The scattering of α-particles by matter

Abstract In a preliminary note (‘Roy. Soc. Proc.’ A, vol. 81, p. 174, 1908) on the above subject, experiments were described which gave direct evidence of the scattering of the α-particles. In those experiments a strong source of α-radiation was placed at one end of a long exhausted tube, and the α-particles, after passing through a narrow slit, fell upon a zinc sulphide screen sealed to the other end of the tube. When the pressure inside the tube was very low, the narrow line of scintillations which marked the place of incidence of the α-particles on the screen was well defined, but when the rays on their way to the screen passed through gas or through thin metal foils the edges of this line of scintillations became indistinct. The amount of scattering could be estimated for different foils by placing them in the path of the rays and noting the distribution of the scintillations on the screen. The present investigation was undertaken with a view to obtain a quantitative measurement of the scattering by determining the most probable angle through which an α-particle of definite range is turned by passing through a given thickness of matter. The following are the chief points investigated:— (1) Determination of the amount of scattering produced in different thicknesses of the same material. (2) Comparison of the amounts of scattering produced in different materials. (3) Relation between the velocity of the α-particles and the amount of their scattering.