The Origin of Actinium

Abstract

THE question of the origin of actinium is one of very great interest at the present time. The law governing the position of the radio-elements in the periodic table led A. S. Russell, K. Fajans, and myself independently to predict the existence of a new member of the uranium series, the direct product of uranium-X, occupying the vacant place in the periodic table in the VA family, the heaviest known representative of which is tantalum. I suggested that if this “eka-tantalum” disintegrated dually, as in the case of the C-members occupying the place in the VB family, one mode with the expulsion of a β and the other with the expulsion of an α ray, the product of the first mode would be uranium-II., and of the second actinium. This could only have remained undetected if eka-tantalum had a very long period. The suggestion was disproved almost at once by the discovery of the missing element by Fajans and Beer, which has since been confirmed by Hahn and Meitner, and also by Fleck in this laboratory. It turns out to be a very short-lived member with a period of average life of about 1·7 minutes, and gives β rays only, the hard rays before ascribed to uranium-X, which itself gives only soft β rays.