Abstracts of Technical Articles from Bell System Sources 



A New High Vacuum System} J. A. Becker and E. K. Jaycox. 

 A new high vacuum pumping system is described in which oil is used 

 in a diffusion type pump, and a trap containing activated cocoanut 

 charcoal replaces the usual liquid air trap. The system is capable 

 of attaining a pressure of 2 X 10~^mm. Hg. A high degree of vacuum 

 can be attained at least as quickly as with a mercury diffusion pump 

 and liquid air trap. The system is especially adapted to maintaining 

 a low pressure for several days in apparatus which cannot conven- 

 iently be sealed off from the pumps. 



Phenomena in Oxide Coated Filaments II. Origin of Enhanced 

 Emission} J. A. Becker and R. W. Sears. Various theories have 

 been advanced regarding the mechanism of emission of electrons from 

 oxide coated filaments. These theories postulate that: (1) the active 

 layer is ia) at the outer oxide surface, {h) at the core-oxide interface; 

 (2) the thermionic electrons come from {a) the adsorbed barium, ib) the 

 oxide just underneath the adsorbed layer; (3) the current is carried 

 through the oxide coating by (a) an entirely electrolytic process, {b) 

 thermionic electrons which come from the core, diffuse through the 

 pores of the coating and form a space charge therein, (f) electrolytic 

 conduction through the oxide crystals and thermionic conduction 

 between crystals, {d) electronic conduction, a small portion being 

 carried by ions. A number of experiments were designed to test these 

 various hypotheses. These experiments show that: (1) When barium 

 is brought to the outer surface of the oxide, either by electrolysis or 

 evaporation from an external source, the emission increases at first, 

 passes through a maximum and then decreases. This change in 

 activity is similar to that for barium on tungsten. (2) When oxygen 

 is brought to the surface of the oxide of an activated filament, the 

 activity decreases rapidly at first and then more slowly. (3) In these 

 two respects, a filament with a core made of an alloy called "Konel" 

 and consisting of nickel, cobalt, iron and titanium acts just like 

 filaments with other cores. (4) When the oxide was stripped from a 

 Konel core filament, the activity decreased by a factor of 6000. (5) 

 The emission-limited current is independent of the area of the core 



1 Rev. Sci. Inslruments, December, 1931. 

 '^Pkys. Rev., December 15, 1931. 



318 



