Excitation of y Rays hy a Rays. 



195 



a sulphur stopper provided with a guard-ring in the usual 

 manner. The face of the ionization-chamber through which 



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the rays entered was of aluminium 0'08 mm. thick. This face 

 was made airtight by inserting a ring of rubber between 

 the aluminium sheet and the flange F'F', and then tightly 

 clamping the flanges FF, F'F' by means of nuts. The 

 ionization-chamber, with the exception of the face, was 

 enclosed in lead 3 mm. thick. 



The measurements described above were now repeated 

 when the ionization-chamber was filled with carbon bisul- 

 phide or methyl iodide at their vapour pressures. It was 

 found that the ionization produced in the chamber when the 

 inner tube' was gold was about 5 per cent, greater than when 

 the inner tube was aluminium. Some of the measurements 

 obtained with carbon bisulphide are given in the table. The 

 ionization when the inner tube was aluminium is taken as 

 100 in each case. 



Inner tube Al. 



Inner table Au. 



100 



1048 



100 



1042 



100 



1048 



. 100 



1053 



100 



104-8 



100 



1050 



