Measurement of the 89-keV-state-to-ground-state quadrupole-moment ratio inRu99

The ratio of nuclear quadrupole moments of the first excited state with respect to the ground state in ${}_{}{}^{99}{}_{}{}^{}\mathrm{Ru}$ has been determined from Mössbauer effect measurements with single crystal absorbers of ruthenocene. The result, $\frac{Q_1}{Q_0}=2.93\mathrm{}\pm 0.07$, when combined with a recent measurement of $Q_0$, gives the value $Q_1=0.23\mathrm{}\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}_2$. An improved value for the $\frac{E2\mathrm{}}{M1\mathrm{}}$ amplitude mixing ratio $\delta =-1.56\mathrm{}\pm 0.02$ is determined from magnetic hyperfine spectra obtained with an absorber of ruthenium dissolved in iron. A determination of the angle between the axis of the electric field gradient and each of the three crystal axes of ruthenocene is in good agreement with the crystal structure reported for this compound. The recoil-free fraction was found to vary with respect to orientation of the crystal axes by a factor of greater than 2.