Structure of $^{13}$Be probed via secondary beam reactions

G. Randisi; A. Leprince; H. Al Falou; N.A. Orr; F.M. Marqués; N.L. Achouri; J.C. Angélique; N. Ashwood; B. Bastin; T. Bloxham; B. A. Brown; W. N. Catford; N. Curtis; F. Delaunay; M. Freer; E. de Góes Brennand; P. Haigh; F. Hanappe; C. Harlin; B. Laurent; J.L. Lecouey; A. Ninane; N. Patterson; D. Price; L. Stuttgé; J. S. Thomas

Structure of $^{13}$Be probed via secondary beam reactions

G. Randisi ¹ A. Leprince ¹ H. Al Falou ¹ N.A. Orr ¹ F.M. Marqués ¹ N.L. Achouri ¹ J.C. Angélique ¹ N. Ashwood B. Bastin ^{1, 2} T. Bloxham B. A. Brown W. N. Catford N. Curtis F. Delaunay ¹ M. Freer E. de Góes Brennand P. Haigh F. Hanappe C. Harlin B. Laurent ¹ J.L. Lecouey ¹ A. Ninane N. Patterson D. Price L. Stuttgé ³ J. S. Thomas

1 LPCC - Laboratoire de physique corpusculaire de Caen

2 GANIL - Grand Accélérateur National d'Ions Lourds

3 IPHC - Institut Pluridisciplinaire Hubert Curien

Abstract : The low-lying level structure of the unbound neutron-rich nucleus $^{13}$Be has been investigated via breakup on a carbon target of secondary beams of $^{14,15}$B at 35 MeV/nucleon. The coincident detection of the beam velocity $^{12}$Be fragments and neutrons permitted the invariant mass of the $^{12}$Be+$n$ and $^{12}$Be+$n$+$n$ systems to be reconstructed. In the case of the breakup of $^{15}$B, a very narrow structure at threshold was observed in the $^{12}$Be+$n$ channel. Contrary to earlier stable beam fragmentation studies which identified this as a strongly interacting $s$-wave virtual state in $^{13}$Be, analysis here of the $^{12}$Be+$n$+$n$ events demonstrated that this was an artifact resulting from the sequential-decay of the $^{14}$Be(2$^+$) state. Single-proton removal from $^{14}$B was found to populate a broad low-lying structure some 0.70 MeV above the neutron-decay threshold in addition to a less prominent feature at around 2.4 MeV. Based on the selectivity of the reaction and a comparison with (0-3)$\hbar\omega$ shell-model calculations, the low-lying structure is concluded to most probably arise from closely spaced J$^\pi$=1/2$^+$ and 5/2$^+$ resonances (E$_r$=0.40$\pm$0.03 and 0.85$^{+0.15}_{-0.11}$ MeV), whilst the broad higher-lying feature is a second 5/2$^+$ level (E$_r$=2.35$\pm$0.14 MeV). Taken in conjunction with earlier studies, it would appear that the lowest 1/2$^+$ and 1/2$^-$ levels lie relatively close together below 1 MeV.

Document type :

Journal articles

Domain :

Physics [physics] / Nuclear Experiment [nucl-ex]

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http://hal.in2p3.fr/in2p3-00920222
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Submitted on : Wednesday, December 18, 2013 - 9:11:47 AM
Last modification on : Tuesday, May 14, 2019 - 10:29:10 AM

Structure of $^{13}$Be probed via secondary beam reactions

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Structure of $^{13}$Be probed via secondary beam reactions

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