Quasi-elastic Scattering of Neutrons

In solids random motions of atoms may take place in connection with disorder; for instance diffusion of interstitials in solid solutions or orientation fluctuations in molecular solids. Experimentally these motions are observed mostly by resonance and relaxation techni­ ques, by optical spectroscopy and, recently, by neutron spectroscopy. In comparison to the other me­ thods neutron spectroscopy has the advantage, that it permits an observation of these motions not only in time but also in space. Moreover, as neutron scattering can be described in first Born a p p ro x im a tio n th e evaluation of experi­ mental data is comparatively simple. The intensity of neutrons scattered into solid angle dD and into an energy interval dE is proportional to the differential cross-section 2