Abstract
When thermal or ultraviolet radiation is focused upon a thermionic cathode, the resulting elevation of the cathode temperature causes the thermionic emission current to increase. Hence a thermionic diode may be used to measure radiation intensity, and it provides a convenient technique for measuring the spectral emissivities of materials at high temperatures. Also thermionic diodes may provide new techniques for detecting molecular beams and for studying chemical reactions at surfaces. Reported here are experimental data on the effect of thermal and ultraviolet radiation on the electron emission from a tungsten cathode. At high cathode temperatures, the increase in thermionic emission produced by ultraviolet radiation is much larger than the photoelectric emission. The results are described by a simple expression derived from the Richardson equation for thermionic emission.
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