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

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

JOURNAL OF ENVIRONMENTAL RADIOACTIVITY

ELSEVIER SCI LTD

Lugar: New York; Año: 2012 vol. 105 p. 30 - 39

0265-931X

Surface and depth profile (down to 50 cm) concentrations of 232Th chain, 226Ra, and 40K nuclides 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 are compared with superficial activities determined in soils on the nearest of an Atomic Center, located in Ezeiza region, Argentina. The hyperfine and magnetic properties of Fe phases of soil profiles were characterized by Mössbauer spectroscopy, magnetic hysteresis loops and AC magnetic susceptibility, respectively. For all the samples, the activity of the 235U chain was lower than the detection limit. No dependence of the activity of the 232Th natural chain on depth was observed, whereas variations for 226Ra and 40K activities were determined. The higher activities values were established in the coastal soils. In the Ezeiza zone, the surface activities are in the order of those determined for La Plata region. Positive correlations, determined by the Pearson correlation coefficients, were established between 40K, 226Ra and 232Th activity concentrations of the whole set of soils. The annual external equivalent dose for adults, estimated from the soil activities data, was similar for La Plata and Ezeiza regions, with average values of 0.103 ± 0.005 mSv and 0.08±0.02 mSv, respectively. The magnetic measurements disclose the existence of magnetite and hematite because of the Verwey and Morin transitions, respectively, exhibited in the shape of the thermal dependence of the AC magnetic susceptibility. The Mössbauer spectra of all soils were made up of a sextet associated with -Fe2O3, a paramagnetic relaxation component, and Fe+3 and Fe+2 doublets. The spectra of inland soils reveal the presence of a second sextet, associated to Fe3O4. A negative correlation was found between the activity concentrations and the -Fe2O3 and Fe3O4 relative fractions, whereas a positive correlation was found between the Fe3+ relative fraction and the 40K activity.