  The dipole response of the N=50 nucleus 90Zr was studied in photon-scattering
experiments at the electron linear accelerator ELBE with bremsstrahlung
produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV. We identified
189 levels up to an excitation energy of 12.9 MeV. Statistical methods were
applied to estimate intensities of inelastic transitions and to correct the
intensities of the ground-state transitions for their branching ratios. In this
way we derived the photoabsorption cross section up to the neutron-separation
energy. This cross section matches well the photoabsorption cross section
obtained from (gamma,n) data and thus provides information about the extension
of the dipole-strength distribution toward energies below the
neutron-separation energy. An enhancement of E1 strength has been found in the
range of 6 MeV to 11 MeV. Calculations within the framework of the
quasiparticle-phonon model ascribe this strength to a vibration of the
excessive neutrons against the N = Z neutron-proton core, giving rise to a
pygmy dipole resonance.
