Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A new portable sampling system was developed to extract Radium isotopes from large volumes (up to 300 L) of fresh surface- and ground-waters of low Ra-activities (<5 mBq/L). Ra is quantitatively adsorbed on a small amount (6.5 g) of MnO2-coated acrylic fibers, which are then dried and burned at 600 °C in the laboratory. The resulting Mn-oxide powder (about 2 cm3 when compacted) is then analyzed through gamma-ray spectrometry which allows measurement of the whole Ra quartet (226Ra, 228Ra, 224Ra and 223Ra) in a single counting of a few days. The usual relative standard combined uncertainties (1σ) are 2–3% for 226Ra, 228Ra and 224Ra; and less than 10% for 223Ra. 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 low 226Ra activities (1–4 mBq/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 and 223Ra) appear to be mainly influenced by near-surface desorption/recoil processes for most of the sampling sites.
ISSN: 0969-8043

hal-01491281
https://hal.archives-ouvertes.fr/hal-01491281
DOI : 10.1016/j.apradiso.2016.12.010

Éditeur(s) : HAL CCSD Springer
Résumé : The analysis of gamma ray measurements provides valuable information about the basement's lithospherical model and the radioactive elements contained in the subsurface. To be exploited, the raw data need pre-processing operations which consist of corrections of the Compton effect, altimetry and the aircraft background, and 2D interpolations. These transformations may modify the data's stochastic component which reflects heterogeneities of the investigated medium. In this study, a fractal analysis is carried out on airborne gamma ray data measured in the Hoggar's area (Algeria). First, it is shown that the analyzed data exhibit fractal properties. Due to the dependence of the latter on the spatial location of the measures, the data can be considered as paths of multifractional Brownian motions. Another result worth noting is that the fractal nature of the raw data is not modified by the pre-processing operations. The fractal analysis can be then performed on the raw spectrometric measurements without submitting them to any pre-processing; thus, the stochastic component of the measurements is kept intact.
ISSN: 1866-7411

hal-00817494
https://hal.archives-ouvertes.fr/hal-00817494
DOI : 10.1007/s12517-011-0407-3

Éditeur(s) : HAL CCSD Elsevier
Résumé : Our method for the simultaneous determination of the four natural Ra isotopes (Ra-226, Ra-228, Ra-224 and Ra-223) in thermal waters involves a separation of Ra on a selective filter (3 M EMPORE (TM) Radium Rad disk), and a single counting using a broad-energy HPGe detector (BE Ge manufactured by CANBERRA (TM)). The calculation of Ra-223 and (228)a activities requires interference and cascade summing corrections. The Ra-226 activities in CO2-rich thermal waters of the Lodeve Basin (South of France) range from 530 to 2240 mBq/l. The low (Ra-228/Ra-226) activity ratios (0.19-0.29) suggest that Ra is mostly derived from the aquifer carbonates. The short-lived Ra-224 and Ra-223 are probably added to the water through recoil or desorption processes from Th-enriched coatings on the fracture walls.
ISSN: 0969-8043

hal-00475587
https://hal.archives-ouvertes.fr/hal-00475587
DOI : 10.1016/j.apradiso.2009.10.056