Microscopic shell-model description of transitional nuclei

A recently proposed microscopic version of the Bohr-Mottelson collective model, defined by the following dynamical symmetry chain Sp(12, R) superset of SU(1,1) circle times SO (6) superset of U(1) circle times SUpn(3) circle times SO(2) superset of 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 Ru-104 and Os-192. Detailed shell-model results are presented for the excitation levels of the ground and gamma bands in Ru-104, and the ground, gamma, and beta bands in Os-192, 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.