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

3He offers over three orders of magnitude difference between the ortho-and para-spin states in its absorption cross section for epithermal neutrons. Polarized 3He cells serve as neutron spin filters for preparation of intense beams of polarized neutrons, and as spin analyzers for determining polarization of scattered neutrons. While super-mirrors offer an alternative, 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, cells placed in beam lines or adjacent to scattering targets. These systems suffer from compromises. The NPDGamma 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. Analyzers of unusual geometries are difficult to illuminate. Ex-situ polarization, separated operation of the polarizer with polarized gas delivery to the cells, has been exploited successfully in Europe. Metastability Exchange Optical Pumping (MEOP) used for that system, however, requires a large volume for polarization and specialized compression equipment, at high cost. Xemed and the University of New Hampshire have partially completed a prototype large-scale 3He SEOP polarizer funded by the NIH for cost-effective medical diagnostic imaging. We propose to adapt our 3He polarization technology for use as an ex-situ system for neutron spin filters and analyzers. Our system, appropriately adapted, would be located by the side of the neutron beam line and utilize multi-kilowatt lasers to produce up to 30 liters per day of 3He polarized as high as 75% or more. In Phase I we propose to fully investigate the high polarization capabilities of the system, primarily through implementing our flowing oil thermal stabilization system, reconfiguring our multi-kilowatt laser for few-milliradian divergence, fabricating three aluminosilicate cells, and testing them for long lifetime and low X-factor. In Phase II we propose to utilize a non-ferrous compressor to circulate the 3He through a low pressure loop to demonstrate its capabilities in a spin filter or analyzer application. 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 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 (MRI).