A calorimeter in the form of a 15° cone has been constructed and evaluated for use as a “black” radiation detector. The internal surface of the cone is coated with colloidal graphite to enhance the absorptance. Spectral emissivity and reflectance measurements of the blackening material are used to estimate the effective absorptance of the conical receiver. To reduce many of the difficulties associated with a dc system, this detector is used with an ac amplifying system at a frequency of 1 cps. The spectral response of three commercial thermocouples is compared with that of the conical receiver.
W. L. EISENMAN, R. L. BATES, and J. D. MERRIAM, "Black Radiation Detector," J. Opt. Soc. Am. 53, 729-732 (1963)