Backbending in the pear-shaped 223(90)Th nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides

International audience; Relatively neutron-rich thorium isotopes lie at the heart of a nuclear region of nuclei exhibiting octupole correlation effects. The detailed level structure of Th223 has been investigated in measurements of γ radiation following the fusion-evaporation channel of the Pb208(O18,3n)Th223 reaction at 85 MeV beam energy. The level structure has been extended up to spin 49/2, and 33 new γ rays have been added using triple-γ coincidence data. The spins and parities of the newly observed states have been confirmed by angular distribution ratios. In addition to the two known yrast bands based on a K=5/2 configuration, a non-yrast band has been established up to spin 35/2. We…