Removal of radon progeny from delicate surfaces

TL;DR

This study shows that simple wiping with acetone can significantly reduce radon progeny contamination on copper and silicon surfaces, potentially easing air exposure constraints in sensitive experiments.

Contribution

Demonstrates an effective, simple cleaning method to remove radon progeny from delicate surfaces, improving background control in rare event searches.

Findings

Approximately 50% removal of $^{210}Po$ achieved

Long-lived $^{210}Pb$ also effectively removed from copper

Additional wiping has limited impact on copper, uncertain on silicon

Abstract

$^{210}Po$ $\alpha$-decay driven neutron background is a concern for many rare event search experiments. It is a difficult to control background because its radiogenic component depends on the air exposure history of parts. In this study, we demonstrate that about half of the radon progeny $^{210}Po$ can be removed from copper and silicon surfaces relatively easily by wiping a copper sample with acetone wetted tissue and a silicon detector with acetone soaked cotton balls. For a copper sample we demonstrate that long-lived $^{210}Pb$ is removed with similar effectiveness. For copper, allocated the longest counting time, additional wiping was found to be largely ineffective. For silicon, the removal effectiveness has large uncertainties. Additional cleaning showed a small but statistically significant effect. Capitalizing on this trivial cleaning step will allow experiments to relax their requirements on the allowable air exposure time during construction, leading to cost and time savings.