First Candidates For Gamma Vibrational Bands Built On The [505]11/2(-) Neutron Orbital In Odd-a Dy Isotopes

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd-155(alpha, 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 K-pi = 2(+)gamma vibrational band, built on the [505]11/2(-) neutron orbital, in both odd-A Dy-155,Dy-157 isotopes. The coupling of the first excited K = 0(+) states or the so-called beta vibrational bands at 661 and 676 keV in Dy-154 and Dy-156 to the [505]11/2(-) orbital, to produce a K-pi = 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.