L-subshell-ionization cross sections of tungsten by electron impact near the threshold region

L-subshell-ionization cross sections σ3/σ2 and σ2/σ1 for L3, L2, and L1 levels for tungsten have been measured by electron impact at incident electron energies from about one to three times the ionization threshold energy of the L1 subshell. Ionization cross sections for the L1, L2, and L3 levels were deduced from the measured intensity radiations Lβ3, Lβ1, and Lβ2 and using known values for the fluorescence yields, radiative transition probabilities, and Coster-Kronig parameters. The x-ray spectra were obtained with a curved crystal spectrometer (50 cm radius) and recorded on photographic film. Comparison is made with experimental measurements of Chu-Nan Chang and theoretical calculations of Gryzinski and McGuire. A good agreement is achieved for electron-beam energies E0≥1.25 times the energy E1 of L1-level ionization