Photon-Channeled-Ion Coincidence Measurements to Investigate the Impact-Parameter Dependence of X-Ray Excitation

60-MeV I ions were injected into the open (111) planar channels of thin Au single crystals. Characteristic I and Au $M$ x rays excited in the crystal were measured in coincidence with the transmitted ions. The ion energy identified their oscillation amplitude in the channel; this allowed determination of the impact-parameter dependence of x-ray excitation in small-angle collisions.