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Polarized 3HE Spin Filters for Neutron Science

Published

Author(s)

Thomas R. Gentile, Wei-Chen N. Chen

Abstract

The large spin dependence of the absorption cross section for neutrons by 3He gas provides a method to polarize neutron beams. For certain applications, such polarized 3He-based neutron "spin filters" have advantages over conventional neutron optical polarizing methods. Spin filters operate at all neutron wavelengths, can cover a large angular range and/or a large energy range, and decouple neutron polarization from energy selection. Both spin-exchange optical pumping (SEOP) and metastability-exchange optical pumping (MEOP) are currently being employed to polarize 3He spin filters at various neutron facilities worldwide. I will focus on the development and application of SEOP-based neutron spin filters at the National Institute of Standards and Technology (NIST), Center for Neutron Research (NCNR). The combination of long relaxation time spin filter cells, high power spectrally narrowed diode lasers, and the use of Rb/K mixtures have allowed us to reach 3He polarizations up to 85 % in spin filter cells ~ 1 liter in volume. Studies have revealed limits to the achievable polarization from temperature-dependent relaxation and unexplained magnetic field dependence for relaxation in SEOP cells. Applications include neutron scattering methods such as triple-axis spectrometry and small angle neutron scattering, and fundamental neutron physics. In most neutron scattering applications, cells are transported to the beam line and stored in a magnetically shielded solenoid or box. A recent focus has been apparatus for wide-angle neutron polarization analysis. A measurement of the spin-dependence of the neutron-3He scattering length was performed with a small, polarized 3He cell located inside a neutron interferometer. A precision measurement of the neutron polarization for this experiment was also performed with a 3He spin filter. Use of spin filters in high flux neutron beams have revealed beam-induced alkali-metal relaxation and long term effects on SEOP spin filter cells
Proceedings Title
Proceedings of Science
Volume
022
Conference Dates
September 9-13, 2013
Conference Location
Charlottesville, VA
Conference Title
Same

Keywords

3HE, neutron science

Citation

, T. and Chen, W. (2014), Polarized 3HE Spin Filters for Neutron Science, Proceedings of Science, Charlottesville, VA, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914929 (Accessed April 17, 2024)
Created February 12, 2014, Updated February 19, 2017