NMR-propagator measurements in porous media in the presence of surface relaxation and internal fields

We measure the probability distribution P(ζ) — the propagator — of molecular displacements on Stokes flow through a pack of microporous glass beads and a carbonate rock. An optimized sampling of q-space is introduced for the measurement of a P(ζ) and its first moment 〈ζ〉. Our results delineate and provide an understanding of the experimental regimes where background fields and surface relaxation distort the measured propagators.