Radiation and Ionization of Helium. 



The ionization of abnormal helium atoms by electron 

 bombardment. 



763 



This was tested by causing a considerable number of 

 abnormal helium atoms to be produced in the main tube by 

 the absorption of radiation produced in the side tube, and 

 then investigating the effect of bombarding these abnormal 

 atoms by electrons from the lower filament having velocities 

 below 20*4 volts. For this purpose the side filament was 

 made very hot so as to produce a copious supply of radiation. 

 The arrangement of the electric fields in the main tube was 

 that used in obtaining an (I— R) curve, i.e. the potential 

 difference V 4 was such as to cause ionization to give a 

 positive current, and the photoelectric action of radiation to 

 give a negative (furrent. In the absence of bombarding 

 electrons from the lower filament, a negative current was 

 measured as a result of the handing-on of radiation produced 

 originally by the electron impacts with helium atoms in the 

 side tube. The extent to which ionization results from the 

 electron impacts with abnormal atoms was indicated by 

 the extent to which this negative current was reduced when 

 the lower filament supplied bombarding electrons, allowance 

 being made for the collection of positive ions liberated by 

 the electron bombardment of the platinum gauzes in the 

 main tube. In order to eliminate any possible spurious 

 effects connected with change of temperature of the filaments, 

 both filaments were maintained at constant temperatures 

 throughout these observations, and the potential differences 

 V 1 and V 5 , which control the velocities of the two electron 

 streams, were alone varied. The following are examples of 

 the results obtained : — 



Pressure of helium 0*326 mm. 

 Electron emission from lower filament (V]=20 volts) 6'0 X 10 -6 ampere. 

 Electron emission from side filament (V 5 = 20 volts) 10-6xl0~ 5 ampere 



I. 



II. 



ii r. 



IV. 





Current (10" 12 amp.) 

 clue to the activity of 

 the side filament only. 



Current (10~ 12 amp.) 



due to the activity of 



the lower filament only. 



Algebraic sum 

 of currents 

 (10- 12 amp.) 



Observed current 



(10 ~ 12 amp.) when both 



filaments were active. 





V 5 = 30 volts. V^O. 



V 3 = 14 volts. | V\ (volts). 



in I. and II. 



V 5 = 30 volts. 



V, (volts). 





-5-14 



4- 0-492 



14-2 



-4-65 



-4-49 



14-2 





-5-39 



•4- 1-81 



15-6 



-3'f>8 



-306 



15-6 



-5-89 



4- 5-81 



17-1 



--0 08 



4-0 07 



17-1 



-G-00 



+ 12-00 



18-5 



+ 000 



4-6-74 



18*5 





E 2 



