Design and construction of a gallium fixed-point blackbody at CENAM

Abstract

For temperatures below silver fixed-point defined by the International Temperature Scale of 1990, a transfer radiation thermometer can be calibrated using either of two calibration schemes: a variable temperature blackbody with a standard platinum resistance thermometer as a reference, or with a set of fixed-point blackbodies. CENAM is presently working with the first scheme, and it is developing fixed-point blackbodies to have the capability to work with the second scheme too. For this purpose a gallium fixed-point blackbody to calibrate CENAM's transfer radiation thermometer was designed and constructed. The blackbody cavity has a cylindro-cone shape with effective emissivity equal to $0.9992 \pm 0.0004$ in the 8 $\mu$m to 14 $\mu$m wavelength range. The radiance temperature of the gallium fixed-point blackbody was estimated to have an expanded uncertainty of 54 mK, with a coverage factor $k = 2$.