Typical Cases of Ionization by X-Kays. 'Ml 



(It) Radiations from the gas or vapour studied : 



(4) Scattered X-rays ; 



(5) Transformed X-rays ; 



(6) Corpuscular rays. 



A few notes on each of these are necessary before 

 attempting to interpret the results of experiments : — 



(1) The energy scattered by light-elements has been 

 studied by the writer. This radiation being of the same 

 type as the primary produces the same relative ionizations 

 as the primary. As it is not directed in a parallel beam, 

 however, there must be a small error in the correction for 

 absorption as applied to the primary beam. The error 

 introduced is, however, exceedingly small. 



(2) No characteristic X-radintion of penetrating power 

 between the extreme limits of the primary radiations used 

 is emitted by Al — the material of: the ionization chamber. 

 Extremelv " soft"" radiations, if they produce an appreciable 

 ionization, are included in the correction applied for the 

 corpuscular radiation from Al. 



(3) The secondary corpuscular radiation from Al produced 

 an appreciable ionization in some cases. Correction has 

 been made for this from the results given by Mr. Sadler *. 

 The maximum correction was about 20 per cent, of the total 

 ionization. 



(4) The energy of the rays scattered by the gas was, 

 in these experiments, always a negligible fraction of the 

 energy of primary radiation and consequently produced a 

 negligible ionization. 



(5) The secondary X-rays known to be emitted by the 

 elements in ethyl bromide produced in the ionization 

 chamber used not more than about 1 per cent, of the total 

 ionization. The ionization produced by exceedingly soft 

 secondary X-rays is unknown. It is included in what will 

 be called the direct ionization of the X-rays. 



(6) The corpuscular radiations from the elements in ethyl 

 bromide will be discussed later. 



The homogeneous beams of X-ravs were passed through 

 air, 0, C0 2 , SH 2 , S0 2 , coal-gas/ X 2 0, C 2 H 5 Br, CH 3 I, 

 Se 2 Cl 2 , SnCl 2 . After correcting for absorption in the ionized 

 gas, and for the effects of secondary corpuscular radiation 

 from the walls of the ionization chamber, the results given 

 in the following Table were obtained from experiments on 

 air, carbonic acid, and ethyl bromide mixed \vjth air. 



* Phil. Mag. March 1910, pp. 337-356. 



