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Radon (Rn-222) level variations on a regional scale: influence of the basement trace element (U, Th) geochemistry on radon exhalation rates.


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Mot de passe :

Ielsch, G; Thieblemont, D; Labed, V; Richon, P; Tymen, G; Ferry, C; Robe, MC; Baubron, JC; Bechennec, F. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY, 53: (1) 75-90

Type de document > *Article de revue

Mots clés > études environnementales radon, géologie, radon

Unité de recherche > IRSN/DEI/SARG/LERAR

Auteurs > IELSCH Géraldine, ROBE Marie-Christine

Date de publication > 01/01/2001

Résumé

The approach proposed in this study provides insight into the influence of the basement geochemistry on the spatial distribution of radon (Rn-222) levels both at the soil/atmosphere interface and in the atmosphere. We combine different types of in situ radon measurements and a geochemical classification of the lithologies, based on 1/50 000 geological maps, and on their trace element (U, Th) contents. The advantages of this approach are validated by a survey of astable basement area of Hercynian age, located in South Brittany (western France) and characterized by metamorphic rocks and granitoids displaying a wide range of uranium contents. The radon source-term of the lithologies, their uranium content, is most likely to be the primary parameter which controls the radon concentrations in the outdoor environment. Indeed, the highest radon levels (greater than or equal to 100 Bq m(-3) in the atmosphere, greater than or equal to 100 mBq m(-2) s(-1) at the surface of the soil) are mostly observed on lithologies whose mean uranium content can exceed 8 ppm and which correspond to peraluminous leucogranites or metagranitoids derived from uraniferous granitoids.