New Description of the Doublet Bands in Doubly Odd Nuclei

The experimentally observed $Delta I = 1$ doublet bands in some odd-odd nuclei are analyzed within the orthosymplectic extension of the Interacting Vector Boson Model (IVBM). A new, purely collective interpretation of these bands is given on the basis of the obtained boson-fermion dynamical symmetry of the model. It is illustrated by its application to three odd-odd nuclei from the $Asim 130$ region, namely $^{126}Pr$, $^{134}Pr$ and $^{132}La$. The theoretical predictions for the energy levels of the doublet bands as well as $E2$ and $M1$ transition probabilities between the states of the yrast band in the last two nuclei are compared with experiment and the results of other theoretical approaches. The obtained results reveal the applicability of the orthosymplectic extension of the IVBM.

Transition probabilities in the U(6) limit of the Symplectic Interacting Vector Boson Model

The tensor properties of the algebra generators and the basis are determined in respect to the reduction chain $Sp(12,R) supset U(6)% supset U(3)otimes U(2)supset O(3)otimes (U(1)otimes U(1))$, which defines one of the dynamical symmetries of the Interacting Vector Boson Model. The action of the Sp(12,R) generators as transition operators between the basis states is presented. Analytical expressions for their matrix elements in the symmetry-adapted basis are obtained. As an example the matrix elements of the E2 transition operator between collective states of the ground band are determined and compared with the experimental data for the corresponding intraband transition probabilities of nuclei in the actinide and rare earth region. On the basis of this application the important role of the symplectic extension of the model is analyzed.