Thermal neutron optical experiments with tuneable many-bounce channel-cut crystals

We realized the first tuneable channel-cut crystals to be used as monochromator and analyzer in a double-crystal diffractometer and demonstrated the superior operation for ultra small angle scattering. With this new system it was possible to measure the ultra small angle scattering from a single 14-μm glass fibre, the small angle scattering from an Al wedge and the diffraction pattern of a Si phase grating. The last measurement was only possible due to the reduction of the Darwin width of both crystals from 5.7 sec of arc (natural Darwin width) to 1.4 sec of arc.