A step toward CNO solar neutrino detection in liquid scintillators

The detection of CNO solar neutrinos in ultrapure liquid scintillator detectors is limited by the background produced by bismuth-210 nuclei that undergo beta-decay to polonium-210 with a lifetime of similar to 7 days. Polonium-210 nuclei are unstable and decay with a lifetime equal to similar to 200 days emitting alpha particles that can be also detected. In this Letter, we show that the Bi-210 background can be determined by looking at the time evolution of alpha-decay rate of Po-210, provided that alpha particle detection efficiency is stable over the data acquisition period and external sources of Po-210 are negligible. A sufficient accuracy can be obtained in a relatively short time. As an example, if the initial Po-210 event rate is similar to 2000 cpd/100 ton or lower, a Borexino-like detector could start discerning CNO neutrino signal from Bi-210 background in Delta t similar to 1 yr. (C) 2011 Elsevier B.V. All rights reserved.