Radon daughter removal from PTFE surfaces and its application in liquid xenon detectors

TL;DR

This study evaluates cleaning methods to remove radon daughters from PTFE surfaces used in liquid xenon detectors, showing significant differences in removal efficiency between decay chains and assessing the impact on detector purity.

Contribution

It provides new insights into cleaning procedures for PTFE to reduce radon daughter contamination in liquid xenon detectors.

Findings

Removal of $^{222}$Rn daughters was about 2 times effective.

Removal of $^{220}$Rn daughters was up to 10 times more effective.

Nitric acid cleaning impacts liquid xenon purity.

Abstract

Long-lived radon daughters are a critical background source in experiments searching for low-energy rare events. Originating from radon in ambient air, radioactive polonium, bismuth and lead isotopes plate-out on materials that are later employed in the experiment. In this paper, we examine cleaning procedures for their capability to remove radon daughters from PTFE surfaces, a material often used in liquid xenon TPCs. We found a large difference between the removal efficiency obtained for the decay chains of $^{222}$Rn and $^{220}$Rn, respectively. This indicates that the plate-out mechanism has an effect on the cleaning success. While the long-lived $^{222}$Rn daughters could be reduced by a factor of ~2, the removal of $^{220}$Rn daughters was up to 10 times more efficient depending on the treatment. Furthermore, the impact of a nitric acid based PTFE cleaning on the liquid xenon purity is investigated in a small-scale liquid xenon TPC.