Contribution of near-edge processes to attenuation of the characteristic X-rays in elements with 48 ≤ Z ≤ 83

Abstract

Attenuation of the characteristic K X-rays in the 48Cd, 50Sn, 52Te, 64Gd, 65Tb, 66Dy, 68Er, 74Ta, 75Re, 79Au, 82Pb and 83Bi elements have been measured with especial emphasis for the X-ray energies ( E in) in the region of respective K-shell/L i subshell ( i = 1, 2, 3) ionization threshold ( B K/ B Li). The characteristic X-rays were obtained from different fluorescent target elements excited by the X-rays and γ-rays emitted from the 55Fe and 241Am radioisotopes, respectively. The measurements were performed using an energy-dispersive detection set up involving a low-energy Ge detector. The measured attenuation coefficients for the X-rays with energies away from ionization thresholds of the attenuator element are found to be in good agreement with the available theoretical coefficients, which incorporate contributions of the photoionization, and the Rayleigh and Compton scattering processes. However, the measured attenuation coefficients are found to deviate significantly from the theoretical values for the X-rays with energies in vicinity of B K/Li. The observed alteration is attributed to the X-ray Absorption Fine Structure (XAFS) for negative B K/Li − E in values, and the K-shell/L i subshell resonant Raman scattering (RRS) process for positive B K/Li − E in values. Systematic of the K-shell/L i subshell RRS contribution to attenuation of the X-rays are discussed in terms of the respective oscillator density and fraction of electrons available in the K-shell/L i subshell Lorentzian profile of the attenuation element below E in.