Abstracts of Technical Articles from Bell System Sources (01 July 1933)

Thermionic and Adsorption Characteristics of Thorium on Tungsten} and JOSEPHA. BECKER . Variation of thermionic emission of tungsten with surface density of adsorbed thorium.--· Thorium was deposited on a tungsten ribbon by evaporation from a thorium wire. A study was made of the dependence of the thermionic WALTER H . BRATTAIN l 2 Proc. I. R. E,, April, 1933. Phys. Rev., March 15. 1933. 371 372 BELL SYSTEM TECHNICAL JOURNAL emission on the two parameters: T, the temperature, and /, a quantity which is proportional to the amount of thorium on the tungsten surface. 

At a fixed temperature 1274° K it was found that as the amount of thorium on the tungsten surface was increased, the thermionic emission increased to a maximum, then decreased, and asymptotically approached a constant value. For the maximum, / is defined to be 1.0. The maximum value and the final constant value of the emission current were respectively 5.7 X 105 and 5.7 X 104 times the value of emission current characteristic of clean tungsten. Moreover the final constant value of the emission agreed to within a factor of 2 with the value characteristic of clean thorium. 

From / = 0.0 to / = 0.8 the relation between the emission current and / satisfied the following empirical equation logwi = - 3 . 1 4 - 6.54e~2,38/, where i is the emission current in amperes per cm2. For 0.8 < / < 2.0, the values of emission currents are tabulated. For any fixed /, the emission obeys Richardson's equation. All the Richardson lines for 0 < / < 1 intersect in a common point at an extrapolated temperature of 12,500° K, and f o r / ^ 1 the lines intersect in a common point for which the temperature is 3250° K.