Shape transitions in odd-mass γ -soft nuclei within the interacting boson-fermion model based on the Gogny energy density functional

Abstract

The interacting boson-fermion model (IBFM), with parameters determined from the microscopic Hartree-Fock-Bogoliubov (HFB) approximation, based on the parametrization D1M of the Gogny energy density functional (EDF), is employed to study the structural evolution in odd-mass γ-soft nuclei. The deformation energy surfaces of even-even nuclei, single-particle energies and occupation probabilities of the corresponding odd-mass systems have been obtained within the constrained HFB approach. Those building blocks are then used as a microscopic input to build the IBFM Hamiltonian. The coupling constants of the boson-fermion interaction terms are taken as free parameters, fitted to reproduce experimental low-lying spectra. The diagonalization of the IBFM Hamiltonian provides the spectroscopic properties for the studied odd-mass nuclei. The procedure has been applied to compute low-energy excitation spectra and electromagnetic transition rates, in the case of the γ-soft odd-mass systems 129−137 Ba, 127−135 Xe, 129−137 La and 127−135 Cs. The calculations provide a reasonable agreement with the available experimental data and agree well with previous results based on the relativistic mean-field approximation.

Review of Shape Phase Transition Studies for Bose-Fermi Systems: The Effect of the Odd-Particle on the Bosonic Core

“…Evidence of quantum phase transitions in odd systems were reported in recent works [27][28][29][30][31][32][33][34]. The experimental evidence for transition from spherical to the γ-unstable shapes in odd-mass 127−137 Ba and 101−109 Rh, and 123−135 Xe nuclei was presented in Refs.…”

“…[27,28,32] and analyzed by calculating their nuclear properties, such as B(E2) values and two-neutron separation energies, within the IBFM model for the U BF (5)-O BF (6) transition along the isotopic chain. The signatures of the quantum shape phase transition in odd-mass 129−137 Ba, 129−137 La, 127−135 Xe, and 127−135 Cs nuclei in the A ≈ 130 mass region were studied by taking into account their bosonic cores 128−136 Ba for 129−137 Ba, 129−137 La, and 126−134 Xe [30,31]. These cores empirically exhibit a transition from nearly spherical to γ-soft shape.…”

“…We would like to mention that other relevant contributions to the topic of shape phase transitions in odd-even nuclei have been presented in the last 15 years in Refs. [10,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”

Quadrupole deformation of Xe130 measured in a Coulomb-excitation experiment

“…Understanding the evolution of collectivity along an isotopic chain and, in particular, describing the structure of transitional nuclei, has long proved to be a challenge for nuclear theory and nuclear structure models. For the even-even Xe isotopes, past work has focused on calculations employing the general Bohr Hamiltonian [1,[4][5][6], the nuclear shell model [7], and the interacting boson model (IBM) [8,9], where the light Xe isotopes have been suggested to represent a transition point between spherical vibrators and γ -soft rotors, e.g., Refs. [10,11].…”

“…[10,11]. In addition, odd-mass nuclei in this region were explored in detail in recent mapped-IBM calculations [8,9].…”