﻿Absorption of X-Rays and Fluorescent X-Ray Spectra. 993 



elements, and the atomic weight of these elements. The 

 points obtained by experiments with the actual Ni-radiation 

 are shown by crosses ( x ) and those by experiments on 

 radiations of neighbouring penetrating power by circles (O). 



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Atomic weight or /taso.fe/NG element. 



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Showing absorption of a homogeneous X-radiation by equal masses of 

 various elements. The particular radiation used is characteristic 

 of elements of atomic weight 61*3 and 160 approximately (series 

 K and L respectively). For more penetrating radiations the 

 maxima and minima are further to the right : for more absorbable 

 radiations they are to the left. 



It may be observed that the absorption increases with the 

 atomic weight of the absorbing substance, as long as the 

 fluorescent X-radiations of the same series are intensely 

 excited in the absorbing substance. When, however, the 

 atomic weight of the absorbing element becomes so high and 

 its fluorescent radiation of either series K or series L so 

 penetrating that it is not excited (or is only slightly excited) 

 by the radiation used, then the absorption suddenly drops. 

 We thus get a general rise of absorption with atomic weight 

 of the absorbing substance, with sudden drops within a much 

 narrower region of atomic weights. The letters L, M, N, &c. 

 indicate the spectral lines emitted under exposure to the 

 particular radiation dealt with. These explain the rise and 

 fall in the curve. Thus, the particular radiation used (Ni 

 radiation of series K) is capable of exciting in elements of 

 lower atomic weight than 61*3 the radiations of series K, L, 

 M, &c. In elements of atomic weight from 61'3 to about 

 160, it excites radiations of series L, M, &c, but not of 

 series K. Less energy of the particular primary radiation 

 is thus absorbed than would have been the case if K radia- 

 tion had been excited. Again, in elements of higher atomic 



PhiL Mag. S. 6. Vol. 23. No. 138. June 1912. 3 T 



