Cluster emission, transfer and capture in nuclear reactions

Many nuclear reactions involve the emission or capture of clusters of nucleons such as deuterons, tritons, helions and α particles as well as nucleons, and these cluster reactions are of particular interest for the study of nuclear structure and nuclear reaction mechanisms. They provide important information on the single particle and on the multiparticle character of nuclear states, and so have been widely used as powerful nuclear spectroscopic tools. The mechanisms of cluster reactions show special features such as the competition between pickup and knockout processes and the contributions of several successive steps in the reaction. The inverse cluster capture reactions and the transfer reactions provide similar information. eview presents a summary of the principal theories used to analyse the experimental data on those reactions, in particular the compound nucleus theory, the direct reaction and the pre-equilibrium theories. The overall character of the reaction, together with the relative contributions of the competing reaction mechanisms, change as the energy of the projectile rises from the low-energy region (below 20 MeV) through medium energies (20–200 MeV) to the relativistic ones. Early calculations used semi-classical theories, which are indeed still useful for certain purposes, and now these have been supplemented by fully quantum-mechanical theories. These are all described, together with the models used for particular reactions. esent state of the analyses of many reactions is summarized, starting with the nucleon-induced reactions (p,d) and (n,d) and their inverses, then (p,3He), (p,t) and (p,α) and the corresponding neutron reactions. The subsequent sections consider α-induced reactions and lastly electron-, pion- and kaon-induced reactions. Finally, the present state of knowledge of cluster reactions is summarized, and several problems identified.