Low-temperature 3He NMR studies in aged palladium tritide.

Experimental results from a NMR study of {sup 3}He in nanometer-sized microbubbles in aged palladium tritide over the temperature range 4--300 K are presented. A determination of the rigid-lattice--line-shape second moment at 4 K provides a value for the density of {sup 3}He that is in good agreement with the value inferred for the same sample from an analysis of {sup 3}He spin-lattice relaxation data over the range 50--300 K. This latter analysis is based on the hypothesis of a melting transition for a distribution of densities, and assumes that the bulk helium equation of state applies to helium in the nanometer-sized bubbles. This latter assumption is supported by the agreement between the two independent density determinations. Line-shape analyses reveal narrowing of the {sup 3}He spectrum at about 35 K, which agrees with a prediction of motional narrowing based on an extrapolation of {sup 3}He diffusivity data determined over the range 100--250 K in an earlier study of aged palladium tritide. The observation of coexisting broad and narrow components in the free-induction decay at 40 K provides direct evidence for a distribution of {sup 3}He densities in aged palladium tritide. Because the melting temperature and the rigid-lattice second moment aremore » both strong functions of density, the NMR techniques described here provide a sensitive measure of the density distribution and related properties.« less