[mclennan-treleaven] residual IONISATION IN GASES 



119 



with alpha rays the arrangement used is that shewn in Fig. 5. A very 

 small piece of copper coated with polonium was placed on the end 

 of a brass rod which was attached to a brass plate and inserted in the 

 drying chamber mentioned above in a manner shewn by the diagram. 

 In this case as in the experiments with the beta radiation the readings 

 were taken with the gases first under natural conditions and after- 

 wards with them traversed by the alpha radiation. 



300 



290 



\~ ZQO 



o 



> z^o 



zeo 



-eso 



240 



230 



220 



200 



190 



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Fig. 3. 



Fig 4. 



Fig 5. 



In the experiments with gamma radiation a small quantity of 

 radium bromide was sealed up in a glass tube. This tube was then 

 placed in the cylinder of zinc with walls about 2 cm. thick which was 

 held in position, Figs. 6 and 7, against one of the plane sides of the 

 ioionisatn chamber of the electrometer. In this set of experiments 



