Measurement of the dipole response of neutron-rich nuclei in the A similar to 20 region

Coulomb break up of the neutron-rich C-15,C-17 and O17-22 isotopes has been studied experimentally using secondary beams at energies of 500-600 MeV/u. A comparison between differential cross sections, dsigma/dE*, with that obtained from a binary model shows that the main ground-state configuration of C-15 is C-14(0(+)) circle times nu(S1/2), as expected. For C-17, our preliminary data analysis reveals that the predominant (similar to64%) configuration of the ground state is C-16(2(+)) circle times nu(s,d). For O17-22, the low-lying El strength amounts up to about 12% of the energy weighted sum rule strength depending on neutron number. The energy weighted El strength (integrated up to 15 MeV excitation energy) increases up to O-20 then decreases for O-21,O-22. These data are compared to a shell model calculation. (C) 2002 Elsevier Science B.V. All rights reserved.