Integrated management of the radioactivity in waters from Guarani aquifer

• Grant number: 05/03773-4
• Support Opportunities: Regular Research Grants
• Duration: February 01, 2006 - January 31, 2008
• Field of knowledge: Physical Sciences and Mathematics - Geosciences
• Principal Investigator: Daniel Marcos Bonotto
• Grantee: Daniel Marcos Bonotto
• Host Institution: Instituto de Geociências e Ciências Exatas (IGCE). Universidade Estadual Paulista (UNESP). Campus de Rio Claro. Rio Claro , SP, Brazil

Abstract

The enhancement of radionuclides in hydrological resources due to technological processes (for instance, mining/processing of minerals containing radioelements, phosphate fertilizers), nuclear tests, discharge of effluents in nuclear power plants, armed conflict utilizing nuclear weapons, or handling of manufactured radioactive sources caused the World Health Organization to establish in its present legislation (WHO, 2004) a great list of radionuclides whose activity concentration for ingestion in waters is subjected to evaluation and comparison with guidance values. The naturally occurring radionuclides are less frequent than the man-made ones, and comprise the H-3, C-14, and those belonging to the decay series of U-238 (i.e. U-238, U-234, Th-230, Th-234, Ra-226, Rn-222, Pb-210, Po-210, Bi-210), U-235 (i.e. U-235, Th-227, Th-231, Pa-231, Ra-223) and Th-232 (i.e. Th-232, Th-228, Ra-228, Ra-224); the K-40 presence in waters was considered during the evaluation of the gross-beta radioactivity. The gross alpha and beta measurements performed in dry residue of the samples are important parameters involving the water quality in terms of radiological aspects. The calibration procedure is critical, as analytical errors of up to 100% have been reported during the evaluation of the gross alpha activity, depending on the standard utilized. Additionally, another problem related to the absorption process also occurs due to the fact that the measurements are made in the dry residue, i.e. samples possessing higher dry residue tend to absorb the emitted radiation before its interaction with the detector. This is a process that causes reduction on the counting efficiency of the sample, as the results are "artificially” lowered. The results of previous studies focused the presence of U-238, U-234, Ra-226, Ra-228, Rn-222, Pb-214 and Bi-214 in groundwaters from Guarani aquifer, under different aspects... (AU)