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  • Author or Editor: Fernando Oliveira x
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Abstract  

The accuracy of alpha spectrometry in the determination of uranium isotopes at various concentrations levels and with various isotope ratios was tested in a round robin international intercomparison exercise. Results of isotope activity/mass and isotope mass ratios obtained by alpha spectrometry were accurate in a wide range of uranium masses and in isotopic ratios typical of depleted, natural, and low enriched uranium samples. Determinations by alpha spectrometry compared very satisfactorily in accuracy with those by mass spectrometry. For example, determination of U isotopes in natural uranium by alpha spectrometry agreed with mass spectrometry determinations at within ±1%. However, the 236U isotope, particularly if present in activities much lower than 235U, might not be determined accurately due to overlap in the alpha particle energies of these two uranium isotopes.

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Abstract  

Analyses of soils, irrigation waters, agriculture products (lettuce), green pasture, and cheese were performed in samples collected in the area of the old Urgeiriça uranium mine and milling facilities, Centre-North of Portugal, in order to assess the transfer of uranium series radionuclides in the environment and to man. Soils close to milling tailings display an enhancement of radioactivity. In the drainage basin of the stream Ribeira da Pantanha, receiving drainage from the tailings piles and discharges from the acid mine water treatment plant, there was enhancement of uranium series radionuclide concentrations in water and suspended matter. Agriculture products from kitchen gardens irrigated with water from the Ribeira da Pantanha show an increase of radioactivity, mainly due to uranium isotopes. Agriculture products from other kitchen gardens in this area, irrigated with groundwater, as well pasture and cheese produced locally from sheep milk did not show enhanced radionuclide concentrations. In the Urgeiriça area, some soils display radionuclide concentrations higher than soils in reference areas and, in agriculture products grown there, 226Ra was the radionuclide more concentrated by vegetables. Through ingestion of these products 226Ra may be the main contributor to the increment of radiation dose received by local population.

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Abstract  

Cellulose was chemically modified with SOCl2 to obtain chlorodeoxycellulose, followed by a reaction that gave bonded ethylene-1,2-diamine (en), producing 6-(2′-aminoethylamino)-6-deoxycellulose. The reactions were carried out without the presence of solvent, in water or in N,N′-dimethylformamide, in which the highest amount of amino compound was incorporated onto the biopolymer backbone. The X-ray diffraction patterns for the chlorodeoxycellulose indicate new crystallinities that result from hydrogen bonds established through bonded chorine atoms and the remaining hydroxyl groups, while all the aminodeoxycelluloses were amorphous compounds. Thermal stabilities, for all aminated celluloses gave lower final mass losses than for the chlorinated biopolymer, whose value is lower than unmodified cellulose.

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