Critical analysis of soft X-ray cross section data

Abstract

A project is in progress in the national Bureau of Standards (NBS) Photon and Charged Particle Data Center to collect and evaluate photon cross section data in the X-ray region 100 eV to 100 keV. This project complements earlier NBS evaluations and compilations which focused primarily on energies above 10 keV. The NBS collection of experimental total attenuation coefficients (10 eV to above 10 GeV) abstracted from the literature is now computerized to facilitate use and for future updates. These experimental results have been compared systematically with a theoretical photoabsorption calculation by Scofield, and also with a semi-empirical compilation by Henke et al. Sample graphical comparisons of measured data with the Scofield theoretical results are presented here for silicon and uranium. Silicon data from an International Union of Crystallography project are also presented. Discrepancies and uncertainties in the various experimental data sets are typically 5 to 50% or more in the soft X-ray region. However, systematic trends can be seen which suggest that the Scofield theoretical values, taken as a whole, are not improved by the Hartree-Slater to Hartree-Fock renormalization in this photon energy region.