K-SHELL, L-SHELL, AND M-SHELL IONIZATION OF ATOMS BY ELECTRON AND POSITRON-IMPACT

The plane-wave Born approximation with Coulomb, relativistic, and exch ange corrections is employed to obtain the K-, L1-, L2-, L3-, and M-sh ell ionization cross sections of a number of atoms bombarded by electr ons and positrons in the energy range varying from the threshold of io nization to 1 GeV. Transverse interaction of virtual photons with atom s is also included and it is found to be of great significance for imp act energies greater than about 1 MeV. For K- and L-shell ionization, good agreement between the theoretical values and various experimental data for electron-impact cross sections is obtained. However, for the M shell, the theory overestimates the experimental cross sections. Fo r positron impact the agreement between the present results and the li mited experimental data is found to be quite satisfactory.