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Journal Articles Physical Review C Year : 2017

Effective proton-neutron interaction near the drip line from unbound states in $^{25,26}$F

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M. Vandebrouck
  • Function : Author
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T. Aumann
  • Function : Author
C. Caesar
  • Function : Author
M. Holl
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V. Panin
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F. Wamers
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S.R. Stroberg
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J.D. Holt
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H. Alvarez-Pol
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L. Atar
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V. Avdeichikov
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S. Beceiro-Novo
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D. Bemmerer
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J. Benlliure
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C. A. Bertulani
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S.K. Bogner
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J.M. Boillos
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K. Boretzky
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M.J.G. Borge
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M. Caamano
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E. Casarejos
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W. Catford
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J. Cederkäll
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M. Chartier
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L. Chulkov
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D. Cortina-Gil
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E. Cravo
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R. Crespo
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U. Datta Pramanik
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P. Diaz Fernandez
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I. Dillmann
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Z. Elekes
J. Enders
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O. Ershova
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A. Estrade
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F. Farinon
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L.M. Fraile
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M. Freer
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D. Galaviz
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H. Geissel
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R. Gernhauser
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J. Gibelin
P. Golubev
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K. Göbel
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J. Hagdahl
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T. Heftrich
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M. Heil
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M. Heine
A. Heinz
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A. Henriques
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H. Hergert
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A. Hufnagel
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A. Ignatov
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H.T. Johansson
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B. Jonson
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J. Kahlbow
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N. Kalantar-Nayestanaki
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R. Kanungo
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A. Kelic-Heil
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A. Knyazev
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T. Kröll
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N. Kurz
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M. Labiche
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C. Langer
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T. Le Bleis
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R. Lemmon
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S. Lindberg
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J. Machado
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J. Marganiec
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F.M. Marqués
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A. Movsesyan
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E. Nacher
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M. Najafi
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E. Nikolskii
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T. Nilsson
C. Nociforo
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S. Paschalis
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A. Perea
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M. Petri
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S. Pietri
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R. Plag
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R. Reifarth
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G. Ribeiro
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C. Rigollet
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M. Röder
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D. Rossi
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D. Savran
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H. Scheit
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A. Schwenk
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H. Simon
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I. Syndikus
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J. Taylor
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O. Tengblad
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R. Thies
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Y. Togano
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P. Velho
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V. Volkov
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A. Wagner
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H. Weick
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C. Wheldon
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G. Wilson
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J.S. Winfield
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P. Woods
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D. Yakorev
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M. Zhukov
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A. Zilges
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K. Zuber
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Abstract

Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The $^{26}$F nucleus, composed of a deeply bound $\pi0d_{5/2}$ proton and an unbound $\nu0d_{3/2}$ neutron on top of an $^{24}$O core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a $J^{\pi} = 1^{+}_1 - 4^{+}_1$ multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The $J^{\pi} = 1^{+}_1, 2^{+}_1,4^{+}_1$ bound states have been determined, and only a clear identification of the $J^{\pi} =3^{+}_1$ is missing. Purpose: We wish to complete the study of the $J^{\pi} = 1^{+}_1 - 4^{+}_1$ multiplet in $^{26}$F, by studying the energy and width of the $J^{\pi} =3^{+}_1$ unbound state. The method was firstly validated by the study of unbound states in $^{25}$F, for which resonances were already observed in a previous experiment. Method: Radioactive beams of $^{26}$Ne and $^{27}$Ne, produced at about $440A$\,MeV by the FRagment Separator at the GSI facility, were used to populate unbound states in $^{25}$F and $^{26}$F via one-proton knockout reactions on a CH$_2$ target, located at the object focal point of the R$^3$B/LAND setup. The detection of emitted $\gamma$-rays and neutrons, added to the reconstruction of the momentum vector of the $A-1$ nuclei, allowed the determination of the energy of three unbound states in $^{25}$F and two in $^{26}$F. Results: Based on its width and decay properties, the first unbound state in $^{25}$F is proposed to be a $J^{\pi} = 1/2^-$ arising from a $p_{1/2}$ proton-hole state. In $^{26}$F, the first resonance at 323(33)~keV is proposed to be the $J^{\pi} =3^{+}_1$ member of the $J^{\pi} = 1^{+}_1 - 4^{+}_1$ multiplet. Energies of observed states in $^{25,26}$F have been compared to calculations using the independent-particle shell model, a phenomenological shell-model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton-neutron interaction is weakened by about 30-40\% in comparison to the models, pointing to the need of implementing the role of the continuum in theoretical descriptions, or to a wrong determination of the atomic mass of $^{26}$F.
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Dates and versions

in2p3-01568314 , version 1 (25-07-2017)

Identifiers

Cite

M. Vandebrouck, A. Lepailleur, O. Sorlin, T. Aumann, C. Caesar, et al.. Effective proton-neutron interaction near the drip line from unbound states in $^{25,26}$F. Physical Review C, 2017, 96, pp.054305. ⟨10.1103/PhysRevC.96.054305⟩. ⟨in2p3-01568314⟩
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