K-shell ionization of carbon by 1- to 18-MeV protons

Cross sections for $K$-shell ionization have been determined from relative x-ray yields normalized to Auger-electron-production data at low proton energies. The asymptotic form of the plane-wave Born approximation reproduces the data at high energies, but the binary encounter approximation underestimates the cross sections in this region by a factor of 2.