Manciiester Memoirs, \'ol. liii. (1909), A'(^. \*]t. 



XII. Differences in the Decay of the Radium 

 Emanation. 



By Professor E. RUTHKRFORD, F.R.S., 



AM) 



Y. TUOMIKOSKI. 



Received mid read March 2jrd, igog. 



Determinations of the rate of decay of activity of the 

 radium emanation have been made by various methods 

 by a number of observers. The activity has been found 

 to decrease exponentially with the time with a period 

 (/>., time taken to fall to half value), varying in different 

 cases between 375 and 3'99 days. 



Experiments were begun a few months ago by 

 Mr. Tuomikoski to determine the decay of the radium 

 emanation over a wide range of activity. For this pur- 

 pose a large amount of emanation was enclosed in sealed 

 tubes, and the decay of activit}' measured by the 7 rays, 

 using for the purpose an electroscope surrounded by lead. 

 The rate of decay of the emanation has been found to be 

 irregular, depending upon the treatment to which the 

 emanation had been subjected. For example, a sample 

 of emanation, purified by condensation with liquid air, 

 commenced to decay for the first five days with an 

 average period of 3"58 days. Between 5 and 20 days 

 the average period was 375 days, while between 20 and 

 40 days the decay has been nearly exponential with a 

 period of 3'85 days. Another preparation of emanation 



April yt/i, igog. 



