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Measurements have been made of the fraction of an electron beam backscattered from thin films of copper and gold at incident energies from 5 to 25 kev. The results from very thin films indicate that approximately 50% of backscattering from a solid target must be due to single scattering. A comparison with existing theories shows that the results can be fitted by a combination of the single scattering treatment of Everhart and the albedo theory of Bothe, if recent experimental values of the electron range are inserted. A degree of agreement also obtains with the comprehensive theory of backscattering due to Dashen. The fraction of the electron beam absorbed in a film of given thickness, found by subtracting the sum of the transmitted and backscattered fractions from unity, may be corrected by a simple procedure to give the fraction absorbed in a layer of equal thickness at the surface of a solid target. The resulting electron distribution in depth is obtained for different incident energies; that for copper at 20 kev agrees fairly well with a Monte Carlo calculation. The fraction of the energy absorbed within given depth and the energy dissipated per unit thickness are similarly derived. The latter distributions are sharply peaked just below the surface. Those for 20 kev agree well with the computations of Spencer, but less closely with Ehrenberg and King's observations of cathodoluminescence in phosphors. Regarded as a depth-dose distribution, the curve for copper at 20 kev agrees in general form with the measurements of characteristic x-ray production made by Castaing and Descamps. But there are significant differences between the energy distributions for copper and gold at the same incident energy, and also between the distributions at 10 and 20 kev, which may have implications for electron probe microanalysis.
Cosslett et al. (1965) studied this question.