INTEGRAL CROSS SECTIONS OF IONIZATION OF L-SUBSHELLS OF TUNGSTEN ATOMS UNDER ELECTRON BOMBARDMENT NEAR ENERGETIC THRESHOLD

摘要

The relative intensities h = I(β_1)/I(β_3) and g = I(β_2,15)/I(β_3) of Lβ_1, Lβ_(2,15), and Lβ_3 lines of the X-ray emission Lβ spectrum of tungsten atoms W are experimentally studied under electron bombardment in a range of accelerating voltages U — 13/35 kV, On the basis of the derived experimental data, the ratios of the integral cross sections σ_2/σ_1 and σ_3/σ_1 of ionization of L_1, L_2, and L_3 subshells are determined. For the account of the electron beam energy reduction under deepening in the substance of a specimen, the effective energy of electrons was used. It is revealed that the distinctions between the results of calculation in the classical model of binary collisions (MBC), those by the semiempiric Bethe formula with parameters derived for the K-shell ionization (BK), and the experimental values of σ_2/σ_1 and σ_3/σ_1 do not fall outside the limits of experimental errors (8/10 .% for σ_2/σ_1 and 13/15 % for σ_3/σ_1) in the region U ≥ 17 kV. In the near-threshold region U < 16 kV, a good agreement between experimental data and theoretical results based on the MBC is preserved, whereas the differences between BK-calculations and experiment grow essentially, by reaching 30% for σ_2/σ_1 and 45% for σ_3/σ_1 at U = 13 kV. The parameters in the semiempiric Bethe formula are determined and can be used in calculations of the integral cross sections of ionization of L_1, L_2, and L_3 subshells.