Intermediate Structure in the Photon Interaction Cross Sections of Sn and Zr

Photon scattering cross sections were measured with 70-keV resolution from 6 to 9 MeV in Sn, and from 8.5 to 12.5 MeV in Zr. A new method of analysis is used to infer relatively reliable total photon interaction cross sections. Both the elastic scattering and the total interaction cross sections vary more rapidly with energy than had been anticipated; the best identified localization of transition strength is between 11.4 and 11.8 MeV in Zr. The average total interaction cross sections are qualitatively similar to, but about 50% larger than, an extrapolation of the electric dipole giant resonance. The cross sections are large enough to imply that electric dipole interaction dominates at most energies. The relative probability of photon scattering and photoproton emission is very sensitive to correlations between proton widths and ground-state $\gamma$-ray widths. There is no evidence for width correlations associated with the additional strength concentrated near 11.5 MeV in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$.