NONYRAST STATES AND SHAPE COEXISTENCE IN OS-172

Previous studies of 172Os noted an anomaly in the behaviour of the mom ent of inertia of the yrast band at low spin. A phenomenological model of shape coexistence based on interacting rotational bands was propos ed to explain this anomaly and this model predicted low-lying non-yras t states. In order to test these predictions, the beta-decay of 172Ir has been used to populate 172Os. Excited states have been observed and classified into positive-parity ''quasi-beta'' and ''quasi-gamma'' ba nds and a negative-parity band. The energies of the quasi-beta band st ates are seen to be in general agreement with the predictions of the p henomenological model and the model is refined to take into account th e new data. The bands involved are determined to have significantly di fferent moments of inertia.