Radiative electron capture in relativistic ion–atom collisions and the photoelectric effect in hydrogen-like high-Z systems

In recent years, radiative electron capture (REC) in high-energy ion–atom collisions from a low-Z target into a bare (or few-electron) high-Z projectile up to U 92 + has been studied in great detail. This process, in which an electron is transferred from the target to the projectile with the simultaneous emission of a photon, plays an important role in spectroscopic studies of high-Z few-electron atoms. Being the inverse reaction of the atomic photoelectric effect, it also provides a means of investigating the latter in a high-energy regime that is otherwise almost inaccessible. In the present article, the experimental techniques as well as the theoretical developments are reviewed, and a summary of results is given.