The transmission of electrons in the energy range 0-40 kev by thin plastic and metal films with surface densities of 0.023-1.57 mg/${\mathrm{cm}}^2$ has been measured in detail. The range-energy data resulting is prescribed fairly well by Bethe's average energy-loss theory. One of the films was used as a G-M counter window in a beta-ray spectrometer. The application of the transmission data to the beta-ray spectrum obtained for ${\mathrm{Pm}}^{147}$ gave some over-correction, as judged by the Fermi plot, which was attributable chiefly to the unavoidable difference between the collection geometry of the transmission measurement and that of the G-M counter.

• Received 25 January 1954

DOI:https://doi.org/10.1103/PhysRev.94.960