title: Radon (222Rn) level variations on a regional scale: influence of the basement trace element (U, Th) geochemistry on radon exhalation rates.
abstract: The approach proposed in this study provides insight into the influence of the basement geochemistry on the spatial distribution of radon (222Rn) 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 a stable 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 (> or = 100 Bq m-3 in the atmosphere, > or = 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.
authors.affiliation: Institut de Protection et de Sureté Nucléaire, DPRE/SERGD/LEIRPA, B.P. 6, 92265 Fontenay-aux-Roses, France. geraldine.ielsch@ipsn.fr
authors.forename: G
authors.initials: G
authors.lastname: Ielsch
authors.forename: D
authors.initials: D
authors.lastname: Thiéblemont
authors.forename: V
authors.initials: V
authors.lastname: Labed
authors.forename: P
authors.initials: P
authors.lastname: Richon
authors.forename: G
authors.initials: G
authors.lastname: Tymen
authors.forename: C
authors.initials: C
authors.lastname: Ferry
authors.forename: M C
authors.initials: MC
authors.lastname: Robé
authors.forename: J C
authors.initials: JC
authors.lastname: Baubron
authors.forename: F
authors.initials: F
authors.lastname: Béchennec
mesh_terms: D005602:France; D055593:Geological Phenomena; D005844:Geology; D011886:Radon / Q000032:analysis*; D012987:Soil; D014131:Trace Elements; D014501:Uranium / Q000032:analysis
chemical_list: D012987:Soil; D014131:Trace Elements; D014501:Uranium; D011886:Radon