146 THE ROYAL SOCIETY OF CANADA 



These numbers (S) agree fairly well with the experimental values. 

 Carbon and iron give about the same value and lead about 45% that of 

 iron. The scattered radiation from the lead is about 40 % of that from 

 the iron . 



Now consider Table 2 (b). In this case the scattered radiation 

 leaves the radiator from the same side as the primary rays enter and 

 make about the same angle with the normal. Assuming the radiators 

 to be thick enough to give the maximum amount of scattered radiation, 

 the intensity of scattered radiation will be approximately proportional 

 to p/m + ^ 



p /i and X having the same meanings as before 



Forcarbonp= l-GS /x = 0-074 X = 0.132 



p/fi + \ = 8'2 

 " iron P = 7.7 M = 0.30 X = 0-75 



P/H + X = 7 • 3 

 " lead P =11-4 m = 0-56 X = 6-9C 



p/)u + X = l-ô 



or about 5 times as much radiation should escape from the carbon and 

 iron radiators as from the lead radiator and this is what is found experi- 

 mentally. The quantity scattered is therefore approximately inde- 

 pendent of the radiator. 



2. The quality of the radiation scattered depends on the angle 

 of scattering and not on the nature of the radiator. 



The tables show ver}^ well Florance's result that the greater the 

 angle of scattering the softer the radiation. Florance found that after 

 the rays passed through six millimetres of lead the quality of the scat- 

 tered radiation was approximately independent of the radiator. In 

 the present case the rays for the lead radiator are on the whole more 

 penetrating but this is mainly due to the much greater absorption of 

 the softer rays in the lead radiator. 



3. The softer the 7 radiation the greater the percentage of it 

 is scattered per unit mass. 



It is well known that when the y rays of radium pass through 

 lead they become on the whole more penetrating, (See figures for in- 

 tensity of primary rays). As the primary rays are "hardened," the 

 scattered radiation should become more penetrating. This has been 

 proved by Madsen and Florance and can be seen in Tables 1 and 2. 

 If the softer rays are scattered more per unit mass than the harder rays 

 and we compare the intensity of the scattered radiation with that of 

 the primary, the ratio of the two should decrease as the rays become 

 "harder." The ratio does decrease, e.g., when the primary rays pass 

 through a lead screen 1'29 cms. thick, the intensity of the scattered 



