Abstract
THERE seems to be little room for doubt that the apparent thermionic A (the A derived from a Richardson line) of at least some clean metals is genuinely less than the upper theoretical limit for this quantity, Ae, the value of which is 120 amp. cm.-2 deg.-2. Thus, for tungsten, tantalum and molybdenum, which are among the metals for which the most reliable data are available, values of 60–100, 60 and 55 amp. cm.2 deg.2 respectively have been obtained, and, if surface roughness had been taken into account, somewhat smaller values still must have been found. It would, of course, be quite possible to attribute these results to an imperfect transmission of the electrons through the emitting surfaces, assuming the apparent A to be the true A. There is, however, a known effect which, unless compensated for by other effects, must make the apparent A less than the true A by a factor of at least 2 or 3, and which would, therefore, account for the order of magnitude of the observed data on the assumption of practically perfect transmission.
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R. H. Fowler, Proc. Roy. Soc., A, 122, 36; 1929.
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REIMANN, A. The Apparent Thermionic Constant A of Clean Metals. Nature 133, 833 (1934). https://doi.org/10.1038/133833a0
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DOI: https://doi.org/10.1038/133833a0
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