Theoretical angular dependence of L3 sub-shell X-rays following photoionization

Abstract

Angular distribution studies are made for L3 sub-shell X-rays of high Z elements; W, Pt, Hg, Pb, and U in the angular span 0°–180° at incident photon energies; near L3 edge, where considerable anisotropy is anticipated and at 60 keV, the energy of experimental interest from standard laboratory source Am-241. Angular distribution of X-rays originating from L3 sub-shell vacancies for each element is derived from theoretical alignment parameter already evaluated under non-relativistic dipole approximation (NDA) in a point Coulomb potential (A20) and in a screened Coulomb potential (A20*) that accommodates the effect of screened nuclear drag on electron wave function, and analytical perturbation theory (A20**). The normalized Lℓ and Lα intensity distributions show more anisotropy at L3 threshold than at 60 keV for all the elements and under all theoretical models. Besides this, the anisotropy for Lℓ is larger than Lα which comprises the unresolved Lα1 and Lα2 lines with opposite anisotropy. The angular distribution trends are almost similar for all the elements. The anisotropy values at L3 threshold energy are assuredly greater than the reported experimental uncertainties (5–8 %) of X-ray intensities. Anisotropy magnitude is found sensitive to the theoretical models. The present anisotropy trends resemble the results of Zhang et al (Journal of Quantitative Spectroscopy and Radiative Transfer, 244 (2020) 106844), however, the values are not quite same.