On Improving the Validity of Wire Screen “Unattached” Fraction Rn Daughter Measurements

Abstract

Wire screens are commonly used to estimate "unattached" Rn daughter fractions in ambient and mine atmospheres. However, it is now recognized that the "unattached" fraction is in reality an ultrafine cluster mode in the 0.5-3 nm size range and that the collection efficiency versus particle diameter characteristics of wire screens do not permit a distinct separation of the "unattached" and "attached" fractions. Wire screen penetration theory and a semi-empirically corrected diffusion coefficient equation are used to characterize "unattached" fraction measurements as a function of experimental parameters. Collection efficiency curves are estimated for previously published wire screen "unattached" fraction measurements, and improvements in wire screen methods for such measurements are discussed.

Gas-Nanoparticle Scattering: A Molecular View of Momentum Accommodation Function

“…Diffuse scattering creates larger drag, smaller ion mobility, and diffusion velocity than do specular scattering. Although an analysis of available experimental data [13][14][15][16][17] led us to suggest that the specular-to-diffuse transition occurs for a particle radius about 2.5 nm [7], close to the observation in [10,18], little is known about what causes diffuse scattering and why the specular-to-diffuse transition occurs.…”

Attachment of radon progeny to cigarette-smoke aerosols

“…To measure their size distribution, or diffusion coefficient spectrum, mve have fabricated a graded-screen dffisisn battery. The use of graded-screen difisior I batteries for the measurement of the distribution in diffision coefficient of the radon1 progeny has been described by other investigators (34,35,40). The battery used here is a 6-stage device consisting 16,50, 80,200,325, and 500 mesh stainless-steel screens ;!5 mm in diameter.…”

Simulation Studies of Reconstruction Algorithms for the Determination of Optimum Operating Parameters and Resolution of Graded Screen Array Systems (Nonconventional Diffusion Batteries)

“…For d, > 2 nm, the particle diffusion coefficient may be calculated from the Einstein-Cunningham equation (Freidlander, 1977). For particle/ cluster diameter, d, < 2 nm, kinetic theory (Loeb, 1961) < 2 nm can be derived and is presented elsewhere (Ramamurthi and Hopke, 1989). The form of Eq.…”

“…This diameter can be approximately determined as d,(50%) (nm) for 2.5 X l o p 4 < KVF < 0.40 (Ramamurthi and Hopke, 1989).…”