Abstract
This blackbody at the gold point was newly designed and constructed to establish the temperature scale above the gold point (1064.43°) by the definition of the International Practical Temperature Scale of 1968 (IPTS-68).
The blackbody is composed of a graphite crucible and a furnace. The graphite crucible contained a 0.9kg gold ingot with purity of 0.99999 in which opens a reentrant graphite cavity forming a blackbody. The effective emissivity of the cavity was evaluated to be 0.99998. The furnace can maintain the temperature of the crucible at 1064.5° with a power supply as low as about 800W by the aid of the radiation shield. The temperature along the furnace axis is maintained within 0.1K by two control blocks.
At the blackbody of the gold point, the slope of the straight lines on the observed freezing plateau and the dispersion of the replication gave estimations that the desired blackbody radiation was correctly realized within the precision of the multiplicative comparator of the spectral radiance which was used to compare the spectral radiance of the blackbody with that of a tungsten strip lamp.
Thus the accuracy of the blackbody at the gold point (ΔLλ[T68(Au)]/Lλ[T68(Au)]) is expected to be better than 0.0001.
