The All-Russia Institute of Technical Physics and Electronics has built a hign-precision apparatus for reproducing the units of numerical concentration and particle size for aerosols, suspensions, and powders in the concentration range from 4-107 to 4-1013 m -3 with average particle sizes of 1-1t30/,tm.The apparatus is intended to provide metrological support to working means of measuring the concentrations and sizes of particles used in industry, ecology, and environmental protection, e.g., flour milling and cement production, powder metallurgy, monitoring effluents and drinking water, military-industry applications, agriculture, and so on. The number of such instruments runs to many thousands.The apparatus consists of an aerosol generator, equipment for measuring particle concentration and size, an IBM PC/AT 486 computer, software, and a set of glass test plates. The apparatus employs small-angle laser-beam scattering [1] on the basis of Fraunhofer diffraction and Beer's law; the technique is used widely in aerosol research [2, 4].The following is the scattering indicatrix in the Fraun_hofer approximation: = 7 al (013) dp , _(1) t(13) ~to f(p) pz 2 P 0 in which ~ is a normalization factor,/3 the scattering angle, p = 7ra/X, I o and X are the intensity and wavelength of the laser beam, a particle diameter, f(p) the distribution, and Jl(x) a Bessel function of the first kind and first order. When f(p) is determined from the current values of the indicatrix, the solution to (l) is [5]
