The Isotopic Ratio Measurement of Uranium in the Form of Hydrolyzed Uranium Hexafluoride by Inductively Coupled Plasma Multiple Collector Mass Spectrometry

摘要

An inductively coupled plasma-multiple collector-mass spectrometer (ICP-MC-MS) has been used to measure the isotopic composition of uranium in three solutions of uranium hexafluoride. The ~(235)U:~(238)U ratio of each sample solution ranged from approximately 0.007 to 0.03 to 1.0. The measurements are linear over this range and the precision and accuracy are comparable, if not superior, to that obtained by thermal ionization mass spectrometry (TIMS). However, acceptable isotopic ratio measurement of uranium hexafluoride solutions is not possible by TIMS because the presence of fluoride ions severely limits analytical precision. Hence, the fluoride must be removed prior to analysis. This necessitates a chemical purification stage which adds both time and expense to the measurement process. This study reports direct, high precision, accurate uranium isotope ratio measurements on solutions of uranium hexafluoride. The instrumental time required for the analysis of 15 uranium samples with the ICP-MC-MS totals 135 min. This compares with an estimated time requirement of 600 min by TIMS and a time of 900 min by UF_(6) gas mass spectrometry.