Dipole excitations in nuclei

Abstract

Dipole strengths of nuclear excitations to GDR energies in neutron excess nuclei are investigated in a theoretical approach based on EDF and QPM theory. Recent developments of the method, including a reaction theory, have been applied in spectroscopic studies of two-phonon states, pygmy and giant resonances, thus demonstrating its effectiveness. Besides the single-particle nature of the excited nuclear states from the PDR region, different properties of the low-energy dipole strength emerge from the analysis of inelastic photon-, proton- and alpha-scattering spectral distributions and branching ratios, from which the fine structure of the low-energy dipole strength and the role of quasicontinuum coupling can be probed. Experimentally, the determination of the dipole strength distribution and the associated photoabsorption cross section requires knowledge of the intensity distribution of the ground state transitions and their branching ratios. These quantities cannot be derived directly from the measured spectra. However, they can be determined theoretically from our microscopic calculations, which contribute to the understanding of the experimental data.