How it works

• Beam from cold guide H15 arrives at vertically focussing graphite monochromators.
• The monochromatic beam passes through a Be filter and arrives at the supermirror bender polariser.
• The neutrons are polarised in the z-direction.
• The neutrons pass through a Mezei spin-flipper, which is "off" when measuring non-spin-flip cross-sections, and "on" when measuring spin-flip cross-sections.
• The neutrons are rotated into the x, y or z direction using 3 orthogonal Helmotz coils situated at the sample position.
• After scattering from the sample the neutrons are analysed for final spin state, and detected using the 3 multi-analyser/detector banks, with 22 supermirror bender analysers and 44 3He detector tubes in each bank

Experiments on D7 are performed to investigate diffuse scattering from disordered systems – magnetic & non-magnetic. The diffracted intensities measured at D7 makes it possible to model such disordered systems.

How neutron spins behave

Here D7 is shown in its spin-flip (SF) configuration.

• Unpolarised neutrons are reflected by the graphite monochromator.
• The incident neutron beam is polarised by the supermirror bender polariser.
• For measurement of SF cross-sections, the neutrons are spin flipped by the flipper.
  Flipper is turned off when measuring non spin-flip (NSF) cross-sections.
• The neutrons are reflected and also partially spin-flipped by the sample.
• The spin-up neutrons are transmitted and spin-down neutrons are absorbed the supermirror bender analyser before being detected.