ABSTRACT
We report the direct measurement of the 7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV 7Be neutrinos is 49+/-3stat+/-4syst counts/(day.100 ton). The hypothesis of no oscillation for 7Be solar neutrinos is inconsistent with our measurement at the 4sigma C.L. Our result is the first direct measurement of the survival probability for solar nu(e) in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of 7Be, pp, and CNO solar nu(e), and the limit on the effective neutrino magnetic moment using solar neutrinos.
ABSTRACT
For the Borexino solar neutrino experiment a concentration line for 222Rn from a large volume of nitrogen gas has been constructed. It is based on cryo-adsorption in a charcoal trap of very low intrinsic 226Ra contamination. Consequently, the blank for activity from the daughter nuclide 222Rn is very low. 222Rn is recorded with proportional counters. This allows the detection of Rn at concentrations below the microBq/m3 level in gaseous nitrogen. The removal of radon from liquid nitrogen is achieved by direct adsorption in the liquid phase. 222Rn-measurements on evaporated nitrogen with and without previous purification are reported.
