Isoscalar and isovector dipole mode in β-stable and drip line nuclei

Abstract

The isoscalar and the isovector dipole mode in nuclei are investigated, using the self-consistent Hartree-Fock plus the random-phase approximation with Skyrme interactions. Including simultaneously both the isoscalar and the isovector correlation, the RPA response function is estimated in the coordinate space so as to take into account properly the continuum effect. In β-stable nuclei such as 208Pb the frequency of the isovector giant dipole resonance (IVGDR) is lower than that of the isoscalar giant dipole resonance (ISGDR, compression mode). In contrast, in higher drip line nuclei a major part of the isoscalar compression dipole strength lies at an energy much lower than the energy of the IVGDR, due to the threshold effect of loosely-bound nucleons. The transition densities and displacement fields of ISGDR and IVGDR are discussed in comparison with collective model predictions.