﻿246 



Dr. 0. Hahn on the Ionization Ranges 



ionization was measured within 1*0 cm. from the active wire ; 

 and as it is very unlikely that a new set of a. particles should 

 enter the ionization-chamber below 1*0 cm., we have to con- 

 clude that the active deposit of actinium emits one set of 



10 



Fig. 1. 

















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/* 



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13 





2 3 



Ionization. 



a particles which are able to traverse a distance of 5*50 cms. 

 of air. Since the active deposit of thorium emits two 

 different kinds of a rays, we see here one interesting point of 

 distinction in the disintegration series of thorium and actinium. 



Ionization Curve of Actinium X. 



The determination of the exact range of the a particles 

 emitted from actinium X presents very great difficulties on 

 account of the continuous production of emanation from it. 

 The actinium X was prepared by the well-known method used 

 for the separation of thorium X as described in the previous 

 communication. When precipitating the actinium solution 

 with ammonia, the precipitate as a whole does not come down 

 at once. If one filters therefore too early, the filtrate, at first 

 quite clear, soon becomes cloudy, and another small precipitate 

 can be obtained. For the purpose of the experiment a very 

 thin film of actinium X is required, and for this purpose a 



