Concentration of electric dipole strength below the neutron separation   energy in N = 82 nuclei
  The semi-magic nuclei Ba-138, Ce-140, and Sm-144 have been investigated in photon scattering experiments up to an excitation energy of about 10 MeV. The distribution of the electric dipole strength shows a resonance like structure at energies between 5.5 and 8 MeV exhausting up to 1% of the isovector E1 Energy Weighted Sum Rule. 
A. Zilges, S. Volz, M. Babilon, T. Hartmann, P. Mohr and K. Vogt