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

Abstract

The alignment parameter A20 of 73Ta, 74W, and 79Au ions after L3 subshell ionization by electron impact has been determined experimentally and theoretically in the wide energy range (1.02-10.2)EL3, where EL3 is the L3 ionization threshold. The A20 values have been deduced from measurements of the Ll (L3 → M1), Lα2 (L3 → M4), and Lα1 (L3 → M5) 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 6EL3 , but an unpredicted inversion in the sign of A20 is observed above this energy.