The paper is devoted to investigations of spin-lattice relaxation ation determined by nuclear dipole-dipole interactions for processes in 99% 13 C-enriched diamonds. Relaxation time measpin-1 2 nuclei and T imp 1 is the impurity component of the spinsurements were performed as a function of orientation, magnetic lattice relaxation time determined by 13 C nuclear interactions field, and temperature. Both experimental results and theoretical with paramagnetic centers. The first term in Eq. [1] usually discussion are presented. Multiexponential behavior of nuclear can be considered negligibly small-according to the theory magnetization recovery was observed. There was found no signifiof Waller (11). For a material with 100% 13 C enrichment cant influence of the diamond orientation on the nuclear spinthe thermally induced lattice vibrations only modulate the lattice relaxation. The field dependence of the spin-lattice relaxnuclear dipole-dipole interactions marginally, leading to reation time was found to be proportional to the second power of laxation times T lat 1 much longer than the impurity contributhe magnetic field. The temperature measurements showed a weak increase of the spin-lattice relaxation time with decreasing tem-tion. Therefore, relaxation time in diamonds is mostly deterperature. Possible mechanisms of impurity relaxation are considmined by the trapped paramagnetic impurities. The model ered and compared with the experimental data. ᭧ 1998 Academic Press for impurity relaxation is the following: (i) the relaxed electrons of a paramagnetic impurity relax very effectively nearby 13 C spins; (ii) these 13 C spins in turn relax their 8