| Thirty years ago, the first solar neutrino detector proved fusion reactions power the Sun. However, the total rate detected in this and all subsequent solar neutrino experiments is consistently two to three times lower than predicted by the Standard Solar Model. Current experiments seek to explain this “solar neutrino puzzle” through non-standard particle properties, like neutrino mass and flavor mixing, within the context of the MSW theory. The detection of the monoenergetic 7Be solar neutrino is the missing clue for the solution of the solar neutrino problem; this constitutes the main physics goal of Borexino, a real-time, high-statistics solar neutrino detector located under the Gran Sasso mountain, in Italy.; In the first part of this thesis, I present a Monte Carlo study of the expected performance of Borexino, with simulations of the neutrino rate, the external y background and the α/β/γ activity in the scintillator. The Standard Solar Model predicts a solar neutrino rate of about 60 events/day in Borexino in the 0.25–0.8 MeV window, mostly due to 7Be neutrinos. Given the design scintillator radiopurity levels (10−16 g/g 238U and 232Th and 10−14 g/g K), Borexino will detect such a rate with a ∼2.4% statistical error, after one year. In the MSW Small (Large) Angle scenario, the predicted rate of ∼13 (33) events/day will be detected with 8% (4%) error. The sensitivity of Borexino to 8B and pp neutrinos and to a Galactic supernova event is also discussed.; The second part of this dissertation is devoted to the liquid scintillator containment vessel, an 8.5 m diameter sphere built of bonded panels of 0.125 mm polymer film. Through an extensive materials testing program we have identified an amorphous nylon-6 film which meets all the critical requirements for the success of Borexino. I describe tests of tensile strength, measurements of 222Rn diffusion through thin nylon films and of optical clarity. I discuss how the materials' radiopurity and mechanical properties affect the detector design and physics potential and present models that, incorporating the measured properties, yield a containment vessel that will safely operate for the ten-year lifetime of Borexino. |
