Approximate total Fe content determined by Mössbauer spectrometry: Application to determine the correlation between gamma-ray-emitter activities and total content of Fe phases in soils of the Province of Buenos Aires, Argentina.

Pearson correlation coefficients between 40K, 226Ra and 232Th activities and the total Fe phase fractions yielded by Mössbauer spectroscopy have been calculated for soils of the Province of Buenos Aires, Argentina. Total fractions of Fe phases have been obtained from the relative fractions reported in previous works weighted by the Fe soil content and the recoilless-fraction of each Fe phase. An approximate method based on the relationship between the Mössbauer spectral absorption area (obtained from the 57Fe Mössbauer data) and the total Fe concentration (determined by colorimetric methods, after microwave assisted acid digestion of soil samples) has been used for the first time to determine the Fe concentration in soils with an accuracy of 15%. Protocol to extend the method for unknown samples is also discussed. The determined new coefficients differ from those reported previously. A significant and positive correlation between the total fraction of Fe2+ and the 40K activity values has been obtained. This result validates the hypothesis put forward in a previous work, i.e., that illite captures the 40K existing in the soil. In addition, with the new approximation, the Pearson correlation coefficients for the other natural radionuclides give values that indicate that the methodology reported here is appropriate to study the correlations between the activity values with the total fractions of Fe phases.

Assessment of natural radioactivity levels and their relationship with soil characteristics in undisturbed soils of the northeast of Buenos Aires province, Argentina.

Surface and depth profile concentrations (down to 50 cm) of ²³²Th chain, ²²6Ra, and 4°K radionuclides were determined in undisturbed coastal and inland soils of La Plata city region, Argentina, through their gamma-ray activity using a high-purity Ge detector spectrometer. These results were compared with superficial activities determined in soils from the surroundings of the Centro Atómico Ezeiza (Ezeiza Atomic Center) located in Ezeiza, Buenos Aires Province, Argentina. The hyperfine and magnetic Fe phase's properties of soil profiles were characterized by Mössbauer spectroscopy, magnetic hysteresis loops and AC magnetic susceptibility. No dependence of the activity of the ²³²Th natural chain on depth was found, whereas variations for ²²6Ra and 4°K activities were observed. Positive correlations, determined by the Pearson correlation coefficients, were established between 4°K, ²²6Ra and ²³²Th activity concentrations for the whole set of soil samples. The annual external equivalent dose for adults was similar for La Plata and Ezeiza regions, with average values of 0.08 ± 0.01 mSv and 0.06 ± 0.02 mSv, respectively. The thermal dependence of the AC magnetic susceptibility revealed the existence of magnetite and hematite. The Mössbauer spectra of all soils were made up of signals associated with α-Fe2O3, a paramagnetic relaxation component, and Fe³âº and Fe²âº doublets. In addition, the spectra of inland soils revealed the presence of Fe3O4. A negative correlation was found between the activity concentrations and the α-Fe2O3 and Fe3O4 relative fractions, whereas a positive correlation was found between the Fe³âº relative fraction and the 4°K activity.

Vibrational and 57Fe-Mössbauer spectra of FeTbGe2O7.

The infrared, Raman and 57Fe-Mössbauer spectra of FeTbGe2O7 were recorded and analyzed on the basis of its crystallographic data. For comparative purposes, similar measurements were also performed with FeYGe2O7 and with other isostructural compounds containing different lanthanide cations.