Collectivity in the light radon nuclei measured directly via Coulomb excitation

Abstract : 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.
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Physical Review C, American Physical Society, 2015, 91, pp.064313. 〈10.1103/PhysRevC.91.064313〉
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Soumis le : mercredi 9 mars 2016 - 15:14:42
Dernière modification le : mercredi 21 mars 2018 - 18:57:50

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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, American Physical Society, 2015, 91, pp.064313. 〈10.1103/PhysRevC.91.064313〉. 〈in2p3-01285636〉

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