Long-time behavior of nuclear spin decays in various lattices

The transverse NMR decays of 129Xe in polycrystalline xenon were recently shown to have a universal property: in the long-time regime these decays all converge to the same sinusoidally modulated exponential function irrespective of the initial transverse spin configuration prepared by a sequence of one or more radio frequency pulses. The present work constitutes a more comprehensive survey of this phenomenon. It examines transverse decays for several different isotopic concentrations of 129Xe, employs additional pulse sequences, and performs similar measurements in a different material: 19F in single-crystal and polycrystalline CaF2. With the possible exception of polycrystalline CaF2 where the observation of the long-time behavior is limited by the experimental resolution, all these systems display the long-time universal behavior characterized by particular values of the exponential decay coefficient and beat frequency that were unique for each lattice. This behavior has been theoretically predicted based on the notion of microscopic chaos.