Restricted diffusion within a single pore

The time-dependent diffusion of 3 He 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 3 He 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 3 He 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.