﻿822 Impact Ionization by Positive JI-Ions in Hydrogen, 



Table I. 



Total 



ace. P.D. 



(x+y). 



(Volts). 



Current 



+ ive ionizing 



leaving cylinder. 



(Scale Divns.). 



•o, 



Ionization 

 current. 



[10- 10 amp.]. 

 O, 



cyc 2 . 



5-6 

 67 



36 



+ 50 

 + 100 



9 

 15 



92 



+60 

 + 120 

 + 145 

 +290 



10 

 20 

 23 

 60 



6 

 6 

 6-3 



4-8 



Hydrogen jt? = "02 rum. Hg. V=18yolts. 



= 100 volts. 



The positive ionizing current was varied by varying the 

 filament current. The results show that the amount of 

 ionization is proportional to the ionizing current. The 

 former current collected under a field of 100 volts is probably 

 increased by the fact that the original electrons released 

 by the positive ions themselves produce some fresh ions by 

 collision. By obtaining the ratio of the two currents we 

 can estimate a maximum value for the efficiency of the 

 positive ions as ionizers. The ratio of the ionization current 

 to the ionizing current for the results in Table I. is about 

 1/130. Thus of at least 130 positive ions reaching ihe 

 ionization chamber G 2 E, only one ionizes a molecule of 

 hydrogen. Electrons accelerated through the same voltage 

 and at the same pressure in hydrogen would produce about 

 one positive ion per ionizing electron *. Hence when 

 moving with these low velocities, the efficiency of an electron 

 is much greater than that of the positive ion in producing 

 ionization by collision. Most of: the energy of the positive 

 ions is lost probably in non-ionizing collisions. 



Summary. 



An attempt is made to formulate the conditions governing 

 the exchange of energy when an atom is ionized by impact 

 or by the absorption of radiation. This is applied to fchfl 

 case of ionization by positive-ion impact with the conclusion 

 4hat the ionization potential for positive-ion impact in a gas 



* J. B. Johnson, Phys. Rev. 1917, p. 609. 



