  Using a novel NMR scheme we observed persistence in 1-D gas diffusion.
Analytical approximations and numerical simulations have indicated that for an
initially random array of spins undergoing diffusion, the probability p(t) that
the average spin magnetization in a given region has not changed sign (i.e.,
``persists'') up to time t follows a power law t^{-\theta}, where \theta\
depends on the dimensionality of the system. Using laser-polarized ^{129}Xe
gas, we prepared an initial ``quasirandom'' 1D array of spin magnetization and
then monitored the ensemble's evolution due to diffusion using real-time NMR
imaging. Our measurements are consistent with analytical and numerical
predictions of \theta \approx 0.12.
