A new method for measurement of lithium isotopes with nuclear applications

Abstract

Extreme isotope abundance ratios occur naturally, but also result from enrichment processes required for various industrial applications. The range of elements used for these industrial applications spans essentially the entire periodic table; thus, the need for a low cost (both in labor and finance) analytical technique to measure isotopic enrichments that create extreme isotope abundance ratios has never been greater. Molten salt reactors are one such application, where high purity 7Li is required for cooling processes due to its low neutron cross-section compared to 6Li. Several new technologies are required for these reactors to be viable, both technically and financially, including an efficient method for enrichment of 7Li. Many methods are being tested, but there is a need for a high-performance, high-throughput method for determination of extreme lithium isotope abundance ratios. High abundance sensitivity mass spectrometry provides a path forward for measurement of lithium isotopes. Here, we present a new method for measuring enriched lithium isotope ratios by using multi-collector inductively coupled plasma mass spectrometry and combined faraday-ion counting detectors. We carefully characterize the abundance sensitivity and background signals associated with combined Faraday-ion counting techniques. To test the accuracy of the method, we measured lithium isotopic compositions of a suite of pure lithium salts using the standard static faraday measurement and compare those results to isotope ratios measured using the new method. Isotope ratios of the two techniques agree to within 1.5‰. We also achieved 7Li isotope abundance for a previously characterized enriched lithium salts within 0.0035%, indicating that the technique will provide a way forward for measuring enriched lithium isotope ratios in nuclear materials. The technique can be applied to any element with unnatural isotopic compositions and/or extreme abundance ratios.