THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



FKBRUARl 





XXV. Secondary 7 Radiation. By D. C. H. FlorancK' 

 M.A., M.Sc, Assistant Lecturer and Demonstrator, Uni- 

 versity of Manchester * . 



ryiHERE has been considerable discussion during the pas^ 

 JL few years regarding the homogeneity of the 7 rays 

 emitted by radium C. As a result of an investigation by 

 Mr. and Mrs. Soddy and Mr. Russell t it was concluded that 

 the 7 rays of radium were initially homogeneous, and that 

 the absorption of the 7 rays was strictly exponential up to a 

 thickness of 22 cm. of lead. It was not known till after 

 their experiments that radium B emitted some 7 rays whose 

 penetrating power is considerably less than those emitted by 

 radium C. It is clear, therefore, that the 7 rays emitted by 

 radium were initially complex. 



Rutherford and Richardson J have shown that Ww 7 rays 

 of radium B consist of three types which are exponentially 

 absorbed in aluminium with absorption coefficients 230 

 cm. -1 and 40 cm. -1 and 0*51 cm. -1 respectively, while 

 the 7 rays from radium C consist essentially of one type 

 which are also exponentially absorbed in aluminium with 

 an absorption coefficient 0*115 cm. -1 . Rutherford § has, 

 moreover, put forward the view that the 7 rays of radium C 



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



t Mr. & Mrs. Soddv and Mr. Russell, Phil. Mao-. Mav 1010. 



1 Rutherford & Richardson, Phil. Mao. Mav 1913. 



§ Rutherford, Phil. Mag. October 1012. 



Phil. Mag. S. 6. Vol. 27. No. 158. Feb. 1914. Q 



