NMR study of thorium hydrides (${\mathrm{Th}}_4$${\mathrm{H}}_{15}$, Th${\mathrm{H}}_2$) and deuteride (${\mathrm{Th}}_4$${\mathrm{D}}_{15}$)

Thorium hydride was studied using NMR techniques. Relaxation times of protons and deuterons in ${\mathrm{Th}}_4$ ${\mathrm{H}}_{15}$ and ${\mathrm{Th}}_4$ ${\mathrm{D}}_{15}$ were measured over a wide temperature range. Different diffusion processes in different temperature regions were observed. In the range $417\lesssim T\left(°\mathrm{K}\right)\lesssim 526$ the activation energy for hydrogen (or deuterium) diffusion was calculated to be $E_a\simeq 14.7$ kcal/mole. The preexponential factor ${\tau }_0$ was calculated to be ${\tau }_0\simeq {10}^{-14\mathrm{}}$ sec for hydrogen, and ${\tau }_0^{\mathrm{D}}\simeq \sqrt{2}{\tau }_0^{\mathrm{H}}$ for deuterium. The frequency of the quadrupole interaction of the deuterons ${\nu }_Q$ was found to be in the range $37.4\lesssim {\nu }_Q\lesssim 43.2$ kHz. The electronic contribution to the relaxation in samples of Th${\mathrm{H}}_2$ and ${\mathrm{Th}}_4$ ${\mathrm{H}}_{15}$ was calculated from spin-lattice relaxation-time measurements at low temperatures ($78<~T<~300°$K). While in Th${\mathrm{H}}_2$ this contribution can be given as ${\left(T_{1}T\right)}_e=567\mathrm{}\pm 30$ sec °K in the above temperature range, that of ${\mathrm{Th}}_4$ ${\mathrm{H}}_{15}$ has been found to be temperature dependent. Analysis of this temperature dependence and that of the Knight shift (measured by Lau et al.) permitted an estimation of the hyperfine fields of the $s$ and $d$ electrons at the site of the proton. In view of the NMR results it is suggested that $f$ electrons are not present in a significant amount on the Fermi level.