7 Jl Analysis of Gamma Rays from Radium B and Radium C. 



observed with X rays on account of the difficulty of ob- 

 taining X rays of sufficient penetrating power to excite it. 

 It is of interest to note that Chadwick and Russell * have 

 found that three types of radiation were excited by the 

 a rays in ionium. Two of these types, /a/D = 8'o5 and 

 ^,/D = 0*lf), appear to be analogous to the two types of 

 radiation from radium B, but it is doubtful whether the very 

 soft type (yLt/D = 400j observed by them in ionium is given 

 out by radium B or radium C, although, as we have seen, 

 careful experiments have been made to test this point. 

 There appears to be little room for doubt that the 7 rays at 

 any rate from radium B-f-C are to be regarded as types of 

 characteristic radiation from these elements. It is of interest 

 to note that the energy of the soft 7 radiation from radium B 

 is very small compared with the energy of the more pene- 

 trating types of 7 radiation from radium B and radium C. 

 Chadwick and Russell, on the other hand, found that the 

 soft types of 7 rays excited hj the a rays in ionium were 

 relatively far more prominent. The bearing of these results 

 on the general theory of the connexion between /3 and 7 rays 

 which led to these experiments will be discussed in detail 

 in a later paper. 



Summary. 



The 7 rays from radium B consist of at least two distinct 

 groups, each of which is absorbed exponentially in aluminium 

 with absorption coefficients /j, = 40 and /x = 0'51 (cm.) 



-1 



re- 



spectively. The first group of 7 rays is much less penetrating 

 than the X rays excited in an ordinary focus-tube. The 

 7 rays from radium consist essentially of one type which 

 are absorbed exponentially in aluminium with a value 

 fx = 0*115. No evidence was obtained of the emission from 

 radium C of the groups of radiation observed from radium B. 

 The absorption of the rays by lead does not follow an 

 exponential law. 



The general evidence indicates that these radiations are to 

 be regarded as types of characteristic radiation from the 

 elements in question analogous to the characteristic X radia- 

 tions excited in elements by X rays. 



Experiments are now in progress to analyse by the methods 



outlined in this paper the 7 radiations from all the radioactive 



elements which emit /3 and 7 rays. The analysis of the 



7 radiation from a ray products is being undertaken by 



Chadwick and Russell in this Laboratory. 



University of Manchester, 

 March. 6, 1913. 



* Chadwick and Russell, Proc. Roy. Soc. A. lxxxviii. p. 217 (1013). 



