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Simultaneous description of low-lying positive and negative parity bands in heavy even-even nuclei

The low-lying spectra including the first few excited positive and negative parity bands of some heavy even-even nuclei from the rare earth and actinide mass regions are investigated within the framework of the symplectic Interacting Vector Boson Model with Sp(12,$R$) dynamical symmetry group. Symplectic dynamical symmetries allow the change of the number of excitation quanta or phonons building the collective states providing for larger representation spaces and richer subalgebraic structures to incorporate more complex nuclear spectra. The theoretical predictions for the energy levels and the electromagnetic transitions between the collective states of the ground state band and $K^π=0^{-}$ band are compared with experiment and some other collective models incorporating octupole and/or dipole degrees of freedom. The energy staggering which is a sensitive indicator of the octupole correlations in the even-even nuclei is also calculated and compared with experiment. The results obtained for the energy levels, energy staggering and transition strengths reveal the relevance of the used dynamical symmetry of the model for the simultaneous description of both positive and negative parity low-lying collective bands.