628 Transformation of the Radioactive Emanations. 



Fajans has suggested that the name radium C 2 should be 

 given to the new product of period 1*4 minutes. No 

 attempt has been made in the Table to differentiate between 

 the products of the transformation of the two component 

 substances. The main series is supposed to follow the group 

 as a whole. 



In regard to thorium, it is proposed that the matter in the 

 active deposit, which always emits the two distinct types of 

 a rays, should be called as a whole thorium C, and that its 

 possible components should be called thorium Q> Y and thorium 

 C 2 . This nomenclature has certain advantages, for in the first 

 place on this scheme all the C products emit a rays, and the 

 D products emit /3 rays. In the second place, there is at present 

 no definite evidence that the components of thorium C are 

 successive products in the ordinary sense. The question of the 

 exact type of the transformation occurring in thorium is a 

 difficult one. If thorium C : and thorium C 2 are successive 

 products, it is to be expected that a considerable quantity of 

 C 2 should be obtained by recoil under suitable conditions. 

 Hahn, however, was unable to obtain any evidence of the 

 separation of thorium C 2 by recoil, and in consequence con- 

 cluded that the period of the latter must be very short. On 

 the other hand, Geiger and Marsden failed to observe any 

 double scintillations from thorium C or any groupings of 

 the scintillations small intervals of time apart*. 



This evidence is difficult to reconcile with the view that 

 the changes are successive in the ordinaiw sense. Additional 

 support to this conclusion is given by the observations first 

 made by Bronson, and afterwards confirmed by the scintilla- 

 tion method by Geiger and Marsden, that the thorium 

 emanation together with its short-period product emits four 

 a particles for two from the products thorium C^ + thorium 

 C 2 in equilibrium with it. This is difficult to account for on 

 the view of successive products, unless it be supposed that 

 both the emanation and the new product emit two a particles 

 for one from thorium C l and one from thorium 2 . The 

 evidence as a whole points strongly to the conclusion that the 

 products are not successive, but are connected in some unusual 

 way. There are several modes of tranformation possible to 

 account for the observed facts ; but it is desirable to delay 

 the discussion of these points until more experimental data 

 are available. 



As in the case of radium C, thorium D is supposed to be 



* These experiments made some time ago by Geiger and Marsden have 

 uot so far been published. A more detailed account will be published by 

 them in a later paper. 



