Theory of Mössbauer line broadening due to correlated diffusion in crystals

The line-broadening effect of correlations between successive jumps of a Mössbauer atom is investigated. The ’’encounter model’’ originally developed for nuclear-magnetic-resonance diffusion studies is applied to describe temporal and spatial correlations which may cause significantly smaller linewidths than a random-walk diffusion mechanism. This straightforward analytic generalization of the random-walk results is capable of eliminating some of the earlier discrepancies between diffusion constants determined from radio-tracer and Mössbauer experiments.