of Gamma Rays from Radium B and Radium C. 733 



appears to vary from //, = 11 to /jl^=2'8 about, but it is 

 difficult by this method to fix the values with much accuracy. 

 These results are in general agreement with the experiments 

 of Moseley and Makower, who showed that the absorption 

 coefficient of the 7 rays from radium B for lead varied 

 between /jl=6 and yu, = 4 about. 



It is thus seen that the two types of y radiation which are 

 exponentially absorbed by aluminium both show irregular 

 absorption curves when lead is used as absorbing material. 

 It is intended in a later paper to discuss in more detail the 

 relative absorption curves in lead and aluminium, and their 

 bearing on the question of the homogeneity of the radiations 

 concerned. 



General discussion of results. 



The results of the analysis of the 7 radiation from radium 

 B and radium C are included in the following table. The 

 density D of the aluminium was taken as 2*71. 





Ab3orption 

 coefficient in 

 aluminium. 



Mass absorption 

 coefficient in 

 aluminium. 



Absorption 



coefficient in 



lead. 





I 230? 



\ 40 (cm.)" 1 



1 0-51 „ 



0-115 „ 



14-7 (cm.) -1 

 0-188 „ 



0-0424 „ 



varying from 11 

 to 2-8 (cm.)-l. 



0-50 (cm.) -1 after 

 traA r ersing 1 cm. 

 of lead. 



It is seen that radium C emits essentially only one type 

 of 7 radiation, while radium B certainly emits two, and 

 possibly three. In a previous paper, one of us pointed out 

 that the rays from radium C correspond in penetrating power 

 to the " characteristic X radiation" of the K series to be 

 expected from an element of atomic weight 214. The soft 

 radiation from radium B (/a/D = 14'7) undoubtedly cor- 

 responds closely in penetrating power to the radiation of the 

 L series to be expected from an element of atomic weight 

 214. For example, Chapman * found that the value of fi/D 

 in aluminium for the characteristic X radiation from bismuth 

 (atomic weight 208" 5) was 16*1, while the value of p/D for 

 thorium (atomic weight 232) was 8*0. It seems reasonable 

 to suppose that the second type of 7 radiation from radium B 

 (yLt/D = '188) also corresponds to a type of characteristic 

 radiation from heavy elements which has not so far been 



* Chapman, Proc. Roy. Soc. A. lxxxvi. p. 439 (1912). 



