﻿y-.Ray Activity of Radium Emanation. 



303 



value of fi (cm. -1 ) with decreasing thickness of absorption 

 material (see Table I.) is to be expected, since Rutherford 

 and Richardson (loc. cit.) showed that radium B emits 

 certainly two types of radiation having absorption coefficients 

 in aluminium of 0*51 cm, -1 and 40*0 cm. -1 , and possibly a 

 third type (/a=230 , 0~ 1 in aluminium). 



Fig. 2; — liise of y activity from Radium emanation through 

 ]2'6 mm. of lead. 



%Max. 





I 







f 



Activity 



T 













1 



C-30 













I, 







Ex-perimem 



-a/ ri e 





/ 













I; 



0-50 













/! 











fi 





0-40 











i 













f; 





0-30 











/ 











/ 







0-20 









/,' 



























/> 













V 







0-10 







/,' 











^/s' 



■■'' 













^' 







Y 77/77<P /o 



m/hs. 



The absorption coefficients in lead only, given in Table I., 

 are corrected for obliquity of the rays entering the electro- 

 scope, and King's correction is used as given in Case II. 

 of his paper *, 



I* /O0- cos 0/O* sec 0] 



I 



1 — cos 



where 1^ and I are the intensities of the radiation emerging 

 through a plate of thickness t cm. and incident radiation 

 respectively, /u, the absorption coefficient expressed in cm." 1 , 

 and 6 the semi-angle of the cone of rays entering the 

 electroscope. 



vol. xxiii. p. 248(1912). 



