The role of multiple ionization and subshell coupling effects in L-shell ionization of Au by oxygen ions

Abstract

The ionization of L-subshell electrons in gold by the impact of 0.4-2.2 MeV amu-1 O ions was studied by observing excited Lγ(L-N, O) x-rays. We demonstrate that both the multiple ionization in outer M- and N-shells as well as the coupling effects in the L-shell play an important role in understanding the measured L-subshell ionization cross sections. The multiple ionization was found to be important in two aspects: first, the analysis of x-ray energy shifts and line broadening was crucial for proper interpretation of measured x-ray spectra; second, the additional vacancies in the M- and N-shells substantially influenced the L1-subshell fluorescence and Coster-Kronig (CK) yields, mainly by closing strong L1-L3M4,5 CK transitions. The data are compared with the simplified coupled-channels calculations using the `coupled-subshell model' (CSM) based on the semiclassical approximation (SCA), which describes both direct Coulomb ionization as well as the L-subshell couplings within the same theoretical approach. A good agreement of the present data with the theoretical predictions based on the discussed SCA-CSM approach is observed. Present findings partly explain the long-standing problem of inadequate theoretical description of L-shell ionization by heavy ion impact.

L-subshell ionization of heavy elements by S ions with energy of 0.4–3.8MeV/amu

“…As we showed previously [2][3][4], for atoms ionized by heavy projectiles the ionization probabilities (p M , p N , p O ) for the M-, N-shells and partly for O-shell [5], can be extracted from the measured L X-ray spectra, as they are strongly modified by the multiple ionization effects. The influence of the multiple ionization on the fluorescence (x i ) and Coster-Kronig (f ij ) yields has been discussed in terms of the statistical procedure of Larkins [6].…”

“…1). The measured X-ray spectra were analyzed using the developed fitting procedure [2][3][4], which allows adequate estimation of X-ray line intensities, energies and widths as well as the ionization probabilities for outer M-and N-shell from the X-ray spectra modified for the multiple ionization effects. In this way, seven dominant X-ray transitions have been resolved, namely L c5 , L c1 , L c2 , L c3 , L c6 , L c4 and L c4 0 .…”

“…The influence of the multiple ionization on the atomic parameters and the coupling effect for the L-subshell ionization cross sections is discussed. The procedure is identical to the methods developed in our previous papers on L-shell ionization induced by Oand Si-ions [2][3][4]. Existing experimental studies concerning the L-shell ionization generated by S ions in heavy elements are limited to the low energy measurement of Dhal et al [7] for gold, which reports about three times lower cross sections then ours.…”

L shell x ray production in high-Z elements using 4–6MeV/u fluorine ions

“…While PIXE originated and continues using light ions such as protons or alphas [6][7][8][9][10][11][12][13][14][15][16],there is an increasing interest to use heavy ions for PIXE analysis due to higher cross sections and thereby better sensitivity [17]. While discrepancies between theories and experiment were attributed to multiple ionization even with protons [18], multiple-ionization effect has been known for decades in L-shell ionization by heavier ions [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. However this effect is still rarely addressed for the x-ray emission elemental analysis in the aftermath of ionization by such ions.…”