Universal cross sections forK-shell ionization by heavy charged particles. II. Intermediate particle velocities

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Abstract
Experimental K-shell ionization cross sections of Al13 and Ni28 are reported for ions of H11, H12, He24, Li36, and Li37 with kinetic energies in the range from 2 to 36 MeV, and of Ni28 for ions of C612, O816, and F919 in the range from 4 to 90 MeV. The theory of direct Coulomb K-shell ionization, as developed in an earlier paper [Phys. Rev. A 7, 983 (1973)] for projectiles of atomic number Z1, small compared to the target atomic number Z2, and of velocities v1 small compared to the target K-shell electron velocity v2K, i.e., v1≪v2K, is extended to intermediate velocities v1≃v2K. New effects appear. They add to the Z12-proportional cross sections one derives from linear-response theories for direct ionizations. They are attributed to the polarization of the target K shell in the field of the projectile, and to electron capture by the projectile. Guided by the perturbed stationary-state theory of atomic collisions, the polarization effects are incorporated so that the theory retains the unifying aspects of the cross sections derived in the plane-wave Born approximation, but the variables now contain the nonlinear effects as scaling factors. Electron-capture cross sections are added. When v1≫v2K, such contributions subside, and one retrieves the cross sections of the linear-response approximation. The theory predicts