Thoron daughters

Nuclear Energy Agency (NEA), Dosimetry Aspects of Exposure to Radon and Thoron Daughters, report by a group of experts, Paris, OECD (1982). 

The general characteristics of these ions have been reviewed by Bricard and Pradel (1966). The attachment of radon and thoron daughter ions to aerosols including condensation nuclei has been studied by a number of investigators (Raabe, 1968 McLaughlin, 1972 Porstendorfer and Mercer, 1979 and Busigin, et al., 1981), and will not be considered further in this paper. We turn now to some experimental results that bear directly on the characteristics of the radon daughter ions. 

Radon concentrations were measured by use of calibrated Lucas scintillation flasks, while radon and thoron daughters and the resulting potential alpha energy concentration (PAECj were determined using filter samples (Thomas, 1972) and a continuous electrostatic precipitator (Andrews et al., 1984). The radon daughter positive... 

Bigu, J., Radon Daughter and Thoron Daughter Deposition Velocity and Unattached Fraction Under Laboratory-Controlled Conditions and in Underground Uranium Mines, Aerosol Sci., 16 157-165 (1985). 

The same kind of optimization has been performed for the thoron daughters. In the calculations the sampling period was set at 30 min and the first decay time interval is started after the decay of the radon daughters (270 min). For a total measurement time of 16 hours the optimized MMC of Pb-212 and Bi-212 are respectively 0.02 Bq/m and 60 Bq/m (270-370 min, 540-960 min). Better results for Bi-212 are obtained with only one decay time interval and an estimation of the ratio of Pb-212 to Bi-212 out of the removal processes (ventilation and deposition of the attached thoron daughters). The influence of the removal rate on the potential alpha energy concentration is small. For the decay interval (270-960 min) the MMC of Pb-212 is 0.014 Bq/m, assuming the sum of the removal rates to be 0.6+0.5/h. 

NEA Experts Report, Dosimetry aspects of exposure to radon and thoron daughter products, OECD-NEA (1983)... 

Table II. Summary of Mean Monthly Activity Median Aerodynamic Diameters (AMAD) and Geometric Standard Deviations (tfg) of Radon and Thoron Daughter Size Distributions in Ambient Aerosols...

James, A.C., J.R. Greenhalgh and A. Birchall, A Dosimetric Model for Tissues of the Human Respiratory Tract at Risk from Inhaled Radon and Thoron Daughters, in Radiation Protection. A Systematic Approach to Safety, Vol 2, pp. 1045-1048, Pergamon, Oxford (1980). 

The dry deposition velocity of lead-212, a thoron (thoron or radon-220 itself originating from thorium-232) decay product has been reported to be in the range 0.03-0.6 cm/sec (Bigu 1985 Rangarajan et al. 1986). These low deposition velocities indicate that the thoron daughter, stable lead, may have a long residence time in the atmosphere with respect to dry deposition. 

Bigu J. 1985. Radon daughter and thoron daughter deposition velocity and unattached fraction under laboratory-controlled conditions and in underground uranium mines. J Aerosol Sci 16 157-165. 

Gunning C, Scott AG. 1982. Radon and thoron daughters in housing. Health Phys 42 527-528. 

To maintain perspective, we must consider artificial radioactivity in comparison with the natural radioactivity with which man has learned to live, and some with which he hasn t (such as the radon and thoron daughters of uranium). To provide good information efficiently we who are working on various aspects of this problem need to trade ideas and criticisms and techniques of sampling, analysis, data reduction, and interpretation. 

This paper deals mainly with the condensation of trace concentrations of radioactive vapor onto spherical particles of a substrate. For this situation the relation between the engineering approach, the molecular approach, and the fluid-dynamic approach are illustrated for several different cases of rate limitation. From these considerations criteria are derived for the use of basic physical and chemical parameters to predict the rate-controlling step or steps. Finally, the effect of changing temperature is considered and the groundwork is thereby laid for a kinetic approach to predicting fallout formation. The relation of these approaches to the escape of fission products from reactor fuel and to the deposition of radon and thoron daughters on dust particles in a uranium mine is indicated. 

Stephenson, J., Stevens, D.C. Morton, D.S. (1971) Removal of radon and thoron daughter products from glass fibre air sample filters. Annals of Occupational Hygiene, 14, 309-19. 

Thorium is normally present in low concentrations in gold-bearing ores its presence is indicated by detectable concentrations of thoron daughters in return air in most gold mines that are, or were, uranium producers. In some areas thorium is present in elevated concentrations in a layer of black mineral sand above the gold bearing reef. Thorium or its decay products have also been detected in some radium bearing scales in acid plants. 

Solli H, Andersen A, Stranden E, et al. 1985. Cancer incidence among workers exposed to radon and thoron daughters in a niobium mine. Scand J Work Environ Health 11 7-13. 

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