C-13 RELAXATION IN NATURAL DIAMOND

C-13 spin-lattice relaxation times in the laboratory frame have been m easured for one type la diamond and one type IIa diamond. Spin-lattice relaxation times for polarization in a field of 47 kG are shorter tha n spin-lattice relaxation times associated with the depolarization in a field of 47 kG after dynamic nuclear polarization in a field of 3.4 kG, If the C-13 magnetization is inverted after dynamic nuclear polari zation, the spin-lattice relaxation time is shortened, but it is still longer than the corresponding value for polarization in a field of 47 kG. It is suggested that spin-lattice relaxation via paramagnetic imp urities is the main spin-lattice relaxation mechanism. A qualitative e xplanation is offered for the observed relaxation times. (C) 1997 Else vier Science B.V.