Secondary Homogeneous X Radiation. 

 Secondary Radiation from an Alloy. 



899 



This experiment was made to determine whether an appre- 

 ciable part of the homogeneous secondary radiation from an 

 element is due to the subsequent bombardment of atoms by 

 the electrons liberated by the primary pulses. 



A primary beam of X rays, of a degree of hardness 

 sufficient to excite homogeneous copper radiation without 

 directly stimulating the homogeneous silver rays, was allowed 

 to fall on an alloy plate consisting of two parts of silver to 

 one of copper, and the resultant secondary beam was received 

 by two electroscopes, one of which was used to test the 

 penetrating power of the beam while the other served to 

 standardize the intensity. Since the copper radiation was 

 excited, corpuscular radiation accompanied it and the object 

 of the experiment was to see if these electrons ejected from 

 the copper on bombarding the silver atoms made them give 

 off their characteristic secondary radiation. If this had 

 happened the silver radiation would have been superimposed 

 on the copper, and the difference between the absorption 

 coefficients by aluminium of the copper and silver radiations 

 in this composite beam w r ould have enabled each to be dis- 

 tinguished. If on the other hand this effect was small or 

 possibly non-existent, the radiation from the alloy would 

 have corresponded to that from a pure copper plate. 



When the radiation from the alloy was allowed to pass 

 into the electroscope without previously passing through any 

 absorbing plates, the percentage absorption of the beam by a 

 thin sheet of aluminium placed in the path of the rays was 

 found not to differ from that of a beam from a pure copper 

 plate ; examined in this way the radiation from the alloy was 

 indistinguishable from a homogeneous copper radiation, 

 as shown by the following mean readings : — 



Percentage absorption by aluminium"] 

 sheet (-001(53 cm. thick) after 33 per 1 

 cent, absorption of homogeneous j 

 copper radiation J 



Coiteh. 



Alloy. 



330 



32-7 



In order, however, to magnify the effect which would have 

 been given by any silver radiation in the rays from the alloy, 

 the beam was allowed to pass, before being analysed, through 

 a thickness of aluminium which absorbed 70 per cent, of the 

 incident copper radiation, while this thickness only cut down 

 the much more penetrating homogeneous radiation from a 



