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Elastic scattering of electrons and positrons

Electrons and positrons interact with matter through several competing mechanisms, elastic and inelastic scattering being the most abundant. Elastic scattering is considered as the non-radiative interaction between the projectile electron or positron and a target atom/molecule in which the internal energy of the target is not changed. Elastic scattering has a prominent influence on the transport of fast electrons and positrons in matter. In elastic collisions, these particles may undergo large deflections and, as a result, the space distribution of dose from electrons and positrons depends strongly on the elastic scattering properties of the medium. Knowledge of elastic-scattering cross sections of electrons and positrons is needed in modeling the deposition of energy when beams of these particles or any form of ionizing radiation interact with matter. Specific application fields range from radiation dosimetry, radiation therapy, radiation processing, radiation sensors, and radiation protection to atmospheric studies, plasma physics and material analysis (e.g., by electron-probe microanalysis, analytical electron microscopy, Auger-electron spectroscopy, and X-ray photoelectron spectroscopy). International Commission for Radiation Units and Measurements (ICRU) formed in 2000 a Report Committee to prepare the ICRU Report on "Elastic Scattering of Electrons and Positrons". The Report contains theoretical background of elastic scattering, description of measurement methods, and comparison of the experimental and theoretical cross sections (differential, integral elastic and momentum transfer. The CD ROM with the original software for calculating DCS will be distributed with the Report. Several examples of comparison of the experimental and theoretical cross sections are presented in the paper. A large part of the available experimental data is obtained for atomic gases, particularly for a limited group of atoms such as hydrogen and the rare gases. Experimental data for molecules are very limited, as well as these for positron scattering.

elastic scattering; electrons; positrons

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