Radiative recombination into high-Z few-electron ions: Cross sections and angular distributions

The radiative electron capture into high-Z, few-electron ions is studies in the framework of the density matrix, based on Dirac’s equation. In this formalism, all the properties of the photons and the (remaining) ions can be described, independent from their initial shell structure or polarization. Detailed computations have first been carried out for the total and angle-differential cross sections, following the capture of an electron into hydrogen-U⁹¹⁺ and lithiumlike U⁸⁹⁺ ions. From these calculations, which were performed in two different approximations, it is shown that many-electron interactions affect the angular distribution at low projectile energies by about 5%. Apart from describing the (angular-dependent) capture cross sections, our formalism is also appropriate to explore the subsequent Kα,β photon emission, if the electron is captured into an excited state of the ion, the polarization of the photons and ions as well as the interplay of the radiative with other, nonradiative capture processes in the future.