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

Background: In our recent work [M. J. Ermamatov, Phys. Rev. C 94, 024610 (2016)0556-281310.1103/PhysRevC.94.024610], the two-neutron transfer induced by the (O18,O16) reaction was studied for O16 nucleus. Theoretical analysis of the low-lying states of O18 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 O18 nucleus. In order to achieve a comprehensive picture, we revisit the experimental data for the O16(t,p)O18 reaction at 15 MeV bombarding energy. We also include new experimental cross sections for the high-lying states of the O18 residual nucleus, populated in the O16(O18,O16)O18 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 O18 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 O16(t,p)O18 data well, leading to natural parity states in the O18 nucleus without the need of adjustable parameters. The same methods are applied to the O16(O18,O16)O18 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.