Atomic alignment of 73Ta, 74W , and 79Au after L3 subshell ionization by 10–100-keV electron impact

Abstract

The alignment parameter ${A}_{20}$ of $_{73}\mathrm{Ta}, _{74}\mathrm{W}$, and $_{79}\mathrm{Au}$ ions after ${L}_{3}$ subshell ionization by electron impact has been determined experimentally and theoretically in the wide energy range $(1.02--10.2){E}_{{L}_{3}}$, where ${E}_{{L}_{3}}$ is the ${L}_{3}$ ionization threshold. The ${A}_{20}$ values have been deduced from measurements of the $L\ensuremath{\ell}$ (${L}_{3}\ensuremath{\rightarrow}{M}_{1}$), $L{\ensuremath{\alpha}}_{2}$ (${L}_{3}\ensuremath{\rightarrow}{M}_{4}$), and $L{\ensuremath{\alpha}}_{1}$ (${L}_{3}\ensuremath{\rightarrow}{M}_{5}$) x-ray angular distributions using thin targets. The beam energies have been selected above the threshold energy of each $L$ subshell in order to also investigate the influence of the Coster-Kronig transitions on the anisotropy of x-ray emission. The results provide a clear indication of alignment and agree with calculations carried out within the plane-wave Born approximation up to about $6{E}_{{L}_{3}}$, but an unpredicted inversion in the sign of ${A}_{20}$ is observed above this energy.