﻿308 Mr. H. G. J. Moseley and Dr. W. Makower on 



Finally, fig. 3, curve E gives interesting information on 

 the question o£ the amount of radium (J 2 produced from 

 radium G\. It has been suggested by Fajans * that radium 2 

 is produced only in small quantity from radium C l5 so that if 

 7 rays as well as /3 rays are emitted by this product, they 

 would not be likely to contribute more than a small percentage 

 of the total y radiation from the active deposit. The agree- 

 ment between theory and experiment shown in fig. 3, curve E, 

 for the case of 2*3 cm. of lead, proves that radium C 2 cannot 

 emit any considerable amount of hard y radiation. If 

 radium C 2 contributed 10 per cent, of the total radiation, 

 there would have been obtained a detectable deviation from 

 curve E, fig. 3. The activities measured for the first few 

 minutes were so small that the small differences between 

 theory and experiment may be disregarded. The results are 

 therefore in agreement with the result obtained by Fajans 

 that radium C 2 is formed from radium Ci as a side product, 

 and is not in the direct radioactive series. 



Summary. 



(1) 7 rays of absorption coefficient about 4 cm. -1 for lead 

 between the thicknesses 3 mm. and 5'94 mm. and about 6 cm. -1 

 between 0'97 mm. and 1*72 mm. are emitted by radium B. 

 These rays contribute about 12 per cent, to the total ionization 

 produced by the active deposit measured through 3 mm. of 

 lead and not more than 1 per cent, through 2'3 cm. of lead. 

 Radium B appears, therefore, to give no hard y radiation. 



(2) Radium C 2 , if it emits y rays at all, gives an amount 

 too small to be detected by the method used. 



Our best thanks are due to Professor Rutherford for his 

 interest in this research, and for lending us some unpublished 

 observations for comparison with our results. 



Appendix. 



Table for calculating the rise and fall of activity from Pure 

 Radium Emanation under different conditions. 



Column II. gives the number of atoms of radium C present 

 at different times in a closed vessel after admitting pure 

 emanation. The maximum value, which is taken as unity, 

 occurs after 258 minutes. The numbers are calculated from 

 the equation : 



_ W^ i ^"\ e~^^ 



X = l,2,3,4 



2 



Fajans, Physik. Zeitschr. xii. p. 369 (1911). 



