Displacement fields of excited states in stable and neutron drip-line nuclei

Abstract

We study displacement fields of multipole excitations in a halo nucleus 4 11Be 7 and a skin nucleus 20 60Ca 40 in comparison with those of collective states in a β-stable nucleus 82 208Pb 126. The self-consistent Hartree-Fock calculation plus the random phase approximation with Skyrme interactions is performed in the coordinate space, taking into account the proton and neutron degree of freedom. Transition densities, radial current components and displacement fields of giant resonances in drip-line nuclei are found very similar to those in β stable nuclei. The isovector giant resonances are not properly understood in terms of any available collective models, while the isoscalar giant resonances are in a good approximation expressed by collective models. It is found that the radial velocity of the highest-lying peak of isovector giant multipole resonances vanishes at a radius slightly outside the surface. It is shown that transition densities and current components of the excitations just above the threshold of the drip-line nuclei are extended to far outside the nuclear surface, where the displacement fields show a simple pattern.