In-situ Polarized 3He-Based Neutron Polarization Analyzer for SNS Magnetism Reflectometer

We report here the construction and neutron transmission test results of an in-situ polarized 3He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3He nuclei of a cell of 3He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3He gas is continuously polarized in-situ on the instrument. Neutron transmission measurements showed that 73% 3He polarization was reached in this setup.