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XVIII. Note on the Excitation ofy Rays by ft Rays. 

 By Jadwiga Szmidt (Petrograd) *. 



IT was shown by J. A. Gray t that the /3 rays from radium E 

 falling on metallic radiators produce a certain amount 

 of secondary radiation of a 7-ray type. The penetrating 

 power of this secondary radiation was found to vary largely, 

 being as a rule softer the lower the atomic weight of the 

 radiator. A similar result holds when cathode particles fall 

 on the radiator t or when X rays of suitable penetrating 

 power fall on the radiator, exciting its characteristic radia- 

 tion §. It was thought of interest to determine whether the 

 secondary 7 and X rays were identical by compariug their 

 absorption in aluminium. 



The particular arrangement originally used by Gray not 

 being suitable for the purpose, the following method was 

 adopted : — 



The source E, — radium D in equilibrium with its product 

 radium E — was placed in a strong magnetic field and the 



Fig. 1. 







N 





R 



B 





A 







S 





primary /3 rays therefore could not strike the metallic sheet 

 under investigation, when the latter was placed at A (fig. 1). 

 The metallic sheet absorbed the primary 7-radiation to a 



* Communicated by Sir Ernest Rutherford, F.R.S. 

 t J. A. Grav, Proc. Eoy. Soc, A. vol. lxxxv. p. 131 (1911). 

 X Beatty, Proc. Roy. Soc. A, vol. lxxxvii. p. 511 (1013). 

 § Barkla and Sadler, Phil. Mag. vol. xvii. p. 739 (1909;. 



