﻿of the a Rays of Actinium. 251 



The curves in fig. 4 do not of themselves show whether the 

 radioactinium preparation was initially freed from actinium, 

 for the latter does not emit any rays. The activity of radio- 

 actinium and its products after reaching a maximum in about 

 20 days commences to decay and ultimately, according to an 

 exponential law, with a period of about 20 days. If actinium 

 were present the activity of the preparation would not decay 

 to zero, but would finally reach a constant value depending 

 on the amount of actinium present. This is obviously the 

 case, since actinium gives rise to radioactinium and its 

 successive products. 



3 4 



Ionization. 



We see, however, from the curve shown in fig. 5 thnt no 

 sensible amount of actinium could have been present. 

 Curve a is the same as curve c in fig. 4, and is due to radio- 

 actinium at its maximum activity when in equilibrium with 

 its successive products. The curves b and c were obtained 

 39 and 71 days respectively after a maximum had been 

 reached. It is seen that the curves are all similar, showing 

 that the activity due to each product decays at the same rate. 

 The initial activities, due to the /3 rays and the natural leak 

 of the vessel, are partly increased (curve a), partly decreased 

 (curve c), in order to show distinctly the initial portions of 

 the three curves separated from one another. The ionization 

 (curve c) begins very nearly at the correct maximum range 



