Rn-222 Determination in Drinking Water Samples in a Region with Elevated Natural Radioactivity in Brazil: Comparison Between Liquid Scintillation Counting and Gamma Spectrometry

Radon is a naturally occurring noble gas. It can easily diffuse into the environment. It is found in waters which are in contact with rocks having high uranium concentration (Desideri et al., 2005). Radon gas is considered to be one of the natural radioactive elements with greatest mobility in the terrestrial crust. Conventional chemical analysis of water does not place emphasis on the study of dissolved gases; however, their determination is important, due to their reactivity and their mobility (Alfaro et al., 2002). There are three Radon isotopes, but only 222Rn is generally taken into consideration because it has a sufficiently long half-life (T1/2 = 3.82 days) and can accumulate in the environment. The origin of 222Rn in houses is either from uranium rich soil or through the use of building materials rich in 226Ra such as tailings from uranium mining, or due to well water. Naturally Occurring Radioactive Materials (NORM) areas are located in Brazil in zones of volcanic alkaline intrusion in the interior of Minas Gerais State (Sohrabi, 1998). These areas are characterized by elevated natural radioactivity. In the case of Radon, its presence can provide information concerning the radioactive elements present in a rock, the origin of water and flow Abstract 222Rn concentrations were determined in twenty one drinking water samples from the Poços de Caldas region. Samples were taken from wells that provide potable water and brought immediately to the Radiochemistry Laboratory. Two different systems were employed to determine 222Rn, a Packard TRI-CARB 2700TR Liquid Scintillation Detection System (LSC) and a Canberra Gamma Spectrometer with Germanium Detector Model GX4519 with a relative efficiency of 45 %. A Marinelli Flask was used for the Gamma Spectrometry analysis. 222Rn concentration range varied from 1.5 ± 0.5 BqL-1 to 234 ± 20.00 BqL-1 in the LSC method and from 9 ± 3 BqL-1 to 208 ± 22 BqL-1 in the Gamma Spectrometry method. Considering that the maximum concentration found was lower than 250 BqL-1, a maximum personal dose of 0.75 mSv.year-1 can be calculated based on epidemiological studies showing that a daily ingestion of one liter of water containing 100 BqL-1 should give a dose of only 0.3 mSv.year-1. This study concluded that the concentration values obtained for drinking water samples collected in the Poços de Caldas region are not dangerous for the local population. The risk associated with ingesting water containing a low radon concentration is negligible as reported in other studies.