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

We study displacement fields of multipole excitations in a halo nucleus Be- 11(4)7 and a skin nucleus Ca-60(20)40 in comparison with those of collectiv e states in a beta-stable nucleus Pb-208(82)126. The self-consistent Hartre e-Fock calculation plus the random phase approximation with Skyrme interact ions is performed in the coordinate space, taking into account the proton a nd neutron degree of freedom. Transition densities, radial current componen ts and displacement fields of giant resonances in drip-line nuclei are foun d very similar to those in beta stable nuclei. The isovector giant resonanc es 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 sli ghtly outside the surface. It is shown that transition densities and curren t components of the excitations just above the threshold of the drip-line n uclei are extended to far outside the nuclear surface, where the displaceme nt fields show a simple pattern. (C) 1999 Elsevier Science B.V.