Projectile Charge and Velocity Dependence ofL-Subshell Ionization Cross Section Ratios for Heavy Elements

$L$-subshell ionization cross-section ratios for heavy elements induced by protons, $\alpha \text{'}s$, carbon ions, and oxygen ions in the range 0.5 to 6.0 MeV/amu have been investigated. The resulting ratios of $\frac{{\sigma }_{L_1}}{{\sigma }_{L_2}}$ and $\frac{{\sigma }_{L_3}}{{\sigma }_{L_2}}$ show large deviations from the plane-wave-Born-approximation, semiclassical-approximation, and binary-encounter-approximation predictions below 2 MeV/amu. These deviations are more pronounced for higher projectile charges.