Decay ofHf181

The decay of ${\mathrm{Hf}}^{181}$ to ${\mathrm{Ta}}^{181}$ was studied by angular correlation measurements ($133K-482\mathrm{}\gamma$, $133\gamma -482\mathrm{}\gamma$, and $133\gamma -482\mathrm{}K$, energies being given in kev), conversion coefficient measurements [${\alpha }_K\mathrm{}\left(133\right)=0.50\mathrm{}\pm 0.06$, ${\alpha }_K\mathrm{}\left(136\right)=1.2\mathrm{}\pm 0.2$, ${\alpha }_K\mathrm{}\left(346\right)=0.038\mathrm{}\pm 0.007$, ${\alpha }_K\mathrm{}\left(482\right)=0.023\mathrm{}\pm 0.002$], $\frac{K}{L}$ ratios, and coincidence measurements. The weak 137-kev transition, first observed by Mihelich, was placed in the decay by delayed coincidence measurements. The spin assignments are in excellent agreement with the calculations of Nilsson on the strong-coupling model. Comparison of $K-\gamma$ and $\gamma -\gamma$ correlation coefficients in the Hf${\mathrm{O}}_2$ sources fails to show any after effects of $K$-hole formation on the correlation coefficients. The discrepancy between the $\frac{E2\mathrm{}}{M1\mathrm{}}$ ratio obtained from $\gamma -\gamma$ correlation measurements and conversion coefficient measurements in the 482-kev transition is discussed in terms of the improved finite nuclear size corrections to $M1\mathrm{}$ conversion coefficients described by Church and Weneser.