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

Abstract

-Graded screen array (GSA) systems (nonconventional wire screen diffusion batteries) are increasingly finding application in the measurement of radioactive ultrafine cluster aerosols (0.5-5 nm in diameter), where conventional diffusion batteries are of limited utility. The GSA systems typically consist of varying mesh number, single/multiple wire screen stages operated either in series or in parallel, with the choice of a wide range of wire screen parameters and sampling flow rates. Numerical simulations studies of the expectation-maximization and Twomey size distribution reconstruction algorithms have yielded concepts that permit the optimization of GSA operating parameters, together with the determination of the potential size resolution of experimental GSA systems, the effects of random errors in the data, and algorithm stopping criteria. In general, a choice of wire screen operating parameters that result in the uniform fractioning of the sampled distribution among the various GSA stages and the inference of size intervals with successive midpoint diameters differing in diffusion coefficients by about one order of magnitude were found to be beneficial to the reconstruction process.

Characterization of Radon Decay Products in a Domestic Environment

“…For indoor air, a sequence of a 15-minute sampling interval with counting, a 60-minute counting interval, and a 15-minute delay time would permit a deter- mination of the concentration and size distribution of each of the decay products and the total potential alpha energy concentration every 90 minutes. Using the penetration characteristics of each GSA stage and the measured detection efficiency of each sampler, the activity size distributions can then be calculated from the observed stage activities using the reconstruction algorithms described by Ramamurthi and Hopke (1990). A Monte Car10 stability analysis was performed for each size distribution.…”

The development and field testing of a system for determination of ultrafine activity particle size distribution and working levels

“…The counts associated with the two alpha peaks (P0-218 and Po-214) are calculated from the alpha spectra after background subtraction. Given the knowledge of the penetration characteristics of each GSA stage and the measured detection efficiency of each sampler, the activity Size distributions can then be calculated from the observed stage activities using the reconstruction algorithms described by Ramamurthi and Hopke (1990b).…”

Intercomparison of Four Methods to Determine Size Distributions of Low-Concentration (∼ 100 cm−3), Ultrafine Aerosols (3 <Dp< 10 nm) with Illustrative Data from the Arctic

“…Measurements of winter (March/April) aerosols in Novosibirsk were reported. Diffusion batteries with activity measurements have also been used to determine size distributions of ultrafine (0.5-5 nm) radon daughter products (Knutson et al, 1988;Ramamurthi and Hopke, 1990).…”