Transactions of the Royal Society of Canada 



SECTION III 



Series III 



MAY, 1921 



Vol. XV 



The Characteristic K — Radiation from Boron 



By a. Ll. Hughes, Research Professor of Physics, Queen's University, 



Kingston, Ont. 



(Presented by Professor A. L. Clark, F.R.S.C). 



(Read May Meeting, 1921) 



The wave lengths of the K series of characteristic X radiations 

 have been measured for nearly all elements by Moseley and his 

 successors. The square root of the frequency of the characteristic 

 X-rays is, to a close approximation, a linear function of the atomic 

 number of the element. This relation has not been tested out for 

 elements lighter than sodium as no crystal has been found, or is 

 likely to be found, with a spacing between its planes sufficiently great 

 to measure the comparatively long wave lengths which are to be ex- 

 pected from the light elements. These wave lengths are too long 

 to be measured by a crystal grating and probably too short to be 

 measured by any diffraction grating hitherto made. The method 

 adopted in this investigation is an indirect one involving the use of 

 the quantum relation. 



Apparatus. — Electrons of a definite speed from a hot tungsten 

 cathode, T, were allowed to fall on a boron^ target, B (Fig. 1) and the 



HE/1TING CURRENT 



A/ 



>^ 



TO ELECTROMETER 



EARTH 

 B-BûRO/y T/IR6ET 



O T0 320 yOLTS 



-é- 400 l/VLTS 



-lOyOLTS 



F/G. I 



1 The writer wishes to thank Dr. W. R. Witney of the General Electric Company 

 for his kindness in supplying the boron. 



