Comments on the departure from theZ2dependence in ionization by heavy projectiles

The yields for sulfur, scandium, iron, and copper $K$ x rays produced in collisions with oxygen and fluorine projectiles have been measured over a large range of impact velocities (${\eta }^{\frac{1}{2}}\simeq 0.2-0.8$). These yields, when scaled by the corresponding velocity-matched protoninduced yields, $\frac{\sigma \mathrm{}\left(Z\right)\mathrm{}}{Z^2\sigma \mathrm{}\left(1\right)\mathrm{}}$, all cross the unity value at ${\eta }^{\frac{1}{2}}$ above the values suggested in a previous theoretical paper but do approach increased-binding predictions with decreasing ${\eta }^{\frac{1}{2}}$.