Wheelock — Nature of Ionization Produced hj a Rays. 239 



In the case of ionization by /3 rays, the ions are distributed 

 throughout the vohime of the gas, and general recombination, 

 which depends upon tlie number of ions per c.c. in tlie gas, 

 would be gi'eater as the ionization is increased. It would not 

 be expected that the ratio of the currents obtained with two 

 sources of different intensities wonld be the same for different 

 potential gradients. This is in accord with the ordinary theory 

 of volume ionization and with all experiments hitherto made on 

 ionization produced by )S, 7, and Rontgen rays. 



On the other hand, when a gas is ionized by a rays, if the 

 ions are formed in columns along the path of the a particle, an 

 electric field applied along the path, that is along the axis of 

 the column so formed, would not break up the cohunn and the 

 recombination occurring would be between ions belonging to 

 the same column. It would be expected that the ratio of the 

 currents obtained with sources of different intensities would 

 he constant for different potential gradients applied, since each 

 a particle makes the same number of ions in its path, and the 

 density of ionization would be the same in any one column. 



When the field is applied at right angles to the direction 

 of the column, each column would be separated into two, one of 

 positive and the other of negative ions. 



With the perpendicular field two cases present themselves : 

 first when the source is so weak that there are very few a par- 

 ticles given off; second, when a stronger source is used. 



In the first case, very few columns would exist in the ion- 

 ization chamber during the time required for the ions present 

 to be carried over to the receiving plate by the electric field. 

 The ions of one column would have little chance to recombine 

 with those of another in going across the chamber. 



In the second case, with the stronger source, enough columns 

 might exist in the chamber at any one time, so that the ions of 

 one column would, when the field is applied, come within the 

 sphere of influence of those of the opposite sign from another 

 column. Recombination might then take place not only 

 between ions of the same column but between those of different 

 columns. 



In this case the ratio of the currents obtained with a given 

 field would not be constant, because of the added recombina- 

 tion of ions of different columns, which would vary with the 

 number of columns present in the chamber. 



To apply this test for the existence of ions in columns it is 

 necessary to obtain curves from sources of different intensity, 

 with both parallel and perpendicular fields. 



(a) Curves were obtained with the radio-active source bare 

 and when covered with a wire gauze to cut out part of the a 

 particles. The density of ionization would be the same wher- 

 ever ions exists, i. e., within the columns. 



