Made available in DSpace on 2014-10-09T12:52:14Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:12Z (GMT). No. of bitstreams: 0 / Neste trabalho foi estabelecido um procedimento para determinação da razão isotópica 238U/235U em amostras de UF6, utilizando-se um espectrômetro de massas quadrupolar com ionização por impacto eletrônico e detecção de íons por copo de Faraday ou multiplicador de elétrons. Para tanto, o espectrômetro foi otimizado, determinando-se os parâmetros para a fonte de íons que proporcionassem a maior intensidade de corrente iônica, mantendo o pico de forma arredondada, para a massa correspondente ao isótopo mais abundante; a resolução que reduzisse os efeitos não lineares e o número de ciclos analíticos que reduzisse a incerteza nos resultados. O processo de medição foi caracterizado quanto: aos efeitos de discriminação de massa, linearidade e efeito memória. A discriminação de massas mostrou ser linearmente dependente da pressão da amostra no tanque de expansão nas faixas de 0,15 a 0,30 mbar e de 0,30 a 0,40 mbar. O espectrômetro mostrou-se linear na medição de razões isotópicas entre 0,005 e 0,045. Os fatores de memória para a fonte de íons e para o sistema de introdução são, respectivamente, 1,000 ± 0,001 e 1,003 ± 0,003; o primeiro pode ser desprezado e o segundo eliminado por procedimentos de lavagem do sistema de introdução. O trabalho apresenta, em sua parte final, um roteiro para as análises de amostras de UF6 e a determinação das incertezas nos resultados. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:30:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:15Z (GMT). No. of bitstreams: 1 01365.pdf: 962669 bytes, checksum: e02b455c6b91c9ff1df7371c13f0e5fb (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The determination of the isotopic composition of single uranium oxide particles, size 0.3-2 μm, for nuclear safeguards is current performed by either thermal ionisation mass spectrometry (TIMS) or Secondary Ion Mass Spectrometry (SIMS). Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS), a well-established analytical technique for determining the isotopic composition of solid materials, has the potential to be another method by which single uranium oxide particles can be analysed, complementing established protocol, but requires optimisation. In this study the ability of LA-ICP-MS to determine the isotopic composition, principally 234U/238U, 235U/238U and 236U/238U, of glass reference materials and sub-micron uranium oxide particles is investigated. To achieve the best detection efficiency a prototype high-speed ablation cell and injector design, designed previously at Loughborough University, was coupled to a high efficiency multi collector (MC-) ICP-MS. As a result an increase in signal-to-noise ratio and a measured detection efficiency of 5-7% was achieved for a LA-MC-ICP-MS system. The capability of the LA-MC-ICP-MS system, for the determination of the uranium isotopic composition of single particles was compared to a more established low-volume ablation cell. A source of additional uncertainty, blind time arising from incompatibilities with the mixed detector array of the MC-ICP-MS was identified. The impact of the additional uncertainty on isotope ratio analysis was modeled and a method developed to filter out affected data. LA-ICP-MS and LA-MC-ICP-MS were used to successfully determine the uranium isotopic compositions of sub-micron uranium oxide particles, of a known certified composition. A sample planchet containing particles of two distinct isotopic compositions was resolved. The utility of three data evaluation strategies to determine the isotopic composition of single uranium oxide particles was investigated. The necessity and advantages of calculating isotope ratios using the geometric mean is demonstrated, which has application for isotope ratio analysis performed on all forms of mass spectrometry. A novel approach to prepare particulate samples for laser ablation analysis, cytocentrifugation, is described. By using as the solvent, a mixture of nail polish and acetone, dispersed particles are held in a strong film layer thin enough to allow embedded particles to be imaged by SEM-EDX. A sample of uranium oxide particles in an environmental matrix prepared using cytocentrifugation is analysed by LA-MC-ICP-MS and their isotopic composition resolved.

No description available.

Yes / Cattle (Bos taurus) are biologically able to breed year-round, potentially giving farmers the freedom to choose a calving strategy to best meet their economic goals. Thus, an accurate method to determine cattle birth seasonality from archaeological remains would prove to be a valuable tool when investigating a prehistoric farming community. This paper presents the results of intra-tooth isotope ratio analysis (δ18O, δ13C) of first, second and third molars from 15 cattle. The principal outcome is a possible new approach to determining cattle birth seasonality utilizing both carbon and oxygen isotope ratio measurements of first molar enamel. Although this technique requires verification through more extensive testing, particularly of modern material, initial results suggest that it may produce more accurate predictions of birth seasonality than techniques based on intra-tooth δ18O measurements of second and third molars.

No description available.

A major uncertainty in soil carbon studies is how inputs of fresh plant-derived carbon affect the turnover of existing soil organic matter (SOM) by so-called priming effects. Priming may occur directly as a result of nutrient mining by existing microbial communities, or indirectly via microbial population adjustments. Soil type and conditions may also influence the intensity and direction of priming effects. However the mechanisms are poorly understood. The objectives of this study were (1) to investigate how additions of labile C4 substrate affected SOM turnover in two contrasting unplanted C3 soils (clayey fertile from Temple Balsall, Warwickshire (TB) and sandy acid from Shuttleworth, Bedfordshire (SH) using13 C isotope shifts; (2) to investigate the influence of rhizodeposition from plant roots on SOM turnover in the same two soils planted with a C4 grass; (3) to assess an automated field system for measuring soil temperature, moisture and photosynthesis sensitivities of SOM turnover in the same two soils over diurnal to seasonal time scales. I used a combination of laboratory incubation, glasshouse and field experiments. In the soil incubation experiment, I made daily applications of either a maize root extract or sucrose to soil microcosms at rates simulating grassland rhizodeposition, and followed soil respiration (Rs) and its δ13 C over 19 days. I inferred the extent of priming from the δ13 C of Rs and the δ13 C of substrate and soil end-members. There were positive priming effects in both soils in response to the two substrates. In the SH soil there were no differences in priming effects between the substrates. However in the TB soil, sucrose produced greater priming effects than maize root extract, and priming effects with sucrose increased over time whereas with maize root extract declined after the first week. I explain these effects in terms of the greater fertility of the TB soil and resulting greater microbial nitrogen mineralization induced by priming. Because the maize root extract contained some nitrogen, over time microbial nitrogen requirements were satisfied without priming whereas with sucrose the nitrogen demand increased over time. In the glasshouse experiment, I planted C4 Kikuyu grass (Pennisetum clandestinum) in pots with the same two soils. The extent of rhizodeposition by the plants was altered by intermittently clipping the grass in half the pots (there were also unplanted controls) and priming effects were inferred from the δ13 C of Rs and the δ13 C of plant and soil end-members. Unclipped plants in both soils generated positive priming effects, while clipping reduced priming in TB soil and produced negligible PEs in SH soil. Microbial nutrient mining of SOM again explained the observed PEs in this experiment. Photosynthesis was a major driver of priming effects in the planted systems. In the third experiment, I found that the tested automated chamber system provided reliable measurements of Rs and net ecosystem exchange (NEE), and it was possible to draw relations for the dependency of Rs and NEE on key environmental drivers. Collectively, the results contribute to a better understanding of the mechanisms of priming effects and highlight possibilities for further research. The methods developed here will allow high temporal and spatial resolution measurements of Rs and NEE under field conditions, using stable isotope methods to separate fluxes into plant- and soil-derived components. Keywords: Soil respiration, soil moisture, soil temperature, Isotope ratio, maize root, flux chamber, climate change, organic matter, rhizodeposition.

Em ambientes poluídos como a região metropolitana de São Paulo é imprescindível o conhecimento da natureza da poluição para que sejam estabelecidos procedimentos de minimização ou de controle das emissões. O estudo da poluição atmosférica já vem sendo realizado há muitos anos, sendo os componentes inorgânicos estudados a partir da determinação em amostras coletadas em filtros, soluções, entre outros meios. Neste trabalho é apresentado um método de determinação da razão isotópica de enxofre utilizando a técnica da Espectrometria de Massas com Plasma de Argônio como fonte de íons. O uso de um espectrômetro de massas de dupla focalização com fonte de íons por plasma de argônio, HR-ICPMS, o qual atinge resoluções (m/&#916;m) de até 8000, permitiu a resolução dos pfcoS dos isótopos 32S e 34S das interferência isobáricas mais comuns e/ou intensas, assim as medições foram realizadas utilizando-se diretamente as m/z dos isótopos do enxofre: A discriminação de massa foi avaliada analisando-se o material de referência NIST 8555 Sulfeto de Prata. A discriminação de massa em elementos leves como é o caso do enxofre é mais acentuada do que para os mais pesados. Assim, uma solução do material de referência era analisada a cada seqüência de 5 ou 6 soluções das amostras. A razão isotópica do enxofre foi determinada em amostras de ar atmosférico coletadas em Sâo Paulo, Ilha Rei George; na Península Antártica e diretamente do escapamento de um carro movido a gasolina e a diesel, utilizando-se um amostrador de grandes volumes e um conjunto de filtros composto de: um filtro de fibra de vidro para a coleta da fração grossa seguido de dois filtros de celulose impregnados com uma mistura de KOH e trietanolamina para a coleta do SO2 e sua oxidação a SO42-. Dois procedimentos de extração dos compostos de enxofre foram utilizados: uma somente com água e outra mais enérgica com ácido nítrico em forno de microondas. Os resultados obtidos indícaram que os dois procedimentos de extração resultam em soluções com composição isotópica diferentes. Além disso, a razão isotópica entre as soluções provenientes dos filtros de fibra de vidro e de celulose são também diferentes. Provavelmente, devido ao fracionamento existente em função da forma química do enxofre presente preferencialmente numa fração ou noutra. A análise quantitativa dos metais revelou uma presença de Fe em concentrações altas (5000-20000 ng/m3), enquanto que os demais (Mn, Cu, Cr, Ni, V, Sr, Cd, Co, Nd, Gd, Ir, Rh, Zr, Re e Ag) estavam presentes em concentrações mais baixas (< 300 ng/m3). Pelas características da amostragem, o Fe foi associado à ressuspensão do solo. O Nd, Gd, Ir, Rh, Re e Ag puderam ser tanto associados à ressuspensão do solo quanto à emissões por automóveis. O Mn, Cu, Cr, Ni, V e Sr foram associados à emissões devido à queima de combustíveis fósseis. / Polluted areas like the Great São Paulo nave a compltex pollution composition. The knowledge of this composition is essential in order to minimize or controt tne dífferent sources. Several atmospheric pollution studies have been done analyzing the inorganic fraction in samples collected in filters, solutions and other media. In this study, the sulfur isotopic ratio determination by using the mass spectrometry with an argon plasma as a source of ions is presented. A double focusing sector field mass spectrometer with an argon plasma, HR-ICPMS, was used. Since 8000 resolution (m/&#916;m} can be achieved, the 32S and 34S sulfur isotopes can be directly measured with no interferences from the common isobaric interferences (oxygen compounds). Tne isotopic ratio was determined in materials collected by using a high volume sampler. These samples were collected in São Paulo, in the King George Island; Antarctic and directly from the gases exhaust of agasoline and diesel vehicles. Two different filters were used : an external glass fiber filter was used to collect the gross fraction followed by two KOH-Triethanolamine impregnated cellulose filter to collect S)2. Two extraction procedures were used. The first one is an energetic extraction with nitric acid and micro-wave heating and the second one only with water being the soluble sulfur compounds extracted from the filters after had left 24 hours in a beaker with water. Mass discrimination was evaluated by analyzing the NlST 8555 Silver Sulphide Reference Material. As the mass discrimination is more prominent in light elements, the reference material solution was analyzed within a sequence of 5 or 6 samples. The results indicated dífferent isotopic ratio between the solutions obtained with these two extraction procedures. Different isotopic ratios were also observed in the sulfur isotopic composition in the gross and the fine fraction. This is probably due to different sulfur species present preferentially in a given fraction. The quantitative analyses of metals revealed a high Fe concentration (5000-20000 ng/m3) and lower concentrations (<300 ng/m3) to the others (Mn, Cu, Cr, Ní, V, Sr, Co, Co, Ncf, Go, Ir, Rh, Zr, Re and Ag). lron was associated to the soil dust. Neodymium, Gd, Ir, Rh, Re and Ag were associated to the soil dust and to the vehicles emissions. Manganese, Cu, Cr, Ni, V and Sr were associated to the vehicles emissions.

<p>This paper deals with three mediaeval churches in the town Visby, Gotland. These churches were located in different areas in Visby. Allegedly the areas where St Hans and Ste Gertrud were located were inhabited by wealthier people, and the more peripheral area where St Mikael was located was where the poor lived. Therefore, the people that were buried at St Mikael should be of lower social status than the people buried at St Hans and Ste Gertrud. Based on the fact that an individuals diet was dependant on his or hers social status, dietary studies on skeletal remains from the three different churches have been conducted to find out dietary patterns among the individuals buried at each church respectively. The studies have included stable isotope ratio analyses, δ13C and δ15N, in human bone collagen. The results support the hypothesis that there were differences between individuals buried at different churches as stated above.</p>

The use of gas chromatography isotope ratio mass spectrometry (GC-IRMS) for compound specific stable isotope analysis is an underutilized technique because of the complexity of the instrumentation and high analytical costs. However stable isotopic data, when coupled with concentration measurements, can provide additional information on a compounds production, transformation, loss, and cycling within the biosphere and atmosphere. A GC-IRMS system was developed to accurately and precisely measure δ13C values for numerous oxygenated volatile organic compounds (OVOCs) having natural and anthropogenic sources. The OVOCs include methanol, ethanol, acetone, methyl ethyl ketone, 2-pentanone, and 3-pentanone. Guided by the requirements for analysis of trace components in air, the GC-IRMS system was developed with the goals of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the IRMS. The technique relied on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. Measurements were performed on samples collected from two distinct sources (i.e. biogenic and vehicle emissions) and ambient air collected from downtown Miami and Everglades National Park. However, the instrumentation and the method have the capability to analyze a variety of source and ambient samples. The measured isotopic signatures that were obtained from source and ambient samples provide a new isotopic constraint for atmospheric chemists and can serve as a new way to evaluate their models and budgets for many OVOCs. In almost all cases, OVOCs emitted from fuel combustion were enriched in 13C when compared to the natural emissions of plants. This was particularly true for ethanol gas emitted in vehicle exhaust, which was observed to have a uniquely enriched isotopic signature that was attributed to ethanol’s corn origin and use as an alternative fuel or fuel additive. Results from this effort show that ethanol’s unique isotopic signature can be incorporated into air chemistry models for fingerprinting and source apportionment purposes and can be used as a stable isotopic tracer for biofuel inputs to the atmosphere on local to regional scales.