Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes

N. Kesteloot , B. Bastin (1) , L. P. Gaffney , K. Wrzosek-Lipska , K. Auranen , C. Bauer , M. Bender (2) , V. Bildstein , A. Blazhev , S. Bönig , N. Bree , E. Clément (1) , T. E. Cocolios , A. Damyanova , I. Darby , H. de Witte , D. Di Julio , J. Diriken , C. Fransen , J. E. García-Ramos , R. Gernhäuser , T. Grahn , P.-H. Heenen , H. Hess , K. Heyde , M. Huyse , J. Iwanicki , U. Jakobsson , J. Konki , T. Kröll , B. Laurent (3) , N. Lecesne (1) , R. Lutter , J. Pakarinen , P. Peura , E. Piselli , L. Próchniak , P. Rahkila , E. Rapisarda , P. Reiter , M. Scheck , M. Seidlitz , M. Sferrazza , B. Siebeck , M. Sjodin (1) , H. Tornqvist , E. Traykov (1) , J. van de Walle , P. van Duppen , M. Vermeulen , D. Voulot , N. Warr , F. Wenander , K. Wimmer , M. Zielińska (3)

1 GANIL - Grand Accélérateur National d'Ions Lourds
2 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
3 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers

Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient $^{196,198,200,202}$Po isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, $^{200,202}$Po, the transitional and diagonal matrix elements of the $2^+ _1$ state are determined. In $^{196,198}$Po multistep Coulomb excitation is observed, populating the $4^+_1$ , $0^+ _2$ , and $2^+_2$ states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from $^{196}$Po onwards. Three model descriptions are used to compare to the data. Calculations with the beyond-mean-field model, the interacting boson model, and the general Bohr Hamiltonian model show partial agreement with the experimental data. Finally, calculations with a phenomenological two-level mixing model hint at the mixing of a spherical structure with a weakly deformed rotational structure.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

N. Kesteloot, B. Bastin, L. P. Gaffney, K. Wrzosek-Lipska, K. Auranen, et al.. Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes. Physical Review C, 2015, 92 (5), pp.054301. ⟨10.1103/PhysRevC.92.054301⟩. ⟨in2p3-01225279⟩