Semimicroscopic description of backbending phenomena in some deformed even-even nuclei

Abstract

The mechanism of backbending is semi-phenomenologically investigated based on the hybridization of two rotational bands. These bands are defined by treating a model Hamiltonian describing two interacting subsystems: a set of particles moving in a deformed mean-field and interacting among themselves through an effective pairing force and a phenomenological deformed core whose intrinsic ground state is an axially symmetric coherent boson state. The two components interact with each other by a quadrupole-quadrupole and a spin-spin interaction. The total Hamiltonian is considered in the space of states with good angular momentum, projected from a quadrupole deformed product function. The single-particle factor function defines the nature of the rotational bands, one corresponding to the ground band in which all particles are paired and another one built upon a i 13/2 neutron broken pair. The formalism is applied to six deformed even-even nuclei, known as being good backbenders. Agreement between theory and experiment is fairly good.

Comparative Phenomenological Description of Even-Even Isotopes at Mass Region A ≈ 70

“…Previous works showed that there is a clear evidence for a major change in the nature of the ground state levels below I = 18 ћ in even-even nuclei in that region [1]- [8]. Furthermore, at higher spin values a very regular structure develops.…”

Semi-microscopic description of the double backbending in some deformed even–even rare earth nuclei

“…Also, in the Nilsson model, the last filled neutron state has = 1/2, while the last proton occupies the state = 7/2. The choice of the K = 1/2 sub-state as the Fermi level of the neutron system was made in [27] to describe the first backbending. As for considering the K = 7/2 Fermi level for the proton system, breaking the corresponding pair and aligning the resulting quasiparticle angular momenta to that of the core as prerequisite conditions of the second backbending, these features are in full agreement with the microscopic formalism used in the literature.…”

“…In a previous publication [27], we proposed a semi-microscopic model for the description of the backbending phenomenon within the band-mixing picture. The rotational bands implied in the mixing procedure were defined by the angular momentum projection from quadrupole deformed product states and a model Hamiltonian describing a set of intruder neutrons interacting among themselves through pairing forces and coupled to a phenomenological deformed core.…”

“…The model was meant to reproduce only the first backbending, which was done quite well for six even-even nuclei from the rare earth region. Besides the reproduction of the backbending plots, the formalism [27] also provided some useful information regarding the rotational alignment of the particles moving in an intruder orbital.…”

“…In this paper, we extend the formalism from [27] to the second backbending induced by a proton broken pair. This is done by performing the mixing of four rotational bands.…”