Multi-Collector Extreme Ultraviolet Laser Mass Spectrometry (MC-EUV-MS): Using High-Energy Photoionization for High-Spatial-Resolution Isotope Ratio Mapping of Actinide Materials

Abstract Isotope maps are typically collected with a multi-collector mass spectrometer (MC-MS) coupled to a high-spatial-resolution ionization source, yet few ionization sources compatible with MC-MS systems can operate robustly at the submicron scale. To meet this need, we couple an extreme ultraviolet (EUV) laser photon-based ionization source to a modified Thermo Scientific NeptunePlus MC-MS by removing and replacing the inductively coupled plasma (ICP) with the EUV laser system, herein called the MC-EUV-MS. The 46.9 nm EUV laser light is focused to sub-micrometer spots for sample ablation while simultaneously realizing high-energy photoionization using 26.4 eV photons. Thus, the EUV probe combines ablation and ionization in a single pulse. We characterize the newly built MC-EUV-MS by analyzing different actinide-bearing materials. We achieve a sample utilization efficiency (SUE) of 0.006% for 238U using the NIST 610 and 612 glasses at a low +2 kV extraction voltage for accelerating ions off the sample. Higher extraction voltages up to +5 kV point to increased ion yields. We measure 235U/238U isotope ratios from three uranium samples ranging from natural to low enriched. We demonstrate the high spatial resolution of the MC-EUV-MS by mapping uranium oxide microparticles using 500 nm ablation spots. Compared to isotope maps collected over the same sample area using large geometry secondary ion mass spectrometry, the MC-EUV-MS shows significantly higher spatial resolution within the scope of this study.