Evolution of nuclear shapes in 157–161yb as a function of spin and neutron number

Abstract The population distributions of the entry states, the entry lines 〈E ∗ > versus multiplicity, the energy spectra and the angular distributions of the continuum γ -rays as a function of multiplicity in 157–161 yb from the reactions of 136 MeV and 149 MeV 20 Ne with 144 Nd and 146 Nd have been investigated with a 4π multidetector system gated with a Ge detector. The observed entry lines and γ -decay modes indicate changes in the nuclear structure with increasing spin. This systematic change for N = 87– 91 Yb isotopes suggests an evolution of nuclear shapes from prolate at low spins to particle aligned oblate structure for 157 yb and 158 yb followed by the onset of high-K bands built on largely deformed oblate states at increasingly higher spin between 38 and 50 kh with increasing neutron number for 157–161 yb. Furthermore evidence for an evolution to triaxial shape at I ⋍ 50 for 158 yb was found.