Boson expansion description of collective states in osmium and platinum isotopes

The boson expansion theory, based on which successful explanations were made earlier of collective properties of Ru, Pd, Sm, and other isotopes, is applied here to the Os and Pt isotopes. The nuclei are characterized by the fact that their energy spectra and the $E2\mathrm{}$ transitions embody in themselves a very strong $\gamma$-unstable nature, nevertheless having quadrupole moments $Q\left(2_1^{+}\right)$ which are large, being negative in Os and positive in the Pt isotopes. It is shown that all these properties can be predicted using the present approach.