Breakup dynamics of a neutron-halo system at sub-barrier incident energies

Abstract

The understanding of the nuclear breakup dynamics at sub-barrier incident energies, remains a hot subject in Nuclear Physics. In this dissertation, the breakup of the weaklybound neutron-halo 11Be nucleus impinging on a lead target is investigated for sub-barrier and around the Coulomb barrier incident energies. As theoretical framework, the continuum discretized coupled channels (CDCC) formalism is used. The fundamental mathematical description of this formalism leading to a discretized set of coupled di erential equations is outlined and the analytical expressions of the resulting coupling matrix elements as well as the breakup cross sections are derived. The convergence of the angular-distributions breakup cross section is rst checked against various numerical parameters that are used in the numerical solution of the coupled di erential equations. The stability of the numerical calculations is further tested by comparing the numerical results with the available experimental data. Comparison of breakup cross section with the total fusion cross section, it is reported that for incident energies below the Coulomb barrier, the breakup cross section is more important than the total fusion cross section. This observation has also been reported in the breakup of the proton-halo 8B on the same target nucleus, in a similar incident energy range. It is found that this importance of the breakup cross section over its fusion counterpart is due to a strong enhancement of the breakup cross section by the continuumcontinuum couplings. These couplings are otherwise known to strongly suppress the breakup cross section for incident energies above the Coulomb barrier. In order to further probe the enhancement of the breakup cross section by the continuumcontinuum couplings, the e ect of these couplings on its Coulomb and nuclear breakup components is analysed. It is shown that at sub-barrier incident energies, the continuumcontinuum couplings strongly enhance the Coulomb breakup cross section, whereas they strongly suppress the nuclear breakup cross section. It followed that the enhancement of the total breakup cross section by these couplings comes exclusively from its Coulomb component. The argument is that the enhancement of the Coulomb breakup cross section below the Coulomb barrier by the continuum-continuum couplings can be explained by the projectile breakup on its outgoing trajectory. A dominant breakup channel over other reaction channels at deep sub-barrier energies could be comprehensive to breakup of weakly-bound systems and may be justified by the projectile breakup on its outgoing trajectory. A paper manuscript based on these results has been submitted for review in the journal of European Physical Letters.