Spin-Lattice Relaxation Time forI127in KI in the Temperature Range 2°K to 20°K

Abstract

The spin-lattice relaxation time, $T_1$, for ${\mathrm{I}}^{127}$ in both single crystal and powdered KI has been measured in the temperature range 2°K to 20°K using a Pound-Watkins type nuclear magnetic resonance spectrometer. In the liquid hydrogen temperature range $T_1$ is approximately the same for both the single crystal and the powder specimens, varying from 20 sec at 20°K to 70 sec at 14°K. Both the temperature dependence and the magnitude of $T_1$ in this temperature range can be explained on the basis of a theory of nuclear quadrupolar spin-lattice relaxation proposed by Van Kranendonk. In the liquid helium temperature range (2°K to 4°K), $T_1$ is constant within experimental error. For the single crystal $T_1=6.9\mathrm{}\times {10}^3$ sec and for the powder specimen $T_1=6.0\mathrm{}\times {10}^2$ sec in this temperature range. These values of $T_1$ are less by orders of magnitude than is predicted using Van Kranendonk's theory. The ${\mathrm{I}}^{127}$ resonance (spin $I=\frac{5}{2}$ in units of $\hslash$) consisted of a narrow (less than 1 gauss half-width) central line with broad (>15 gauss) weak wings. This is attributed, according to Pound, to a shift in the nuclear magnetic energy levels brought about by the interaction of the nuclear quadrupole moment with electric field gradients present in the specimens.