Photon interactions below 9 MeV in Ba and Ce

Elastic scattering of monoenergetic tagged photons from natural barium and cerium targets was measured at 135° for excitations between 4.5 and 9.0 MeV. The data were used to infer the respective total absorption cross sections below neutron emission threshold, and the results are compared with (γ,n) measurements and with the predictions of a quasiparticle-phonon calculation in ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}$. The low energy dipole absorption is found to be generally consistent with an extrapolation of the tail of the E1 giant resonance, and to be substantially underestimated by the quasiparticle-phonon theory.