Observation of Ultra-Slow Translational Diffusion in Metallic Lithium by Magnetic Resonance

The theory of a new magnetic-resonance technique for studying the ultra slow motion of atoms was presented in a previous paper. In this paper, we present its experimental confirmation for the case of translational diffusion in lithium metal. By this technique the mean time between atomic jumps $\tau$ can be measured provided that $\tau$ is less than the spin-lattice relaxation time $T_1$, permitting study of much slower rates of motion than previously has been possible using magnetic resonance. For lithium metal we have measured over nine orders of magnitude from $\tau ={10}^{-9\mathrm{}}$ sec to $\tau =1\mathrm{}$ sec, thereby extending by nearly five decades the results previously obtained by Holcomb and Norberg using conventional techniques. We have applied a new spin-temperature theory to the analysis of our low-temperature results in the range of its validity, $T_1>\tau >T_2$. By studying the variation of our relaxation time with the rf field strength $H_1$, we have unambiguously demonstrated the validity of the spin-temperature theory and the invalidity of perturbation theories in describing relaxation due to infrequent atomic motions in weak applied fields.