254 Wheeloch — Nature of Ionization Produced hy a Rays. 

 Tlie results obtained are shown in the following table : 



Pressure 354™™. 













Experimental 



Calculated 



Volts /cm. 



Current 



% lack 



Current 



^ lack 



5 



1-01 



9-2 



7-24 



6-1 



10 



1-21 



7-4 



7-33 



4-9 



20 



7-24 



7-1 



7-46 



3-2 



40 



1-6 



2-5 



7-51 ' 



2-6 



100 



1-1Q 



0-4 



7-60 



1-4 



200 



7-79 



0-0 



7-71 



0-0 



Pressure 224™™. 











5 



5-34 



5-7 



5-45 



3-2 



10 



5-5 



2-8 



5-57 



1-06 



20 



5-53 



2-3 



5-57 



1-06 



100 5-66 0-0 5-63 O'O 



By comparing the calculated with the experimental results, 

 it is seen that the calculated curves approach saturation more 

 quickly than the experimental curves. 



In calculating the above curves it was assumed that the 

 radius of the columns was not appreciably affected by the dimi- 

 nution of pressure. If the radius of the column should vary 

 inversely as the pressure, calculation shows that for 5 volts/cm. 

 the lack of saturation reduces to about 1 per cent. 



Although the above equation does not fit the experimental 

 curve at atmospheric pressure, it seems allowable to use it to 

 test the effect of changing the pressure, as has been done above. 



The fact that the calculated curves for reduced pressures ap- 

 proach saturation more quickly than the experimental curves 

 seems to be another reason for concluding that the effect of 

 general recombination of the ions within the columns does not 

 wholly account for tlie lack of saturation experimentally 

 obtained, but that initial i-ecombination in the Bragg sense has 

 an appreciable effect. 



Summary of Results. 



(1) For a gas ionized by a rays the ions are formed in col- 

 umns along the trajectory of the a particle. These columns are 

 not broken up by a field applied along the axes of the columns 

 and the positive and negative ions have to pass each other in 

 going to the plates of the ionization chamber, while a field at 

 right angles to the columns produces a separation of the posi- 

 tive and negative ions by breaking each column up into two. 



(2) With the parallel field, the ionization is proportional to 

 the intensity of the source, even when far from saturation. 



