SÃntese e caracterizaÃÃo da alumina para dosimetria termoluminescente

AUTOR(ES)

VinÃcius Saito Monteiro de Barros

DATA DE PUBLICAÇÃO

2008

RESUMO

Carbon-doped aluminum oxide (J-Al2O3:C) is an important material for the dosimetry of ionizing radiation using a thermoluminescent readout. This material presents a sensibility to radiation that is 50 times more sensitive than LiF:Mg,Ti. However, its fabrication usually employs crystal growing methods and high temperature laboratory infra-structure and highly reducing atmospheres. Therefore, the aim of this work is to study and characterize two alternative routes to the synthesis of J-Al2O3:C: the Electrochemical and Combustion methods. In the Electrochemical method, samples were obtained by oxidation of an aluminum sheet (99,99%), in oxalic acid, with a constant voltage applied. In the Combustion method, samples were fabricated by mixing adequate amounts of aluminum nitrate, urea and a dopant material (Mg, Si, Eu, Eu-Mg, Eu-Si, Tb, Tb-Mg). The reactants were heated to 500 ÂC until the reaction occurred, and then the samples were annealed at temperatures between 600 and 1500 ÂC. For the Electrochemical method, results showed a linear relationship between the TL intensity and absorbed dose in air for Co-60 gamma radiation, between 0,5 and 4,5 Gy. The fabrication parameters that resulted in the highest TL sensitivity were: 0,10 M oxalic acid concentration, 130 V applied voltage and 300 min anodization time. Scanning Electronic Microscopy (SEM) showed that the pellets produced with these parameters had pores with 40 to 80 nm in diameter and that the pores corresponded to 10% of the surface area of the samples. For the Combustion method, samples presented a linear TL relationship with absorbed dose in air for Co-60 gamma radiation, between 0,5 and 5 Gy. The highest TL sensitivities were found for the Tb and Tb-Mg doped samples, annealed at 1500 ÂC for 4 h. These samples presented a characteristic TL emission curves with two peaks, at 190 and 350 ÂC. From the results, it was possible to conclude that the Combustion synthesis route produced more sensitive samples than the anodization method. The materials obtained from these methods open new perspectives in the development of dosimeters for thermoluminescent dosimetry applications

ASSUNTO(S)

Ãxido de alumÃnio thermoluminescent dosimetry combustion synthesis sÃntese por combustÃo aluminum oxide engenharia nuclear dosimetria termoluminescente eletroquÃmica electrochemistry

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