444 



The Radioactivity of Uranium. 



22 days. The uranium recovers its power of giving /3 rays 

 just as fast as the uranium X loses its power, and for equal 

 times the proportion of the total activity recovered by the 











































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Time, in Days 



uranium is equal to the proportion of the total activity lost 

 by the uranium X. The laws of decay and recovery are 

 represented therefore, as in the case of thorium, by the two 

 equations 



¥=*-" (I-) 



1—e 



■ (II.) 



I in ea^h case representing the maximum activity (this being 

 in the first equation the initial, and in the second the final 

 activity), and I* the activity after time t, \ being the same con- 

 stant in each case. When t is expressed in days the numerical 

 value of X is approximately 0'031. In the case of thorium 

 the half value is reached after 4 days, and the value of \ is 

 about 0-173. 



As in the case of thorium, uranium that has partially re- 

 covered its activity gives on repeating the separation a new 

 quantity of uranium X proportional to the amount of activity 

 recovered. The constant activity of the /3 rays of uranium 

 is therefore maintained by the continuous production of 

 uranium X at a constant rate, and represents the equilibrium 

 point where the decay of the activity of the uranium X present 

 is balanced by the steady production of fresh uranium X. 



