Dipole response of Sr-88 up to the neutron-separation energy

The dipole response of the magic N=50 nucleus ^{88}Sr was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 9.0, 13.2, and 16.0 MeV. 160 levels were identified up to an excitation energy of 12 MeV.
By using polarized photons linear polarizations of about 50 gamma transitions were measured that enabled parity assignments to the corresponding states. In the energy range of 6 -- 12 MeV we identified only one M1 transition while all other transitions have E1 character. Thus, E1 character was proven for 63\% of the total dipole strength found for the observed levels in the given energy range. Statistical methods were applied in order to filter out inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we obtained 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 towards energies below the neutron-separation energy. An enhancement of E1 strength at 6 -- 11 MeV may be considered as an indication for a Pygmy Dipole Resonance.