[pound] absorption OF THE DIFFERENT TYPES OF BETA RAYS 69 



VII I. Summary of Results. 



1. The /? radiation from radium bromide which includes the 

 /? radiations from all the radium products in the equilibrium state 

 will not produce any ionisation on the far side of a plate of aluminium 

 7 mms. in thickness, of a plate of tin 2.5 mms. in thickness, or of a plate 

 of lead .9 mms. in thickness. 



2. The maximum secondary radiation emitted from the front 

 side of plates of the metals aluminium, tin, and lead, when bombarded 

 by ft rays are given by the following thicknesses: 



Aluminium 0.4 mms. 



Tin 0.24 mms. 



Lead 0.16 mms. 



3. The transmitted secondary radiations excited by y rays in 

 lead and tin are more penetrating than the transmitted secondary 

 radiation excited in aluminium by the same rays. 



4. When /? rays are allowed to fall in turn on reflectors of 

 different metals, it is found that the greater the density of the metal 

 from which the reflector is made the greater is the penetrability of the 

 reflected secondary rays excited by the ft radiation. 



5. From the experiments on the transmission of ft rays through 

 sheets of aluminium foil, it has been shewn that when very thin sheets 

 of the metal are used, the ionisation at first contributed by the trans- 

 mitted secondary radiation excited by the ft rays is greater than 

 that lost through absorption of the primary rays. 



In conclusion I wish to express my best thanks to Prof. McLennan, 

 at whose suggestion the investigation was undertaken, for his help and 

 advice and unfailing kindness throughout the course of the research. 



