Non-yrast states and shape co-existence in light Pt isotopes

Low-lying states in the even-even light platinum isotopes Pt-176, Pt-178, P t-180 and Pt-182 have been populated using beta(+)/EC decay from parent gol d nuclei, created in (HI,xn) reactions. State energies, spins and parities and gamma-ray branching ratios were determined using gamma-ray and electron spectroscopy. Whereas non-yrast states were observed in Pt-178, Pt-180 and Pt-182, none were seen in Pt-176. The excitation energies of the observed states are analysed in terms of a band-mixing model, yielding the moments o f inertia of the unperturbed bands. Branching ratios and ground-state-band quadrupole moments are calculated and compared with experimental values. Th e results indicate that the two lowest-lying 0(+) states in each of the lig ht Pt isotopes are formed from the mixing of two intrinsic states of differ ent deformation, and other low-lying states can be described as admixtures of rotational states built on these intrinsic states, and on gamma-vibratio nal states. (C) 1999 Elsevier Science B.V. All rights reserved.