Research progress of direct nuclear reactions induced by halo nuclei

<p indent="0mm">Direct reactions are fundamental mechanisms of nuclear reactions, and are basic tools to study nuclear structures. We review our recent studies of direct reactions induced by halo nuclei and related theoretical problems, focusing on the breakup coupling effects and their role in studying the single-particle structure of weakly-bound nuclei. For this, essential theoretical ingredients of the continuum discretized coupled channel (CDCC) method are firstly introduced. After this, the breakup coupling effects in the elastic scattering angular distributions of weakly-bound nuclei are discussed, focusing on the origin of the distinguished differences in the elastic scattering angular distributions of weakly-bound neutron rich nuclei, such as ⁶He and ¹¹Be, and those of weakly-bound proton rich nuclei, such as ⁸B and ⁹C, where the nuclear-Coulomb interference peaks are greatly reduced in the former cases and not much reduced in the latter cases. Analysis with CDCC calculations suggests that it is caused by the Coulomb and/or the centrifugal barriers between the valence proton and the core nuclei, which hindered the breakup coupling effects on the elastic scattering angular distributions of the proton-rich nuclei even when the separation energy of the valence proton is very low. This suggests that the single-particle structure plays an important role in nuclear reactions induced by weakly-bound nuclei. On the other hand, this also means that properties of the single particle structure of atomic nuclei can be effectively studied by measuring the angular distributions of elastic scattering and breakup cross sections. With this respect, we introduced the ratio method, which suggests that ratios of the elastic scattering and breakup cross sections can be taken as a new sensitive observable to study the single particle structure of weakly-bound nuclei. The underlying theory, namely the recoil excitation and breakup model, is introduced, which suggests that, under conditions that (1) the valence-target interaction can be seen as negligibly small compared with the core-target interaction, and (2) the incident energy is sufficiently high so that the adiabatic approximation can be used, the elastic scattering and breakup reaction angular distributions can be factorized by a form factor and the elastic scattering angular distribution of a structureless point particle from the target nucleus. The form factors are only determined by the single particle wave functions of the valence nucleon in the ground state, the excited state and the continuum states of the valence-core system. The effectiveness of the ratio method is demonstrated with results of calculations for proton-rich nuclei, ¹⁷F, ²⁵Al, and ²⁷P on a ¹²C target at <sc>60 MeV</sc>/nucleon. Two other types of direct reactions which are also effective tools for studying the single-particle structure of atomic nuclei, namely, single-nucleon transfer reactions and single-nucleon removal reactions are also introduced, focusing on the improvement of the theoretical descriptions of these reactions, i.e., applications of the CDCC method for (<italic>d</italic>,<italic>p</italic>) reactions, and the multiple scattering effects in intermediate-energy nuclear reactions in Glauber model calculations. Examples of studies about the reactions induced by light heavy weakly-bound/halo nuclei, such as ⁶Li, ⁸B, ⁹C, ¹¹Be, and ¹⁷C are shown. Attention is also drawn on recent development of the CDCC method such as effects of core excitation in the description of elastic scattering and breakup reactions and effects of closed channels in description of fusion reactions at around the Coulomb barrier energies of weakly-bound stable nucleus ⁶Li on various target nuclei.