Relative cross sections for L- and M-shell ionization by electron impact

Results from measurements and calculations of relative L- and M-shell ioniz ation cross sections by electron impact are presented. Measurements were pe rformed fur elements Te, Au and Bi on an electron microprobe with specimens consisting of extremely thin films of the studied element deposited on thi n, self-supporting, carbon layers. The relative variation of the ionization cross section was obtained by counting the number of characteristic X-rays from the considered element and shell, for varying incident electron energ ies, from the ionization energy up to 40 keV. Measured data were corrected to account for the energy-dependent spread of the electron beam within the active film and for the ionization due to the electrons backscattered from the carbon layer, using Monte Carlo simulation. Cross sections were evaluat ed in the Born approximation using an optical-data model with numerically e valuated dipole photoelectric cross sections. Calculated ionization cross s ection were converted to vacancy production cross sections, which can be di rectly compared with our experimental data.