The inner shell process produced by the collision of highly charged ion with medium atoms near the Bragg peak is an important frontier area of atomic physics under extreme conditions such as celestial plasmas and controlled nuclear fusion plasmas. Because of the special complexity of the inner shell process produced by the collision of ions with atoms in the Bragg peak energy region and the relevant experimental research is less, limited by the experimental conditions, there remain some interesting and unanswered questions.

We report the experimental data of X-ray spectra produced by the impact of Xe²⁰⁺ with 6.0 MeV kinetic energy on V, Fe, Ni, Cu, and Zn surface in the National Laboratory of Heavy Ion Research Facility in Lanzhou, China. The generation mechanism of X-ray with energy of 1.60 keV is analyzed. The results show that when Xe²⁰⁺ without initial holes interacts with different targets, the Mα X-ray of Xe is not observed, but X-ray with energy twice as great as that of Xe Mα X-ray is observed in the experiment, which is called Xe Mαα X-ray and considered to be generated by the two-electron-one-photon process of Xe on the upper surface of the target. The existence time of the first-generation hollow atoms on the upper surface is calculated by using the classical over-barrier model when Xe²⁰⁺ interacts with different targets, which is consistent with the variation of Mαα X-ray yield with the atomic number of target, therefore it is further proved that Mαα X-ray is formed by the two-electron one-photon process of Xe on the upper surface of the target. Of course, this conclusion needs further analyzing and verifying with more experimental data.