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Design and Evaluation of Large Aperture Gallium Fixed Point Blackbody



V B. Khromchenko, Sergey Mekhontsev, Leonard Hanssen


To complement existing water bath blackbodies which are now serving as NIST primary standard sources in the temperature range from 15 C to 75 C, a gallium fixed point blackbody has been recently built. The main objectives of the project included creating an extended area radiation source with a target emissivity of 0.9999, capable of operating either inside a cryo-vacuum chamber or in a standard laboratory environment. A minimal aperture diameter of 45 mm is necessary for the calibration of radiometers with a collimated input geometry or large spot size.This paper describes the design and performance evaluation of the gallium fixed point blackbody, including the calculation and measurements of directional effective emissivity, estimates of uncertainty due to the temperature drop across the interface between the pure metal and radiating surfaces, as well as the radiometrically obtained spatial uniformity of radiance temperature and the melting plateau stability. Another important test is the measurement of the cavity reflectance, which was achieved by using total integrated scatter measurements at a laser wavelength of 10.6 microns. The result allows one to predict the performance under the low background conditions of a cryo-chamber. Finally, results of the spectral radiance comparison with the NIST water bath blackbody are provided.The experimental results are in good agreement with predicted values and demonstrate the potential of our approach. It is anticipated that after completion of the characterization, a similar source operating at the water triple point will be constructed.
International Journal of Thermophysics


blackbody, emissivity, fixed point, gallium


Khromchenko, V. , Mekhontsev, S. and Hanssen, L. (2021), Design and Evaluation of Large Aperture Gallium Fixed Point Blackbody, International Journal of Thermophysics, [online], (Accessed April 13, 2024)
Created October 12, 2021