Characterization of neutron optics elements using neutron multireflections experiment

Metallic multilayers are more and more used in the fabrication of efficient neutron optics elements. Neutron reflectivity is the ideal tool for the characterization of these multilayer devices. However, for these developments, the most interesting part of the reflectivity curve is situated in regions where the reflectivity coefficient R is close to one. In that part of the curve, a good precision in the measurement of the reflectivity is difficult to obtain using the classical one reflection measurements since differences between the incoming and the reflected beams are weak. At the Leon Brillouin Laboratory in Saclay, we have developed a neutron multireflections experiment. Compared with one reflection measurement, it enables us to increase the accuracy on the deviation from 1 of the reflectivity by a factor up to 12. This technique has been used on classical 58Ni neutron guide elements as well as on two multilayer systems. These new measurements have been compared with classical reflectivity experiments performed on the same elements. ((orig.))