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

Experimental K-shell ionization cross sections of ₁₃Al and ₂₈Ni are reported for ions of ₁¹H, ₁²H, ₂⁴He, ₃⁶Li, and ₃⁷Li with kinetic energies in the range from 2 to 36 MeV, and of ₂₈Ni for ions of ₆¹²C, ₈¹⁶O, and ₉¹⁹F 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., v₁v2K, is extended to intermediate velocities v₁v2K. 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 v₁v2K, such contributions subside, and one retrieves the cross sections of the linear-response approximation. The theory predicts K-shell ionization cross sections for projectiles with Z₁Z₂<0.5 at all velocities in a comprehensive manner. It agrees with experimental data covering six orders of magnitude for collisions partners with Z₁Z₂ ranging from 0.03 to 0.3 and v₁v2K from 0.07 to 2.