Two-electron one-photon transitions into the doubly ionizedKshell

Correlated two-electron transitions into the doubly ionized K shell have been observed in Al-Al, O-Ca, Ca-Ca, Fe-Fe, Fe-Ni, Ni-Fe, and Ni-Ni collisions at beam energies between 24 and 40 MeV. In these transitions one photon carries away the entire two-electron transition energy. The cross sections for the characteristic radiation and the two-electron radiation have been determined. The measured branching ratios between the single- and double-electron transition into the doubly ionized K shell are compared with various theoretical predictions. The theoretical and experimental results are found to be in qualitative agreement.