Back-Scattering of Megavolt Electrons from Thick Targets

Abstract

Measurements are reported of the number and energy of the electrons which rebound from thick metal targets bombarded at normal incidence by monoenergetic electrons of from 1 to 3 Mev. The ratio of back-scattered to incident electron current, measured for twelve metal targets, was found to vary from 0.47 for 1-Mev electrons incident on U to 0.01 for 3-Mev electrons on Be. The total energy scattered backward from targets of Al, Cu, and Pb bombarded with 1- to 3.5-Mev electrons was determined by calorimetric methods. This energy diminished from 34% of the incident energy for Pb bombarded with 1-Mev electrons to 1% for Al bombarded with 3.5-Mev electrons. The dependence of the number and energy of the back-scattered electrons on the atomic number of the target and on the incident electron energy is discussed.