Properties of the 5.256-MeV State in ${\mathrm{Si}}^{29}$: Evidence for a Rotational Band with $K^{\pi }={\frac{7}{2}}^{-}$

The spin of the 5.256-MeV level in ${\mathrm{Si}}^{29}$ has been determined to be $J=\frac{9}{2}$; its mean lifetime has been measured to be ${\tau }_m=(0.95\mathrm{}\pm 0.15)\times {10}^{-13\mathrm{}}$ sec. The electromagnetic decay of this state is >90% via cascade radiation through the $J^{\pi }={\frac{7}{2}}^{-}$ state of ${\mathrm{Si}}^{29}$ at 3.624 MeV, with $E_{\gamma }=1631.3\mathrm{}\pm 0.5$ keV; the transition has quadrupole/dipole admixture $\delta =-0.49\mathrm{}\pm 0.07$. This multipole mixing together with the measured lifetime fix parity $\pi =-1\mathrm{}$ for this state.