[eve] secondary > rays due to the > rays of radium C 11 



TABLE VII. See Figure 4. 



Radium in steel 2.2 cms. thickness. 

 Lead screens. 



From these results and diagrams the following deductions may be 

 made : — 



1. It is noteworthy that the radium in 2.2 cms. of nickel steel 

 gives an effect about 1.5 times as great as when the radium is in 1 cm. 

 of lead. From the relative densities we should expect 2.2 cms. of 

 steel to be equivalent to 1.5 cms. of lead and, therefore, the radium in 

 the steel cylinder should give, by the density law, two-thirds the effect 

 of the radium in the lead. It actually gives one-and-a-half times as 

 much. This remarkable result was confirmed by direct reading of the 

 primary y rays using different electroscopes. Thus the primary 

 y rays traverse steel much more readily than lead, but the rays passing 

 through iron are subsequently absorbed more readily by lead than if 

 the radium were in lead. The values for A the coefficient of absorp- 

 tion by lead, between 2 and 4 mms. were as follows: — 



Radium in lead (1 cm.) = .47 ) primary 



Radium in steel (2.2 cms.) =1.1 r y 



Radium in steel (4 cms.) = .75 ' rays. 



2. The secondary rays of the y type from lead are feeble com- 

 pared with those from iron or brick. This is true whether the radium 

 is in iron or lead and whether the absorbing screens are of aluminium or 

 lead. 



3. It will be seen that 1 or 2 mm. of aluminium or lead absorb 

 the kathode rays from the lead, iron or brick radiators acted upon by 

 y rays. 



4. J\''ith radium in steel, and with aluminium screens, brick gave 

 more secondary rays than iron. In the other three cases brick gave 

 less than iron. However, 5 cms. of iron give almost maximum secon- 



