THE GROUND-STATE STRUCTURE AND THE SOFT DIPOLE MODE OF THE HE-6 NUCLEUS

The ground-state properties of He-6 have been studied in the cluster-orbital shell-model assuming the structure of He-4 + n + n. The interactions acting between the constituent particles are chosen consistently with all available data. The particle-stable ground state is obtained. The calculated proton and neutron densities of He-6 are found to satisfactorily reproduce the total reaction cross sections. The same model has been applied to study the electric dipole strength corresponding to the soft dipole mode in excited states. A very strong enhancement of the dipole strength is predicted between 4 and 7 MeV. This leads to the enhanced electromagnetic dissociation cross sections relevant to the (He-6, He-4) projectile fragmentation. The theoretical prediction is, however, smaller than the value deduced from the experimental systematics. The implication of this discrepancy is discussed from the viewpoint of the sum rule for the soft dipole mode.