﻿322 Prof. Barkla and Mr. Simons on Ionization 



between the ionization in ilie two mixtures, SH 2 and 2 

 being ionized to a greater extent than S0 2 and H 2 , the ratio 

 being found to be 1'16 and 1*17 in two separate experiments 

 (Table I.) when the Ag X- radiation (series K) was used as 

 the ionizing agent. 



These results appear to us to furnish conclusive proof that 



(1) ionization by X-rays is not fundamentally atomic, but 

 depends to a certain extent on chemical combination ; 



(2) equal absorption of X-rays and their secondary rays are 

 accompanied by unequal ionizations. 



Direct experiments on ionization and absorption certainly 

 point to the conclusion chat when a definite amount of energy 

 of X-radiation is absorbed, and with it all known secondary 

 radiations, the ionization accompanying this absorption 

 depends to a certain extent on the nature of the absorbing 

 substance. Thus, comparing the absorption of the Gu or Zn 

 X-radiation (series K.) in SH 2 and air, the ratio of the 

 absorption coefficients for the two gases under similar 

 conditions of temperature and pressure —11*3, or =ll'b* 

 allowing for scattering. 



But the ratio of ionizations in the gases is l-A'7. 



Thus, using Cu X-radiation, 



-*=14-7. 



(X — s) qTT 



\z ~ 2 =llv6 



Similarly, 





!»=ll-7. 



1 air 



(X -^=12-7 



Xow there is strong evidence that the fluorescent X- 

 radiaticns from air are much softer than those from S (^which 

 is the important term in Sfl 2 and in S0 2 ), and that a much 

 greater proportion of these are absorbed in air than of 

 S X- radiations in SH 2 or S0. 2 . And it may be shown that 

 in these experiments the S X-radiation escaping from the 

 ionization-chamber was not more than 4 or 5 per cent, of 

 the whole fluorescent X-radiation, and therefore much less 

 of the whole energy absorbed ; consequently the energy 

 escaping from the air must have been inappreciable. Again, 

 practically all the corpuscular radiations were absorbed, so 

 that unless there were excited in air by Cu X-radiation, 

 X-radiations more penetrating than any of which we know 



* v is tLe fraction of the absorption coefficient due to scattering. 



A 



