Determinação da composição isotópica de estrôncio em águas naturais: exemplos de sua aplicação em águas subsuperficiais da zona costeira na região Bragantina-PA/ Determination of strontium isotopic composition in natural waters: examples of application in subsurface waters of the coastal zone of Bragantina region, Pará
Resumo em inglês Analytical procedures used for determining the concentrations and isotope composition of strontium in subsurface waters, by mass spectrometry, are described. Sampling was performed in coastal plateaus, salt marsh and mangrove environments in the coastal region of Pará. Coastal plateau waters have delta87Sr between 1.51 and 6.26 and Sr concentration bellow 58 ppb. Salt marsh waters show delta87Sr between 0.55 and 0.90 and Sr concentration between 93 and 114 ppm, while (mais) mangrove waters have delta87Sr around zero and Sr concentration above 15 ppm. Differences in the 87Sr/86Sr ratio in these subsurface waters are detected, as well as seasonal variations in the coastal pleteau waters.
Síntese e caracterização estrutural do niobato de potássio e estrôncio com estrutura tipo Tetragonal Tungstênio Bronze TTB/ Synthesis and structural characterization of strontium potassium niobate oxide with tetragonal tungstenium bronze TTB type structure
Resumo em português A fase nanoestruturada KSr2Nb5O15, foi sintetizada pelo método de mistura mecânica de óxidos por moagem de alta eficiência e por via química, utilizando o método dos precursores poliméricos, em forno tipo tubo sob atmosfera de O2 durante 10 h. A análise por difração de raios X dos pós calcinados a 1150 ºC foi realizada pelo método de Rietveld utilizando-se o software FullProf. A análise dos parâmetros estruturais obtidos via método de Rietveld mostrou um s (mais) istema tetragonal com estrutura tipo tetragonal tungstênio bronze. A partir das reflexões observadas, há apenas evidência da regra [(0kl) k = 2n], a qual é compatível com o grupo espacial centrossimétrico P4bm, o qual foi utilizado para o refinamento. O volume da célula unitária obtido na análise dos pós de KSr2Nb5O15 obtidos por síntese química e por moagem de alta eficiência foi 611,90 Å³ e 611,95 Å³, respectivamente. Resumo em inglês The nanostructured KSr2Nb5O15 phase was synthesized by both routes, the high efficiency milling and the polymeric precursor, in a furnace under O2 atmosphere during 10 h. The Rietveld X-ray diffraction analysis of the calcined powders at 1150 ºC was performed using the FullProf software. The XRD pattern analysis showed a tetragonal system with the tetragonal tungsten bronze structure. From the observed reflections, there is only evidence of the rule existence [(0kl) k = (mais) 2n], which is compatible with the centrosymmetric space group P4bm, which was used for the refinement. The unit cell volume obtained for the KSr2Nb5O15 powders prepared by chemical synthesis and by high efficiency milling were equal to 611,90 Å³ and 611,95 Å³, respectively.
Resumo em inglês Several hundreds of artificial radionuclides are produced as the result of human activities, such as the applications of nuclear reactors and particle accelerators, testing of nuclear weapons and nuclear accidents. Many of these radionuclides are short-lived and decay quickly after their production, but some of them are longer-lived and are released into the environment. From the radiological point of view the most important radionuclides are cesium-137, strontium-90 and (mais) plutonium-239, due to their chemical and nuclear characteristics. The two first radioisotopes present long half life (30 and 28 years), high fission yields and chemical behaviour similar to potassium and calcium, respectively. No stable element exists for plutonium-239, that presents high radiotoxicity, long half-life (24000 years) and some marine organisms accumulate plutonium at high levels. The radionuclides introduced into marine environment undergo various physical, chemical and biological processes taking place in the sea. These processes may be due to physical dispersion or complicated chemical and biological interactions of the radionuclides with inorganic and organic suspend matter, variety of living organisms, bottom sediments, etc. The behaviour of radionuclides in the sea depends primarily on their chemical properties, but it may also be influenced by properties of interacting matrices and other environmental factors. The major route of radiation exposure of man to artificial radionuclides occuring in the marine environment is through ingestion of radiologically contamined marine organisms. This paper summarizes the main sources of contamination in the marine environment and presents an overview covering the oceanic distribution of anthropogenic radionuclides in the FAO regions. A great number of measurements of artificial radionuclides have been carried out on various marine environmental samples in different oceans over the world, being cesium-137 the most widely measured radionuclide. Radionuclide concentrations vary from region to region, according to the specific sources of contamination. In some regions, such as the Irish Sea, the Baltic Sea and the Black Sea, the concentrations depend on the inputs due to discharges from reprocessing facilities and from Chernobyl accident. In Brazil, the artificial radioactivity is low and corresponds to typical deposition values due to fallout for the Southern Hemisphere.