782 Distribution of Secondary Ttontgen Radiation. 



Table VII. 





Angle the direction of the 

 portion of the secondary 

 beam considered makes 

 with primary beam. 



Percentage absorption by 

 aluminium (V15 thick 

 subsequent to absorption 

 in column 3. 



Amount 

 previously 

 absorbed. 





90 

 150 



32-8 

 30-5 



none 

 none 



90 

 150 



90 

 150 



25-5 

 23-6 

 13-6 

 15-6 



none 

 none 

 25-5 

 23-6 



(a) gives the results for a thin carbon radiator, 3 mm., and 

 (6) for a thick one. 



fluorescent radiations respectively. The softer iron radiation 

 would make the radiation at right angles to the primary 

 beam softer, while the fluorescent carbon radiation would 

 make it harder than the radiation in a direction making 150° 

 with the primary beam. 



An aluminium radiator was also tried. The values of 



y- and y— for it were greater than for carbon. This in- 



J-90 J-90 



dicated a greater amount of extra radiation from aluminium, 

 but the evidence is not conclusive, as the hard fluorescent 

 radiation of aluminium will be much harder than that of 

 carbon, and will be excited in much smaller proportions. 

 The absence of the fluorescent radiation in the aluminium 



would make the ratio j— and 



i» 



greater than for carbon. 



Summary, 



1. The variation of the distribution of the scattered radia- 

 tion produced in carbon by beams of Rontgen rays differing 

 in penetrating power has been investigated, and unexpected 

 results have been obtained. 



(a) When the hard portions of a hard primary beam were 

 used the ratios ^^ and y 4 both increased, but with very 



i-90 -1-90 



hard beams both decreased. 



