﻿732 Mr. R. W. Varder on the 



■ A ought to be equal to c 2 m /K. With the exception 



o£ the first value, we see that — . decreases slowly with 



increasing velocity, as should be expected from theory since 

 K increases slowly with increasing velocity. 



The fact that the aluminium absorption curve is approxi- 

 mately linear must result from a chance balancing of the 

 opposing effects of scattering and diminution of velocity. If 

 we had no scattering or straggling we should expect to have 

 a curve similar in shape to a Bragg «-ray curve. 



For a substance like paper, which contains only elements 

 of low atomic weight, the effect of scattering is less important 

 than for aluminium, so that a greater fraction of /3 rays will 

 penetrate a given thickness of matter. This is seen from the 

 fact that the absorption curve for filter-paper (fig. 6) is 



Fig. 6. 



THICKNESS IN GMS. PER CM? 



concave to the origin. For substances, like tin and platinum, 

 of ^ high atomic weight fewer particles penetrate a given 

 thickness, and the curves are convex towards the origin 

 (fig. 6). 



