Nuclear response to two-neutron transfer via the (18O,16O) reaction

A systematic study of the response of nuclei to the (18O,16O) two-neutron transfer reaction at 84 MeV incident energy was pursued at the Catania INFN-LNS laboratory. The experiments were performed using several solid targets from light (9Be, 11B, 12,13C, 16O, 28Si) to heavier ones (58,64Ni, 120Sn, 208Pb). The 16O ejectiles were detected at forward angles by the MAGNEX magnetic spectrometer. Thanks to an innovative technique the ejectiles were identified without the need of time of flight measurements. Exploiting the large momentum acceptance (≈ 25%) and solid angle (50 msr) of the spectrometer, energy spectra were obtained with a relevant yield up to about 20 MeV excitation energy. The application of the powerful trajectory reconstruction technique did allow to get energy spectra with energy resolution of about 150 keV and angular distributions with angular resolution better than 0.3°. A common feature observed with light nuclei is the appearance of unknown resonant structures at for example 10.5 and 13.6 MeV in 15C and 16 MeV in 14C. The strong population of these latter together with the measured width can reveal the excitation of a collective mode connected with the transfer of a pair. The measurement of the angular distributions can indicate if a transfer of a correlated neutron pair in L = 0 configuration, compatible with the Giant Pairing Vibration mode, is involved. Theoretical calculations were performed in order to estimate the contribution of the break-up of both two correlated neutrons and two independent ones.