730 Prof. Rutherford and Mr. Richardson : Analysis 



due to the fact that radium B initially provides about 70 per 

 cent, of the total ionization due to radium B + C instead of 

 the 12 per cent, observed by Moseley and Makower under 

 their experimental conditions with air in the testing vessel. 



Analysis of the rays from radium C. 



Experiments were next made to settle which of the types 

 of 7 radiation were to be ascribed to radium B and which to 

 radium C. It is not convenient to use radium B itself as a 

 source, as there is a rapid growth of radium C from it. By 

 von Lerch's method, however, it is possible to obtain a strong 

 deposit of pure radium C on a metal plate placed in an acid 

 solution of the active deposit radium B + C. Since radium 

 loses half its activity in 19*7 minutes, a large number of 

 experiments were necessary to determine with accuracy the 

 absorption curves for the y rays emitted from it. The type 

 of curve obtained with radium C on nickel is shown in fig. 5. 



Fig. 5. 

 Initial portion of HaC curve (on nickel). 



•8 1-2 1-6 20 



Mms. of Aluminium. 



24 



It is seen that a very soft 7 radiation is present, but after 

 passing through two millimetres of aluminium the absorption 

 is exponential with a value of /x=*115. This soft radiation 

 was much more readily absorbed than the 7 radiation, /^ = 40, 

 obtained when the emanation was used as a source. It thus 

 seemed probable that this soft radiation was excited in the 

 nickel by the radiation from the radium C deposited on it. 



