Nuclear Dipole Response of Bound States in N=82 Nuclei Below Particle Threshold

Nuclear resonance fluorescence measurements have been performed on N=82 nuclei using 100\% linearly polarized $\gamma$-ray beams at the High-Intensity $\gamma$-ray Source (HI$\vec{\gamma}$S) at energies below the particle emission threshold. The low-lying dipole excitations have been related to the so-called ``pygmy'' dipole resonance. The electric dipole character of this low-energy mode of excitation was experimentally verified from E$_{\gamma}$=4.5-8.5 MeV. Missing dipole strength is revealed in inelastic scattering measurements using the monoenergetic HI$\vec{\gamma}$S beams. The dipole-strength distribution will be compared with microscopic calculations within the framework of the quasiparticle-phonon model.