Water Heat Pipe Blackbody as a Reference Spectral Radiance Source Between 50 C and 250 C
Mart Noorma, Sergey Mekhontsev, V B. Khromchenko, Maritoni A. Litorja, Claus Cagran, Jinan Zeng, Leonard M. Hanssen
Realization of a radiometric temperature scale for near ambient temperatures with high accuracy is crucial for a number of demanding military and commercial applications. Reliable radiation sources with high stability and good spatial uniformity have to be developed as reference and working standards. Traditionally, the temperature scale, maintained at the National Institute of Standards and Technology (NIST), has relied on water bath and oil bath blackbodies in this temperature range. Recently, a water heat pipe blackbody has been used at NIST as a spectral radiance source in a spectral emissivity measurement facility. Now a new, more versatile high emissivity water heat pipe blackbody has been designed and characterized to be used as a reference radiance source for the radiometric temperature scale realization between 50 C and 250 C. Furthermore, it will serve as a reference source for the infrared spectral radiance measurements between 2.5 m and 20 m. The calculated spectral emissivity of the painted copper alloy cavity has been verified by reflectance measurements using a CO2 laser at 10.6 m wavelength. The spatial uniformity and stability of the blackbody have been characterized. Two independent realizations of the radiometric temperature scale are compared in order to verify the accuracy of the scale. Radiance temperature, calculated from the cavity temperature measured with a calibrated PRT contact thermometer and from the emissivity of the cavity, is compared to the radiance temperature, directly measured with a reference pyrometer, which has been calibrated with a set of fixed point blackbodies.