A New Method for Determining the Thermionic Work Functions of Metals and Its Application to Nickel

A new procedure for determining thermionic work functions of metals has been developed. The metal sample is in the form of an approximate sphere and is heated by electron bombardment from an auxiliary filament which is disconnected when measurements are made. Electron emission from the cooling sample charges a condenser which, at predetermined times, is discharged through a ballistic galvanometer. Temperatures are determined by a Pt, Pt+10 percent Rh thermocouple spot-welded to the sample. The thermionic constants are obtained from the equation: ${log}_{10}\left(\frac{T^2}{\mathrm{SQ}}\right)={log}_{10}\left(\frac{2.3}{\mathrm{aA}}\right)+\frac{\Phi }{(1.988\mathrm{}\times {10}^{-4\mathrm{}}T)}$ where $Q$ is the quantity of charge yet to flow upon cooling the sample from a given temperature to absolute zero and $-S$ is the slope of the $logQ$ vs. time curve. This equation is derived from Richardson's. The values of the thermionic constants obtained by applying this method to the case of thoroughly outgassed nickel are found to be $\Phi =5.03\mathrm{}\pm 0.05$ volts and $A=1.38\mathrm{}\times {10}^3$ amp./${\mathrm{cm}}^2$ ${\mathrm{deg}.\mathrm{}}^2$.