Collectivity of the low-lying dipole strength in relativistic random phaseapproximation

The relativistic random phase approximation is applied in the analysis of t he evolution of the isovector dipole response in nuclei with a large neutro n excess. The self-consistent framework of relativistic mean-field theory, which has been very successfully applied in the description of groundstate properties of nuclei far from the valley of beta -stability, is extended to study the possible onset of low-energy collective isovector dipole modes i n nuclei with extreme isospin values. (C) 2001 Elsevier Science B.V. All ri ghts reserved.