The neutron capture process

The nature of the neutron capture process depends on the coupling of the incident neutron with target nucleons. Weak, intermediate and strong coupling assumptions are discussed which lead to the application of single particle, doorway and statistical models. While the Bohr statistical model has widespread application, there is abundant evidence for the intermediate coupling assumption in which the distribution of single particle strength is limited to local resonances only. External capture is shown to be important in both potential and resonant reactions. Width correlations for resonances and final states are predicted by the valance model and are observed near the magic neutron numbers. However quasiparticle-phonon interactions can be more dominant, and evidence for the relationship between quasiparticle hierarchy and level density is presented. The capture mechanism in 54Fe is highlighted. (Auth.)