﻿188 Origin of the ft Rays emitted by Thorium and Actinium. 



Conclusion . 



The above investigations have shown that actinium freed 

 from actinium X still possesses considerable a ray activity, 

 and that this cannot be due to actinium itself, but must be 

 ascribed to the presence of the product radioactinium, earlier 

 discovered by Hahn. A method for separating radioactinium 

 from actinium was found. Actinium itself is a rayless 

 substance. 



It is shown that the products thorium X, actinium X, and 

 the actinium emanation emit only a, rays. Thus among the 

 numerous products of thorium and actinium, only the last of 

 the. series of products emit ft rays. All the other products 

 either emit oniy a rays or are rayless. The ft rays emitted by 

 thorium in equilibrium arise only from the product thorium B 

 or thorium C, and most probably the latter; the ft rays from 

 actinium come only from actinium B. Such a result brings 

 out clearly the remarkable similarity that exists between 

 the modes of transformation of thorium and actinium, not 

 only in reference to the number and chemical properties 

 of their products, but also in regard to the rays emitted by 

 them. 



In the Bakerian Lecture, 1901, Rutherford pointed out 

 that the emission of ft rays only in the final rapid transfor- 

 mations of the radio-elements was probably more than a 

 coincidence, and marked a definite stage in the career of 

 disintegration of the atoms. In the case of thorium, or of 

 actinium, the expulsion of a j6 particle, as well as of an 

 a particle, occurs only in the last rapid change, and the 

 atoms of the resulting product are either permanently stable 

 or are transformed very slowly. In the case of radium, 

 the expulsion of a ft particle together with an a particle 

 occurs only in the product radium C, and the resulting 

 product radium D is comparatively stable. This peculiarity 

 in the mode of transformation of the radio-elements is 

 certainly striking, and may prove to be of some theoretical 

 importance. 



I sincerely thank Professor Rutherford for the help 

 he has given to me during this work, which I undertook 

 at his suggestion, and for his guidance in the study of 

 radioactivity. 



McDonald Physics Building, McGill University, 

 Montreal, May 15, 1906. 



