3Neutral Current Detectors for the Sudbury Neutrino Observatory

Current solar neutrino experiments indicate the possibility of neutrino oscillations. These flavour oscillations can be confirmed or refuted by the Sudbury Neutrino Observatory (SNO), a 1,000 tonne heavy water Čerenkov detector presently under construction. This detector will measure the 8B νe flux and energy spectrum via a pure charge current reaction, and independently the 8B total ν flux via a pure neutral current reaction. The experiment is thus self-normalizing and does not rely on the predictions of solar models to search for neutrino oscillations. The default method suggested for observing the neutron produced in the neutral current reaction proposed by the SNO collaboration is to dope the heavy water with 35Cl in the form of dissolved salt and observe the γ shower produced by neutron capture. Presented here is an alternative method for observing the neutral current neutron by using 3He proportional counters, distributed throughout the detector. The total length of detectors will approach half a mile. The pulse shape analysis techniques developed through the course of this thesis are used to differentiate the neutron signal from the inherent α backgrounds present in the walls of the detector and also as a method of assaying the radiopurity of the counters. As proof of principle, experiments have been running at the Waste Isolation Pilot Plant in Carlsbad, New Mexico, using prototype detectors. The results of these experiments show that the use of 3He proportional counters inside the SNO detector is feasible and will not cause an appreciable increase in backgrounds. In addition, discrete neutral current detectors have the particular advantage over the default method of being able to identify neutral current events on an event by event basis.