Backbending in the pear-shaped $^{223}_{90}$Th nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides

G. Maquart (1) , L. Augey (1) , L. Chaix (1) , I. Companis (1) , C. Ducoin (1) , J. Dudouet (1) , D. Guinet (1) , G. Lehaut (1) , C. Mancuso (1) , N. Redon (1) , O. Stézowski (1) , A. Vancraeyenest (1) , A. Astier (2) , F. Azaiez , S. Courtin (3) , D. Curien (3) , I. Deloncle (2) , O. Dorvaux (3) , G. Duchêne (3) , B. Gall (3) , T. Grahn , P. Greenlees , A. Herzan , K. Hauschild (2) , U. Jakobsson , P. Jones , R. Julin , S. Juutinen , S. Ketelhut , M. Leino , A. Lopez-Martens , P. Nieminen , P. Petkov (2) , P. Peura , M.G. Porquet (2) , P. Rahkila , S. Rinta-Antila , M. Rousseau (3) , P. Ruotsalainen , M. Sandzelius , J. Sarén , C. Scholey , J. Sorri , S. Stolze , J. Uusitalo

1 IPNL - Institut de Physique Nucléaire de Lyon
2 CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière
3 IPHC - Institut Pluridisciplinaire Hubert Curien

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 interpret this new structure as based on the same configuration as the yrast band in Th221 having dominant K=1/2 contribution. At the highest spin a backbending occurs around a rotational frequency of ℏω=0.23 MeV, very close to the one predicted in Th222, where a sharp transition to a reflection-symmetric shape is expected.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

G. Maquart, L. Augey, L. Chaix, I. Companis, C. Ducoin, et al.. Backbending in the pear-shaped $^{223}_{90}$Th nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides. Phys.Rev.C, 2017, 95 (3), pp.034304. ⟨10.1103/PhysRevC.95.034304⟩. ⟨hal-01554416⟩