Comprehensive study of radon progeny attachment to surfaces

Abstract

Low energy, low rate experiments, such as searches for neutrinoless double $\ensuremath{\beta}$ decay and dark matter, require unprecedentedly low levels of background in order to deliver their full science potential. $^{210}\mathrm{Po}$ driven, neutron induced background, caused by nuclear $(\ensuremath{\alpha},n)$ reactions on low-$Z$ materials, direct background contributions of the $^{210}\mathrm{Po}\phantom{\rule{4pt}{0ex}}\ensuremath{\alpha}$ radiation and desorption of the $^{210}\mathrm{Pb}$ progeny $^{210}\mathrm{Bi}$ from surfaces into the detector medium are of particular of concern. These backgrounds depend on details of the components' exposure to radon-loaded laboratory air and, thus, their handling history. The attachment rates of airborne radon progeny to surfaces, needed for the estimation of these background rates, are poorly understood. This article reports the results of a campaign comprising of more than 1200 attachment measurements, performed for nine different materials. Correlations of the attachment with environmental parameters such as air exchange rate, electrical surface potential, temperature, atmospheric pressure, and relative humidity have been studied and found to be significant only in case of the first two. Attachment modeling, using the Jacobi model, is compared to data.