γ rays from an extranuclear direct capture process

Direct electric dipole capture γ-ray transitions are calculated for a numbers of cases of charged particle capture in nuclei. It is found that when the γ-ray energy is sufficiently low — below about 2 MeV — the capture matrix element is determined by regions external to the usual “nuclear radius”. A number of cases of this type are discussed and the calculations compared with experiment. The calculations are extended to the keV region in those cases when the process is of astrophysical interest