Dynamic Nuclear Enhancement in Metallic Sodium

Abstract

A double-resonance spectrometer was constructed capable of making accurate measurements of all the dynamical variables expressed in the master equation governing the time evolution of the dynamic nuclear enhancement of a single sodium sample. This system could measure the rate of rise of the nuclear polarization after the onset of saturation, the rate of decay of the polarization after the saturation was removed, and the nuclear $T_1$ by the standard 180°-90° pulse method. It was found that each of these processes had the same time constant $T_1=13.2\mathrm{}\pm 0.2$ msec within experimental error, in agreement with theory. The steadystate enhancement as a function of electron saturation gave a value of the "leakage coefficient" $f$ to be 0.88±0.05 (at 29°C). The values of $T_1$ and $f$ enable one to calculate ${T_1}^e$ (the spin-lattice relaxation time due to the conduction-electron-nuclear contact interaction) to be 14.9±0.8 msec. These data demonstrate that the electron-nuclear contact interaction is the dominant mode of nuclear relaxation for sodium at room temperature.