QUASIPARTICLES, PHONONS AND BEYOND (NUCLEAR STRUCTURE CALCULATIONS IN A LARGE DOMAIN OF EXCITATION ENERGIES)

The complex structure of low-lying as well as those of high-lying states is discussed within multiphonon approach. The approach is based on Quasiparticle-Phonon Model. This microscopic model goes beyond the quasiparticle random-phase approximation by treating a Hamiltonian of separable form in a microscopic multiphonon basis. It is therefore able to describe the anharmonic features of collective modes. In the case of low-lying part of excitations the model has close correspondence with the proton-neutron interacting boson model. Within the model highly-excited singleparticle states in nuclei are coupled with the excitations of a more complex character, first of all with collective phonon-like modes of the core. Although, on the level of one and two-phonon admixtures, the fully chaotic GOE regime is not reached, the eigenstates of the model carry significant degree of complexity that can be quantified with the aid of correlational invariant entropy.