Spin diffusion and nuclear spin-lattice relaxation in irradiated solids: amultiple-pulse NQR study

We present a detailed theoretical and experimental NQR multiple-pulse spin- locking study of spin-lattice relaxation and spin diffusion processes in th e presence of paramagnetic impurities in solids. The relaxation function of the nuclear spin system at the beginning of the relaxation process is give n by exp (- t/T-ip)(alpha), where T-1 rho is spin-lattice relaxation time i n rotating frame and alpha = d/6, d is the sample dimensionality. Then the relaxation proceeds asymptotically to an exponential function of time, whic h was attributed to the spin-diffusion regime. Using the experimental data obtained from the analysis of those two relaxation regimes in gamma-irradia ted powdered NaClO3, spin diffusion coefficient has been determined and the radius of the diffusion barrier has been estimated. (C) 1999 Elsevier Scie nce B.V. All rights reserved.