Microscopic Study Of The Shape Phase Transition And Shape Coexistence In Atomic Nuclei

In recent years,people have discovered many novel phenomena or laws in unstable exotic nuclei.In particular,the nuclear shape phase transition and shape coexistence of nuclei involving important scientific issues,such as the evolution of the microscopic shell structure,new dynamical symmetry,and microscopic origin of collectivity,are frontier topics in nuclear physics.In order to systematically study the shape phase transition and shape coexistence of atomic nuclei,it is necessary to self-consistently describe the nature of the ground state and low-excited state of the atomic nucleus.Covariant density functional theory(CDFT)has achieved great success in describing the properties of ground state properties of nuclei,and has become one of the most important microscopic theoretical methods for atomic nuclei.In order to self-consistently describe the excitation spectrum and electromagnetic transition properties of atomic nuclei,beyond the mean field approximation is necessary.In recent years,our group has developed a microscopic collective Hamiltonian model(5DCH-CDFT)based on covariant density functional theory,which has achieved a unified and self-consistent description of the low excitation spectrum of atomic nuclei.In this thesis,we have used the microscopic collective Hamiltonian model to systematically analyze the evolution of the six even-even isotopic chains of Er,Yb,Hf,W,Os and Pt as the neutron number changes from 102 to 124.It is found that:1)The potential energy surfaces display a transition from prolate to oblate/triaxial,and then to near spherical shapes as the neutron number increases;2)The corresponding 5DCH model calculations reproduce the empirical isotopic trend of the characteristic collective observables and confirm the overall shape transition in this region;3)It is emphasized that a rapid shape transition between prolate and oblate shapes is predicted in Er and Yb isotopic chains while it becomes smooth for higher-Z isotopic chains and signature for rigid triaxial deformation is found in the transitional isotopes,e.g.194W and 192-1960s by analyzing the energy staggering and probability density distribution in the ? bands;4)Finally,the calculated low-lying spectra for 184Er and 186Yb demonstrate a remarkable multi-shape coexistence of medium-deformed oblate,medium-and large-deformed prolate shapes in both nuclei.