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Population of the 2(ms)(+) mixed-symmetry state of Ba-140 with the alpha-transfer reaction

Abstract : Background: Identification of proton-neutron mixed-symmetric one-quadrupole phonon excitations (the 2(ms)(+) states) of atomic nuclei provides information on the isovector part of the residual nucleon-nucleon interaction. It was predicted that the 2(ms)(+) state of particular nuclei close to the U(5) limit of the interacting boson model, in particular Ba-140, should be considerably populated by alpha-transfer reactions [C. E. Alonso et al., Phys. Rev. C 78, 017301 (2008)]. Purpose: We aim at the identification of the 2(ms)(+) mixed-symmetry state (MSS) of radioactive Ba-140 and investigate its population by the alpha-transfer reaction as a suitable tool to selectively populate MSSs and as a potential new signature for its mixed-symmetric character. Method: A gamma-ray spectroscopy experiment was performed in inverse kinematics in order to populate the 2(ms)(+) state of Ba-140 by alpha-transfer from a C-nat target on Xe-136 beam ions. The population of the candidate for the 2(ms)(+) state of Ba-140 was measured relative to the population of the 2(1)(+) state. Results: The candidate for the 2(ms)(+) state of Ba-140 was populated by a transfer three times weaker than predicted. Another 2(+) state that can be ruled out as the MSS was in turn as strongly populated by the a transfer as predicted for the MSS. Conclusions: The relative population of 2(+) states by alpha-transfer cannot serve as a new signature for MSSs, since other 2(+) states are also strongly populated. Nevertheless, the substantial population of the MSS candidate of Ba-140 by alpha transfer qualifies this type of reaction as suitable tool to excite MSSs and study their electromagnetic decay properties.
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Contributor : Emilie Bonnardel <>
Submitted on : Tuesday, November 24, 2015 - 11:11:15 AM
Last modification on : Monday, February 10, 2020 - 6:14:09 PM

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C. Stahl, J. Leske, C. Bauer, D. Bazzacco, E. Farnea, et al.. Population of the 2(ms)(+) mixed-symmetry state of Ba-140 with the alpha-transfer reaction. Physical Review C, American Physical Society, 2015, 92 (issue 4), pp.044324. ⟨10.1103/PhysRevC.92.044324⟩. ⟨in2p3-01232789⟩



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