Determination of the activity concentration of 226Ra, 232Th, 40K and the concentration of 222Rn in soil samples of the Campos Gerais region (Paraná)

Abstract

In the Campos Gerais region of Paraná there are few literature that evaluate the concentrations of natural radioactivity. Thus, the aim of the present work was to determine activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and ²²²Rn concentration in soil samples from Telêmaco Borba, Tibagi, Curiúva, Ventania, Lageado Bonito and Ortigueira. The soil samples, with about 2 kg, were collected on the surface at points near the river bed, making sure that the soil is not under the agriculture influence. Gamma-ray spectrometry analyzes were performed with a NaI(Tl) scintillation detector, with dimensions of 76 mm in diameter, 152 mm in height and 8 cm of lead shield. The ²²²Rn concentration determinations were performed by means of the sealed can technique, using as track detector a polycarbonate of domestic manufacture. The results obtained for the activity concentration varied from <4.2 ± 1.2 Bq.kg^-1 to 290.2 ± 1.7 Bq.kg^-1 for the ⁴⁰K, of 23.3 ± 1.1 Bq. kg^-1 to 36.5 ± 1.1 Bq.kg^-1 for the ²²⁶Ra and from 52.6 ± 1.9 Bq.kg^-1 to 70.5 ± 2 Bq.kg^-1 for the ²³²Th. The results for the ²²²Rn concentration ranged from 4 ± 3 Bq.m^-3 to 1147 ± 326 Bq.m^-3. Two of the six soil samples presented radon concentrations above the threshold established by the European Commission for Radiological Protection of 200 Bq.m^-3, for internal environments. The concentrations of ²²⁶Ra and ²³²Th are within the limits, showing the importance of future investigating the origin of this radon.