E1Decay of Members of the Low-LyingKπ=12−Band inNa23

A state at $E_x=6.350\mathrm{}$ MeV in ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ is shown to have $J^{\pi }={\frac{9}{2}}^{-}$ and is assigned to the rotational band based on the ${\mathrm{½}}^{-}$ state at 2.640 MeV. Its $\gamma$-ray decay lifetime and branching ratios are determined and combined with known information about the proposed $J=\frac{1}{2}$ to ${\frac{7}{2}}^{-}$ members of this band to show that there is an anomalous $E1\mathrm{}$ decay pattern between the members of this band and the members of the ground-state band. This anomalous pattern can be explained using the Nilsson model with band mixing.