Abstract
The tracks of about 600,000 Th C and C' alpha-particle tracks were photographed in a Wilson cloud chamber filled with a mixture of neon and deuterium. An analysis of the elastic collisions with neon atoms gave points on a range-velocity diagram which fitted Eaton's curve fairly well except at the lower end. Reasons are given for thinking that this curve should be lowered slightly in the region of small velocities. A range-velocity curve is obtained from the collisions with deuterons. On the very reasonable assumption that, for a given velocity, the ranges of two isotopes are proportional to their masses, this curve indicates that Mano's calculations for protons are correct even for small velocities. It is shown that these collisions are elastic even when a high energy alpha-particle imparts considerable energy to a deuteron. No sign of inelastic collisions with either deuterons or neon atoms was obtained, although some were expected for the latter. The possible reasons for their nonappearance are discussed.

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