On the scattering of Homogeneous β-Rays and the number of Electrons in the Atom

Abstract The subject of the transmission of β-rays through matter has, from time to time, received considerable attention. Apart from any intrinsic interest the problems involved are of considerable theoretical importance. Owing to the high velocity of the β-rays, the collisions, to which the absorption of the rays must be ascribed, take place not with the atom as a whole, but with its constituent parts, and thus from a study of the behaviour of the rays during their passage through matter we may hope to gain considerable information as to the constitution of the atom. Until very recently it was thought that the phenomena involved in the absorption of the β-rays were very simple. It was early shown that the β-rays from a single radioactive substance, such as uranium X for example, were absorbed by light substances, such as aluminium, according to an exponential law. For the heavier elements, such as tin or platinum, the absorption curve at first descended rather more steeply than the true exponential, but finally became exponential after the rays had passed through some small thickness of the absorbing material. This law has been tested for a large number of elements and compounds by the present writer, and with a high degree of accuracy, for a few substances, by N. R. Campbell.