Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the ${}^{155}\mathrm{Gd}(\alpha ,2n){}^{157}\mathrm{Dy}$ and ${}^{148}\mathrm{Nd}({}^{12}\mathrm{C},5n){}^{155}\mathrm{Dy}$ reactions at 25 and 65 MeV, respectively. We report high-$K$ bands, which are conjectured to be the first candidates of a $K^{\pi }=2^{+}\gamma$ vibrational band, built on the $\left[505\right]11/2^{-}$ neutron orbital, in both odd-$A{}^{155,157}\mathrm{Dy}$ isotopes. The coupling of the first excited $K=0^{+}$ states or the so-called β vibrational bands at 661 and 676 keV in ${}^{154}\mathrm{Dy}$ and ${}^{156}\mathrm{Dy}$ to the $\left[505\right]11/2^{-}$ orbital, to produce a $K^{\pi }=11/2^{-}$ band, was not observed in both ${}^{155}\mathrm{Dy}$ and ${}^{157}\mathrm{Dy}$, respectively. The implication of these findings on the interpretation of the first excited $0^{+}$ states in the core nuclei ${}^{154}\mathrm{Dy}$ and ${}^{156}\mathrm{Dy}$ are also discussed.

• Received 23 December 2019
• Accepted 18 March 2020

DOI:https://doi.org/10.1103/PhysRevC.101.044312