D3 - The Spin Polarised Hot Neutron Beam Facility

Simulated experiment

From neutron source to detector in a high-field configuration

Neutrons from the reactor are moderated in the graphite hot source so that the maximum flux is at a short wavelength.

  • Hot neutrons enter beam tube H4 and go to the polarising monochromator which diffracts only neutrons with a given wavelength and spin polarisation.
  • The guide-field maintains the polarisation state of this beam.
  • The cryoflipper reverses alternately the polarisation state of the beam.
  • The sample - a ferromagnetic or paramagnetic single crystal - is in a magnetic field and is cooled down or warmed up in a cryostat.
  • For each Bragg reflection, the peak intensity depends on each polarisation state of the beam. A Fourier component of the magnetisation distribution in the crystal is obtained from the two intensities.

D3 is a polarised hot-neutron diffractometer

  • The sample is lowered through the variable temperature insert of the cryomagnet into the beam.
  • It is rotated so that a given set of crystal planes diffracts the beam.
  • The detector is rotated and lifted towards the diffracted beam.
  • The magnetisation distribution shown in the corner is derived from the ratio of the intensities measured with the two polarisations.