904 Mr. F. P. Slater on Excitation ofy Radiation 



alone, owing to the relatively weak 7-rays from radium B r 

 and in consequence the ratio for equal 7-ray activities of 

 thorium C and radium C, as obtained above, must be 

 multiplied by a correction factor. This factor was taken 

 from a paper by Moseley and Makower *. The results 

 were as follows : — 



Eadium C. Thorium C. 

 Number of a particles per miri. per mg. 



(if wheel were removed) 3350 2180 



Number of particles counted 940 899 



Eati 



No. per mg. ofThC 2180 



JNo. per mg. of EaC 3350 



Eatio No - per mg. o f ThC 2180 100 _ 



a 10 No. per mg. of Ea act. dep. '" 3350 X 100 ~~ 



This ratio is now being determined accurately by Professor 

 Schlundt. and Mr. Shenstone in this laboratory. 



XCIX. The Excitation of 7 Radiation by u Particles from 

 Radium Emanation. By F. P. Slater, B.A., M.Sc.f 



Introduction. 

 PART I. 



CHAD WICK t has shown that the «-rays of Radium C 

 excite a small but detectable quantity of 7 radiation 

 when they impinge on matter. From the character of his 

 experiments this radiation could arise solely from the bom- 

 bardment of atoms of matter, and not from the radioactive 

 material itself. The radiation was of a comparatively soft 

 nature, and it would have been almost impossible to have 

 detected a small quantity of penetrating radiation among the 

 intense and highly penetrating primary 7 radiation always 

 associated with radium C. 



In a later paper Chadwick and Russell § using' ionium 

 sources, which emit practically no primary (3 and 7 rays, 

 were able to make a detailed examination of the 7 radiation 

 excited by the a particles, and found three types of soft, 

 medium, and hard penetrating power. This radiation was 

 excited in the active material itself or the thorium mixed 

 with it. 



* Moseley and Makower, Phil. Mag. 1912. 



t Communicated bv Prof. Sir E, Rutherford, F.R.S. 



% Chadwick, Phil. Mag. xxv. p. 193 (1913). 



§ Chadwick and Russell, Proc. Roy. Soc. A. vol. lxxxviii. (1913). 



