Stopping Power of Organic Foils for 6 Mev Alphas

The stopping power of several thin organic foils has been measured relative to air at 6 Mev. A simple cut-off method provided a direct comparison with air using natural alphas from ThC'. Mean atomic stopping powers relative to air are: polythene, 0.422; polyvinyl alcohol, 0.515; cellulose acetate, 0.617; regenerated cellulose, 0.597; Mylar, 0.627. Values are also given for the mg per ${\mathrm{cm}}^2$ of each foil equivalent in stopping power to one cm of air. The experimental stopping powers are reproducible to within two percent and average about three percent below values calculated using the additive law and mean excitation potentials for H, C, N, and O taken from the literature.