  We report initial NMR studies of i) xenon gas diffusion in model
heterogeneous porous media, and ii) continuous flow laser-polarized xenon gas.
Both areas utilize the Pulsed Gradient Spin Echo techniques in the gas-phase,
with the aim of obtaining more sophisticated information than just
translational self-diffusion coefficients - a brief overview of this area is
provided in the introduction. The heterogeneous or multiple-length scale model
porous media consisted of random packs of mixed glass beads of two different
sizes. We focus on observing the approach of the time-dependent gas diffusion
coefficient, D(t), (an indicator of mean squared displacement) to the long-time
asymptote, with the aim of understanding the long-length scale structural
information that may be derived from a heterogeneous porous system. The Pade
approximation is used to interpolate D(t) data between the short and long time
limits. Initial studies of continuous flow laser-polarized xenon gas
demonstrate velocity-sensitive imaging of much higher flows than can generally
be obtained with liquids (20 - 200 mm/s). Gas velocity imaging is, however,
found to be limited to a resolution of about 1 mm/s due to the high diffusivity
of gases compared to liquids. We also present the first gas-phase NMR
scattering, or diffusive-diffraction, data: namely, flow-enhanced structural
features in the echo attenuation data from laser-polarized xenon flowing
through a 2 mm glass bead pack.
