146 Jauncey — Effect of a Magnetic Field. 



Art. XVIII. — The Effect of a Magnetic Field on the Initial 

 Recombination of the Ions Produced by X-Hays in Air ; 

 by CI. E. M. Jauncey. 



§ 1. Introduction. 



Assuming a given number of ions to be distributed uniformly 

 throughout a gas and using the known coefficient of recom- 

 bination and the known mobilities of the ions, the saturation 

 voltage can be calculated for an ionization chamber of known 

 dimensions. This calculated saturation voltage is much less 

 than the observed saturation voltage when the gas is ionized 

 by a-rays. It, therefore, appears that ions, produced by a-rays, 

 recombine at an abnormally high rate when first formed. This 

 abnormal recombination is known as initial recombination. 



The generally accepted explanation of this fact is that con- 

 ditions are abnormally favorable for recombination along 

 the path of an a-particle where the ions are much crowded 

 together. 



"W. H. Bragg* has pointed out that the recombination of 

 ions may be complicated or influenced by the fact that when a 

 pair of ions is first formed the ejected electron may not have 

 sufficient velocity to break away from the parent atom and a 

 strong electric field would tend to complete this incipient ion- 

 ization. Thus one effect of the electric field would be to 

 actually increase the rate of formation of ions and under these 

 conditions there may be no such thing as saturation voltage. 

 A gas ionized by X-rays shows to a small degree the effects of 

 initial recombination. In this case the excessive density of 

 the ions in the region of formation cannot be used as an ex- 

 planation for initial recombination. The only available ex- 

 planation seems to be the above hypothesis of Bragg. 



If a magnetic field is applied to a gas ionized by X-rays 

 then the electron which is ejected from an atom by means of 

 the ionizing agent will follow a curved path and will therefore 

 remain for a longer time near the parent atom and so there 

 will be a greater chance of it being drawn back into the atom. 



Furthermore Bragg in his " Studies in Badioactivity " cites 

 many experiments which support the hypothesis that a gas is 

 not to any great extent directly ionized by the X-rays but by 

 the secondary high-speed cathode rays which are produced by 

 the direct action of the X-rays. In contradiction to this, 

 Kleemanf concluded from one of his experiments that as much 

 as half the ionization in an air-filled chamber was due to the 



* Studies in Eadioactivity, p. 73. 



f Cambridge Phil. Soc, Proc. 15, pp. 169-177. 



