Investigating enhanced thorium ionization in TIMS using Re/Pt porous ion emitters

Abstract

Thermal ionization mass spectrometry (TIMS) is a widely used, benchmark method in actinide isotopic analyses efforts relevant to various nuclear and geological fields. Despite significant previous use and inherent advantages, however, poor sample ionization continues to hamper the use of TIMS in the measurement of trace species; actinide ionization efficiencies frequently fall below 0.1 % using traditional instrument sources. These low efficiencies seriously limit the ability to measure several highly refractory metals (e.g. U and Th) that may provide key signatures data in non-proliferation, safeguards and forensics efforts. Herein, a relatively new TIMS ion source strategy, employing porous ion emitters (PIEs) atop traditional filament assemblies, is investigated for the first time as a straightforward means of enhancing the ionization of Th, arguably a worst case scenario for TIMS-based actinide measurements. These sources yielded up to 410 % greater Th sample utilization, relative to previously published values and in-house measurements collected using traditional methods. Accompanying scanning electron microscopy investigations provide preliminary insight into the mechanisms of PIE functioning and explore the impacts of extended heating on the constructed source’s structure and composition.