(18O,16O) Two-neutron transfer reactions for spectroscopic studies

Full text: The 12C(18O,16O)14C and 13C(18O,17O)14C transfer reactions have been studied at 84 MeV incident energy at the INFN-LNS laboratory in Catania (Italy). The 16O and 17O ejectiles were detected at forward angles by the MAGNEX large acceptance magnetic spectrometer. Q-value spectra up to about 20 MeV and angular distributions were obtained with resolution of about 150 keV in energy and 0.2 deg in angle. In particular, excited states with relevant 1p-3h configuration with respect to the 16O core are mainly populated by the (18O,17O) reaction while states with known 2p-4h configuration are excited by the (18O,16O). This demonstrates the clear selectivity of such reactions. The shape of the measured angular distributions is found to be sensibly dependent on the transferred angular momentum. A theoretical description based on exact finite range coupled reaction channel calculations using the double folding Sao Paulo potential is used for the first time to analyze the data. The good agreement with the experimental cross section demonstrates that, despite the heavy ions involved, the one-step transfer of a two-neutron pair is dominant in the (18O,16O) reaction. A comparison with Distorted Wave Born Approximation calculations using the same potential shows that effects of channel couplings is visible but small. Supplementary two-neutron sequential transfer calculation are performed within the two-step DWBA formalism, introducing the intermediate partition 13C + 17O. This accounts only for a negligible contribution to the absolute cross section. As a consequence, the possibility to extract two-particle spectroscopic factor and, more in general, information on nuclear structure is demonstrated. (author)