Radon depletion in xenon boil-off gas

TL;DR

This study demonstrates that cryogenic distillation can significantly reduce radon levels in xenon gas, improving the purity of xenon for rare event detection.

Contribution

First experimental evidence showing radon depletion in xenon boil-off gas using cryogenic distillation techniques.

Findings

Radon reduction factor of ≥4 in boil-off xenon gas.

Effective separation of radon from xenon at the 10^{-15} mol/mol level.

Use of semiconductor and proportional counters for radon detection.

Abstract

An important background in detectors using liquid xenon for rare event searches arises from the decays of radon and its daughters. We report for the first time a reduction of $^{222}$Rn in the gas phase above a liquid xenon reservoir. We show a reduction factor of $\gtrsim 4$ for the $^{222}$Rn concentration in boil-off xenon gas compared to the radon enriched liquid phase. A semiconductor-based $\alpha$-detector and miniaturized proportional counters are used to detect the radon. As the radon depletion in the boil-off gas is understood as a single-stage distillation process, this result establishes the suitability of cryogenic distillation to separate radon from xenon down to the $10^{-15}\,$mol/mol level.