Simons David S, Fassett John D
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8371, USA.
Dakota Consulting, Inc., 1110 Bonifant Street, Silver Spring, MD 20910, USA.
J Anal At Spectrom. 2017 Feb;32(2):393-401. doi: 10.1039/C6JA00402D. Epub 2017 Jan 12.
The determination of the relative isotopic abundance by secondary ion mass spectrometry of U in uranium-containing material is complicated by the presence of UH ions at the same nominal mass as the uranium isotopic peak. The net intensity of the U signal is usually determined by a peak-stripping procedure, whereby the UH contribution is obtained by applying the UH/U ratio to the U signal. The subtraction of one signal from another has consequences for the uncertainty of the final U abundance determination that may be especially significant when the amount of sample is limited, as is the case with small uranium particles that are of great interest for nuclear safeguards. We have developed a model based on Poisson counting statistics to determine the effects of various parameters on the uncertainty of the U abundance, including uranium enrichment level, hydride-to-parent ratio, uranium mass consumed during analysis, single multichannel counting, and sample substrate composition. The model predictions have been successfully tested against experimental measurements of uranium oxide particles of both 3% and 90% enrichment in U.
通过二次离子质谱法测定含铀材料中铀的相对同位素丰度时，由于UH离子与铀同位素峰具有相同的标称质量，使得该测定过程变得复杂。U信号的净强度通常通过峰剥离程序来确定，即通过将UH/U比值应用于U信号来获得UH的贡献。从一个信号中减去另一个信号会对最终U丰度测定的不确定度产生影响，当样品量有限时，这种影响可能尤为显著，例如对于核保障具有重要意义的小铀颗粒就是这种情况。我们基于泊松计数统计开发了一个模型，以确定各种参数对U丰度不确定度的影响，这些参数包括铀富集水平、氢化物与母体的比例、分析过程中消耗的铀质量、单通道或多通道计数以及样品基质组成。该模型预测已成功地与U富集度为3%和90%的氧化铀颗粒的实验测量结果进行了对比测试。
