Extension of the binary-encounter-dipole model to relativistic incident electrons - art. no. 052710

Formulas for the total ionization cross section by electron impact based on the binary-encounter-dipole (BED) model and its simpler version, the binar y-encounter-Bethe (BEB) model are extended to relativistic incident electro n energies. Total ionization cross sections for the hydrogen and helium ato ms from the new relativistic formulas are compared to experimental data. Re lativistic effects double the total ionization cross section of H and He at incident electron energy approximate to 300 keV and dominate the cross sec tion thereafter. A simple modification of the original BED-BEB formulas is: proposed for applications to ion targets and inner-shell electrons of neut ral atoms and molecules. The relativistic and nonrelativistic BEB cross sec tions are compared to the K-shell ionization cross sections by electron imp act for the carbon, argon, nickel, niobium, and silver atoms. For carbon an d argon, the relativistic effects are small, and both forms of the BEB cros s sections agree well with available experimental data. For the nickel and heavier atoms, the relativistic increase of cross sections becomes noticeab le from about 100 keV and higher in the incident electron energy. The empir ical formula by Casnati ef al. [J.. Phys. B 15, 155 (1982)] after correctin g for relativistic effects as shown by Quarles [Phys. Rev. A 13, 1278 (1976 )] agrees well with the BEB cross sections for light atoms. However, the pe ak values of the Casnati cross sections become higher than the relativistic BEB peak cross sections as the atomic number increases. The BEB model is a lso applied to the total ionization cross section of the xenon atom, and th e theory agrees well with experiments at low incident electron energies, bu t disagrees with experiment at relativistic incident energies.