Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He

We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute He-3 in solid He-4 in the temperature range 0.01 <= T <= 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the He-4 lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of He-3 impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies.