Halo Structure of the Neutron-Dripline Nucleus $^{19}$B

K.J. Cook , T. Nakamura , Y. Kondo , K. Hagino , K. Ogata , A.T. Saito , N.L. Achouri (1) , T. Aumann , H. Baba , F. Delaunay (1) , Q. Deshayes (1) , P. Doornenbal , N. Fukuda , J. Gibelin (1) , J.W. Hwang , N. Inabe , T. Isobe , D. Kameda , D. Kanno , S. Kim , N. Kobayashi , T. Kobayashi , T. Kubo , S. Leblond (1) , J. Lee , F.M. Marqués (1) , R. Minakata , T. Motobayashi , K. Muto , T. Murakami , D. Murai , T. Nakashima , N. Nakatsuka , A. Navin (2) , S. Nishi , S. Ogoshi , N.A. Orr (1) , H. Otsu , H. Sato , Y. Satou , Y. Shimizu , H. Suzuki , K. Takahashi , H. Takeda , S. Takeuchi , R. Tanaka , Y. Togano , J. Tsubota , A.G. Tuff , M. Vandebrouck (3) , K. Yoneda

1 LPCC - Laboratoire de physique corpusculaire de Caen
2 GANIL - Grand Accélérateur National d'Ions Lourds
3 IPNO - Institut de Physique Nucléaire d'Orsay

The heaviest bound isotope of boron B19 has been investigated using exclusive measurements of its Coulomb dissociation, into B17 and two neutrons, in collisions with Pb at 220  MeV/nucleon. Enhanced electric dipole (E1) strength is observed just above the two-neutron decay threshold with an integrated E1 strength of B(E1)=1.64±0.06(stat)±0.12(sys)  e2 fm2 for relative energies below 6 MeV. This feature, known as a soft E1 excitation, provides the first firm evidence that B19 has a prominent two-neutron halo. Three-body calculations that reproduce the energy spectrum indicate that the valence neutrons have a significant s-wave configuration and exhibit a dineutronlike correlation.

Mots clés: Nuclear Physics

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

K.J. Cook, T. Nakamura, Y. Kondo, K. Hagino, K. Ogata, et al.. Halo Structure of the Neutron-Dripline Nucleus $^{19}$B. Physical Review Letters, 2020, 124 (21), pp.212503. ⟨10.1103/PhysRevLett.124.212503⟩. ⟨hal-02870791⟩