Microscopic nature of the photon strength function: stable and unstable Ni and Sn isotopes

Abstract

The pygmy-dipole resonances and photon strength functions in stable and unstable Ni and Sn isotopes are calculated within the microscopic self-consistent version of the Extended Theory of Finite Fermi Systems that includes the QRPA and phonon coupling effects and uses the known Skyrme forces SLy4. The pygmy dipole resonance in 72Ni is predicted with the mean energy of 12.4 MeV and with the energy-weighted sum rule exhausting 25.6% of the total strength. The microscopically obtained photon E1 strength functions are used to calculate radiative neutron capture cross sections, gamma-ray spectra, and average radiative widths. Our main conclusion is that in all these quantities it is necessary to take the phonon coupling effects into account.