Abstract: | The Sudbury Neutrino Observatory will permit a comparison of the rate of neutral-current neutrino interactions to charged-current interactions, which is a test of neutrino mixing and mass. The neutral-current process can be measured by: a) comparison of the rate for electron elastic scattering to the pure charged-current rate on deuterium, b) neutron capture on Cl ions added to the heavy water, and, c) neutron capture in an array of 3He-filled proportional counters. The design and construction of suitable proportional counters are described. |