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XXV. The Growth of Radium C from Radium B. 

 By K. Fajaxs, Ph.D., and W. Makower, M.A., JD.Sc* 



IT has recently been shown by Fajans f that the product 

 RaC 2 , discovered by Hahn and Meitner J, has a period 

 ot 1*4 minutes and emits (3 rays and that the a. rays from 

 RaC cannot be ascribed either to RaC 2 or to an unknown 

 product following it in the direct radioactive series. The 

 conclusion was therefore drawn that a rays are emitted by 

 RaC 1? the product whose period is known to be between 

 19 and 19*5 minutes. It was also shown that RaC 2 could be 

 obtained from RaC x by recoil only in minute quantities, 

 whereas RaD is obtained by this method in an amount 

 theoretically to be expected from an a-ray recoil. On this 

 account Fajans concludes that RaC 2 is not in the direct line 

 of disintegration products of radium between RaC^ and RaD, 

 but constitutes a side branch from the main series, so that 

 RaCi may give rise on disintegration either to RaD or 

 to RaC 2 . 



There are some important questions arising out of this 

 conclusion, and it is the object of this paper to answer them. 

 In the first place, we have to find out whether the whole of 

 the j3 radiation from RaC is due to RaC 2 or whether RaCj. 

 also emits these rays ; in the second place, we have to 

 investigate what proportion of the atoms of RaCi give rise 

 to RaD and to RaC 2 respectively. 



The method of experiment consisted in observing the rise 

 and fall of activity of a plate coated with pure RaB obtained 

 by recoil from RaA. If the activity is measured by hard 

 (3 rays then, assuming that RaB emits only soft rays, and 

 knowing that RaC emits some very penetrating rays, the 

 activity should at first be nothing and gradually rise to a 

 maximum as RaC is formed and then fall off with time. 

 The exact shape of the curve will, however, depend on 

 whether the j3 rays arise only from radium C 2 or from 

 radium Ci as well. In figure 1 are given the curves calcu- 

 lated for the two extreme cases; the curve A refers to the 

 case in which RaCi alone emits /3 rays and is calculated from 

 the formula 



Gi= ^d' e J • ' • () 



* Communicated by Prof. E. Rutherford, F.R.S. 

 t K. Fajans, Physih. Zeitschr. xii. p. 869 (.191 1). 

 J Hahn and Meitner, PJnjsik. Zeitschr. x. p. 697 (1909). 



