  The dynamics of 3He atoms in solid 4He have been investigated by measuring
the NMR relaxation times T1, T2 in the region where a significant non-classical
rotational inertia fraction (NCRIF) has been reported. For 3He concentrations
x3 = 16 ppm and 24 ppm, changes are observed for both the spin-lattice
relaxation time T1 and the spin-spin relaxation time T2 at the temperatures
corresponding to the onset of NCRIF and, at lower temperatures, to the 3He-4He
phase separation. The magnitudes of T1 and T2 at temperatures above the phase
separation agree roughly with existing theory based on the tunneling of 3He
impurities in the elastic strain field due to isotopic mismatch. However, a
distinct peak in T1 and a less well-resolved feature in T2 are observed near
the reported NCRIF onset temperature, in contrast to the
temperature-independent relaxation times predicted by the tunneling theory.
