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Awarded to Owen Willans Richardson for thermionic emission and its emission law. He received the prize in 1929.^[ref]

Physics.^[ref]

In his Nobel lecture, delivered on 12 December 1929 for the 1928 prize, Owen Willans Richardson recalled heating wires for weeks while hand-pumping away gas released by the apparatus. With platinum, he found a finite emission per unit area that rose rapidly with temperature. His initial 1901 formula used $T^{1/2}$; he preferred the $T^2$ form in 1911.^[ref]

The early apparatus surrounded a heated platinum wire with a metal cylinder connected to earth through a galvanometer. Wire electrical resistance supplied the temperature readout. After checking collection saturation, Richardson measured at a wire potential of $-120\mathrm{V}$, over roughly $1300$–$1600\mathrm{K}$; reversing polarity suppressed the negative discharge.^[ref]

The inference rests on several controls. A temperature sweep probes thermal escape; reversing the collecting electric field tests the sign of the mobile electric charge; varying collection voltage tests whether transport is limiting. Prolonged pumping and heating test whether a transient gas release is responsible. These controls address different alternatives, and none by itself establishes a clean, uniform surface.

For a modern repetition, stabilize each temperature, measure the collector electric current against collecting electric potential difference, and record the pressure and surface preparation. Repeat selected temperatures after cooling to reveal drift. Use the collection plateau and the actual emitting area to construct a Richardson plot. The resulting slope estimates the work function only within the stated surface and transport assumptions; it does not turn an uncontrolled wire into a reference material.

The coefficient $A$ has dimensions of electric current density divided by squared temperature. For ideal nonrelativistic particles with the free electron mass, two spin states, a planar uniform surface, and unit escape transmission, the thermionic tail-flux derivation giveswhere $e$ is the positive elementary charge and $h$ is the Planck constant. The two area units differ by a factor of $10^4$. A fitted $A$ need not equal $A_0$: reflection at the surface, the electronic band structure, and uncertain emitting area affect the inferred coefficient. A constant escape transmission $\tau$ would give $A=\tau A_0$ in this simple model; an energy-dependent transmission generally requires an integral instead.

The name joins Owen Willans Richardson with Saul Dushman. Dushman's 1923 paper develops a thermodynamic treatment of Electron emission analogous to evaporation and evaluates the prefactor using quantum ideas.^[ref]