Positive and negative thermionic emission from tungsten
H. B. Wahlin, L. V. Whitney
The positive and negative thermionic emission and the rate of evaporation of neutral atoms have been studied for well outgassed tungsten. To fix a reliable temperature scale the spectral emissivity for λ=0.669μ has been determined for a cylinder heated in a vacuum. The emissivity has been found to be a constant and equal to 0.46 from 1200°K–2200°K. A determination of the heat of evaporation of neutral atoms gave a value of 8.44 ev. The electron work function was found to be 4.55 ev with an A of 75 amp./cm2/degree2 until the filament was heated to a temperature of 3100°K, after which the work function was 4.63 ev and the value of A was 212. The average positive ion work function was 11.93 ev. This value closes the thermionic cycle if Russell's value of 8.1 for the ionization potential is used. © 1936 The American Physical Society.
