The a Particles emitted by the Active Deposits of Thorium and Actinium

Abstract

In a previous Paper (Proc. Phys. Soc., Aug., 1911) the authors showed that if α-particles are counted on a zinc sulphide screen at a mean rate of μ per second, then the probability of occurrence of a time interval, of length between t and t + δt, is μe - μt. This formula may be applied, to test whether two α-particles are given off simultaneously from a disintegrating atom or whether in any source of α-particles there exist two successive α-ray products, the latter being of short life. In the previous Paper Uranium and Polonium were shown not to give such irregularities, and in the present Paper the same result has been found for Actinium and Thorium active deposits, although experiments of various investigators pointed to the probability of positive results. The experiments further suggest a lateral disintegration in Thorium active deposit, and this is proved to be the case by results which show that the two α-ray products in Thor. Act. Dep. (Th. C1 and C2) do not give an equal number of α-particles when the active deposit is in equilibrium, which is required by the ordinary disintegration theory. Thus it is concluded that of the atoms Th. C, 35 per cent. give rise to α-particles of 4.8 cm. range and 65 per cent. to α-particles of 8.5 cm. range, with probably the intermediate emission of β-particles. Various cognate questions are also discussed in the Paper.