Nuclear Physics A 779 (2006) 1–20 The photoresponse of stable N = 82 nuclei below 10 MeV ✩ S. Volz a,∗ , N. Tsoneva b,c , M. Babilon a , M. Elvers a , J. Hasper a , R.-D. Herzberg d , H. Lenske b , K. Lindenberg a , D. Savran a , A. Zilges a a Institut für Kernphysik, TU Darmstadt, Schlossgartenstraße 9, D-64289 Darmstadt, Germany b Institut für Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen, Germany c Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria d Department of Physics, The University of Liverpool, Liverpool L69 7ZE, United Kingdom Received 11 April 2006; received in revised form 16 August 2006; accepted 25 August 2006 Available online 25 September 2006 Abstract High resolution photon scattering experiments were performed at the 10 MeV bremsstrahlung facility of the electron accelerator S-DALINAC at TU Darmstadt to investigate the semi-magic N = 82 nuclei 138 Ba, 140 Ce, 142 Nd and 144 Sm. Energies and absolute strengths of dipole transitions below 10 MeV were determined in a model independent way. A concentration of electric dipole excitations exhausting up to 1% of the isovector E1 energy weighted sum rule is observed in all four nuclei around 6.5 MeV. Calculations in the framework of the Quasiparticle-Phonon Model (QPM) reproduce the gross experimental features.  2006 Elsevier B.V. All rights reserved. PACS: 21.10.-k; 23.20.-g; 25.20.Dc; 27.40.+z Keywords: NUCLEAR REACTIONS 138 Ba(γ,γ ′ ), E = 9.2 MeV bremsstrahlung; 140 Ce, 142 Nd, 144 Sm(γ,γ ′ ), E = 7.6, 9.9 MeV bremsstrahlung; measured Eγ,Iγ , 138 Ba, 140 Ce, 142 Nd, 144 Sm deduced dipole transition energies, B(E1); comparison with quasiparticle-phonon model predictions ✩ This work was supported by the Deutsche Forschungsgemeinschaft (contracts SFB 634 and Zi 510/2-2). * Corresponding author. E-mail address: volz@ikp.tu-darmstadt.de (S. Volz). 0375-9474/$ – see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2006.08.012