Ex-situ Polarized 3He Neutron Spin Filter and Analyzer System

In the preparation of neutron beams, used at DOE facilities for materials research, polarized 3He offers over three orders of magnitude difference between the ortho and para spin states in its absorption cross section for epithermal neutrons. Cells of polarized 3He are favored in many experiments for their compact size, effectiveness over a broad range of neutron energies, and ability to conveniently have their spin reversed to cancel uncertainties. Existing 3He polarization systems based on alkali Spin Exchange Optical Pumping ,SEOP, use lasers to illuminate cells in situ. However, the NPD Gamma experiment recently found that the neutron beam has an immediate depolarizing effect on the alkali vapor and a long term aging effect leading to milky buildup on the cell walls. This project will adapt existing 3He polarization technology for use as an exsitu system for neutron spin filters and analyzers. The system would be located by the side of the neutron beam line and utilize multikilowatt lasers to produce up to 30 liters per day of 3He polarized. Phase I will investigate the high polarization capabilities of the system, primarily through implementing a flowing oil thermal stabilization system, reconfiguring a multikilowatt laser for milliradian divergence, fabricating three aluminosilicate cells, and testing them for long lifetime and low X factor. Commercial Applications and other Benefits as described by the awardee: Polarized 3He has synergistic applications, not only as a neutron spin filter for producing polarized neutron beams and as a neutron spin analyzer to measure magnetic properties of thin films, but also as an electron beam target and as a contrast agent for measuring regional pulmonary function in diagnostic magnetic resonance imaging