Change in the Optical Properties of BaSO 4 Powder Modified with SiO 2 Nanoparticles upon Sequential and Separate Irradiation by Quanta of Solar Spectrum and Protons

A comparative analysis of changes in the diffuse reflectance spectra (ρ λ ) and the integrated absorption coefficient in the range of 0.2–2.2 μm is performed after the separate and sequential irradiation of a barium-sulfate powder modified with silicon-dioxide nanoparticles ( m BaSO 4 / n SiO 2 ) with 5-keV protons and solar-radiation quanta. The spectra are recorded after each irradiation cycle in vacuum within the irradiation region (in situ). The integrated solar-radiation absorption coefficient of the modified m BaSO 4 / n SiO 2 pigment before irradiation is 0.048, which is several times lower than that of ZnO pigment widely used around the world. The additivity coefficient calculated from the results of sequential and separate irradiation of the m BaSO 4 / n SiO 2 powder decreases by a factor of 7.5–1.052 with an increase in the fluence of 5-keV protons. Assessment of the additivity changes under the action of the spectrum of charged particles in geostationary orbit (as one of the most used and with the most severe radiation conditions) shows that the nonadditivity of separate and sequential exposure to protons and solar-radiation quanta on the pigment for m BaSO 4 / n SiO 2 thermal-control coatings will persist for 1.27 years under these irradiation parameters.