%0 Journal Article
%T Collectivity in the light radon nuclei measured directly via Coulomb excitation
%A L. P. Gaffney
%A A. P. Robinson
%A D. G. Jenkins
%A A. N. Andreyev
%A M. Bender
%A A. Blazhev
%A N. Bree
%A B. Bruyneel
%A P. A. Butler
%A T. E. Cocolios
%A T. Davinson
%A A. N. Deacon
%A H. De Witte
%A D. DiJulio
%A J. Diriken
%A A. Ekstr£¿m
%A Ch. Fransen
%A S. J. Freeman
%A K. Geibel
%A T. Grahn
%A B. Hadinia
%A M. Hass
%A P. -H. Heenen
%A H. Hess
%A M. Huyse
%A U. Jakobsson
%A N. Kesteloot
%A J. Konki
%A Th. Kr£¿ll
%A V. Kumar
%A O. Ivanov
%A S. Martin-Haugh
%A D. M¨¹cher
%A R. Orlandi
%A J. Pakarinen
%A A. Petts
%A P. Peura
%A P. Rahkila
%A P. Reiter
%A M. Scheck
%A M. Seidlitz
%A K. Singh
%A J. F. Smith
%A J. Van de Walle
%A P. Van Duppen
%A D. Voulot
%A R. Wadsworth
%A N. Warr
%A F. Wenander
%A K. Wimmer
%A K. Wrzosek-Lipska
%A M. Zieli¨½ska
%J Physics
%D 2015
%I arXiv
%R 10.1103/PhysRevC.91.064313
%X 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 $\alpha$-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 $^{202}$Rn and $^{204}$Rn 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 $^{202}$Rn and $^{204}$Rn, corresponding to ${B(E2;2^{+}_{1} \to 2^{+}_{1})=29^{+8}_{-8}}$ 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 $^{202}$Rn. 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.
%U http://arxiv.org/abs/1503.03245v1