Chromatographic separation of radioactive noble gases from xenon

TL;DR

This paper presents a chromatographic method using activated charcoal to effectively remove radioactive noble gas impurities like krypton from xenon, significantly reducing background signals for dark matter detection experiments.

Contribution

The study introduces a novel chromatographic separation system that achieves ultra-pure xenon by drastically lowering krypton levels, improving detection sensitivity for WIMP searches.

Findings

Reduced krypton concentration from 130 ppb to 3.5 ppt in 400 kg xenon

Achieved krypton levels below 0.2 ppt in a 50 kg batch after processing

Demonstrated effectiveness of activated charcoal chromatography for noble gas purification

Abstract

The Large Underground Xenon (LUX) experiment operates at the Sanford Underground Research Facility to detect nuclear recoils from the hypothetical Weakly Interacting Massive Particles (WIMPs) on a liquid xenon target. Liquid xenon typically contains trace amounts of the noble radioactive isotopes $^{85}$Kr and $^{39}$Ar that are not removed by the in situ gas purification system. The decays of these isotopes at concentrations typical of research-grade xenon would be a dominant background for a WIMP search exmperiment. To remove these impurities from the liquid xenon, a chromatographic separation system based on adsorption on activated charcoal was built. 400 kg of xenon was processed, reducing the average concentration of krypton from 130 ppb to 3.5 ppt as measured by a cold-trap assisted mass spectroscopy system. A 50 kg batch spiked to 0.001 g/g of krypton was processed twice and reduced to an upper limit of 0.2 ppt.