Axially-Symmetric and Gamma-Unstable Deformations in Nuclei

Abstract

In addition to the rare earth nuclei, there appear band-llke structures in many regions of even-even nuclei whose neutrons are rich or deficient. These band structures are named quasiground, quasi- BETA and quasi- gamma bands as counterparts of these collective states in the well-deformed region. Nuclei having the quasi-ground band are thought to be in transition regions from spherical to deformed and the low-lying quasi- BETA or quasi- gamma band indicates the softness against the BETA or gamma vibration of these nuclei. A method is proposed in order to predict whether a nucleus is preferable to be axially symmetric or gamma -unstable if it is deformed. This method coiisists of introducing an idea of preferred shaPes of the proton and neutron systems in each case. By the preferred shape we mean the preferred direction of deforrnation that the system should have inherently. It can be predicted from the preferred shapes of protons and neutrons whether the deformation of the nucleus is axially symmetric or gamma -unstable. This method is applied to the lighter Ge, Se, Kr and Sr isotopes, the heavier Zr, Mo and Ru isotopes and the lighter Xe, Ba and Ce isotopes and its prediction is compared withmore » the potential energy surfaces of these nuclei calculated within a framework of the time dependent Hartree-Bogoliubov theory with the pairing plus quadrupole force. (auth)« less