Charge-state dependence of inner-shell processes in collisions between highly charged Xe ions and solids at intermediate energies

The x-ray emission during the penetration of 2-6 MeV Xeq+ (q=20,22,26,30) ions into thick solid targets of iron and nickel has been measured. An obvious charge-state and incident-energy dependence of the target-to-projectile vacancy-production cross-section ratios was found for the iron target but not for the nickel target. The results are supported by the vacancy-sharing model and direct ionization theory and imply the great importance of level matching for the inner-shell process. The charge equilibration time of Xe30+ in solid iron was derived to be around 9 fs from the measured x-ray yields.