Published online by Cambridge University Press: 21 February 2011
Several phenomena analogous to those observed in classical optics, such as reflection, refraction and interference, are also observed with slow neutrons. Information on surface properties, described by a refractive index profile, can be extracted from reflection experiments. This information is similar to that obtained by X-ray reflection. However, there are some instances where the new neutron method provides a distinct advantage. The refractive index is related to the scattering length density, a parameter which describes the neutron-matter interaction. Owing to the magnetic interaction, magnetic materials have a neutron spin dependent refractive index, and a critical reflection of polarized neutrons is a particularly sensitive probe of surface magnetism. On the other hand, in contrast to X-rays, neutron scattering length values vary randomly from element to element. Isotopic substitution can then produce a contrast in the scattering length density. Of particular importance is the large difference between hydrogen and deuterium. This is a distinct advantage for studiyng many problems in surface chemistry, particularly in the polymer field.