Near-Threshold $KL$-Ionization of Al Metal Atoms under Electron Bombardment

M. O. Borovyi$^{1}$, Yu. P. Gololobov$^{2}$

$^{1}$Taras Shevchenko National University of Kyiv, 60 Volodymyrska Str., UA-01033 Kyiv, Ukraine
$^{2}$National Transport University, 1 M. Omelyanovycha-Pavlenko Str., UA-01010 Kyiv, Ukraine

The relative intensities of the $K\alpha_{1,2}$ and $K\alpha L^1$ group of X-ray emission lines $\gamma$ = $I$($K\alpha_3$)/[$I$($K\alpha_4$) + $I$($K\alpha{'}$)] and $\eta$ = $I$($K\alpha L^1$)/$I$($K\alpha_{1,2}$) are experimentally investigated under electron bombardment of Al metal in the electron energy range of 2–15 keV. As established, the approach of the electron energy to the $KL_{2,3}$-ionization threshold (energy of threshold $E_{KL}$ = 1.671 keV) is accompanied by an increasing of the relative intensity $\gamma$, which reaches 18% at the smallest achieved beam energy $E$ = 2 keV. The effect indicates the near-threshold increasing in the ratio $\sigma$($^3P$)/$\sigma$($^1P$) of $^1P$- and $^3P$-terms excitation cross sections $KL_{2,3}$-configuration. As shown, such increasing cannot be related to the two-stage ‘shake-off’ mechanism of two-electron ionization, whose efficiency near the energy threshold is significantly reduced. An explanation of the effect by the manifestation of direct two-electron $KL_{2,3}$ ionization at inelastic scattering of electron by the Al atom is proposed. The two-electron excitation 1$s^12p^1$($^1P$)–3$s^14p^1$($^1P$) and $s^12p^1$1($^1P$)–3$s^14p^1$($^3P$) of a helium atom uses as example, it is theoretically shown that as the electron energy comes to the threshold, the ratio $\sigma$($^3P$)/$\sigma$($^1P$) rapidly increases due to an increasing of the exchange interaction. As concluded, the role of the direct two-electron ionization mechanism is dominant in the near-threshold $KL_{2,3}$-ionization of Al metal by electron impact.

Key words: X-ray $K\alpha L^1$ lines, electron impact, two-electron ionization, triplet, singlet term.

URL: http://mfint.imp.kiev.ua/en/abstract/v41/i11/1421.html

DOI: https://doi.org/10.15407/mfint.41.11.1421

PACS: 32.30.Rj, 34.80.Dp, 78.70.En, 79.20.Ap, 79.20.Kz, 82.80.Pv

Citation: M. O. Borovyi and Yu. P. Gololobov, Near-Threshold $KL$-Ionization of Al Metal Atoms under Electron Bombardment, Metallofiz. Noveishie Tekhnol., 41, No. 11: 1421—1431 (2019) (in Ukrainian)

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