Charge state dependence of K X-ray production in thin targets by multicharged silicon ions

Typical data for target K-shell X-ray production cross sections in different charge states q are reviewed. Charge-state dependence is revisited and a small, shallow minimum in the cross section as a function of q, at q=10 or 11 for Si ions, is noted. A number of mechanisms that are considered show a monotonic decrease in cross sections with the decreasing q, which is contrary to the observed trend. We postulate that the increase of K-shell X-ray cross sections, as q becomes smaller, can be understood in terms of a larger ionization probability into L- and higher shells by a greater number of the projectile's electrons, which widens the excitation channels for the K-shell and, hence enhances the K-shell X-ray production cross section with the decreasing q. (orig.)