832 Mr, G. N. Antonoff on Radium 1) 



The Constant of Radium I). 



The determination of the constant of transformation of 

 radium D presents some difficulties, as its period is too loner 

 for direct measurements. Meyer and v. Schweidler found 

 its period to be about 12 years, by comparing the initial 

 activity of radium C with that due to radium F after a 

 known interval had elapsed. In the present experiments a 

 similar method has been adopted, with the difference that the 

 a particles emitted from radium F hare been counted by the 

 scintillation method. This avoids the uncertainty due to the 

 correction for the different ranges of the a. particles from 

 radium G and radium F, 



A known quantity of emanation was sealed np in a glass 

 tube. The emanation was transformed into radium D, and 

 thrs in turn gave rise to radium F (polonium). After a 

 definite interval the tube was opened and the number of 

 scintillations per second from the deposit of polonium in the 

 tube was directly counted. 



An approximate estimate of the period of radium D can 

 at once be made from such an observation. The initial 

 quantity of emanation in the tube was determined in terms 

 of radium by the 7-ray method. The number nof a particles 

 emitted per second from the emanation is known from the 

 counting experiments of Rutherford and Geiger*. If X T is 

 the constant of the emanation the total number of emanation 



atoms present is — =N. Since the time periods of. the 



emanation and its short-lived products are very small com- 

 pared with that of radium D and radium F, it may be supposed 

 as a first approximation that the emanation changes at once 

 into radium D, and that this changes slowly but directly 

 into radium F. On this assumption the number of atoms of 



radium D produced is — . The number of atoms of radium F 



1 X n 

 produced per second is — 2 — , where \ 2 * s the constant of 



Aj 



radium D. Since radium D has a long period of transfor- 

 mation, radium F is initially produced at a nearly constant 

 rate, and the amount of it, S say, present after a time t, is 

 given by 



where A 4 is the constant of radium F. The number of atoms 

 * Proc, Roy. Soc. A, vol. lxxxi, (1908). 



