Specially prepared barium sulfate powders and coatings of these powders with polyvinyl alcohol have been used as working standards of reflectance and for coating integrating spheres. These materials are satisfactory for use in the wavelength range 0.20-2.00 micro. Since the refractive index of barium sulfate is rather low, it is necessary to use fairly thick layers in order to obtain good results. The absolute value of luminous reflectance of the barium sulfate powder, described in this paper, is 0.995 +/- 0.001, and that of the paint, when properly applied, is 0.992 +/- 0.001. The spectral reflectance of this material is higher than that of magnesium oxide, particularly in the uv region of the spectrum. By using barium sulfate as reference standard and as a coating on the integrating spheres of spectrophotometers, it is now possible to measure spectral reflectance reliably in the uv region to 200 nm. Because the reflectance of barium sulfate paint is significantly greater than that of magnes um oxide in the shortwave region, there is a corresponding gain in instrument sensitivity when barium sulfate is used as a sphere coating and as a comparison material.
Corona-discharge devices are commonly used in a variety of research and development applications. They are known to produce a considerable amount of electromagnetic radiation, mainly in the uv region of the spectrum. The mechanism involved is presumed to be the ionization and radiative recombination of the gases surrounding the high-voltage terminal of the device. A series of high-resolution emission spectra of corona discharge has been measured in atmospheres of nitrogen, helium, and air. (The nitrogen and helium are Air Products 99.995% purity, total hydrocarbons less than 0.5 ppm.) These data are presented here and are compared with published spectroscopic reference data. All the emission lines reported in the spectroscopic reference literature were detected, as well as other lines, which may conceivably be due to impurities.
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