Nuclear-structure dependence of the E1 strength located in the giant dipole resonance of heavy nuclei

Using monochromatic photons from (n,) and (p,) capture reactions, the elastic scattering of photons was studied in the mass range A=181238 and energy range E=818 MeV. It is shown that the A dependence of the enhancement of E1 strength located in the giant-dipole resonance as revealed by part of the photoneutron cross sections is confirmed by our photon-scattering data. The possibility is discussed that the concentration of E1 strength in the giant dipole resonance may be larger for closed-shell nuclei as compared to open-shell nuclei.