Radon daughters plate-out as a background source in nEXO neutrinoless double beta decay experiment

nEXO is a planned next-generation experiment searching for the neutrinoless double beta decay of Xe-136. The experiment will utilize a time projection chamber and 5000 kg of isotopically enriched liquid xenon. The projected half-life sensitivity is > 10²⁸ years after 10 years of exposure. Stringent radioactive background control and careful material selection are necessary to achieve such sensitivity.

One of the considered background sources is radon daughter attachment to detector materials during their exposure to air. The decay of Po-210 can produce neutrons via (α, n) reactions, followed by capture on Xe-136, and subsequent β-decay of Xe-137, in turn creating background events. A literature survey reveals a wide range of measured radon daughter attachment lengths. To better understand the causes for this variability our group at the University of Alabama has started a measurement program using various materials relevant for nEXO, monitoring environmental parameters. In this talk I will present the results of our study.