ISSN:
1432-0495
Keywords:
Radon
;
Granitic soil
;
Uranium radiography
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract The abundance and distribution of radioelements on bulk and microscopic scales were investigated in residual granitic-derived soil at a facility for investigating the movement of radon into structures. In bulk soil samples, Ra concentrations range from 0.6 to 1.3 pCi/g, and variations in Ra, Th, and K appear to be controlled mainly by heterogeneities inherited from the parent granitic rock, which contains abundant dikes and inclusions. U in soil and parent rock is concentrated in primary minerals (mainly zircon and sphene), and in secondary sites that are of greater importance for Rn emanation. The main U-bearing secondary sites are weathered sphene, grain boundary coatings, weathered biotite and plagioclase, as well as dense Fe-rich coatings and a REE-phosphate mineral present in near-vertical fracture zones in saprolite underlying shallow loam. Elevated U in these sites generally correlates with high Ti, Al, Fe, and/or P. Preferential distribution of U and Ra on grain boundaries and porous weathered minerals is reflected in relatively high Rn emanation rates in the soil. Highest emanation occurs between 1.3 and 2.3 m depth, where fine pedogenic phasesgibbsite and amorphous silica and Fe-OOH—are most abundant; it is related to fixation of Ra by these phases, which precipitate close to the surface and accumulate at these depths by illuviation. Separation of Ra from U may occur locally, given remobilization of U-series elements from secondary sites, and large differences between Ra and U sorption capabilities of several phases present in the soil. Concentration of U along permeable fracture zones in saprolite suggests that contribution of soil-gas Rn from depth (〉 2 m) could be significant to Rn availability near the surface.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00789328
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