title: Determination of low-level Radium isotope activities in fresh waters by gamma spectrometry.
abstract: A new portable sampling system was developed to extract Radium isotopes from large volumes (up to 300L) of fresh surface- and ground-waters of low Ra-activities (<5mBq/L). Ra is quantitatively adsorbed on a small amount (6.5g) of MnO2-coated acrylic fibers, which are then dried and burned at 600°C in the laboratory. The resulting Mn-oxide powder (about 2cm3when compacted) is then analyzed through gamma-ray spectrometry which allows measurement of the whole Ra quartet (226Ra,228Ra,224Ra and223Ra) in a single counting of a few days. The usual relative standard combined uncertainties (1σ) are 2-3% for226Ra,228Ra and224Ra; and less than 10% for223Ra. This method was applied to the analysis of Ra in karstic waters of the Lez aquifer, and surface- and ground-waters of the upper and middle Vidourle watershed (South of France). The analyzed waters have relatively low226Ra activities (1-4mBq/L) in both cases, regardless of the contrasted geology (Mesozoic limestone vs crystalline Variscan basement), but clearly distinct (228Ra/226Ra) ratios in agreement with the differences in Th/U ratios of the two drained areas. Short-lived Ra isotopes (224Ra and223Ra) appear to be mainly influenced by near-surface desorption/recoil processes for most of the sampling sites.
authors.affiliation: HydroSciences, Montpellier Univ., 34090 Montpellier, France; University of Costa Rica, 11501-2060 San José, Costa Rica. Electronic address: arnold.molina-porras@etu.umontpellier.fr.
authors.forename: Arnold
authors.initials: A
authors.lastname: Molina Porras
authors.affiliation: Geosciences, Montpellier Univ., 34090 Montpellier, France. Electronic address: condomines@gm.univ-montp2.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Condomines
authors.affiliation: HydroSciences, Montpellier Univ., 34090 Montpellier, France. Electronic address: jean-luc.seidel@umontpellier.fr.
authors.forename: Jean Luc
authors.initials: JL
authors.lastname: Seidel
mesh_terms: D004867:Equipment Design; D005602:France; D005618:Fresh Water / Q000737:chemistry; D055593:Geological Phenomena; D011883:Radium / Q000032:analysis*; D013051:Spectrometry, Gamma / Q000295:instrumentation*; D013910:Thorium / Q000032:analysis; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: C000615153:Radium-228; D014875:Water Pollutants, Radioactive; C026062:thorium X; D013910:Thorium; C000615150:Radium-223; C000615152:Radium-226; D011883:Radium
keywords: Fresh-waters; Gamma spectrometry; Groundwaters; Mn-fibers; Radium isotopes