﻿80 Dr. H. L. Bronson on the Periods of 



of aluminium. The calculated values for this curve given in 



Table I. were obtained by assuming that - =1*2. This is 



. . * y 



about the same value for this ratio as was obtained experi- 

 mentally in the previous experiments, where a similar 

 thickness of foil was used. The variation among the three 

 curves is very marked, and in itself would furnish additional 

 evidence, if such were needed, that radium B emits 6 rays, 

 which are less penetrating than those from radium C. 



Table I. 



Time in 

 'minutes. 



Curve 1. 

 Calc. 



Curve 2. Curve 3. 



Obs. 



Calc. Obs. 



Calc. 







1000 



9y-7 



98-1 

 951 

 9L-0 



86-2 



100-0 

 99-0 

 95-7 

 91-2 

 86-0 

 80-3 

 74-9 

 63-9 

 535 

 440 

 35-8 

 29-3 

 18-8 



100-0 100-0 

 989 97-0 

 96 911 

 91-9 i 84-7 

 86-8 78-1 

 81-5 | 70-8 

 75-9 64-2 

 64-7 53-0 

 54-0 42-8 

 445 34-7 

 36-2 279 

 29-3 221 

 18-8 139 

 l 



1000 

 971 

 911 

 84-3 

 78-1 

 70-8 

 64-5 

 53-0 

 430 

 347 

 27-8 

 22-1 

 13-8 



5 



10 



15 



20 



25 



30 



80-9 



40 



69 8 

 58-8 

 48-8 

 400 

 32-4 

 209 



50 



60 



70 



80 



100 







a-Ray Decay Curves, 



The observed and calculated a-ray decay curves of the 

 active deposit from radium are given in Table II. The 

 results are given in this way because it is more accurate than 

 a curve, and because the experimental and theoretical results 

 can thus be easily compared. 



The observed values represent the mean of a very large 

 number of curves taken at different times during the past 

 year and a half. 



The same cylindrical testing- vessel was used in obtaining both 

 "the long- and short-exposure curves. We should therefore 

 expect to find the ratio of the a-ray ionization due to the two 

 products A and C the same for both, curves. In the calcu- 

 lations for the long-exposure curve this ratio was taken as 1"24, 

 and for the short-exposure curve as 1'26, a very satisfactory 

 agreement. This ratio is only constant under exactly similar 

 experimental conditions, and with a sufficiently large testing- 

 vessel would become less than unity, since an a particle from 

 .radium has a much longer ionizing path than one from 



