Collective rotational bands at low excitation energy in Os 186: Vibrational and rotational degrees of freedom

Collective structures in Os186 have been investigated through the W186(He4,4n)Os186 reaction, at a beam energy of 48 MeV. The low-lying bands built on the excited 02+, 22+, and 43+ states have been extended up to spins of 12+, 15+, and 8+, respectively, and a number of new linking transitions were identified. The features of the collective bands in Os186, such as level energies, are presented in the context of a systematic study of the neighboring even-even Os182-192 isotopes. In addition, the validity of the K-selection rule, stemming from a description based on axial symmetry of the nuclear shape, is examined. The observed decays between the rotational bands support a description where K is conserved. However, some K-forbidden decays were also identified, suggesting that a model allowing for small K admixtures is probably required. The experimental data are further compared with calculations using a five-dimensional collective Hamiltonian based on covariant density functional theory. The calculations predict that the collective bands are associated with different nuclear shapes, varying in quadrupole deformation, triaxiality, and softness.