VII] CONTINUOUS PRODUCTION OF RADIO-ACTIVE MATTER 183 
A large number of results of a similar character have been 
obtained from other radio-active products, separated from the 


100 
of Uru 
erable 
ue 
eg 


(ee) 
(=) 


(op) 
(o) 


as 
oO 

Activity Y% of Normal 


bo 
[o) 





Dp 
Kay OFT 
Or. ae 



0 20 40 60 80 100 120 140 160 
Time in Days 
Fig. 36. 
radio-elements, but the cases of thorium and uranium will suffice 
for the present to form a basis for the discussion of the processes 
that are taking place in radio-active bodies. 
121. Theory of the phenomena. ‘These processes of decay 
and recovery go on at exactly the same rate if the substances are 
removed from the neighbourhood of one another, or enclosed in 
lead, or placed in a vacuum tube. It is at first sight a remark- 
able phenomenon that the processes of decay and recovery should 
be so intimately connected, although there is no possibility of 
mutual interaction between them. These results, however, receive 
a complete explanation on the following hypotheses :— 
(1) That there is a constant rate of production of fresh 
radio-active matter by the radio-active body. 
(2) That the activity of the matter decreases according to 
an exponential law with the time from the moment 
of its formation. 
Suppose that gq, particles of new matter are produced per second 
from a given mass of matter. The rate of emission of energy due 
