NMR SELF-DIFFUSION MEASUREMENTS IN A BOUNDED SYSTEM WITH LOSS OF MAGNETIZATION AT THE WALLS

A general treatment of diffusion of spin-bearing species in a bounded medium with loss of magnetization at the boundaries is presented. The effects of the loss of magnetization at the boundaries for pulsed-field-gradient (PFG) NMR diffusion measurements and q-space imaging are calculated and demonstrated. If this wall effect is ignored, e.g., by assuming fully reflecting walls, erroneous results for the barrier spacing (a) and interbarrier diffusion coefficient (D) are obtained. Methods for obtaining the correct values of the parameters a, D, and the loss of the magnetization at the boundaries from experimental results are demonstrated. The consequences of loss of magnetization at the walls for the interpretation and application of PFG NMR results are discussed. © 1993 by Academic Press, Inc.