Mobility of Radionuclides in the Geosphere

Gaseous species, aerosols and species dissolved in aquifers are mobile and easily transported with air or water, respectively. Mobility of solid particles, on the otlier hand, may be caused by dissolution or suspension in water or spreading by wind. 

From near-surface layers, radionuclides are brought to the surface by natural processes and by human activities. Rn produced by decay of in uranium ores is able to escape into the air through crevices. Its decay products are found in the air mainly in the form of aerosols. Ions, such as Ra + and are leached from ores 

Mining of potassium-salt deposits for use of K as a fertilizer brings additional amounts of to the surface of the earth, where it enters the surface waters. 

Radionuclides are also liberated by the burning of coal in thermal power stations. Depending on its origin, coal contains various amounts of U and Th, and these as well as the daughters are released by combustion. Volatile species, in particular Rn, are emitted with the waste gas, Pb and Po are emitted with the fly ash, and the rest, including U and Th, is found in the ash. The global release of Rn is of the order of 10 Bq per year. 

Other activities of man have led to the distribution of appreciable amounts of radionuclides in the atmosphere and on the earth s surface. In the first place nuclear explosions and nuclear weapon tests have to be mentioned, by which Pu and fission products have been deposited on the earth, either directly or via the atmosphere in the form of fall-out. The amount of Pu released by nuclear weapon tests between 1958 and 1981 is estimated at 4.2 tons, of which 2.8 tons were dispersed in the atmosphere and 1.4 tons deposited locally. By underground nuclear explosions about 1.5 tons of Pu have been liberated. Radionuclides released into the air are mainly present in the form of aerosols. 

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