Validation of Parylene Coating to Suppress Alpha Contamination on the Copper Surface in CUORE Bolometers

Abstract

Background rate reduction is of utmost importance for neutrinoless double beta decay experiments like CUORE (Cryogenic Underground Observatory for Rare Events). A major source of background for CUORE comes from surface contamination from inert materials, mainly degraded alphas from the supporting copper structure of the bolometer modules. We investigated a novel alpha background suppression technique using conformal polymer coating with Parylene in a bolometric validation run. A 50 micron thick layer of Parylene coating on the copper structure surface was chosen to effectively range out degraded alphas. The measured alpha background rate and its implications will be discussed.