The Spin Polarised Hot Neutron Beam Facility

Measuring with polarised neutrons in a high magnetic field configuration

  • The unpolarised neutron beam coming from the hot source enters the monochromator area.
  • Under an applied magnetic field, the polarising monochromator diffracts neutrons having a given energy and polarisation sign.
  • Guide-fields are used to maintain the polarisation of the beam. The educated viewer of the animation will notice an error in the direction of the magnetic guide-field  when neutrons arrive at the Meissner Niobium foil.  Up to that point the neutron spins follow adiabatically the magnetic guide field.  As neutron spins are shown down the magnetic field must be down
  • At the entrance of the cryoflipper, before the superconducting foil, the magnetic field is set parallel or anti-parallel to the field applied after the foil. The polarisation rotates adiabatically and crosses the foil.
  • At the exit, the polarisation is parallel or antiparallel to the guide field.
  • A slit reduces the size of the beam to lower the background.
  • The sample, placed in an applied magnetic field, diffracts neutrons which are counted by the detector. The intensity of the diffracted beam depends on the initial polarisation of the beam.