K-shell ionization of Al and Cu for 0.5-40-MeV-proton bombardment

K-shell ionization cross sections of Al and Cu for proton impact have been measured over the projectile-energy range 0.5-40 MeV, and the results are compared with calculations of plane-wave Born approximation (PWBA) and binary-encounter approximation (BEA). In the PWBA calculation, contributions from close and distant collisions are separately estimated by an approximate calculation. It is found that the distant collisions make a predominant contribution in the high-projectile-energy region and the experimental results are in better agreement with the PWBA than the BEA, which takes into account only the close collision.