Assessment of the vertical distribution of natural radionuclides in a mineralized uranium area in south-west Spain

摘要

Low-level alpha spectrometry techniques using semiconductor detectors (PIPS) and liquid scintillation (LKB Quantulus 1220™) were used to determine the activity concentration of ~(238)U, ~(234)U, ~(230)Th, ~(226)Ra, ~(232)Th, and ~(210)Pb in soil samples. The soils were collected from an old disused uranium mine located in southwest Spain. The soils were sampled from areas with different levels of influence from the installation and hence had different levels of contamination. The vertical profiles of the soils (down to 40 cm depth) were studied in order to evaluate the vertical distribution of the natural radionuclides. To determine the origin of these natural radionuclides the Enrichment Factor was used. Also, study of the activity ratios between radionuclides belonging to the same radioactive series allowed us to assess the different types of behaviors of the radionuclides involved. The vertical profiles for the radionuclide members of the ~(238)U series were different at each sampling point, depending on the level of influence of the installation. However, the profiles of each point were similar for the long-lived radionuclides of the ~(238)U series (~(238)U, ~(234)U, ~(230)Th, and ~(226)Ra). Moreover, a major imbalance was observed between ~(210)Pb and ~(226)Ra in the surface layer, due to ~(222)Rn exhalation and the subsequent surface deposition of ~(210)Pb.