Freezing-point-blackbody radiation sources for the 29.78-1084.62 °C temperature range.

Freezing points of In, Sn, Zn, Al, Ag, Au, and Cu, along with the melting point of Ga, are among the defining fixed points of the International Temperature Scale of 1990. Accordingly blackbody sources have been commercially produced that utilize the freezing/melting points of the above metals for precision radiometric calibrations of noncontact thermometers. The cavity emissivity is estimated to be 0.999, and the fixed point metals have a nominal purity of 99.9999%. We analyze the freezing plateau of a Au freezing point blackbody and show that the accuracy of calibrating a narrow-band radiometer at 960 nm is (-0.17 ± 0.02) K.