ICRU Report 77, Elastic Scattering of Electrons and Positrons


The present Report treats cross-section data for elastic scattering of electrons and positrons traversing various materials. Those data are prerequisite for transport analyses through either Monte Carlo simulations or analytic transport theory.

Theoretical methods and experimental techniques for studying elastic scattering of electrons and positrons with atoms and molecules, and in condensed materials, are reviewed. The emphasis is in the range of intermediate and high energies, from a few kiloelectron volts upwards, where the static-field approximation provides an accurate description of elastic collisions. This is also the range of interest in many applications of high-energy radiation, including dosimetry, radiotherapy, and nuclear medicine. The Report includes a detailed description of the theoretical principles and numerical methods involved in the calculations of cross-sections for elastic scattering within the static-field approximation. More elaborate theoretical approaches, suited to lower energies, are also described and used to evaluate the limitations of the static-field approximation. Experimental techniques for measuring elastic-scattering differential cross-sections and related quantities are briefly presented. Available experimental cross-section data are compared with theoretical cross-sections to reveal both the capabilities and the limitations of the static-field approximation. Results from other experimental techniques, mostly surface electron spectroscopies, that are sensitive to elastic scattering are also considered. These techniques provide indirect evidence, usually through Monte Carlo simulations, of the reliability of the theoretical atomic cross-sections and their applicability for describing elastic scattering in condensed matter. The Report is accompanied by an extensive numerical database of differential cross-sections, total cross-sections, and transport cross-sections for elastic scattering of electrons and positrons by neutral atoms. This database covers all elements from hydrogen to einsteinium and the energy range from 50 eV to 100 MeV. The database was generated using the static-field approximation for neutral atoms with finite nuclei and self-consistent Dirac–Fock electron densities. Computer programs for extracting information from the database and for computing multiple-scattering angular distributions are also included in the distribution package.