Measurement of the sign and magnitude of the electric field gradients at Re and Os nuclei as impurities in a hexagonal Lu single crystal

The nuclear orientation technique has been applied to dilute alloys of ${}_{}{}^{182}{}_{}{}^{}\mathrm{Re}$ ($j^{\pi }=2^{+}$) and ${}_{}{}^{183}{}_{}{}^{}\mathrm{Os}$ ($j^{\pi }={\frac{9}{2}}^{+}$) nuclei in a hexagonal Lu single crystal, the activities being produced in situ via the heavy-ion-induced nuclear compound reaction (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $\mathrm{xn}$) with $x=4.5\mathrm{}$ From the $\gamma$ anisotropy at temperatures down to 6 mK the quadrupole interaction frequencies of ${}_{}{}^{182}{}_{}{}^{}\mathrm{Re}\mathrm{Lu}$ and ${}_{}{}^{183}{}_{}{}^{}\mathrm{Os}\mathrm{Lu}$ have been determined as +311 (24) and +403 (20) MHz respectively. The electric field gradients (EFG) are deduced to be $\mathrm{eq}\left(\mathrm{Re}Lu\right)=+6.8\mathrm{}\left(6\right)\mathrm{}\times {10}^{17}$ V/${\mathrm{cm}}^2$ and $\mathrm{eq}\left(\mathrm{Os}Lu\right)=+5.3\mathrm{}\left(5\right)\mathrm{}\times {10}^{17}$ V/${\mathrm{cm}}^2$. The positive sign in both cases indicates that the direction of the EFG at the impurity sites is fixed by the properties of the host lattice.