Identical bands inSr77,Sr78, andRb78: Evidence for a very good spectator orbital

The highest spin states in a ${\mathit{T}}_{\mathit{z}}$=1/2 nucleus have been observed in ${}_{}{}^{77}{}_{}{}^{}\mathrm{Sr}$: ${\mathit{I}}^{\mathrm{\pi }}$=(49/$2^{+}$) and (29/$2^{\mathrm{-}}$). In addition, states up to ${\mathit{I}}^{\mathrm{\pi }}$=(${22}^{+}$) have been seen in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Sr}$. The α=1/2, ${\mathit{g}}_{9/2}$ band and both signature partners of the negative parity band in ${}_{}{}^{77}{}_{}{}^{}\mathrm{Sr}$ were found to be identical to the yrast band in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Sr}$ with relative alignments of 1.22(7)ħ, 0.52(5)ħ(α=1/2), and 0.42(4)ħ(α=-1/2), respectively. In one of the negative parity bands, the identicality persists through the first proton band crossing. The odd spin decay sequence of the $4^{\mathrm{-}}$ band in ${}_{}{}^{78}{}_{}{}^{}\mathrm{Rb}$ is identical to the ground band of ${}_{}{}^{78}{}_{}{}^{}\mathrm{Sr}$ [3.02(3)ħ] at low spin and to the α=1/2, ${\mathit{g}}_{9/2}$ band in ${}_{}{}^{77}{}_{}{}^{}\mathrm{Rb}$ [1.11(3)ħ] at higher spins. These are the only known examples of identical bands in the neutron deficient A=80 region. The analysis indicates that the [301]3/2 Nilsson orbital is a very good spectator orbital.