The Thermionic Emission from Clean Platinum

The thermionic emission from thoroughly outgassed platinum in high vacuum has been measured to one-half percent over the temperature range 1360 to 1750°K, the temperatures being measured by careful optical pyrometry. The values obtained for the thermionic constants of the $T^2$ law are, when corrected for the Schottky effect, $b=72, 820°$K, $\phi =6.27\mathrm{}$ volts, $A=17,000\mathrm{}$ amp/${\mathrm{cm}}^2$ ${\mathrm{deg}}^2$. The value of $\phi$ is possibly in error by not more than 1 percent because of uncertainties in the temperature scale, and agrees within one-half percent with the value of the photoelectric work function previously obtained. The data confirm the previous announcement that for clean platinum $A$ is 250 times greater than the theoretical value of 60.2 amp/${\mathrm{cm}}^2$ ${\mathrm{deg}}^2$.