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The decay of transverse nuclear spin magnetization in a homogeneously broadened solid can be prolonged for a time {T₂}^T₂ by applying a train of 90^ pulses in a modified Carr-Purcell sequence with pulse spacing <T₂. A time-expansion theory which treats the problem from the viewpoint of spin echoes is used to explain an observed proportionality between {T₂}^ and ^-5, and predicts that {T₂}^ depends upon a modified sixth moment of the resonance. An alternative viewpoint, in which one considers the long-time development of the spin system in a periodically modulated rf field H₁ (t), shows that the experiment is closely related to spin locking and explains the fact that {T₂}^T₁ (H₁), the relaxation time parallel to the average rf field, as 0. The experiment offers some possibilities for the study of spin-lattice relaxation in weak fields and for double resonance in the rotating frame.
Waugh et al. (Tue,) studied this question.
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