[ 905 ] 



XCY. The Rate of Decay of the Radioactivity of Polonium. 

 By J. W. Waters, B.Sc, A.R.C.S* 



POLONIUM is generally regarded as identical with 

 radium F, one o£ the products of the disintegration of 

 radium. The nature of the product of disintegration of 

 polonium is a matter of considerable interest. If the 

 product is a solid substance it will accumulate in the course 

 of time, and if it is radioactive its presence will be shown 

 by the deviation of the curve of decay of radioactivity of 

 the polonium from an exponential curve. The rate of decay 

 of radioactivity of a specimen of polonium about five years 

 old has been found during the past few months. Taking the 

 age as five years the activity of the specimen was about 



jqq^ of its initial activity. The rate of decay was found to 



be nearly the same as that found by Mme. Curie for the 

 initial rate. 



The polonium was in the form of a thin deposit on a rod 

 of bismuth. This was mounted inside the case of a gold-leaf 

 electroscope, and the time taken by the image of the gold- 

 leaf to move over a given range of the field of view of the 

 observing microscope was determined at intervals of a few 

 weeks. 



Let the time of transit of the gold-leaf be T seconds. The 

 time taken by the gold-leaf to fall over the same range 

 before the polonium was present was about 12 hours =: 

 43,000 seconds. Then, the radioactivity at any time is 



11 

 proportional to ^ — .^^qq . The values are given in the 



Each is the mean of several observations : — 



following table. 



No. of days. 



T. 



Radioactivity. 

 or 





sec. 









799 



100 00 



20 



876 



91-07 



21 



879 



90-72 



51 



1005 



79-11 



81 



1171 



6761 



80 



1185 



66-77 



98 



1224 



64-5S 



114 



1331 



59-27 



123 



1388 



5674 



* Communicated by the Hon. R. J. Strutt, F.R.S. 

 PHI Mag. S. G. Vol. 19. No. 114. June 1910. 3 N 



