HALO STRUCTURE AND SOFT DIPOLE MODE OF THE HE-6 NUCLEUS IN THE ALPHA+N+N CLUSTER MODEL

The ground-state properties and the soft dipole mode of the He-6 nucleus are investigated by the coupled-rearrangement-channel variational method based on an alpha + n + n cluster model, where the effect of the Pauli principle between the alpha core and valence neutrons is taken into account. A reasonable binding energy is obtained for the ground state with the use of realistic nn and nalpha interactions. The resulting ground-state wave function has a long-range tail in the neutron distribution, clearly indicating the neutron halo structure in the He-6 nucleus. The calculated distribution of the electric-dipole transition to the 1- excited states shows a localization of the strength to a rather broad peak around E(x) congruent-to 2.5 MeV with a width of about 4 MeV.