The generation of positrons in a thick target bombarded by fast electrons

Abstract

Abstract An approximate analytical solution is developed for the distributions in energy and angle of positrons generated by fast electrons incident on a thick radiator (≈ 0.2 radiation lengths). For small angles, the positron energy spectrum may be expressed generally as a function of target thickness, incident electron energy, and a generalised shape function which is tabulated. Numerical estimates of the energy distributions in the forward direction, arising from 25 and 100 MeV electrons incident on a radiator of thickness 0.2 radiation lengths are made, and compared with spectra measured at these energies; the agreement is satisfactory.