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The ranges of electrons in evaporated films of aluminium, copper, silver and gold have been measured for incident energies E0 between 5 and 20 keV. From electron transmission measurements the maximum range and the extrapolated range were determined. Energy loss measurements gave the mean range and the Thomson-Whiddington range, corresponding to the mean energy Em and the most probable energy Ep of the beam, respectively. The mean range, which is directly comparable with that given by the Bethe energy loss law, is found not to be identical with the maximum range as assumed by some authors. In view of its dependence on the experimental conditions, the maximum range appears to have little practical and no theoretical value, whereas the extrapolated range Rx is a reproducible quantity. The extrapolated mass-range ρRx is proportional to E03/2 and is almost independent of atomic number in the energy range studied. A relationship between Rx and the Lenard absorption coefficient is found to exist.
Cosslett et al. (Sun,) studied this question.