³He Spin Filter for n(p,d)

Experiments in fundamental physics were one of the original motivations for ³He-based polarizers. These include measurements of nucleon coupling constants, studies of the weak interactions, and neutron interferometry. The drawing to the left illustrates an experiment to study parity violation in the absorption of neutrons by hydrogen, which allows extraction of the weak isovector pion-nucleon-nucleon coupling. The observable in this experiment is a tiny parity-violating asymmetry that can only be extracted with the use of polarized neutrons. A ³He polarizer is ideal for this experiment because it can polarize a large, highly divergent beam over a large range of energies, the polarization can be easily reversed for systematic tests, and the gamma background is negligible.

Inquiries or comments: david.gilliam@nist.gov
Online: November 1998