The (O-18,O-16) two-neutron transfer reaction at 84 MeV

The (O-18,O-16) two-neutron transfer reaction has been studied at 84 MeV incident energy on different targets. The charged ejectiles produced in the reactions have been momentum analyzed and identified by the MAGNEX spectrometer. Q-value spectra have been extracted with a remarkable energy resolution (FWHM = 160 keV) and several known bound and resonant states have been identified. C-15 excitation energy spectra populated by the C-13(O-18,O-16)C-15 reaction show excited states with well known dominant 2p-4h configuration, similarly to the spectra populated by (p, t) reactions. This demonstrates the clear selectivity of (O-18,O-16) reactions. Two unknown structures at 10.5 MeV and 13.6 MeV have been observed. Calculations based on the removal of two uncorrelated neutrons from the O-18 projectile describe the structure at 10.5 MeV as a resonance of C-15 near the C-13+n+n threshold, while the second bump at 13.6 MeV is not described with such calculations. This model does not account neither for the strong population of the narrow resonances with known 2p-3h configuration observed between S-n and S-2n, because of the lack of n-n correlations. This indicates that also the second bump can have a structure dominated by n-n correlations.