Sample preparation for actinide isotopic analysis using FIB-SEM

Capabilities to extract and analyse nanogram-scale uranium dioxide (UO₂) samples to allow spatial isotopic analysis were established by the development of techniques from wider literature. A Helios 5CX Focussed Ion Beam Scanning Electron Microscope (FIB-SEM) adapted for alpha-emitting radioactive material was used to extract samples of 2-80 ng from a depleted UO₂ pellet. These were analysed by Thermal Ionisation Mass Spectrometry (TIMS) and Triple Quadrupole Inductively Coupled Mass Spectrometry (ICP-QQQ-MS). TIMS produced measurements for ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U weight-percent (wt%) with relative standard uncertainties (RSU) of between 0.26 and 11%. ICP-QQQ-MS measured the ²³⁵U/²³⁸U ratio with an RSU of 37.4%.