Intermediate-State Reorientation of Nuclei Aligned in Cerium Double Nitrate

Radiation patterns and linear polarization of gamma rays from decay of ${\mathrm{Co}}^{57}$ and ${\mathrm{Ce}}^{141}$ aligned at low temperatures by Bleaney's method in cerium double nitrate were studied for evidence of intermediate-state reorientation in this crystal. Influence of spin-spin interactions should be negligible on theoretical grounds. Experimental results, expressed in terms of the mixing ratio $\delta =\pm {\left(\frac{E2\mathrm{}}{M1\mathrm{}}\right)}^{\frac{1}{2}}$ for the $M1+E2\mathrm{}$ gamma transitions and of an attenuation coefficient $Q_k$ in the angular distribution $W\left(\theta \right)=\Sigma Q_k{A}_k{P}_k\left(cos\theta \right)$, are as follows: 123-keV gamma from ${\mathrm{Co}}^{57}$ in Ce-Zn nitrate $Y$ sites, $\delta =+0.148\mathrm{}\pm 0.010$, $Q_2=0.81\mathrm{}\pm 0.10$ at $\frac{1}{T^{*}}=157\mathrm{}$; 145-keV gamma from ${\mathrm{Ce}}^{141}$ in Ce-Mg nitrate, $\delta =+0.085\mathrm{}\pm 0.013$, $Q_2=1.08\mathrm{}\pm 0.08$ at $\frac{1}{T^{*}}=150\mathrm{}$. Comparisons are made with Steenberg's theory of intermediate-state reorientation by static, isotropic hfs coupling in the hard-core limit, and with results of other nuclear alignment experiments involving the same isotopes.