Natural and anthropogenic gamma-ray emitters and iron-bearing compounds distribution in peatlands of the southern Espinhaço mountain chain, Brazil

• Autores: Montes, María Luciana; Mercader, Roberto Carlos; Morais Barral, Uidemar; Silva, A. C.; Fabris, José Domingos; Taylor, Marcela Andrea
• Año de publicación: 2019
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Física; Ingeniería; Peatlands; Radioactivity; Fe; Profiles
• Institución: Universidad Nacional de La Plata

To help understand the dynamics of peatlands forming on the Southern Serra do Espinhaco, Brazil, the occurring natural (²²⁶Ra, ²³²Th, ⁴⁰K) and anthropogenic (¹³⁷Cs) activity of gamma-ray emitters located at three sites, namely the localities of Sao Joao da Chapada (CH), Pinheiro (PIN) and Pau de Fruta (PDF), was studied. The iron compounds were characterized by ⁵⁷Fe Mossbauer spectroscopy. Differences on natural radionuclide levels and distributions were found among the peatland sites, indicating differences on mineral composition, hydric regimes and living. Significant correlation was found only for ²³²Th–²²⁶Ra activity values (Pearson correlation coefficient of − 0.5), which is different from other South American soils, where significant positive correlations among all radionuclides were determined. In PDF and CH, the dose rate results are lower than the worldwide mean value, but in PIN, they are higher because of the relatively high ²²⁶Ra concentration. The only anthropogenic radionuclide is ¹³⁷Cs. The convection–diffusion model fits the CH and PDF activity profiles, although the PIN profile is likely affected by other soil mechanisms as well. Mossbauer spectra reveal Fe³⁺ in two different local environments and the occurrence of hematite in the upper samples of the CH site. The iron concentration decreases with depth. Contrary to soils of other regions, no significant correlation was found between iron species and the natural radioactivity. The studied peatlands exhibit clear differences between their natural and anthropogenic radionuclide distributions to those of mineral soils.
Instituto de Física La Plata
Facultad de Ingeniería