Contributions of F-centers and impurities to spin-lattice relaxation of Na-23 nuclei in a gamma-irradiated NaCl crystal were clearly separated under the condition of a steady-state magnetic saturation. The spin relaxation time of F-centers at 77 K was estimated. The change in impurity contribution to 23Na relaxation as a result of irradiation was studied. (C) 2000 Elsevier Science B.V. All rights reserved.