We have measured the differential Coulomb dissociation cross sections for neutron-rich nuclei in the mass range around A ≈ 20. For the halo nuclei 11Be and 15,17C the observed 'threshold strength' is analyzed aiming to deduce the single particle structure. For the known cases 11Be and 15C the extracted spectroscopic factors are in good agreement with other experiments. The importance of a γ coincidence measurement, which was not applied in earlier experiments on Coulomb dissociation of halo nuclei, is obvious in the 17C case. There, we find that the dominant ground state configuration involves a mixture of s and d wave neutrons coupled to the 2+ excited 16C core state. This excludes a ground state spin of 1/2 for 17C. For the oxygen isotope chain we have measured systematically the evolution of dipole strength in the neutron-rich nuclei A = 17 to A = 22. Excitation-energy differential cross sections were derived up to an excitation energy of 30 MeV. For all neutron-rich oxygen isotopes investigated, soft dipole excitations, well below the giant dipole resonance are observed. This low-lying dipole strength is found to exhaust up to about 10% of the energy weighted classical dipole sum rule if integrated up to 15 MeV excitation energy. The cluster sum rule limit with 16O taken as the core, however, is almost exhausted only for 17O and 18O, while for the more neutron-rich isotopes the experimentally observed strength below 15 MeV decreases with respect to that limit to about 40 % for 22O.
ASJC Scopus subject areas
- Nuclear and High Energy Physics