²³⁶U/²³⁸U Isotopic Ratio Measurements with Accelerator Mass Spectrometry Using the USRM Standard Reference Materials

²³⁶U is a rare isotope of uranium, naturally occurring in ores with an isotopic abundance of ²³⁶U/^natU<1x10^-9 and anthropogenically occurring in soil and water systems as high as ²³⁶U/²³⁸U = 1x10^-3. Its natural abundance varies over a few orders of magnitude between different mine locations and any individual location’s abundance of ²³⁶U has long been considered a unique “fingerprint”-like signature. Only Accelerator Mass Spectrometry (AMS) is capable of measuring this abundance across the full range of natural ²³⁶U abundances. In order to make these measurements more repeatable, and increase accuracy across different AMS facilities, the AMS group at the University of Notre Dame has prepared a series of ²³⁶U reference standards that covers the isotope’s natural abundance range. Verification measurements of standard series will be presented alongside measurements of ores across the continental United States and the Vienna-KkU reference standard. Additionally a detection limit of 1x10^-12 was determined.