Range of electrons and positrons in matter

Abstract

The practical ranges of electrons and positrons of kinetic energy ranging from 0.25 to 5.0 MeV are calculated considering their total inelastic and the multiple Coulomb elastic scattering with the atomic and the nuclear fields of the atoms of an absorbing material. The electrons and positrons are assumed to travel along the direction of incidence until they lose energy to the extent that the calculated mean-square projected angle due to the multiple scattering, on the plane containing the initial direction, becomes so large that their further motion becomes random. The random motion contributes to straggling only. The calculated ranges of electrons and positrons are found to explain satisfactorily the energy dependence and the material dependence of the experimental extrapolated ranges. The ratio of the measured positron range at 1.88 MeV to electron range at 1.77 MeV in Al, Cu, Sn, Yb, and Pb agrees well with the calculation. But there is a large difference in the calculated and experimental ratio of positron to electron range in some rare-earth elements and graphite.