Removal of long-lived $^{222}$Rn daughters by electropolishing thin layers of stainless steel

TL;DR

This study demonstrates that electropolishing less than 1 micron of stainless steel effectively removes radon daughters, significantly reducing contamination and maintaining the functionality of sensitive detector components.

Contribution

It shows that ultra-thin electropolishing can efficiently eliminate radon daughters from stainless steel surfaces, enabling cleaner detector environments without affecting precision parts.

Findings

Electropolishing < 1 μm reduces radon daughter contamination by over 100 times.

Electropolished wires show uniform material removal confirmed by electron microscopy.

The method preserves the energy resolution of the detector.

Abstract

Long-lived alpha and beta emitters in the $^{222}$Rn decay chain on detector surfaces may be the limiting background in many experiments attempting to detect dark matter or neutrinoless double-beta decay. Removal of tens of microns of material via electropolishing has been shown to be effective at removing radon daughters implanted into material surfaces. Some applications, however, require the removal of uniform and significantly smaller thicknesses. Here, we demonstrate that electropolishing < 1 $\mu$m from stainless-steel plates reduces the contamination efficiently, by a factor > 100. Examination of electropolished wires with a scanning electron microscope confirms that the thickness removed is reproducible and reasonably uniform. Together, these tests demonstrate the effectiveness of removal of radon daughters for a proposed low-radiation, multi-wire proportional chamber (the BetaCage), without compromising the screener's energy resolution. More generally, electropolishing thin layers of stainless steel may effectively remove radon daughters without compromising precision-machined parts.