Spin echo small angle neutron scattering experiment

We are building a novel kind of small angle neutron scattering (SANS) instr ument, using a spin echo to detect the scattering. The basis of this instru ment 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 side of the spin flipper are shaped such to produce a very sensitive relati on between the vertical angle of the neutron path and the total precession angle on one side, based on the proportionality of the precession angle in a magnetic field with the length of the neutron path through the field regi on. Any SANS of a sample placed in the instrument changes the symmetry of t he neutron path and therefore decreases the echo. To define the precession regions we use magnetised foils, which rotate the neutron spin from being p arallel to the magnetic held to perpendicular to the held, to start the pre cession. We have built and tested these foils and the hipper. With the comp lete set-up we have measured the first Spin Echo SANS signal. We expect to measure a full correlation function in samples over distances from 5 to 100 0 nm in some minutes. (C) 1999 Elsevier Science B.V. All rights reserved.