Quadrupole collectivity and shapes of Os-Pt nuclei

E2 collective properties for the low-lying states in 186,188,190,192Os and 194Pt have been investigated experimentally by means of Coulomb excitation using 3.3-4.8 MeV/nucleon 40Ca, 58Ni, 136Xe and 208Pb beams. Levels with excitation energies up to 3-4 MeV of the ground-state, γ and 4+ collective bands as well as excited 0+ states were populated in each nucleus studied. For each nucleus studied, a unique and almost complete set of E2 matrix elements for the low-lying states has been determined, which includes both the magnitudes and signs of the transitional and diagonal matrix elements. The completeness of the set of measured E2 matrix elements makes it possible to determine the intrinsic quadrupole deformation for the low-lying states in these nuclei via a model-independent method. The extracted E2 matrix elements are compared with the prediction of various collective models such as the asymmetric rigid rotor model, the γ-soft model of Leander, and the IBA-2 model. The enhanced B(E2) values between the I,quasi-Kπ=4,4+ state and members of the I,quasi-Kπ=2,2+ band are well reproduced by the γ-soft model is consistent with the interpretation of the I,quasi-Kπ=4,4+ state being a two-phonon γ-vibration excitation. (orig.)