Decay of Radio-activity 575 
radium or thorium become coated with a radio-active deposit. The 
rate of decay of this activity depends on the time of exposure to 
the emanation, and does not always show the usual simple type of 
40 
30 
Decay of|Excited Activity 
of Radium— short es 
20 
5 
5 
5 
10 
| 
ies oe, 
ed 
t) 20 40 60 80 100 120 «140 
Time in Minutes 
Fig. 2. 
o 
o 
— 
% I 
“\ 
Ray Curve of Radium Ss 
hort Exposure. 1 Min, 
Intensity of Radiation, 
5 8 
15 30 46 60 76 90 106 T 
Time in Minutes. 
Fig. 3. 
