﻿178 Dr. M. Levin on the Origin of the f$ Rays 



emission of jS rays of considerable penetrating power; for 

 example, those which are able to traverse a thickness of 

 0*1 mm. of aluminium with an absorption of only a few 

 per cent. 



Thorium X. 



In its radioactive transformations thorium gives rise suc- 

 cessively to radiothorium *, thorium X, and the thorium 

 emanation f. The latter forms the active deposit, which 

 contains three distinct products — thorium A, thorium B J, and 

 thorium C§. Rutherford showed that the emanation of 

 thorium emitted only a rays, and that the active deposit 

 emits «, /3, and 7 rays. Since thorium A is a rayless pro- 

 duct, the /3 rays from the active deposit come only from 

 thorium B or thorium C. It was not known with certainty 

 whether or not thorium, radiothorium, or thorium X emitted 

 ft as well as a. rays || . 



In order to settle definitely these points it was necessary 

 to obtain thorium and thorium X as far as possible free from 

 all other products, and to examine whether or not fi rays 

 were emitted. 



Thorium X was separated from thorium in the usual way 

 by precipitating the thorium with ammonia. For the separa- 

 tion of the active deposit from thorium X several methods 

 can be employed. As the active deposit is formed from the 

 emanation, a solution of thorium X can be partly freed from 

 the active deposit by removing the emanation either by rapid 

 boiling or by aspirating air through the solution, until the 

 thorium A, B, and C, initially present in the solution,, have 

 been transformed. Another possible way is to separate chemi- 

 cally or electrochemically thorium A, B, and C from the 

 thorium-X solution by one of the methods employed in the 

 investigations of Schlundt'and Moore IT and of v. Lerch**. 

 It was found, however^ simplest to volatilize the active deposit 

 by heating the thorium X to a high temperature ff. The 

 following procedure was adopted. The ammonia-filtrate 

 was freed from traces of thorium remaining in solution by 

 precipitating several times with ammonia from a concentrated 

 solution ; the solution of thorium X was then dried on a 



* 0. Halm, Jahrb. cl. Radioaktivitat, ii. (1905). 



f Rutherford & Soddy, Phil. Mag. May 1903. 



% Rutherford, Phil. Trans. A. 204. p. 169 (1904). 



§ O. Hahn, Phil. Mag. June 1906. 



|| See Rutherford, ' Radioactivity, 5 1905, p. 363. 

 ^[ Journal of Phys. Chemistry, ix. (1905). 

 ** Wien. Ber. March 1905. 

 ft Miss Gates, Phys. Rev. May 1903. 



