Quasiparticle-phonon interaction in non-magic nuclei

Abstract

A general microscopic approach to describe properties of excited states in non-magic nuclei is formulated. It is based on the consistent use of the Green function method in Fermi systems with Cooper pairing. The main attention is paid to even-even nuclei, but for odd nuclei with pairing some important relations are obtained too. The quasiparticle-phonon interaction which is introduced acts also in the particle-particle channel and gives a quasiparticle-phonon contribution to pairing. When applied to the theory of giant multipole resonances, the approach includes all known sources of resonance width, i.e. QRPA configurations (which correspond to Landau damping in magic nuclei), the single-particle con- tinuum (escape width) and more complex configurations (spreading width). The use of the Green function method makes it possible to include consistently the ground-state correlations induced by the more complex configurations. In the approximation of the collective phonon creation amplitude squared, which is considered in detail here, these are the ground-state correlations caused by two-quasiparticle-phonon configurations; effects of these correlations have been found earlier to be noticeable for magic nuclei. Such a unified approach will give a reasonable description of the giant resonances' integral characteristics including their widths and of some more delicate properties like fine structure and decay characteristics. Physical arguments and earlier results of a similar approach for magic nuclei allow to use the known parameters of the Landau-Migdal non-separable interaction for all non-magic nuclei (except the light ones). This means that the theory developed is suitable for realistic predictions of the properties of unknown nuclei including unstable ones. The inclusion of the single-particle continuum allows to consider also nuclei with separation energy near zero.