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

Low-lying states in the even-even light platinum isotopes ¹⁷⁶Pt, ¹⁷⁸Pt, ¹⁸⁰Pt and ¹⁸²Pt have been populated using β⁺/EC decay from parent gold nuclei, created in (HI,xn) reactions. State energies, spins and parities and γ-ray branching ratios were determined using γ-ray and electron spectroscopy. Whereas non-yrast states were observed in ¹⁷⁸Pt, ¹⁸⁰Pt and ¹⁸²Pt, none were seen in ¹⁷⁶Pt. The excitation energies of the observed states are analysed in terms of a band-mixing model, yielding the moments of inertia of the unperturbed bands. Branching ratios and ground-state-band quadrupole moments are calculated and compared with experimental values. The results indicate that the two lowest-lying 0⁺ states in each of the light Pt isotopes are formed from the mixing of two intrinsic states of different deformation, and other low-lying states can be described as admixtures of rotational states built on these intrinsic states, and on γ-vibrational states.