A new method to estimate elastic scattering cross sections in the X-ray region and the associated anomalous dispersion

Abstract

Using nearly monoenergetic unpolarised Kα radiation, we have measured the elastic scattering cross sections for Pt, Au and Pb in the energy region 5.41 ≤ E ≤ 9.23 keV. The experimental results for Pt, Au and Pb are new. A new X-ray scattering system was assembled using an X-ray tube and secondary targets. In order to improve the peak-to-background ratio and the efficiency of the detection system, particularly in the low-energy region, excitation source, sample and detector assembly were placed in a vacuum chamber at a pressure of 10 −2 mbar. The present system helped considerably in reducing the scattering and background effects, and in removing the interference of Ar K X-rays which fall in the investigated regions. A new method was developed to estimate the degree of monochromaticity, geometrical effects of the measuring system, solid angle correction and some considerations which are necessary in experiments using X-ray tube with secondary target arrangement. Experimental elastic scattering cross sections are compared with theoretical estimates, a combination of relativistic modified form factors with angle independent anomalous scattering factors (RMF + ASFs) and recent theoretical estimates based on the multipole expansion of the second order S-matrix approach. Deviations are observed around the edges (high energy side) indicating the importance of the dispersion correction terms. The present experimental results are useful taking into account that the available calculated values describe the free atom and deviations for a solid have to be expected. This is due to the difference of the electronic structure of the solid in comparison to the free atom as a base for theoretical estimations. However, the comparison of experimental results with theoretical estimates indicates the importance of numerical calculations based on the multipole expansion of the second order S-matrix approach and high energy limit values (RMF + ASFs).