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. Ekström, 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 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, J. F. Smith, J. Van De Walle, P. Van Duppen, D. Voulot, R. Wadsworth, N. Warr, F. Wenander, K. Wimmer, K. Wrzosek-Lipska, M. Zielińska

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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 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 Rn202 and Rn204 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 21+ state was extracted for both Rn202 and Rn204, corresponding to B(E2;21+→01+)=29-8+8 and 43-12+17 W.u., respectively. Additionally, E2 matrix elements connecting the 21+ state with the 41+ and 22+ states were determined in Rn202. 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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