Simultaneous K -Plus- L -Shell Ionization in Light-Ion-Atom Collisions

The probability of simultaneous $K$-plus-$L$-shell ionization in collisions between Ca, Ti, and Fe target atoms and projectiles of 1.5 - 12.5-MeV/amu deuterons and $\ensuremath{\alpha}$ particles has been investigated. The results show that the fraction of $K\ensuremath{\beta}$ x rays emitted in the presence of an $L$-shell vacancy (a) decreases with increasing projectile velocity above a projectile-to-$L$-shell-electron velocity ratio of 1; (b) decreases with increasing target atomic number; and (c) increases with projectile charge (approximately as ${z}_{1}^{2}$). The projectile velocity dependence is in fairly good agreement with a simple classical model based upon the assumption that multiple-vacancy production results from simultaneous Coulomb collisions with $K$-and $L$-shell electrons during the ion's passage through the atom.