Photon scattering studies of the giant dipole resonance in medium weight nuclei

Quasimonochromatic photons have been used to measure elastic and inelastic photon scattering cross sections in the giant dipole resonance region of ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, Fe, ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$, and ${}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}$ in an experiment in which the elastic and inelastic scattering are resolved. The elastic scattering cross sections show clear evidence for isospin splitting of the giant dipole resonance. The inelastic scattering to low-lying vibrational levels, which is a measure of the coupling between the giant dipole resonance and collective surface vibrations, is in qualitative agreement with the predictions of the dynamic collective model. However, when examined in detail, this model does not provide an adequate description of the scattering data.