Gross alpha- and beta-activities in surface and ground water of Rio Grande do Norte, Brazil

Gross α- and β-activities were determined on 37 fresh water samples collected from 14 artificial basins, 13 deep drilled wells, two dug wells, two lakes, two rivers, one spring, and a tap belonging to 30 locations scattered throughout the eastern and central parts of the Brazilian state of Rio Grande do Norte. The surveyed area was about 35 000 km2 with a lithology including both crystalline (18 towns) and sedimentary (12 towns) rocks. Concentrations ranging from <2.8 to 354 Bq m−3 and from 50.5 to 580 Bq m−3 were observed for the gross α- and β-activities, respectively. For the gross β-activity, which was always higher than the corresponding α-activity, the arithmetic mean with its standard deviation was 226 ± 154 Bq m−3. In order to evaluate the radioactive dose due to the ingestion of these waters, a conservative dosimetric calculation was carried out using the dose conversation factors suggested by the ICRP. An average annual effective dose equivalent of 60 ± 42 μSv was obtained together with a range of 14–161 μSv y−1.