Radon decay products formation

The subject of this particular volume relates to aerosol particle physics including aerosol characterisation, the formation mechanism, the aerodynamic size distribution of the activity and aerosol residence time, instrumentation techniques, aerosol collection and sampling, various kinds of environmental (atmospheric aerosols), particularly radioactive aerosols and the special case of radon decay product aerosols (indoors and outdoors) and the unattached fl ac-tion, thoron decay product aerosols, the deposition patterns of aerosol particles in the lung and the subsequent uptake into human subjects and risk assessment. 

Besides cluster formation, the radon decay products attach to the existing aerosol particles within 1-100 s, forming the radioactive aerosols of the radon decay products. Results of the activity size distribution measurements carried out at different places in outdoor air, dwellings and workplaces are presented in Table 5.2. In general, the activity size distribution of the radon... 

In the environment, thorium and its compounds do not degrade or mineralize like many organic compounds, but instead speciate into different chemical compounds and form radioactive decay products. Analytical methods for the quantification of radioactive decay products, such as radium, radon, polonium and lead are available. However, the decay products of thorium are rarely analyzed in environmental samples. Since radon-220 (thoron, a decay product of thorium-232) is a gas, determination of thoron decay products in some environmental samples may be simpler, and their concentrations may be used as an indirect measure of the parent compound in the environment if a secular equilibrium is reached between thorium-232 and all its decay products. There are few analytical methods that will allow quantification of the speciation products formed as a result of environmental interactions of thorium (e.g., formation of complex). A knowledge of the environmental transformation processes of thorium and the compounds formed as a result is important in the understanding of their transport in environmental media. For example, in aquatic media, formation of soluble complexes will increase thorium mobility, whereas formation of insoluble species will enhance its incorporation into the sediment and limit its mobility. 

The radon daughters (RnD) are metal atoms, Po, Bi and Pb, and these atoms are oxidized to the metal oxides very rapidly after formation, e.g. Po—>PoOj. The shortlived RnD have relatively high decay energies. Since these isotopes are formed in succession in a decay series, it follows that for a given mother radon concentration, there will be a certain ratio of the various decay products with regard to each other. This ratio will depend on the age of the mixture of Rn and RnD, since the decay process is time dependent. If a fixed number of Rn atoms are sealed in a closed container at time... 

Radon is a product of the natural radioactive decay of uranium, which occurs naturally in the earth s crust, to radium and then to radon. As radium decays, radon is formed and is released into small air or water-containing pores between soil and rock particles. If this occurs near the soil surface, the radon may be released to ambient air. Radon may also be released into groundwater. If this groundwater reaches the surface, most of the radon gas will quickly be released to ambient air, but small amounts may remain in the water. By far, the major source of radon is its formation in and release from soil and groundwater, with soil contributing the greater amount. Smaller amounts of radon are released from the near surface water of oceans, tailings from mines (particularly uranium... 

Natural distributions of elements in subsurface geologic formations can give rise to ground water or soil zone contamination. Two examples of note are the generation of radioactive decay products (e.g., radon gas, radium) from natural thorium and uranium, and the release of naturally occurring arsenic or selenium from earth materials. 

The graph and Fig. 25-6 are almost exactly the inverse of one another, with the maxima of one being the minima of the other. 73a. The rate of decay depends on both the half-life and the number of radioactive atoms present. In the early stages of the decay chain, the larger number of radium-226, atoms multiplied by the very small decay constant is still larger than the product of the very small number of radon-2 atoms and its much larger decay constant. Only after some time has elapsed, does the rate of decay of radon-222 approach the rate at which it is formed from radium-226 and the amount of radon-222 reaches a maximum. Beyond this point, the rate of decay of radon-222 exceeds its rate of formation. 

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