Secondary Rontgen Radiation from Carbon. 



775 



It is seen that ^— increases with the hardness o£ the rays 



l90 . . . . 



falling on the radiator. That this increase in the ratio is not 



due to the harder portions of: the secondary radiation having 



a high ratio was shown by the low value obtained (1*41) 



when the secondary rays were cut down instead. If we use 



an extremely penetrating beam, then the ratio falls when 



only the hard portions of it fall on the radiation. 



The decrease in the value of: T — for the hard portions of 



I90 



the secondary beam is shown clearly in Table III. 



The values of T — shown in column 2 indicate a steady 



fall in value as the hard portion of the secondary beam is 

 used, if we neglect the initial rise due to the absorption 

 of the iron radiation. The steady rise in the ratio when 

 the hard portions of a primary beam are used, indicate 

 that the fluorescent carbon radiation is only excited by the 

 very hard portions of them. The increase in the ratio is 

 explained by the existence of the " extra " radiation of which 

 more will be said presently. 



(b) Results for Values of ^— . 



These results were all invariably greater than 1*58 for all 

 degrees of hardness of the bulb, the discrepancy increasing 

 with the hardness of the rays used. Table IV. shows the 

 variation of the ratio with the hardness of the secondary 

 radiation used. 



3 E 2 





Table III. 







Thickness of 



aluminium absorbing 



primary rays. 



Values of 

 Il50 

 I90 



Thickness of 



aluminium absorbing 



secondary rays. 



Approximate per cent, 

 of the secondary beam 

 absorbed by alumi- 

 nium in column 3. 





none 



1-64 



none 



none 



1 



none 



1-66 



O'lo mm. 



29 per cent. 



none 



1-53 



0'95 mm. 



70 per cent. 





none 



1-53 



1*8 mm. 



81"4 per cent. 



t 



none 



1-40 



3-2 mm. 



92*3 per cent. 





3 - 2 mm. 



1-67 



none 



none 





