The influence of the giant dipole resonance on radiative strength functions in spherical nuclei

Abstract

The El strength functions for spherical doubly even nuclei are calculated in a wide energy interval including the giant dipole resonance (GDR). A good description of the GDR widths in 124Te, 140Ce and 142Ce is obtained. The calculated values of the radiative strength functions near the neutron binding energy B n are in good agreement with the experimental data. The influence of GDR on the radiative strength functions and on the total photoabsorption cross sections is studied. It is shown that in single-closed-shell nuclei the El strength functions near B n are slightly influenced by the GDR. The values of strength functions are determined by the fragmentation of one-phonon states lying near B n For nuclei far from the closed shells, the influence of GDR on the radiative strength functions increases, and, for example, in 136Ba, 144Nd and 146Nd it becomes essential. The dipole photoabsorption σ γ,t cross sections as functions of the excitation energy are calculated. The existence of substructures but not their energy location is reliably predicted by the theory. The available experimental data confirm the existence of substructures in the energy dependence of σ γ,t It is shown that the Lorentzian extrapolation of the GDR tail proved to be rough for the description of σ γt near B n.