﻿372 Prof. E. Rutherford and Dr. 0. Hahn 



on 



the use of the highly active preparation of radiothorium, 

 separated from the mineral thorianite by Dr. Hahn. 



Radiothorium has been shown by Hahn to produce 

 thorium X, the thorium emanation, and the characteristic 

 active deposit of thorium. It is a product of thorium, 

 probably intermediate between thorium itself and thorium X. 

 Radiothorium consequently exhibits to a very intense degree 

 the characteristic radioactive properties of ordinary com- 

 mercial thorium. 



In previous papers (Phil. Mag. June and July, 1906) Hahn 

 showed from an examination of the ionization curves that the 

 active deposit of thorium emitted two distinct types of rays, 

 one of which had a range 5'0 cms. in air, and the other a 

 range of 8*6 cms. It has not so far been found possible to 

 separate from each other the two a ray products from which 

 these rays are emitted. Since the first product of the active 

 deposit, viz. thorium A, is rayless, these two a ray products 

 have been called thorium B and thorium C. It is not so far 

 possible to decide whether the a particles of range 8*6 cms. 

 belong to the product B or C, but, for convenience, they will 

 be ascribed to thorium C. The ol particles of thorium B thus 

 have a range in air of 5*0 cms. 



Since the active deposit of thorium can be obtained in a 

 very thin film on a fine wire, it forms a very convenient 

 source of ol rays for a determination of the deflexion of the 

 ol rays in a magnetic and electric field. Such an active wire 

 emits two homogeneous types of rays which have ranges in 

 air of 5*0 and 8*6 cms. respectively. Some preliminary 

 results of the determination of the magnetic deflexion of the 

 rays from thorium C have been given in a previous paper by 

 Hahn (loc. cit.). 



The apparatus employed to determine the magnetic 

 deflexion of the rays is the same as that described in a paper 

 of Rutherford (Phil. Mag. ante, pp. 350-1). It is consequently 

 not necessary to describe it further here. The active wire 

 was about 1*5 cm. long, and of diameter 0'43 mm. The 

 photographic plate was in all experiments 4 cms. above the 

 active wire and within 2*5 or 2 cms. above the slit. After 

 placing the active wire in position, the apparatus was 

 exhausted of air. 



The magnetic field, which was kept constant, was reversed 

 every hour, and an experiment usually occupied ten hours. 

 In this time, the activity of the source has decayed to 

 about half of its initial value. The experiments in all 

 cases were comparative, the magnetic deflexion of the ol 



