Two-quasiparticle states in the interacting boson approximation and the structure of even Pt isotopes

The structures of even Pt isotopes are studied with the traditional interacting boson approximation plus one-fermion-pair model. The energy spectra can be reproduced reasonably well if mixing of two bands of different deformation at low spins in these isotopes is considered. An apparent change of structure transiting from ${}_{}{}^{188}{}_{}{}^{}\mathrm{Pt}$ to ${}_{}{}^{186}{}_{}{}^{}\mathrm{Pt}$ was reflected in the different interactions needed to reproduce the energy spectra for heavier Pt isotopes (188≤A≤192) and lighter Pt isotopes (182≤A≤186), respectively. The compression of level spacing occurring between ${10}^{+}$ and ${12}^{+}$ states in heavier Pt isotopes is also obtained. The B(E2) values for ${}_{}{}^{184}{}_{}{}^{}\mathrm{Pt}$ yrast band versus the spins of the depopulating states are calculated and compared with the observed data.