First candidates for $γ$ vibrational bands built on the [505]11/2- neutron orbital in odd-A Dy isotopes

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