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 which includes the QRPA and phonon coupling effects and uses the known Skyrme forces SLy4. The pygmy dipole resonance in $^{72}Ni$ is predicted with the mean energy of 12.4 MeV and the energy-weighted sum rule exhausting 25.6\% of the total strength. The microscopically obtained photon E1 strength functions are used to calculate nuclear reaction properties, i.e the radiative neutron capture cross section, 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.