The isoscalar and isovector collective multipole excitations in exotic nuclei are studied in the framework of a fully self-consistent relativistic continuum random phase approximation(RCRPA). In this method the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single particle Green's function. Di?erent from the cases in stable nuclei, there are strong low-energy excitations in neutron-rich nuclei and proton-rich nuclei. The neutron or proton excess pushes the centroid of the strength function to lower energies and increases the fragmentation of the strength distribution. The e?ect of treating the contribution of continuum exactly is also discussed.
The structural effect is believed to have no influence on the decay properties of medium and heavy-mass nuclei at excitation energies above the pairing gap.These properties can be described by statistical properties using so-called photon strength functions for different multipolarities,and directly related to the photoabsorption cross-section(σabs).σabs is dominated by the electric giant dipole resonance at y energy εγ≤40 MeV.In this study,we construct two kinds of systematic giant dipole resonance parameters by fitting the experimental photoabsorption crosssections.One is based on the microscopic relativistic quasiparticle random phase approximation approach,whereas the other is estimated by the phenomenological models within the Lorentzian representation.Both of them are demonstrated of efficiently describe the experimental photoabsorption cross-sections available for medium to heavymass nuclei,and they can obtain more reliable predictions for the unknown nuclear system.
