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AbstractAbstract
[en] For the optimization of the operational conditions of a multichannel analyser gamma spectrometer, with two 3'' x 3'' NaI (Tl) crystals in opposition, several parameters were studied, which are responsable for the best counting efficiency, in each type of sample to be analysed. Thus, electronic conditions, shielding, sample holding, resolution, geometry (or the sample positioning between the detectors), were investigated. Self-absorption, sample density and the effects of the shape of the containers were also tested. For solid samples, (usually ashed), the best container was found to be a plastic cylinder, with the sample pressed inside. For liquid samples, plastic cylindric flasks were also found to be the best ones. Environmental samples were measured with internal standards for 137Cs and 40K. Results were compared with those obtained by physical (atomic adsorption for K) and radiochemical methods (Cs precipitation by amonium phosphomolibdate). Results show good agreement with the spectrometric analysis. For comparison with environmental samples, standards were prepared, in such a way that they could simulated their physical caracteristics. The minimum detectable activity was determined for 137Cs. Results show values of 0.01 pCi/g for the 1 Kg samples, and 0.004 pCi/g for the 300g ones. By the measurement of 40K, we found this value to be 0.02 mgK/g, in both cases. (author)
[pt]
Na otimizacao das condicoes operacionais de um espectrometro gama multicanal, com dois cristais de NaI(Tl), de 3'' x 3'', em oposicao, foram estudados parametros que fornecessem a melhor eficiencia de contagem para cada tipo de amostra a ser analisada, tais como condicoes eletronicas, blindagem, suporte para amostra, resolucao, geometria ou posicionamento da amostra entre os cristais detectores, auto-absorcao, efeito da densidade, tipos de frascos. Foram escolhidos, para amostras solidas, geralmente sob a forma de cinzas, por recipientes plasticos, cilindricos, onde a amostra e prensada, e frascos cilindricos para amostras liquidas, podendo os cristais detectores ocupar posicao vertical ou horizontal em relacao a amostra. Foram efetuadas medidas em amostras ambientais, usando-se padronizacao interna, para 137Cs e 40K, assim como comparacao com metodos fisicos, (absorcao atomica para K) e radioquimicos (precipitacao de Cs por fosfomolibdato de amonio), cujos resultados apresentaram uma boa concordancia. Visando uma comparacao com diversas amostras ambientais, foram elaborados padroes que simulassem as caracteristicas fisicas das mesmas. Os limites de sensibilidade determinados para o 137Cs,foram de 0,01 pCi/g para amostras de 1 kg, e de 0,004 pCi/g para amostras de 300 g, e de 0,02 mgK/g, pela determinacao de 40K em ambos os casos. (autor)Original Title
Otimizacao das condicoes operacionais de um espectrometrogama multicanal
Source
1974; 47 p; Tese (M.Sc.).
Record Type
Miscellaneous
Literature Type
Thesis/Dissertation
Report Number
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BETA DECAY RADIOISOTOPES, BETA-MINUS DECAY RADIOISOTOPES, BETA-PLUS DECAY RADIOISOTOPES, CESIUM ISOTOPES, ELECTRON CAPTURE RADIOISOTOPES, INTERMEDIATE MASS NUCLEI, ISOMERIC TRANSITION ISOTOPES, ISOTOPES, LIGHT NUCLEI, MEASURING INSTRUMENTS, NUCLEI, ODD-EVEN NUCLEI, ODD-ODD NUCLEI, POTASSIUM ISOTOPES, RADIOISOTOPES, SPECTROMETERS, YEARS LIVING RADIOISOTOPES
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