Installation and Alignment of the N3He Experiment

The n3He experiment is designed to probe the hadronic weak interaction by measuring the parity violating asymmetry between the spin of incoming neutrons and the momentum of outgoing protons following the nuclear break up of a helium three upon absorbing a neutron. Cold neutrons from the SNS are first polarized then allowed to impact a target chamber filled with helium three where the reaction occurs. Energetic particles resulting from the nuclear breakup ionize the helium three gas and are thereby detected as currents by an array of signal wires within the target chamber. In order to make a statistics limited measurement on the order of ±10% systematic alignment errors must be carefully controlled. Of greatest importance are the direction and magnitude of the magnetic field within the experiment, location of the neutron beam centroid, and the alignment of the primary components with respect to them. The equipment and methods utilized to achieve these alignments will be discussed as will the results of the alignment procedures.