On the Measurement of 218Po Diffusivity Using the Two-Filter Method

On the Measurement of 218Po Diffusivity Using the Two-Filter Method

TitleOn the Measurement of 218Po Diffusivity Using the Two-Filter Method
Publication TypeJournal Article
Year of Publication1994
AuthorsAntonius GBM Sasse, Ashok J Gadgil, William W Nazaroff
JournalJournal of Aerosol Science
Volume25
Issue4
Pagination689 - 697
Date Published06/1994
ISSN00218502
Abstract

Determining the diffusion coefficient of 218Po is an important application of the two-filter method (Thomas and LeClare, 1970, Hlth Phys.18, 113). Air containing a known concentration of 222Rn is drawn through a cylindrical tube with filters at both ends. The 218Po activity on the downstream filter relative to the 222Rn concentration in air is interpreted to determine the diffusivity of 218Po. Previously, the interpretation scheme was based on a theoretical analysis of 218Po transport and production in a tube by Tan (1969, Int. J. Heat Mass Trans.12, 471), and Tan and Hsu (1970, Int. J. Heat Mass Trans.13, 1887). Their analysis did not account for radioactive decay of airborne 218Po within the apparatus nor for the perturbation of the fluid flow caused by the flow resistance of the downstream filter. Also, simplified analytical air flow profiles were assumed in that analysis. In this paper, the two-filter method is re-analyzed numerically, by solving the continuity equation, the Navier-Stokes equations and the species conservation equation for a tube. Full account is taken of the effects of radioactive decay of 218Po, and the flow resistance of the downstream filter. The results of the new analysis lead to a downward correction of reported diffusivities of 218Po by about 10–20%.

DOI10.1016/0021-8502(94)90010-8
Short TitleJournal of Aerosol Science
Refereed DesignationRefereed