Evolution of the pygmy dipole resonance in nuclei with neutron excess

Abstract

The electric dipole excitation of various nuclei is calculated with a Random Phase Approximation phenomenological approach. The evolution of the strength distribution in various groups of isotopes, oxygen, calcium, zirconium and tin, is studied. The neutron excess produces $E1$ strength in the low energy region. Indexes to measure the collectivity of the excitation are defined. We studied the behavior of proton and neutron transition densities to determine the isoscalar or isovector nature of the excitation. We observed that in medium-heavy nuclei the low-energy $E1$ excitation has characteristics rather different that those exhibited by the giant dipole resonance. This new type of excitation can be identified as pygmy dipole resonance.

14 pages, 12 figures, 7 tables

References in corpus (4)

• Relativistic RPA plus phonon-coupling analysis of pygmy dipole resonances
• Extended Theory of Finite Fermi Systems: Application to the collective and non-collective E1 strength in ${}^{208}$Pb
• Self-consistent calculations within the Green's function method including particle-phonon coupling and the single-particle continuum
• Pygmy dipole resonance in exotic nuclei