Abstract : 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.
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Submitted on : Friday, November 20, 2020 - 1:52:46 PM Last modification on : Wednesday, March 3, 2021 - 6:27:23 AM
K.J. Cook, T. Nakamura, Y. Kondo, K. Hagino, K. Ogata, et al.. Halo Structure of the Neutron-Dripline Nucleus $^{19}$B. Phys.Rev.Lett., 2020, 124 (21), pp.212503. ⟨10.1103/PhysRevLett.124.212503⟩. ⟨hal-02870791⟩