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 



ioo r 



80 



o 



o* 



t- 



^ 60 



1*40 



a 



20 



60 80 100 



Time in Minutes 



Fig. 2. 



120 140 



p Ray Curve of Radium 

 Short Exposure, i Min. 



15 30 45 60 75 



Time in Mimitfx. 



Fig. 3. 



90 



105 



120 



