Low-lying octupole bands in coherent state model

An extension of the coherent state model (CSM) has been made to describe both negative and positive parity bands . Three bands, with Kπ = 0-, 1-, 2-, respectively, were constructed. The states of each bands are obtained by angular momentum projection from three mutually orthogonal intrinsic states constructed as octupole boson excitations of the three positive parity intrinsic states which in the standard CSM are associated to the ground, beta and gamma bands, respectively. An effective Hamiltonian was constructed so as to achieve maximum decoupling between the bands. We computed the energy spectra and electromagnetic transition probabilities for two rare earth nuclei and three isotopic chains in the actinide region. The agreement between the computed and the experimental energy spectra is very good, except some discrepancies in the upper part of the 0- band in 232 Th, what indicates that the coupling with two-quasi particle states is necessary. It was shown that the model can simulate a static octupole deformation phase by achieving decoupling between the soft octupole mode and quadrupole motion. Also, the experimental E1 branching ratios were fairly well reproduced, specially when a strongly anharmonic E1 operator was used. The model emphasizes the role of quadrupole collectivity in determining the properties of the low-lying negative parity states