A preliminary investigation into the use of molecular oxide and hydride secondary ion relationships for improvement of the ²³⁶U/²³⁸U determination on a NanoSIMS 50L

A NanoSIMS 50L is used to investigate uranium molecular (²³⁵U¹⁶O, ²³⁶U¹⁶O, ²³⁸U¹⁶O, ²³⁵U¹H, ²³⁸U¹H, ²³⁶U¹⁶O¹H, and ²³⁸U¹⁶O¹H) and elemental (²³⁵U, ²³⁶U, and ²³⁸U) secondary ion production during sputtering of synthetic UO₂ and the NIST-610 standard to determine if: (1) the ²³⁶U¹⁶O/²³⁸U¹⁶O molecular oxide ratio performs better than the ²³⁶U/²³⁸U elemental ratio, and (2) there is co-variance between the molecular hydrides and oxides. Despite an order of magnitude greater abundance of ²³⁶U¹⁶O secondary ions (compared to ²³⁶U), the ²³⁶U¹⁶O/²³⁸U¹⁶O ratios are less accurate than the ²³⁶U/²³⁸U ratios. Further work is needed before the higher count rate of the ²³⁶U¹⁶O secondary ion can be used to obtain a better ²³⁶U/²³⁸U ratio. The second objective was undertaken because correction for the interference of ²³⁵U¹H on the ²³⁶U secondary ion species typically utilizes the ²³⁸U¹H/²³⁸U ratio. This becomes problematic in samples containing ²³⁹Pu, so our aim was to understand if the hydride formation rate can be constrained independently of having to measure the ²³⁸U¹H. We document correlations between the hydride (²³⁸U¹H and ²³⁸U¹⁶O¹H) and oxide (²³⁶U¹⁶O) secondary ions, suggesting that pursuing an alternative correction regime is worthwhile.