An Experimental Study of the Nuclear Relaxation Mechanism in Several Crystals

Abstract

The effective nuclear spin-lattice relaxation mechanism has been determined in a number of crystals by observing the relative saturation behaviour of the lines of their quadrupole-split nuclear magnetic resonance spectra. It is shown that all lines and combinations of lines should have the same saturation behaviour if the mechanism is magnetic, and differing behaviour if the mechanism is quadrupolar. The ²³Na relaxation in pure synthetic crystals of sodium nitrate, sodium chlorate and sodium thiosulphate was found in each case to be quadrupolar. The ⁷L1 and ²⁷Al relaxation in natural mineral crystals of spodumene and the ²⁷Al relaxation in a mineral crystal of euclase were found to be magnetic. The ¹¹B relaxation in a pure synthetic crystal of borax was also found to be magnetic. Chemical analysis showed a sufficient concentration of paramagnetic impurity in the mineral specimens to account for the dominance of the magnetic relaxation mechanism, and a sufficiently small concentration of paramagnetic impurity in the three sodium salts to account for the dominance of the quadrupolar mechanism. Despite the purity of the borax crystal, the quadrupole moment of the ¹¹B nuclei is too small to enable the quadrupolar mechanism to compete with the magnetic mechanism.