174 Dr. 0. Halm on Radioactinium. 



after about 17 days, and the maximum o£ the experimental 

 Carve II. is readied after the same interval. In Curve III. 

 the maximum is reached in 14 days. The earlier occurrence 

 of the maximum is to be expected i£ any sensible amount of 

 actinium X is present initially with the radioactinium. In 

 this case not only is the maximum reached earlier, but the 

 increase of activity is also smaller. This is seen to be the 

 case in the experiments, for the activity of Curve II. rises to 

 more than twice its initial value, while in Curve III. it rises 

 to only about 1*5 times. 



The a ray curves are thus in very satisfactory agreement 

 with the theory. The agreement of Curve II. with the 

 theoretical curve is especially good over the whole range of 

 observations. The theoretical activity ultimately decays 

 exponentially with the period of radioactinium — a result in 

 entire harmony with the experiments discussed earlier in the 

 paper. 



The results obtained are thus in complete accordance with 

 the view that radioactinium is an a ray product of period 

 19*5 days, which is transformed into actinium X of period 

 10-2 days. 



(2) ft Ray Curves. 



Radioactinium emits only a rays, and Levin has shown 

 that the ft ray activity of any preparation of actinium arises 

 only from the product actinium B. Disregarding a small 

 time-lag, the amount of actinium B present is proportional 

 to the amount of the parent product actinium X. But we 

 have seen that the number of atoms Q of actinium X present 

 at any time is given by the formula 



Xl — Ao 



The ft ray activity of the radioactinium preparation is pro- 

 portional at any time to the value of Q. 



The theoretical curve for the variation of the ray activity 

 of radioactinium is shown in fig. 2. The activity starts from 

 zero, rises to a maximum after 20 days, and ultimately decays 

 exponentially with the period of radioactinium, viz., 19' 5 days. 

 The experimental observations are shown by crosses on the 

 curve and are seen to lie closely on the theoretical curve. 

 The observations of this particular preparation were not con- 

 tinued after 30 clays, as the preparation was utilized for a 

 further chemical examination. Other observations have shown 

 that the ft ray activity ultimately decays exponentially with 



