Demonstration of radon removal from SF$_6$ using molecular sieves

TL;DR

This study demonstrates that a cooled 5Å molecular sieve effectively reduces radon contamination in SF$_6$ gas, offering a promising method for background reduction in dark matter detection experiments.

Contribution

First demonstration of radon removal from SF$_6$ using a molecular sieve, specifically identifying the 5Å type as effective without absorbing SF$_6$ gas.

Findings

5Å sieve reduced radon by 87% when cooled with dry ice.

Only the 5Å sieve among tested types significantly decreased radon levels.

The method is suitable for ultra-sensitive rare-event physics experiments.

Abstract

The gas SF$_6$ has become of interest as a negative ion drift gas for use in directional dark matter searches. However, as for other targets in such searches, it is important that radon contamination can be removed as this provides a source of unwanted background events. In this work we demonstrate for the first time filtration of radon from SF$_6$ gas by using a molecular sieve. Four types of sieves from Sigma-Aldrich were investigated, namely 3{\AA}, 4{\AA}, 5{\AA} and 13X. A manufactured radon source was used for the tests. This was attached to a closed loop system in which gas was flowed through the filters and a specially adapted Durridge RAD7 radon detector. In these measurements, it was found that only the 5{\AA} type was able to significantly reduce the radon concentration without absorbing the SF$_6$ gas. The sieve was able to reduce the initial radon concentration of 3875 $\pm$ 13 Bqm$^{-3}$ in SF$_6$ gas by 87% when cooled with dry ice. The ability of the cooled 5{\AA} molecular sieve filter to significantly reduce radon concentration from SF$_6$ provides a promising foundation for the construction of a radon filtration setup for future ultra-sensitive SF$_6$ gas rare-event physics experiments.