﻿74: Dr. H. L. Bronson on the Periods of 



successive. He also stated that this problem was o£ too great 

 theoretical importance to be settled without further data. 



During the course or this investigation, occasion was taken 

 to redetermine with care the periods* of the three products 

 A, B, and C, and also to investigate the effect of high tem- 

 peratures on these periods. As a result of these experiments 

 it has already been shown (Amer. Journ. of Science, July 1905, 

 and Phil. Mag. Jan. 1906) that radium C does not have a 

 longer period than radium B, as had been previously supposed. 

 It was also shown that 21 and 2S minutes, the generally 

 accepted values for the periods of the two products B and 

 respectively, were both too large, and that 26 and 19 minutes 

 must be very close to the true periods. These results have 

 recently been confirmed by von Lerch (Sitz. Akad. d. Wiss. 

 Wien. Feb. 1906), who separated the products B and C by 

 electrolysis and obtained 26*7 and 19*5 minutes as their 

 respective periods. 



After making such corrections in the calculations as the 

 above changes made necessary, there still existed larger 

 differences between the theoretical and experimental, curves 

 than could be accounted for by errors of measurement. These 

 differences were especially marked in the early portion of the 

 /5-ray decay curve. 



While the investigation was still in progress, Schmidt 

 (Pliysikalisclien Zeitschrift, Jan. 1906) showed that radium B 

 was not rayless as had been supposed, but that it emitted 

 /3 rays of much less penetrating power than those from 

 radium C. It was at once seen that this would probably 

 account for the observed discrepancies, since the /3 ray activity 

 will evidently decay more rapidly if part of it comes from 

 radium B, than if it is entirely due to radium C. Thus the 

 /3-ray decay curve will not be a function merely of the periods 

 of the three active products, but will also depend upon the ratio 

 of the activities due to the two products B and C. In this 

 paper the word ratio means the ratio when the products 

 are in equilibrium. 



Relative Amounts of Ionization produced by a and ft Rays. 



Since the /? rays from the products B and C have different 

 penetrating powers, the ratio of the ionization produced by 

 these two kinds of rays will not be a constant, but will depend 

 upon the amount of material through which they have to pass, 

 and also upon the shape and size of the testing-vessel. The 



* In this paper the word " period " always means the time required 

 for the activity of any product to decay to half value. 



