A new method of isotope enrichment and separation: preferential embedding of heavier isotopes of Xe into amorphous solid water

In this paper, we examine a new method for isotope separation involving the embedding of atoms and molecules into ice. This method is based upon isotope dependent embedding, i.e. capture, in a cryogenic matrix which exhibits excellent single-pass enrichment as demonstrated successfully for selected isotopes of Xe. This is a totally new method that holds significant promise as a quite general method for enrichment and purification. It is based upon exploiting the energetic and momentum barriers that need to be overcome in order to embed a given isotope or isotopologue into the capture matrix, initially amorphous ice. From our previous experiments, we know that there is a strong dependence of the embedding probability with incident momentum. Using supersonic molecular beam techniques, we generated Xe atomic beams of controlled velocities, relatively narrow velocity distributions due to supersonic expansion, and with all of the entrained isotopes having identical velocities arising from the seeded molecular beam expansion. As we had postulated, the heavier isotope becomes preferentially absorbed, i.e., embedded, in the ice matrix. Herein we demonstrate the efficacy of this method by comparing the capture of Xe-134 and Xe-136 to the reference isotope, Xe-129. Enrichment of the heavier isotopes in the capture matrix was 1.2 for Xe-134 and 1.3 for Xe-136 greater than that expected for natural abundance. Note that enriched isotopic fractions can be collected from either the condensate or the reflected fraction depending on interest in either the heavier or lighter isotope, respectively. Cycling of these single-step enrichment events for all methods can lead to significantly higher levels of purification, and routes to scale-up can be realistically envisioned. This method holds significant promise to be quite general in applicability, including both atomic isotopes or molecular isotopologues across a wide range of particle masses spanning, essentially, the periodic table. This topic has profound implications and significant potential impact for a wide-variety of isotope-based technologies in the physical and biological sciences, medicine, advanced energy and energetic systems, including isotopically-purified materials that exhibit high-performance electronic and thermal characteristics, as well as isotopically purified spin-free materials for use in quantum information science platforms.

Automated summary

This paper introduces a new method based on isotope-dependent embedding for isotope separation by embedding atoms and molecules into ice. The efficacy of the method is demonstrated by comparing the capture of Xe-134 and Xe-136 to the reference isotope Xe-129, showing enrichment of heavier isotopes. The method shows significant promise for general applicability and high levels of purification.