Spectral density functions for quadrupolar nuclear spin relaxation due to translational diffusion

The spectral density functions for relaxation of nuclear spins due to time-dependent electric quadrupole interactions are studied for diffusion of atoms on a crystal structure. It is shown that, for an arbitrary concentration c of diffusing atoms, the spectral density functions and consequent relaxation rates scale with concentration as c(1 − c). The detailed form of the functions can be obtained simply from analysis of the low spin concentration limit, unlike the analogous case for magnetic dipolar relaxation. Some applications to metal-hydrogen systems are described.