The Absorption of High Energy Electrons, Part II

Cloud chamber measurements of the energy loss of electrons in passing through lead and carbon absorbers have been extended up to 11 Mev by using the beta-rays from ${\mathrm{Li}}^8$. The values for the average energy loss for lead are more than 50 percent greater than those predicted by the Bethe-Heitler theory. Part of this difference, at least, is accounted for by the fact that the actual length of path of an electron in lead is somewhat greater than the thickness of the lead. If a reasonable value (1.25 to 1.75) is used for the path length-thickness ratio, the experimental values can be said to be in agreement with theory to within 30 percent. The results for carbon are in good agreement with theory, using a path length-thickness ratio of unity, which is reasonable, because of the smaller amount of scattering in carbon than in lead.