developed employing ns-laser ablation (LA) coupled to multi-collector ICP-MS. The accuracy of the analytical procedure was assured by frequent ( = 65) analysis of a pressed pellet of certified isotopic reference material CRM U-030 (∼3 wt% U). The expanded uncertainty ( = 2) for the (U)/(U) ratio was as low as 0.05%, rising to 0.62% and 1.09% for (U)/(U) and (U)/(U) ratios, respectively. LA-MC-ICP-MS measurements of a pressed pellet of certified isotopic reference material CRM U-020 (∼2 wt% U) before analysis of each sample allowed calculation of the ion counter gains and mass bias correction. Both individual spot analysis and line scan analysis were used to measure (U)/(U), (U)/(U), and (U)/(U) ratios in two low-enriched UO pellets from the fourth Collaborative Materials Exercise (CMX-4), four seized low-enriched UO pellets intercepted from illicit trafficking and one metal sample consisting of depleted U. LA-MC-ICP-MS results of all investigated samples matched well with U isotope ratios obtained by thermal ionisation mass spectrometry (TIMS). This independent confirmation of the LA-MC-ICP-MS results by TIMS underpinned the high quality of generated analytical data. Acquisition of several thousand data points within a couple of minutes during line scan analysis yielded detailed information on the spatial distribution of the U isotopic composition of selected UO pellets, revealing straightforwardly their (in-)homogeneity on the μm-scale. Calculating skewness and half width of the frequency distributions of the (U)/(U) amount ratio allowed the quantitative assessment of the (in-)homogeneity of the investigated samples. This information allows drawing conclusions on the starting materials used for the production of the pellets. From a nuclear forensics perspective, LA-MC-ICP-MS provides quick, accurate results on the spatial distribution of major and minor U isotopes while preserving the sample i.e. piece of evidence, essentially intact.
采用纳秒激光烧蚀（LA）与多接收电感耦合等离子体质谱联用技术，开发了用于快速准确测定固体核材料中铀（U）同位素组成（U、U、U、U）的经过验证的分析测量方案。通过对认证同位素参考物质CRM U - 030（约3 wt% U）的压制颗粒进行频繁（n = 65）分析，确保了分析程序的准确性。（U）/（U）比值的扩展不确定度（k = 2）低至0.05%，（U）/（U）和（U）/（U）比值的扩展不确定度分别升至0.62%和1.09%。在分析每个样品之前，对认证同位素参考物质CRM U - 020（约2 wt% U）的压制颗粒进行LA - MC - ICP - MS测量，可计算离子计数器增益和质量偏置校正。分别使用单点分析和线扫描分析来测量第四次协作材料实验（CMX - 4）中的两个低浓铀UO颗粒、从非法贩运中截获的四个扣押低浓铀UO颗粒以及一个贫化铀金属样品中的（U）/（U）、（U）/（U）和（U）/（U）比值。所有研究样品的LA - MC - ICP - MS结果与热电离质谱（TIMS）获得的铀同位素比值匹配良好。TIMS对LA - MC - ICP - MS结果的这种独立验证支持了所生成分析数据的高质量。在线扫描分析过程中，在几分钟内获取数千个数据点，得到了所选UO颗粒中铀同位素组成空间分布的详细信息，直接揭示了它们在微米尺度上的（非）均匀性。计算（U）/（U）含量比频率分布的偏度和半高宽，可对所研究样品的（非）均匀性进行定量评估。这些信息有助于推断用于制造颗粒的起始材料。从核法医角度来看，LA - MC - ICP - MS能快速、准确地给出主要和次要铀同位素空间分布的结果，同时基本保持样品即证据完好无损。
