[ 419 J 



XLI. The Disintegration Products of Uranium. 

 By Gr. N. Antonoff*. 



IT is now generally accepted that uranium is the primary 

 substance from which ionium and radium with its series 

 of products are derived. In old minerals, all a, ray products 

 in radioactive equilibrium with uranium emit; an equal 

 number of a particles per second except uranium itself, 

 which emits twice as many. Consequently either two « par- 

 ticles are emitted at the disintegration of each atom, or the 

 uranium is in equilibrium with an unseparated a. ray product. 



Actinium and its products also occur in minerals in constant 

 ratio to uranium, but their total activity is much weaker than 

 that of uranium. BoHwoodj has shown that the total 

 activity of actinium together with its products is about 28 

 per cent, of uranium. In explanation of this, Rutherford 

 and others have suggested that actinium is a lateral branch 

 arising at one stage of the uranium-radium series. 



Thorium, although it is almost always present in uranium 

 minerals, is supposed to be an independent radioactive 

 element, because its ratio to uranium in minerals varies 

 within wide limits. 



The investigation of radioactive minerals from the point 

 of view of the disintegration theory has made it clear that 

 ionium and radium &c. are disintegration products of uranium. 

 Also the growth of radium in uranium salts has been directly 

 observed J. On the other hand, it is known that UrX is a 

 direct product of uranium, but at present no definite evidence 

 of the transformation product of the former has been obtained. 

 It has been pointed out by Danne § that UrX separated from 

 a large quantity of uranium leaves a constant « ray activity 

 after complete disintegration. It is not known whether this 

 « ray product has actually grown from UrX, or has been 

 separated from uranium, which generally contains very many 

 radioactive impurities. Soddy ||, however, came to the con- 

 clusion that UrX completely loses its activity with time. 

 Several attempts have also been made to observe the growth 

 of actinium in uranium. The experiments carried out by 

 SoddylT showed that actinium could be detected in some 

 uranium . preparations, but no proofs were given that the 

 original preparations were free from actinium. 



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



t Boltwood, Amer. Journ. Sci. xxv. p. 269 (1908). 



t Soddy, Nat. lxxx. p. 308 (1909) : Phys. Z. x. p. 396 (1909). 



§ Danne, Le Radium, vi. p. 42 (1909). 



|| Soddy, Phil. Mag. xx. p. 342 (1910). 



i\ Soddy, Loc. cit. 



