Backbending in the pear shaped ²²³Th nucleus

An experiment has been realized using the EUROBALL IV array at Strasbourg to study the fission products produced in the reaction ²⁰⁸Pb(¹⁸O,fγ). Nevertheless, the experiment also led to the production of ²²³Th in the fusion-evaporation channel, with three neutrons evaporated. The structure of thorium isotopes is known to present features of octupole collectivity. The aim of the present talk is to report new results about the structure of ²²³Th, with possible consequences on the characterization of its octupole properties. Indeed, the quality of the data allowed us to establish more than 25 new levels and extend the yrast band up to 49/2⁺. This observation has brought to light a sharp backbending occurring at the highest spins promoting the ²²³Th as the heavier thorium isotope having an accident observed in its moment of inertia. The interpretation of this phenomenon in terms of band crossing will be discussed. Moreover, a new non-yrast structure was discovered showing very different features and further details will be presented. This document is composed of an abstract and the slides of the presentation. (authors)