Development of spin-echo small-angle neutron scattering

A polarised neutron spin echo technique is used to build a novel kind of sm all angle neutron scattering (SANS) instrument. The basis of this instrumen t is a symmetric set-up with a spin flipper in the centre, which creates a spin echo, even with a divergent beam. The precession regions on either sid e of the spin flipper are shaped such as to produce a very sensitive relati on between the vertical angle of the neutron path and the total precession angle. Any SANS of a sample placed in the instrument reduces the symmetry o f the neutron path and therefore decreases the echo. Magnetised foils define the precession regions by rotating the neutron spin from being parallel to the magnetic field to perpendicular to the field, t o start the precession. These foils and the flipper were built and tested. A spin echo SANS signal is measured with the complete set-up. It should be possible with this technique to measure within minutes a full correlation function in samples over distances from 5 to 1000 nm.