Plate-out rate

Free Fractions, Attachment Rates, and Plate-Out Rates of Radon Daughters in Houses... 

The environmental conditions for each of the cases considered below are summarized in Table III all these parameters are constant in time. The build up of the nucleation mode of the stable particles and the build up of both the nucleation and accumulation modes of the radon decay products is calculated, and the results are given after a process time of one hour. Figures 1 to 5 show the size distributions of stable and radioactive particles, and Table IV gives the disequilibrium, the equilibrium factor F, the "unattached fraction" f and the plate-out rates for the different daughters. 

Table IV Disequilibrium between radon and its daughter products, equilibrium factor (F) and unattached fraction (fp) with respect to the potential a energy and plate out rates of the unattached RaA, RaB and RaC fractions for the different cases considered. The values prevail after one hour...

We believe that the calculations presented here give a better understanding of the many factors that determine the behavior of radon decay products, and that they explain why such a large range of values is being found of diffusion coefficients of the unattached fraction, of equilibrium constants, plate out rates, etc. (see (1) for a review, (9) for experiments in steel rooms and (10), (11), (12) for field studies in domestic environments). 

Porstendorfer, J., Reineking, A. Becker, K.H. (1987) Free fractions, attachment rates and plate-out rates of radon daughters in houses. In Radon and its Decay Products, ed. P.K. Hopke, Washington D.C., American Chemical Society, pp. 285-300. 

Data on the rate of attachment or deposition, i.e., plate-out of radioactive particles on walls can be used to calculate the particle deposition velocity. Deposition rates can be determined experimentally by measuring the surface activity on some samples... 

This paper deals with the plate-out characteristics of a variety of materials such as metals, plastics, fabrics and powders to the decay products of radon and thoron under laboratory-controlled conditions. In a previous paper, the author reported on measurements on the attachment rate and deposition velocity of radon and thoron decay products (Bigu, 1985). In these experiments, stainless steel discs and filter paper were used. At the time, the assumption was made that the surface a-activity measured was independent of the chemical and physical nature, and conditions, of the surface on which the products were deposited. The present work was partly aimed at verifying this assumption. 

Employing the conditions defined in the three data bases and the appropriate equations derived from the Plate and Rate Theories the physical properties of the column and column packing can be determined and the correct operating conditions identified. The precise column length and particle diameter that will achieve the necessary resolution and provide the analysis in the minimum time can be calculated. It should again be emphasized that, the specifications will be such, that for the specific separation carried out, on the phase system selected and the equipment available, the minimum analysis time will be absolute No other column is possible that will allow the analysis to be carried out in less time. 

NaN, is used as an initiator for emulsion polymerization (Ref 137), as a cellulating agent (Ref 134) and as a retarder (Ref 185) in the manuf of sponge rubber. The addn of NaN, an alkali bicarbonate and an alkali to form a compn of pH 9-12 prevents or reduces plating out or coagulation of styrene and butadiene latexes stored in contact with metals (Ref 162). NaN, is used also to decomp nitrites in the presence of nitrates (Ref 172). The rate of nitrite decompn is increased with an increase in azide concn. Acosta (Ref 172) detd the optimum ratio to be CNaN,/CNaNO, 3-9- Compds of the structure R,R (- 0) (- NH) have been prepd from the corresponding sulfoxide and NaN, + H,S04 in chlf soln (Ref 171) ... 

Now suppose that we are to carry out the same separation at constant current. With the same apparatus, the current cannot exceed 2 mA, the limit imposed by the mass-transfer rate of lO MAg" ". This separation would require 5 x 10 s, or 5.8 days By starting with a higher initial current, say 1 A, which would make it possible to plate out half the silver in 500 s, the time could be shortened, but at the risk of plating out copper accidentally as the rate of mass transfer of silver gradually decreased. Only by interposing a reducible material to consume the excess current without forming solid products could the rate be increased. Such a material should be reducible at the proper current density in just the potential range calculated above. Indeed, such a procedure constitutes an internal form of controlled-potential electrolysis that would permit the same performance as that calculated above for controlled-potential electrolysis. 

We have also pursued electrochemically back-plating of the copper sample to reduce the copper ion concentration and leave in solution impurities such as thorium and uranium, which should not plate out at the half-cell potential of copper. Theoretically, the amount of sample that can be processed in this manner is not limited. All materials including any non-sample electrodes must not add contamination and must be of extreme purity. Also, the amount of copper remaining in solution must be back-plated to <10 (xg/ml, and if a sulfate system is used, which is useful in support of further developing the predictive rejection rate information, then the sulfate ion should be <10 mmol as well. This approach hinges on the rejection rate remaining sufficiently high as to not introduce an undue amount of error. We have measured rejection rates as low as 10 but even at 10 this would only represent a 1% error in the assay result. 

Aramaki et al. [60] confirmed that ultrasonic waves modified cathodic polarization, so that a higher plating rate could be achieved for gold. Walker et al. [52] have found similar results for zinc plated out from a sodium zincate bath. The zinc plated out at a much faster rate in the presence of ultrasound (i.e. 1950 A m 2), when compared to the rate measured using a silent bath (250 A m-2). Similar effects have also been reported for many other metals including chromium [61] and silver [62] for nickel a 5- to 10-fold rate increase was observed [63]. 

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