Elucidation of fundamental properties of helium in metals by nuclear magnetic resonance techniques.

摘要

The nuclear magnetic resonance (NMR) properties of very high density (sup 3)He in metals are discussed in the context of the corresponding properties in relatively high density bulk (sup 3)He. In particular, the effects of the (sup 3)He diffusion on the contribution of the (sup 3)He-(sup 3)He dipolar interaction to the lineshape and to the spin-lattice relaxation parameter (T(sub 1)) are described. It is shown that the temperature dependence of the lineshape and of T(sub 1) are independent sources of information about helium density and also about helium diffusivity. Moreover, T(sub 1) is shown to be a sensitive indicator of melting transitions in bulk (sup 3)He. Palladium tritide is presented as a model system for NMR studies of (sup 3)He in metals. Experimental NMR studies of this system reveal behavior analogous to what has been observed for bulk helium. Evidence for a (sup 3)He phase transition near 250 K is provided by the temperature dependence of T(sub 1). Assuming this to be a melting transition, a density is obtained from the bulk helium EOS that is in good agreement with theory and with swelling measurements on related metal tritides. (sup 3)He NMR measurements have also provided information about the density distribution, helium diffusivity, and mean bubble size in palladium tritide. 22 refs., 8 figs. (ERA citation 16:002182)