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AbstractAbstract
[en] Samples of brazilian calcite, exposed to gamma radiation in laboratory and heated at constant rate of 2.70 C/s, showed three glow peaks at 150, 250 and 350 0C in their thermoluminescent emission curves. The analysis of these peaks, using different models, indicated that they follow a second order kinetics; it has been obtained, for the activation energy, 1.3, 1.5 and 1.7 eV, and, for the pre-exponential factors, 8.1 x 10 14, 6.8 x10 13 and 2.4 x 1012 s-1. Although the total thermoluminescent emission has stayed constant, the relative height of glow peaks has changed with the temperature of annealing in the range of 400 to 700 0C. Exposed samples were also illuminated with ultraviolet light and the resultant curves showed partial or total bleaching or some glow peaks and the growth of peaks at lower temperatures. Samples of virgin calcite, submited to increasing exposures of gamma rays, showed a corresponding enhancement of the optical absorption bands in the range of 25000 to 47000 cm-1 A subsequent illumination of these samples with ultraviolet light produced a decrease of the optical absorption bands at the same range. (author)
[pt]
A cruva de emissao termoluminescente da calcita brasileira exposta a radiacao gama em laboratorio, e aquecida a partir da temperatura ambiente com uma taxa linear de 2,70C/s, apresentou tres picos as temperaturas de 150, 250 e 3500C. Uma analise desses picos utilizando diferentes modelos mostrou que eles obedecem a uma cinetica de segunda ordem e os valores obtidos para as energias de ativacao foram 1,3; 1,5; 1,7 eV e para os fatores pre-exponenciais 8,1x1014s-1, 6,8x1013 s-1, 2,4x1012 s-1. A altura relativa desses picos mudou com a temperatura de tratamento termico no intervalo de 400 a 7000C, porem a emissao termoluminescente total permaneceu constante. Foi verificado que a radiacao ultravioleta tanto preenche quanto esvazia armadilhas com taxas que dependem do grau de preenchimento de cada pico. Medidas de absorcao optica de amostras de calcita virgem irradiadas com radiacao gama com exposicoes crescentes apresentaram um correspondente crrescimento da abosrbancia nas bandas localizadas no intervalo entre 25000 e 47000 cm-1. Uma posterior iluminacao com radiacao ultravioleta produziu sobre essas mesmas bandas uma diminuicao que se acentua com a exposicao. (autor)Original Title
Termoluminescencia da calcita induzida por radiacao gama e ultravioleta
Source
1987; 108 p; Tese (M.Sc.).
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Miscellaneous
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Thesis/Dissertation
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