Abstract
The aim of this study is to evaluate the soil composition, the radioactive isotopes concentration and the outdoor air Kerma in the region of the Uraniferous Province of Lagoa Real, Bahia State, located at northeast of Brazil. It has used data from an airborne gamma-ray survey previously carried out in the region, namely Projeto Sao Timoteo and computer simulations of the soil and radiation transport by the Monte Carlo method. The simulation, considering environmental characteristics, mainly soil chemical composition and density, provide means to evaluate the air Kerma rate due to radionuclides present in the different types of soils. The evaluation was carried out considering the main contributors to the terrestrial natural radioactivity: 40K and the isotopes of the radioactive series of 238U and 232Th. In radiometric studies used to quantify exposure to natural radioactivity, a normal trend showed that regions with high values of the surface distribution of radionuclides had the highest values of air Kerma. The highest value was found for soil type LVe1 (146.40 nGy.h-1 average, ranging from 23.97 nGy.h-1 to 450.62 nGy.h-1), this type of soil and most of the anomalies located in this region, being rich in silica minerals, is of granitic rocks type.
Highlights
In radiometric studies used to quantify exposure to natural radioactivity, a normal trend showed that regions with high values of the surface distribution of radionuclides had the highest values of air Kerma
The results for the air Kerma rates for each type of soil due to 40K is shown in Table 4 and 5 shows the contribution of each radionuclide from the 238U series; Table 6 shows the contribution of each radionuclide from the 232Th series and Table 7 shows the total outdoor air Kerma rate in the Uraniferous Province of Lagoa Real
The dispersion between the minimum and maximum of air Kerma rate due to 40K and the soil types are shown on Table 4 which are typical for radiometric measurements in areas with radioactive anomalies, because of the differences between the values mapped on the anomalies and the surrounding areas
Summary
There are, in this area, thirty three uraniferous anomalies which were identified during an airborne gamma-ray survey, as part of a project called Projeto São Timóteo held in 1979. The average absorbed dose in air was 61.08 nGy.h−1, whereas the highest values are related to the central region of the map. The soils surrounding the province are derived from geologies impoverished in silica, which is composed of basic rocks and ultra-basic and, present depleted levels of K, U and Th
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