The polarisation of electrons by double scattering

Abstract

1. In a previous paper the author has applied the relativistic theory of the electron due to Dirac to the problem of the scattering of electrons by atoms. The main purpose of the investigation was to discover whether any polarisation effect was to be expected when a beam of electrons was scattered by two successive targets. The experiment considered is illustrated in fig. 1. A beam of electrons LT1 is scattered by a target T1, and those that are scattered through a certain angle θ1, are allowed to fall on a second target T2. It was shown that the number of electrons scattered by this second target in any direction T2M making an angle θ2 with T1T2 depends on the angle Ф that the plane T1T2M makes with the plane LT1T2. Ф is taken to be zero when the electron follows the coplanar path LT1T2M. The number scattered along T2M is proportional to 1 + δ cos Φ, where δ is a positive constant depending on θ1, θ2. Thus more electrons are scattered along T2M than T2M' in the figure, the numbers being in the ratio 1 + δ :1 — δ. It should be noted that the theory deals with single nuclear scattering, and is therefore only applicable if the scattering targets are thin foils, sufficiently thin for multiple scattering to be negligible. In the paper quoted it was found that δ is extremely small unless the following conditions are satisfied.