Nuclear shape phase transitions

D Vretenar

doi:10.1051/epjconf/201611704002

Abstract

The evolution of shapes and shape (phase) transitions, including regions of short-lived exotic nuclei that are becoming accessible in experiments at radioactive-beam facilities, are governed by the shell structure of single-nucleon orbitals. In most cases the transition between different shapes is gradual but in a number of examples, with the addition or subtraction of only few nucleons, signatures of abrupt changes in observables are noticed. A quantitative analysis necessitates accurate modelling of the underlying nucleonic dynamics. Important advances have been reported in theoretical studies of complex shapes, especially in the “beyond mean-field” framework based on density functionals.

Highlights

Introduction and theory frameworkThe evolution of equilibrium shapes and the corresponding excitation dynamics present some of the most studied low-energy nuclear phenomena, both experimentally and theoretically [1,2,3,4]
In contrast to spherical shapes that occur for the particular case of single or doubly closed-shell nuclei, deformed equilibrium shapes arise due to strong protonneutron correlations in open-shell nuclei
Far from the β-stability line, in particular, the energy spacings between single-particle levels can be very different from those found in stable nuclei. This can result in reduced spherical shell gaps, modifications of magic numbers, occurrence of islands of inversion, deformed equilibrium shapes and coexistence of shapes with different deformations, and shape transitions

Summary

Introduction and theory framework

The evolution of equilibrium shapes and the corresponding excitation dynamics present some of the most studied low-energy nuclear phenomena, both experimentally and theoretically [1,2,3,4]. The basic implementation of the EDF framework is in terms of self-consistent mean-field (SCMF) models, in which an EDF is constructed as a functional of one-body nucleon densities that correspond to a single product state This approach to nuclear structure is analogous to Kohn-Sham DFT. One constructs a Lagrangian that comprise second-order interaction terms only, with manybody correlations encoded in density-dependent coupling functions This type of RMF-based models has been successfully used in analyses of a variety of structure phenomena, in nuclei along the valley of β-stability, and in exotic nuclei with extreme isospin values and close to the particle drip lines. The details of the particular implementation of the relativistic EDF-based collective Hamiltonian used in the present study can be found in Ref. [6]

Triaxial shapes in germanium isotopes

Octupole shape-phase transitions in Thorium