Thin solid Cu targets were bombarded with Cl ions at incident energies of 40, 50, and 60 MeV. The target K x-ray yields were measured as a function of target thickness. The yield of the Cu target K x rays per scattered projectile increases exponentially with target thickness for all incident Cl charge states from 7+ to 15+ and decreases exponentially with target thickness for the incident Cl charge state 16+. A model calculation which contains the probability for a K vacancy in the projectile as a function of its depth in the target describes the observed behavior. A factor of 8 variation in the Cu K x-ray yield per scattered projectile was observed depending on how the beam was prepared and on what thickness target was used.