Nuclear spin relaxation by translational diffusion in solids

Torrey has developed a theory of dipolar relaxation by atomic diffusion in polycrystalline solids for a model of nearest-neighbour jumps in which the average over crystal orientations was taken in an approximate way. The theory is developed here rigorously in a form which could be readily generalized to a single crystal and to more complicated jump models. As an example it is shown that the Torrey theory for a FCC lattice gives results for T 1 , T 1 rho and T 2 that are 2.5% too large for high temperatures and 1.4% too small for low temperatures. The errors would be larger for a BCC lattice and lattices with low coordination numbers.