Restricted diffusion within a single pore

The time-dependent diffusion of He-3 atoms perpendicular to the axis of a single macroscopically large cylindrical pore is studied using a steady (or constant) gradient-recalled echo sequence. Measurements of the effective He-3 diffusion coefficient extending from the free-diffusion regime to the motionally averaged regime are presented, and are well-described by analytic solutions to the Bloch-Torrey equation based on the gaussian phase approximation. Our data yield the value 0.140(6) m(2)/s for the self diffusion coefficient of He-3 at a temperature of 296 K and a pressure of 1.00 Torr. Adaptations of these methods should enable the study of complex pore geometries as model systems. (C) 2004 Elsevier Inc. All rights reserved.