Analytic treatment of nuclear spin-lattice relaxation for diffusion in a cone model

► We carry out analytic treatment of diffusion equation for rotational wobbling in a cone. ► From it we derive the nuclear spin-lattice relaxation rate. ► The latter is found to behave non-monotonically on the cone half-width. ► This phenomenon takes place for all explored distributions of the cone axes relative the magnetic field. ► The dependence of the rate on the cone half-width yields a maximum similar to that predicted by the model-free approach.