Radiological and hyperfine characterization of soils from the Northeastern region of the Province of Buenos Aires, Argentina

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 Fe^3+? paramagnetic signal. For soil samples from the coastal area, the ??-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 Fe^3+? paramagnetic fraction increases up to 82%, mainly at the expense of the magnetically ordered phase. The main observed activity originates from the decay of ⁴⁰K (540?C750 Bq/kg), followed by ²³⁸U (60?C92 Bq/kg) and ²³²Th (37?C46 Bq/kg) chains. The activity of ²³⁵U was in all the cases lower than the detection limit (L_D?=?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.