Radiological and Hyperfine Characterization of soils from the Northeastern region of the Province of Buenos Aires, Argentina.

M. L. MONTES; R. C. MERCADER; M. A. TAYLOR; J. RUNCO; P. IMBELLONE; P. C. RIVAS; J. DESIMONI

HYPERFINE INTERACTIONS

Springer

Año: 2010

0304-3843

The activity concentrations of both natural (238U and 232Th chains and 40K) and anthropogenic (137Cs) radionuclides down along the soil profile have been determined in soil samples collected from inland and coastal areas of the La Plata River, located in the Northeastern region of the Province of Buenos Aires, Argentina. These studies were complemented with 57Fe Mössbauer spectroscopy characterization, pH, texture and organic carbon content measurements. From Mössbauer results, the sample compositions differ from one area to the other. Spectra from both soil samples are dominated by the Fe3+ paramagnetic signal. For soil samples from the coastal area, the a-Fe2O3 contribution is lower, Fe3O4 was not detected, and the relative areas of each spectral contribution are nearly constant with depth. For samples from the inland area, the Fe3+ paramagnetic fraction increases up to 82%, mainly at the expense of the a-Fe2O3, also Fe3+, but magnetically ordered. The main observed activity originates from the decay of 40K (540 Bq/kg -750 Bq/kg), followed by 238U (60 Bq/kg – 92 Bq/kg) and 232Th (37 Bq/kg - 46 Bq/kg) chains. The activity of 235U was in all the cases lower than the detection limit (LD= 0.02 Bq/kg). The only determined anthropogenic nuclide was 137Cs, arising from the fallout of the Southern Hemisphere nuclear weapon tests. Three of the observed differences in the depth distributions can be described by the dispersion-convection model. A correlation between the natural nuclide activities and the Mössbauer relative fractions was found, whereas no correlation was found between the 137Cs profile and the relative fraction of Fe3O4 or with other iron species