﻿186 Dr. M. Levin on the Origin of the /3 Rays 



this point. In the first place, it can be clearly shown, by 

 several distinct methods, that the residual a ray activity of 

 actinium cannot be ascribed to the presence o£ actinium X. 

 The very small initial value of the ft ray activity shows that 

 very little active deposit was present. If an appreciable 

 amount of actinium X had been present, the a and {3 ray 

 activity should have rapidly increased in the first three hours 

 (see fig. 2). But no such effect was observed. This was 

 corroborated by another distinct method. A current of air 

 was passed through the actinium solution and the emanation 

 rapidly carried into an electroscope. The rate of discharge of 

 the electroscope was very small compared with that observed 

 when an equal current of air was passed through the solution 

 of actinium X previously separated from the actinium. 

 Such a result conclusively shows that the a activity of 

 actinium itself cannot possibly be ascribed to the presence of 

 actinium X. 



An unexpected result was observed too with another pre- 

 paration of actinium. Both a. ray and /3 ray activities rose 

 rapidly and reached a maximum after 20 days instead of the 

 usual 60 days. Half of the maximum value was reached in 

 about 4 days instead of the 10 days, which is to be expected 

 if the recovery of actinium is due to the production of 

 actinium X. In this case, too, the initial /3 activity was very 

 small, but the initial value of the a activity was about 40 

 per cent., a value which could not be explained by the known 

 radioactive changes of actinium. The above preparation of 

 actinium, which behaved so irregularly, was obtained by 

 filtrating the precipitate immediately after adding the ammonia 

 instead of boiling for some time on a water-bath, as recom- 

 mended by Godlewski. 



While this experiment was being repeated, in order to 

 examine more closely this anomalous recovery curve, Dr. 

 Hahn, working in the same laboratory on experiments he had 

 begun several months earlier, came independently to the 

 conclusion that there existed a new a ray product of actinium 

 intermediate between actinium and actinium X, which he 

 has called radioactinium. This product emits a rays and has 

 a period of transformation of about 20 days. A preliminary 

 account of this new product has been given by Dr. Hahn in 

 'Nature' (April 1906). 



Hahn separated the radioactinium from actinium by means 

 of a sulphur precipitate, which carries down the radioactinium, 

 and he has shown that the actinium made inactive in this 

 way recovers its activity with a period of about 20 days. 



