The dynamic structure-factor, S(Q, ®), describes scattered neutrons in terms of the wave-vector transfer Q and the neutron energy-transfer h®, where h = h/2n and h is Planck’s constant. The timescales and corresponding energies of the processes that are accessed by neutron scattering from energy materials are illustrated in Fig. 1.2. A particular strength of neutron scattering is that the size and geometry of the volume explored by the dynamic process is also available, and is shown on the horizontal axis of Fig.1.2.

This is particularly useful when measuring local or long-range diffusive pro­cesses, for example in fuel-cell electrolytes (see Chaps. 9 and 10).

Inelastic peaks usually arise from a periodic motion, and the forces controlling this motion are stronger than those that would define a more diffusive motion. Correspondingly, inelastic peaks usually arise at higher energy than the quasielastic broadening, as illustrated schematically in Fig. 1.3.