Influence of Retardation on the Angular Distribution of Radiative Electron Capture

Abstract

Angular distributions and forward-backward intensities of photons emitted during electron capture have been measured in collisions between fast projectile ions (93-MeV oxygen, 110-123-MeV sulfur) and target atoms. In contrast to previous expectations, the radiation pattern in the laboratory system is not strongly shifted in forward direction but turned out to exhibit forward-backward symmetry independent of the projectile velocity. We attribute these findings to a cancellation between the Doppler-shift and retardation effects.