Radiological and hyperfine characterization of soils Radiological and hyperfine characterization of soils of Buenos Aires, Argentina

摘要

The activity concentrations of both natural ((238)~U and (232)~Th chains and (40)~K) and anthropogenic ((1370~Cs) 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 (57)~Fe Mossbauer spectroscopy characterization, p~H, texture and organic carbon content measurements. From Mossbauer 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 α-Fe_2O_3 contribution is lower, Fe_3O_4 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 (40)~K (540–750 B_q/kg),followed by (238)~U (60–92 B_q/kg) and (232)~Th (37–46 Bq/kg) chains. The activity of (235)~U was in all the cases lower than the detection limit (L_D = 0.02 B_q/kg). The only determined anthropogenic nuclide was (137)~Cs, 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 Mossbauer relative fractions was found, whereas no correlation was found between the (137)~Cs profile and the relative fraction of Fe_3O_4 or with other iron species.