The Relation of Actinium to Uranium

Abstract

AT present the most likely view of the origin of the actinium series is that uranium II undergoes a dual change in which about 96 per cent, of atoms form ionium and the radium series, and the remainder form uranium Y, the product of which, proto-actinium, is the parent of the actinium series. An alternative view is that uranium I undergoes the dual change. In 1917 Piccard from a consideration of the Geiger-Nuttall relation put forward the view that the actinium series might arise from an isotope of uranium, actino-uranium, of atomic weight 240, present in ordinary uranium to the extent of about 8 per cent. Partly from experimental work carried out by Mr. W. P. Widdowson and myself, and partly from a survey of certain general relations in radio-activity, I have come to a different view, which I think represents the facts more adequately than these others. I agree with Piccard in thinking that the parent substance of the actinium series is an isotope of uranium, of atomic weight 240, not genetically connected with it; but differ principally in thinking the atomic weight of actinium is not 232, and that uranium Y is not the immediate parent of protoactinium.