Collectivity in the light radon nuclei measured directly via Coulomb excitation

L. P. Gaffney , A. P. Robinson (1) , D. G. Jenkins , A. N. Andreyev , M. Bender (2) , A. Blazhev , N. Bree , B. Bruyneel , P. A. Butler , T. E. Cocolios , T. Davinson , A. N. Deacon , H. De Witte , D. Dijulio , J. Diriken , A. Ekström , Ch. Fransen , S. J. Freeman (3) , K. Geibel , T. Grahn , B. Hadinia , M. Hass , P.-H. Heenen , H. Hess , M. Huyse , U. Jakobsson , N. Kesteloot , J. Konki , Th. Kröll , V. Kumar , O. Ivanov , S. Martin-Haugh , D. Mücher , R. Orlandi , J. Pakarinen , A. Petts , P. Peura , P. Rahkila , P. Reiter , M. Scheck , M. Seidlitz , K. Singh (4) , J. F. Smith (5) , J. van De Walle , P. Van Duppen , D. Voulot , R. Wadsworth , N. Warr , F. Wenander , K. Wimmer , K. Wrzosek-Lipska , And M. Zielińska

1 Department of Chemistry [Cambridge, UK]
2 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
3 ICM - Institut du Cerveau et de la Moëlle Epinière = Brain and Spine Institute
4 CSIR-National Institute of Oceanography
5 GWPAC - Gravitational-Wave Physics and Astronomy Center

Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron mid-shell at N=104. Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of 202Rn and 204Rn were studied by means of low-energy Coulomb excitation at the REX-ISOLDE facility in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first-excited 2+1 state was extracted for both 202Rn and 204Rn, corresponding to B(E2;2+1→2+1)=29+8−8 W.u. and 43+17−12 W.u., respectively. Additionally, E2 matrix elements connecting the 2+1 state with the 4+1 and 2+2 states were determined in 202Rn. No excited 0+ states were observed in the current data set, possibly due to a limited population of second-order processes at the currently-available beam energies. Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced.

Domaines: Physique Nucléaire Théorique [nucl-th]

L. P. Gaffney, A. P. Robinson, D. G. Jenkins, A. N. Andreyev, M. Bender, et al.. Collectivity in the light radon nuclei measured directly via Coulomb excitation. Physical Review C, 2015, 91, pp.064313. ⟨10.1103/PhysRevC.91.064313⟩. ⟨in2p3-01285636⟩