Comprehensive analysis of high-lying states in 18O populated with (t , p) and (18O, 16O) reactions

Background: In our recent work [M. J. Ermamatov et al., Phys. Rev. C 94, 024610 (2016)], the two-neutron transfer induced by the (O-18, O-16) reaction was studied for O-16 nucleus. Theoretical analysis of the low-lying states of O-18 indicates that the transfer to the ground state proceeds predominantly through simultaneous transfer of the two-neutron system. Purpose: In this work, we extend our previous theoretical analysis towards high-lying states of the O-18 nucleus. In order to achieve a comprehensive picture, we revisit the experimental data for the O-16(t, p)O-18 reaction at 15 MeV bombarding energy. We also include new experimental cross sections for the high-lying states of the O-18 residual nucleus, populated in the O-16(O-18, O-16)O-18 reaction at 84 MeV. Method: The same spectroscopic parameters of the target nucleus were used as input in the coupled channel calculations for the transfer induced by triton and O-18 projectiles. Simultaneous two-neutron transfer is calculated within the coupled reaction channel approach, using the extreme cluster and independent coordinate models. The sequential process is calculated within the distorted-wave Born approximation. Results: Theoretical calculations reproduce the O-16(t, p)O-18 data well, leading to natural parity states in the O-18 nucleus without the need of adjustable parameters. The same methods are applied to the O-16(O-18, O-16)O-18 data and a good agreement is observed. Conclusions: Detailed analyses show the importance of a simultaneous mechanism for the two-neutron transfer reactions. In transferring two neutrons, the pairing correlation plays an important role.