PNNL

Abstract

Radiocontaminants on the surfaces of detector components can be a problematic source of background events for physics experiments searching for rare processes. Exposure to radon is a specific concern because it can result in the relatively long-lived 210Pb (and progeny) being implanted to significant subsurface depths such that removal is challenging. In this article we present results from a broad exploration of cleaning treatments to remove implanted 210Pb and 210Po contamination from silicon, which is an important material used in several rare-event searches. We demonstrate for the first time that heat treatments (“baking”) can effectively mitigate such surface contamination, with the results of a 1200 C bake consistent with near-perfect removal. We also report results using wet-chemistry and plasma-based methods, which show that etching can be highly effective provided the etch depth is sufficiently aggressive. Our survey of cleaning methods suggests consideration of multiple approaches during the different phases of detector construction—not only for silicon-based devices but also other materials—to enable greater flexibility for efficient removal of 210Pb and 210Po surface contamination.