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

Abstract

A state at ${E}_{x}=6.350$ MeV in $^{23}\mathrm{Na}$ is shown to have ${J}^{\ensuremath{\pi}}={\frac{9}{2}}^{\ensuremath{-}}$ and is assigned to the rotational band based on the ${\mathrm{\textonehalf{}}}^{\ensuremath{-}}$ state at 2.640 MeV. Its $\ensuremath{\gamma}$-ray decay lifetime and branching ratios are determined and combined with known information about the proposed $J=\frac{1}{2}$ to ${\frac{7}{2}}^{\ensuremath{-}}$ members of this band to show that there is an anomalous $E1$ 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.