Pygmy Resonances Within a Microscopic Multiphonon Approach

We perform HF+RPA calculations for nuclei with neutron excess in order to study the nature of the low lying dipole states. A detailed analysis shows that they are composed by many particle hole configurations in a cooperative, rather than collective, way. Nevertheless they represent a different mode as is evidenced by their transition densities. Relativistic Coulomb calculations within a microscopic multiphonon approach show that the contributions to the inelastic cross section of low lying multiphonon states is of the order of 10%.