Collectivity in the light radon nuclei measured directly via Coulomb excitation

L. P. Gaffney, A. P. Robinson, D. G. Jenkins, A. N. Andreyev, M. Bender, 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. Ekstrom, Ch. Fransen, S. J. Freeman, K. Geibel, T. GrahnB. Hadinia, M. Hass, P. -H. Heenen, H. Hess, M. Huyse, U. Jakobsson, N. Kesteloot, J. Konki, Th. Kroell, V. Kumar, O. Ivanov, S. Martin-Haugh, D. Muecher, R. Orlandi, J. Pakarinen, A. Petts, P. Peura, P. Rahkila, P. Reiter, M. Scheck, M. Seidlitz, K. Singh, J. F. Smith, J. Van de Walle, P. Van Duppen, D. Voulot, R. Wadsworth, N. Warr, F. Wenander, K. Wimmer, K. Wrzosek-Lipska, M. Zielinska

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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 midshell at N = 104. Purpose: Evidence for shape coexistence has been inferred from a-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 Rn-202 and Rn-204 were studied by means of low-energy Coulomb excitation at the REX-ISOLDE in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first excited 2(1)(+) state was extracted for both Rn-202 and Rn-204, corresponding to B(E2; 2(1)(+) -> 0(1)(+)) = 29(-8)(+8) and 43(-12)(+17) W.u., respectively. Additionally, E2 matrix elements connecting the 2(1)(+) state with the 4(1)(+) and 2(2)(+) states were determined in Rn-202. No excited 0(+) states were observed in the current data set, possibly owing 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.
Original languageEnglish
Article number064313
JournalPhysical Review C
Issue number6
Publication statusPublished - 22 Jun 2015


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