Microscopic shell-model description of transitional nuclei

Abstract

A recently proposed microscopic version of the Bohr-Mottelson collective model, defined by the following dynamical symmetry chain $Sp(12,R) \supset SU(1,1) \otimes SO(6) \supset U(1) \otimes SU_{pn}(3) \otimes SO(2) \supset SO(3)$ of the proton-neutron symplectic model (PNSM), is applied to the microscopic shell-model description of the low-lying collective excitations in two transitional nuclei, namely $^{104}$Ru and $^{192}$Os. Detailed shell-model results are presented for the excitation levels of the ground and $\gamma$ bands in $^{104}$Ru, and the ground, $\gamma$, and $\beta$ bands in $^{192}$Os, as well as for the probability distributions and the quadrupole collectivity. A good overall description is obtained for the excitation energies of the bands under consideration for the two transitional nuclei without using an adjustable kinetic-energy term, as well as for the ground state intraband B(E2) quadrupole collectivity and the known interband B(E2) transition probabilities between the low-lying collective states without the use of an effective charge.