Constant gradient stimulated echo studies of diffusion in porous materials at high spectrometer fields.

A high field strength, constant gradient stimulated-echo pulse sequence is applied to a model heterogeneous system consisting of randomly packed beds of glass microspheres. A multiple exponential analysis of the dependence of the stimulated echo amplitude on diffusion time, delta, yields coefficients that depend explicitly on both the wavevector, q and on the time delay, delta. The wavevector and delta- dependence of the coefficients is analyzed both theoretically and experimentally and shown to be sensitive to the effects of coupled relaxation and diffusion. It is proposed that these effects could be exploited as a new probe of microstructure.