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 LT 1 is scattered by a target T 1 , and those that are scattered through a certain angle θ 1 , are allowed to fall on a second target T 2 . It was shown that the number of electrons scattered by this second target in any direction T 2 M making an angle θ 2 with T 1 T 2 depends on the angle Ф that the plane T 1 T 2 M makes with the plane LT 1 T 2 . Ф is taken to be zero when the electron follows the coplanar path LT 1 T 2 M. The number scattered along T 2 M is proportional to 1 + δ cos Φ , where δ is a positive constant depending on θ 1 , θ 2 . Thus more electrons are scattered along T 2 M than T 2 M' 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.