The interaction between highly charged ions and solid targets has attracted substantial attention in recent years due to its fundamental importance and interesting applications[1-3]. In the low-energy region, many works have been carried out focusing on the evolution of the hollow atoms by analyzing the high-resolution X-ray spectroscopies with a crystal, and the classical over-barrier model has been established to understand such behavior. In the high-energy region, lots of experimental works have been done about the inner-shell ionization by measuring the X-ray production cross section, and many theorieshave been developed to describe such process. However, the experimental and theoretical investigation of the ionization and neutralization for the projectile in the collisions near the Bohr velocity is rare.

Near the Bohr velocity, the projectile, having enough kinetic energy, can interact with the target atoms at a close distance below the surface. In addition to neutralization, it may be ionized. Not only the inner-shell ionization, but also the outer-shell may be multiply ionized. On one hand, this causes the energy shift of the corresponding X-ray and the change of the relative intensity of sub-shell X-rays. On the other hand, this may result in the enhancement of the X-ray fluorescence yield, as the Auger electron emission and Coster-Kroing (CK) transition rate are diminished because of the absence of the outer-shell electrons. In addition, the inner-shell binding energy of the projectile is enlarged by a decrease of the screening generated by a decrease number of the outer-shell electrons. So, it is proposed that the effect of charge state on binding energy should be considered in calculating the inner-shell X-ray production cross section. Here, we would like to present the investigation of evolution of Ar11+ ions in collisions near the Bohr velocity.

Reference :

[1] D. Mitra, M. Sarkar,et.al., Nucl. Instr. Meth. B 268 (2010) 450

[2] J. Reyes-Herrera, J. Miranda, Nucl. Instr. Meth. B 267 (2009) 1767

[3] T. Schenkel, A.V. Hamza, A. V. Barnes, D. H. Progress in Surface Science. Rep 61 (1999) 23