Andrea Pocar
Stanford University
Abstract:
Borexino, a large liquid scintillator neutrino experiment running at the Gran Sasso underground laboratories in Italy, requires unprecedented purity with respect to radioactive contaminations. Its main scientific goal is to measure the low energy portion of the solar neutrino spectrum, in particular the mono-energetic 7Be and pep fluxes. The maximum allowed concentration of the naturally occurring 40K, 232Th, and 238U isotopes within the scintillator is 10E−16 g/g. The intrinsic purity of the liquid scintillator, although necessary, is not sufficient for the success of the experiment, as there exist contamination mechanisms that set very stringent requirements on all components of the detector that come in contact with the scintillator itself. Radon daughter contamination of these surfaces is one such mechanism. I will review the radon-induced backgrounds in the context of Borexino and discuss the measures adopted for minimizing radon daughter contamination during fabrication of the thin nylon vessels for scintillator containment. I will present the design, operation and performance of a novel radon filter specifically developed for supplying radon-scrubbed air to the vessel construction clean room. These radon suppression techniques can be useful to most low-background experiments, such as those for the search of WIMPs and neutrinoless double beta decays.