Microscopic description of the pygmy and giant electric dipole resonances in stable Ca isotopes

Abstract

The properties of the pygmy (PDR) and giant dipole resonance (GDR)in the stable ${}^{40}Ca$,${}^{44}Ca$ and ${}^{48}Ca$ isotopes have been calculated within the \emph{Extended Theory of Finite Fermi Systems}(ETFFS). This approach is based on the random phase approximation (RPA) and includes the single particle continuum as well as the coupling to low-lying collectives states which are considered in a consistent microscopic way. For ${}^{44}Ca$ we also include pairing correlations. We obtain good agreement with the experimental data for the gross properties of both resonances. It is demonstrated that the recently measured A-dependence of the strength of the PDR below 10 MeV is well understood in our model:due to the phonon coupling some of the strength in ${}^{48}Ca$ is simply shifted beyond 10 MeV. The predicted fragmentation of the PDR can be investigated in $(e,e^{\prime })$ and $(\gamma ,{\gamma }^{\prime })$ experiments. Whereas the isovector dipole strength of the PDR is small in all Ca isotopes, we find in this region surprisingly strong isoscalar dipole states, in agreement with an $(\alpha ,{\alpha }^{\prime }\gamma )$ experiment. We conclude that for the detailed understanding of the structure of excited nuclei e.g. the PDR and GDR an approach like the present one is absolutely necessary.

6 figures

References in corpus (1)

• Extended Theory of Finite Fermi Systems: Application to the collective and non-collective E1 strength in ${}^{208}$Pb

Cited by in corpus (5)

• Relativistic quasiparticle time blocking approximation. II. Pygmy dipole resonance in neutron-rich nuclei
• Second RPA and correlated realistic interactions
• Self-consistent calculations of the strength function and radiative neutron capture cross section for stable and unstable tin isotopes
• Nuclear response theory with multiphonon coupling in a covariant framework
• Isoscalar dipole coherence at low energies and forbidden E1 strength