TABLES 683-689.— ELECTRON EMISSION * 



635 



TABLE 683.— ELECTRON EMISSION FOR HOT SOLIDS 



The electron emission from a solid varies with the temperature T (°K) in accordance 

 with the Richardson-Laue-Dushman equation 



I = AT* [exp (-b./T)] (1) 



where / = current in amps cm" 2 , and A and b are constants, characteristic of the material. 

 The constant b„ is ordinarily expressed in terms of electron volts (*„) where 



*„ = 8.620 X 10- 5 b 



or b = 1.160 X 10 4 <9 o (2) 



The values of A and b (or $„) are customarily derived from a plot of log (//T 2 ) 

 versus l/T, where 



log / = log A + 2 log T — 



b„ 



(3) 



2.3037 



and log = log to base 10. 



Hence, <*>„ = 1.986 X 10" 4 (&./2.303) (4) 



Theoretically, <*>„, as determined from thermionic emission data, should be identical with 

 *«, the "work function" from contact potential measurements, and *<•, the work function 

 determined by means of Einstein's equation 



Ve = hv — #, 



where v = frequency for photoelectric emission, V = retarding potential, e = charge on 

 the electron, and h = quantum constant. 



* Prepared by Saul Dushman, General Electric Research Laboratory, Schenectady, N. Y. 



TABLE 684.— ELECTRON EMISSION CONSTANTS FOR METALS AND CARBON 



The table gives emission constants (see preceding equations) for metals and carbon. 

 For other values and comprehensive data on this topic see references in footnote 218. 



Element A \0~*bo <po It T°K 



Barium 60 2.47 2.10 1.5X10" 8 800 



Calcium 60 2.60 2.24 2.9X10" 7 800 



Carbon 30 5.03 4.34 1.4X10-* 2000 



Cesium 162 2.10 1.81 2.5X10" 11 500 



Chromium 48 5.34 4.60 3.8X10" 8 1500 



Cobalt 41 5.12 4.41 1.3X10" 7 1500 



Copper 65 5.08 4.38 5.6X10" 16 1000 



Hafnium 15 4.10 3.53 2.8X10" 4 1600 



Iron 26 5.20 4.48 6.8X10- 10 1000 



Molybdenum 60 5.07 4.37 2.4X10- 3 2000 



Nickel 30 5.35 4.61 2.2X10" 8 1500 



Niobium 37 4.65 4.01 1.2X10" 3 2000 



Palladium 60 5.79 4.99 3.0X10" 8 1600 



Platinum 32 6.17 5.32 1.8X10" B 1600 



Rhenium 200 5.92 5.1 l.OXlO" 4 2000 



Rhodium 33 5.57 4.80 1.1 X10" 4 2000 



Tantalum 55 4.86 4.19 6.2X10" 3 2000 



Thorium 60 3.89 3.35 4.3X 10" 3 1600 



Tungsten 60 5.24 4.52 1.00X10" 3 2000 



Zirconium 330 4.79 4.13 8.5X1Q- 6 1600 



4>e 



2.48-2.51 



2.71 



4.82 



1.91 



4.37 



4.46 



4.63 



4.12 



4.92 



4.92 

 4.05 

 3.3-3.6 

 4.3-4.5 



218 Herring, C, and Nichols, M. H., Rev. Mod. Phys., vol. 21, p. 185, 1949. Rumann, A. L., Therm- 

 ionic emission, John Wiley & Sons, Inc., 1934. Dushman, S., Rev. Mod. Phys., vol. 2, p. 381, 1930. 



SMITHSONIAN PHYSICAL TABLES 



