Cross section for the reaction (γ,n) on heavy nuclei in the energy region of the giant quadrupole resonance

The yields of photoneutrons from 208Pb and 209Bi nuclei are measured in experiments with a bremsstrahlung beam whose endpoint energy lies in the range 7-26 MeV. The data in the range 20-26 MeV are analyzed to obtain information about the structure and parameters of the giant quadrupole resonance. The parameters of Gaussians approximating the shape of cross sections are determined. This makes it possible to estimate the contributions of states forming structures in the integrated cross sections. Experimental cross sections for 208Pb are compared with the strength functions of photoexcitation of 1- and 2+ states. These strength functions are calculated in the quasiparticle-phonon model. 43 refs., 7 figs., 2 tabs