42 Dr. T. Godlewski on Actinium 



the actinium itself is not active, and that the residual activity 

 observed is due to a small quantity of AcX, which is left 

 behind. The interval between the last precipitation and the 

 first measurement was always one hour or more, but this 

 alone would not account for the observed current. It seems 

 very probable that at the moment of the removal of AcX, 

 if the separation were complete, actinium would be entirely 

 devoid of activity. From the point of view of the theory of 

 radioactive changes, this shows that the change of actinium 

 into AcX is not accompanied by either a, /3, or 7 rays or, in 

 other words, is a " ray less " change. 



By means of an electroscope, it was found that actinium X 

 gave out all three kinds of rays a, /3, and 7. Now the pro- 

 ducts of excited activity are very quickly formed owing to 

 the very rapid change of the emanation. The activities of 

 these products are consequently measured together with AcX. 

 It was separately proved that the active deposit gave out 

 /3 rays*. Taking into consideration the analogy with thorium 

 and even with radium, we should expect that the measured 

 P activity of AcX arises not from AcX itself, but from the 

 excited activity resulting from it. There is, however, strong 

 evidence that in the case of actinium the /3 and probably the 

 7 rays are emitted also by AcX itself. For instance, the 

 curves of decay of activity of AcX measured by a and /3 rays 

 are throughout identical, even from their beginning; and 

 further, the activity of AcX measured by /3 rays, five minutes 

 after strong heating, when all the volatile excited activity 

 should be driven off, exhibits a very great initial value, which 

 could not be the case if the rays were emitted only by excited 

 activity. 



It is thus most probable that AcX itself gives rise to all 

 three kinds of rays. 



Source of the Actinium Emanation. 



In the case of thorium the product ThX was intermediate 

 between thorium and its emanation. In order to see whether 

 AcX occupies the same position in actinium, I measured the 

 rate of change with time both of the emanating power of AcX 

 and of actinium from which AcX was removed. The measure- 

 ments of activity of the emanation were made in a cylindrical 

 brass testing- vessel f, in the interior of which three insulated 



* It was found that the excited activity of actinium, measured by 

 /3 rays, after a long exposure decayed according to an exponential law 

 with the time, falling to half value in 30 minutes The complete account 

 of these investigations will be given in another place. 



t See Rutherford, ' Radioactivity,' p. 199, and fig. 37. 



