srrn-:ssi<>\ 



IN KADIO.UTIVK 



The equations for the a rays for any time of exposure can be readily deduced, Imt 

 the expressions are somewhat complicated. 



20. Equations of Rise of Excit<><l .l<tirity. The curves expressing the gradual 

 increase to a maximum of the excited activity produced on a body exposed in the 

 presence of a constant amount of emanation are complementary to the curves of decay 

 for a long exposure. The sum of the ordinates of the rise and decay curves is at any 

 time a constant. This necessarily follows from the theory and can also be simply 

 deduced from d priori considerations. (' Radioactivity,' p. 267.) 



The curves of rise and decay of the excited activity are shown graphically in 

 tig. 13 for both the a and ft rays. The thick line curves are for the rays. The 



100 



60 



30 40 



Time in Minutes. 



Fig. 13. 



difference between the shapes of the decay curves when measured by the a or ft rays 

 is clearly brought out in the figure. The equations representing the rise of activity 

 to a maximum are given below. 

 For the ft and y rays, 



For the a rays, 



- 3'3 c~ 



21. Effect of Temperature. We have so far not considered the evidence on which 

 the 28-minute rather than 21 -minute change is supposed to take place in the matter C. 

 This evidence has been supplied by some recent important experiments of P. CURIE 

 and DANNE* on the volatilization of the active matter deposited by the emanation. 



'Comptes Rendus,' 138, p. 748, 1904. 



