﻿248 



Dr. 0. Halm on the Ionization Ranges 



the source than is shown in fig. 2. Although the rajs of 

 the emanation and actinium B are present, they do not inter- 

 fere with the determination of the maximum range of 

 actinium X. The absence of any well-marked breaks in the 



Pig. 2. 



10 



o 

 § 4 



<bo<j> 

























V 













V 





^ 



i ' 





JL 















12 3 4 5 6 



Ionization. 



curves is to be expected since the emanation and actinium B 

 have about the same range in air, and the cone of rays was 

 not very narrow. 



The result thus shows that the a particles of actinium X 

 have an ionization range in air of about 6*55 cms. 



Ionization Range of the a Particles of Radioactinium. 



This product in the series o£ changes is intermediate be- 

 tween actinium and actinium X. It is transformed into 

 actinium X and its successive products. Radioactinium emits 

 only a rays, and is half transformed in about 20 days*. A 

 full account of its properties is reserved for a later paper, but 

 it is of interest to show how the determination of the ioniza- 

 tion curves of this product at different times throws light on 

 its position among the transformation products of actinium. 



The radioactinium used in this investigation was separated 

 by several distinct methods, but the simplest form of separa- 



* The period of 20 days, as given above, is only approximate and 

 probably slightly too high. 



