Ions produced by j3 and 7 Radiations from Radium. 335 



Equation (3) gives then for the total ionization produced 

 by the 7 rays of" radium C, 



N=^** 8 ?*. 10 ' = 1-08x10" 

 5*7 x 10"° 



pairs of ions per gram of radium per second. 



We are without data for the absorption coefficient of the 

 y rays of radium B by air ; as the effect of these rays is in 

 any case very small, we can, however, make a sufficiently 

 close approximation by assuming fju to be 4*4 times the value 

 for the 7 rays of radium C (the ratio found in the case of 

 absorption by aluminium *). On this assumption we get for 

 the 7 rays of radium B, 



4*4 x 5*7x10 ° 



80 that the total 7 ray ionization is 1*16 x 10 15 , which after 

 correcting in terms of the international radium standard 

 becomes 1*22 xlO 16 pairs of ions per gram of radium per 

 second. 



From the nature of the assumptions made in the course of 

 the calculations, this result can only be regarded as an 

 approximation to the truth. A more accurate value could 

 only be obtained as the result of a much more extended 

 investigation, in which all the data required would be deter- 

 mined under specially suitable conditions. For example, a 

 possible source of error lies in the use of an absorption co- 

 efficient for air, which was determined with an unsymmetrical 

 disposition of the absorbing material around the source. 



In any case the separation of the effects of the very soft 

 y rays from that of the ft rays, and of the soft /3 rays from 

 the « rays would be attended with some uncertainty. 



Discussion of the Results. 



For the a particles emitted by radium C alone, 

 N = 8*46x20 l5 1\ For the 7 rays from radium B and C, 

 N = 1'22 X 10 15 . These quantities are in the ratio 39*4 : 5*7. 

 The corresponding heating effects are 39*4 and 6'4 gram 

 calories per hour per gram of radium, respectively % ; so that 

 the amount of energy expended in making a pair of ions 

 appears to be approximately the same in the two cases. 



* Rutherford and Richardson, loc. cit. 



t Geiger, loc. cit. Geiger's result has been increased by 5 per cent, to 

 bring it to terms of the international standard. 

 X Rutherford and Robinson, loc. cit. 



