Application of the activation analysis using the method of retarded fission neutrons counting for the determination of some fissionable nuclides
Description
A system for the detection and counting of delayed neutrons which allows the analysis of some fissile and fertile nuclides, in samples of milligram size, was developed. This was applied for the analysis of natural uranium and thorium and also for determining the 235U/238U ratio in non-irradiated samples which contain uranium with different degrees of enrichment in 235U. The spectrum of activated neutrons was varied in order to discriminate the nuclides, by covering or not the sample with a material (cadmium or boron) able to absorb low energy neutrons. Determination of 235U/238U ratios, through the number of delayed neutrons, was made by drawing a calibration curve using standards ranging from 0.5% to 93% on 235U; the accuracy of the method was also examined. In a first step, conditions for a simultaneous and non-destructive analysis of uranium and thorium were developed. The interference between these two nuclides was studied, using simulated samples. Real samples were provided by Nuclemon and IAEA. For samples with uranium concentration in the range of percentages and thorium concentration of some ppm, uranium interferes in the determination of thorium through the non-destructive analytical method. For this case, a fast and quantitative chemical method was studied which allows for the separation of thorium from uranium before the determination of throrium concentration by counting the delayed fission neutrons. It was found that the results obtained by both destructive and non-destructive methods are very consistent and can be considered statistically equivalent within a confidence level of 95%. (Author)
Availability note (English)
MF available from INIS under the Report Number.Abstract (Portuguese)
Implantou-se um sistema de deteccao e contagem de neutrons retardados de fissao que possibilita analisar alguns nuclideos fisseis e ferteis em amostras da ordem de miligramas. O metodo foi aplicado a analise de uranio natural e torio. Alem desses, utilizou-se o sistema para determinar a razao 235U/238U em amostras nao irradiadas que contenham uranio com diferentes enriquecimentos em 235U. Para discriminacao das medidas provenientes de um nuclideo ou de outro, variou-se o espectro de neutrons incidentes; para isso, envolveu-se ou nao a amostra em materiais com capacidade de absorver neutrons de energia mais baixa, como cadmio e boro. A determinacao de razoes 235U/238U por meio da medida da producao de neutrons retardados foi feita usando uma reta de calibracao construida com padroes de diferentes enriquecimentos em 235U, determinando-se, assim, a exatidao e precisao do metodo. Numa primeira etapa foram desenvolvidas condicoes para analise nao destrutiva e simultanea de uranio e torio. Com amostras simuladas contendo diferentes proporcoes de uranio natural e torio, estudou-se a interferencia desses elementos. As amostras reais de minerios foram cedidas pela Nuclemon e pela IAEA. Para amostras com teor de uranio da ordem de porcentagens e teor de torio de algumas partes por milhao, o uranio interface na determinacao do torio. Estudou-se um metodo de separacao quimica rapido e quantitativo para o torio, previo a determinacao pela medida dos neutrons retardados de fissao. Os resultados obtidos para o torio, neste caso, foram concordantes estatisticamente, dentro de um nivel de confiabilidade de 95%, com os obtidos por meio da analise nao destrutiva. (Autor)Files
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Additional details
Additional titles
- Original title (Portuguese)
- Aplicacao do metodo de analise por ativacao por contagem de neutrons retardados de fissao para a determinacao de alguns nuclideos fissionaveis
Publishing Information
- Imprint Pagination
- 137 p.
- Report number
- INIS-BR--197
INIS
- Country of Publication
- Brazil
- Country of Input or Organization
- Brazil
- INIS RN
- 15071728
- Subject category
- S37: INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- CALIBRATION STANDARDS; FERTILE MATERIALS; FISSIONABLE MATERIALS; INTERFERING ELEMENTS; ISOTOPE RATIO; NATURAL URANIUM; NEUTRON DETECTION; SEPARATION PROCESSES; THORIUM
- Descriptors DEC
- ACTINIDES; DETECTION; ELEMENTS; MATERIALS; METALS; RADIATION DETECTION; URANIUM