﻿THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OE SCIENCE. 



[SIXTH SERIES.] 



SEPTEMBER 1906, 



XXVI. On the Origin of the /3 Mays emitted by Thorium and 



Actinium. By M. Levin, Ph.D. (Gottinaenf. 



PT^HE following research was undertaken to determine 

 JL which o£ the products of thorium and actinium 

 emitted ft rays. The radiations from the radium products 

 have been completely examined, and it has been shown that 

 penetrating ft rays are emitted only from the last of the 

 rapidly changing products of radium, namely radium Of- 

 H. W. Schmidt J has, however, recently obtained evidence 

 that the supposed rayless product radium B does emit ft rays. 

 but of much less penetrating power than those from radium C. 

 We are not considering here the emission of slow-velocity 

 electrons from the a rays, products first observed by J. J. 

 Thomson §, and later examined by Miss Slater ||. These 

 electrons are emitted at a much slower speed, and have an 

 insignificant power of penetrating matter compared with the 

 ordinary ft rays. Ewers % has recently determined that the 

 velocity of the slow moving electrons emitted from a plate 

 coated with radiotellurium is about 3 x 10 8 cms. per second, 

 or less than one-fiftieth of the average velocity of the ft rays 

 from radium C. In this paper we are considering only the 



* Communicated bv Professor E. Rutherford, F.R.S. 



t Rutherford, Phil.' Trails. A. 204. p. 169 (1904). 



X T/n/s. Zeitschr. vi. p. 897 (1905). 



§ Pr6c. Cambr. Phil. Soc. Nov. 14, 1904. 



I| Phil. Maa-. Oct. 1905. 



II Phys. Zeitschr. vii. no. 5 (1906). 



Phil. Mar/. 8. (>. Vol. 12. No. 69. Sept. 1906. N 



