Quasielastic neutron scattering by hydrogen in transition metals

The quasielastic scattering of slow neutrons by hydrogen in metals is a sensitive method for the investigation of the diffusion process on an atomistic scale. First a review of the theory of the quasielastic neutron scattering by hydrogen in metals is given. Then some methods to measure the quasielastic scattered neutrons are discussed. From measurements of the quasielastic line broadening at small momentum transfers hκ≪2π/lj(lj being the hydrogen jump length) the diffusion constant can be determined. Most of the values determined so far have been compiled. From measurements of the quasielastic line at large momentum transfers hκ⩾2π/lj details of the jump diffusion process can be obtained. The experiments performed so far on the systems PdHx VHx TaHx NbHx and PdAgHx are discussed. Most of the results do not tit to a simple jump diffusion model. It seems to be important to consider the hydrogen motion during the jump phase.