Electromagnetic excitation of neutron-rich oxygen nuclei O17-22

The dipole response of neutron-rich oxygen nuclei O17-22 has been studied u sing the electromagnetic excitation process in heavy ion collisions at beam energies around 600 MeV/nucleon. The subsequent neutron decay after inelas tic scattering of tile secondary beam projectiles on a Pb target was measur ed in a kinematically complete experiment. Differential electromagnetic exc itation cross sections were deduced up to 30 MeV excitation energy. For all isotopes low-lying El strength was obtained exhausting between 5% and 12% of the energy-weighted dipole sum rule.