Uranium isotope ratio measurements by LA-HR-ICP-MS

Abstract

This work describes the utilization of LA-HR-ICP-MS (laser ablation high resolution inductively mass spectrometry) for characterize the uranium isotope ratio of a UO2 pellet supplied and certified by New Brunswick Laboratory (NBL). This method is useful measurements of 233U, 234U, 235U, 236U and 238U, reaching relative standard deviations (RSD) from 1.55% to 2.45%. The Laser ablation ICP-MS technique shows a high level of instability, compromising the precision of the measurements, although could be made some adjustments to improve its stability. To reach the better stability were made the adjustments of laser ablation and ICP-MS parameters, such as RF power, laser beam diameter, defocusing of laser beam, auxiliary gas and sample gas. The parameters which caused the greatest impact in order to improve the stability signal were RF power, defocusing and laser beam diameter. To carry out the adjustments of the parameters was used a glass standard NIST 610, supplied and certified by National Institute of Standards and Technology (NIST). The measurements were carried out on a single spot ablation with low energy density and defocusing, which demonstrated to be the improved way to reach good signal stability. The results presented by the measurements revealed that the Laser ablation ICP-MS technique offers a rapid and accurate way to perform uranium isotope ratios without any sample preparation, since it allows carrying out the measurements straight on the sample, besides to preserve the sample that is very important to safeguards and nuclear forensics.