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CHRNS Neutron Spin Filters: Polarized 3He

Nuclear spin polarized 3He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the strong spin dependence of the neutron absorption cross section for 3He. Compared to commonly used neutron polarizers such as supermirrors and Heusler crystals, neutron spin filters (NSF) have these advantages: 1) they are broadband and can polarize cold, thermal or hot neutrons effectively; 2) they can polarize large area and large divergence neutron beams without adding beam divergence; 3) they are in-line add-on devices, and 4) they can efficiently flip the neutron polarization by reversing the 3He nuclear polarization. This last capability can be performed using the adiabatic fast passage nuclear magnetic resonance technique, thus integrating the polarizer and the flipper into a single neutron polarizing device.

Polarized 3He is used to provide polarized beam capability for various instruments at the NIST Center for Neutron Research. The process involves the polarization of 3He gas contained within a glass cell which is placed on the instrument. By this method, polarized 3He can be used to polarize the neutron beam (polarizer) and/or select out the chosen spin state (analyzer). The high density of polarized 3He gas (1019 to 1020 cm−3) required for an effective neutron polarizer can be produced using two optical pumping methods: spin-exchange (SEOP) {Walker97 , BCV60}, which is performed directly at high pressure (1-10 bar), and metastability-exchange (MEOP) {CSW63}, in which the gas is polarized at low pressure (1 mbar) and then compressed. More detail is provided through the reference links below about neutron spin filters.

The NIST Center for Neutron Research (NCNR) initiated a polarized 3He neutron spin filter program in 2006. The goal is to polarize and/or analyze neutron beams for neutron scattering instruments where 3He NSFs are advantageous. At the NCNR, polarized 3He NSF devices have been applied to diffuse reflectometry, small-angle neutron scattering (SANS), and thermal neutron triple-axis spectrometry (TAS). Applications to more instruments (Multi Axis Crystal Spectrometer, Disk Chopper time-of-flight spectrometer, BT-1 powder diffractometer, Materials Diffractometer, MAGIK reflectometer) are under development. For more information about the capabilities specific to the NCNR neutron spin filter program, please select the provided links.

NSF News and Updates
Updated Data reduction Links
Polarized beam data reduction software links have been updated for Windows 7 and now includes Linux Red Hat 7.
PHADES Test Beam Line
The test beam line is primarily used for 3He NSF and detector development. It can also be used for crystal alignment. See the link to the left for more info.
MACS joins user program
MACS is now part of the NCNR user program. Click on the "MACS" link to the right to find the instrument home page as well as information concerning the use of 3He on MACS. The link contains details about NSF equipment usage, such as instrument, lifetime, cell changes, Q-range, etc. MACS instrument contacts are also listed.

More info to come...
  • SEOP Method
  • NSF Figures of Merit
  • Equipment
  • Instrument Info Slides
  • NSF Publications
  • Data Reduction Links
  • Laser Monitor
  • NSF Polarization Correction
  • Polarized Beam Commands
  • NSF Logbooks
  • Obtaining Beamtime
  • Facility Schedule
  • Monetary Assistance
  • Sample Environment
  • MACS
  • SANS
  • Neutron Spin Filter Instruments

    3He on MACS instrument
    MACSCHRNS logo
    3He on MAGIK instrument
    3He on PHADES instrument
    3He on NG7 SANS instrument
    SANSCHRNS logo
    3He on BT-7 instrument

    NSF Contacts

    Name Office Phone E-mail
    Wangchun Chen (301)975-6222
    Shannon Watson (301)975-6232
    Kathryn Krycka (Magnetic Media) (301)975-8685

    Last modified 10-30-15