Radiative processes in high-energy ion-atom collisions

Instantaneous photon emission in ion-atom collisions is considered from the standpoint of theoretical consistency. The processes discussed include electron bremsstrahlung, radiative electron capture, and atomic bremsstrahlung. Particularly detailed discussion is made on radiative electron capture. Formulas based on nonrelativistic quantum mechanics and on semiclassical theory are found to conflict with each other. The inconsistency is removed by taking the gauge-invariance requirement into consideration on the matrix elements of the interaction of the particle system with the radiation field. Finally, we present an approximation method that satisfies the gauge-invariance requirement. In addition, we show the results of calculations for radiative electron capture by Xe54+ and by U92+ from Be as examples and compare them with experiments as well as calculations based on existing theories. (orig.)