Com o objetivo de monitorar o crescente número de trabalhadores potencialmente expostos à radiação de nêutrons, foi projetado e desenvolvido um dosímetro individual para campos mistos nêutron-gama. O dosímetro proposto foi caracterizado para o espectro de energia de uma fonte de Amerício-Berílio e para o intervalo de dose de interesse da proteção radiológica (até 20 mSv). Para tanto utilizou-se a dosimetria termoluminescente de albedo e a dosimetria de traços nucleares, técnicas consagradas na literatura internacional, empregando materiais de fabricação nacional e de baixo custo. Um policarbonato comercial, denominado SS-1, foi caracterizado para aplicação como detector sólido de traços nucleares. Os parâmetros para revelação química e ampliação dos traços, assim como a metodologia de avaliação dos detectores foram determinados. Estudou-se a resposta dos detectores TLD-600, TLD-700 e SS-1 em campos mistos nêutrongama de uma fonte de Amerício-Berílio e definiu-se um algoritmo para cálculo da dose de nêutrons e de radiação gama. A razão entre as respostas para nêutrons térmicos, de albedo e rápidos permite analisar o espectro ao qual o dosímetro foi submetido e corrigir a resposta do detector de traços para variações no ângulo de incidência da radiação. O novo dosímetro está pronto e apresenta desempenho para ser usado como dosímetro de nêutrons no Brasil. / An individual dosimeter for neutron-gamma mixed field dosimetry was design and developed aiming monitoring the increasing number of workers potentially exposed to neutrons. The proposed dosimeter was characterized to an Americium-Beryllium source spectrum and dose range of radiation protection interest (up to 20 mSv). Thermoluminescent albedo dosimetry and nuclear tracks dosimetry, traditional techniques found in the international literature, with materials of low cost and national production, were used. A commercial polycarbonate, named SS-1, was characterized for solid state tack detector application. The chemical etching parameters and the methodology of detectors evaluation were determined. The response of TLD-600, TLD-700 and SS-1 were studied and algorithms for dose calculation of neutron and gamma radiation of Americium- Beryllium sources were proposed. The ratio between thermal, albedo and fast neutrons responses, allows analyzing the spectrum to which the dosimeter was submitted and correcting the track detector response to variations in the radiation incidence angle. The new dosimeter is fully characterized, having sufficient performance to be applied as neutron dosimeter in Brazil.

Com o objetivo de monitorar o crescente número de trabalhadores potencialmente expostos à radiação de nêutrons, foi projetado e desenvolvido um dosímetro individual para campos mistos nêutron-gama. O dosímetro proposto foi caracterizado para o espectro de energia de uma fonte de Amerício-Berílio e para o intervalo de dose de interesse da proteção radiológica (até 20 mSv). Para tanto utilizou-se a dosimetria termoluminescente de albedo e a dosimetria de traços nucleares, técnicas consagradas na literatura internacional, empregando materiais de fabricação nacional e de baixo custo. Um policarbonato comercial, denominado SS-1, foi caracterizado para aplicação como detector sólido de traços nucleares. Os parâmetros para revelação química e ampliação dos traços, assim como a metodologia de avaliação dos detectores foram determinados. Estudou-se a resposta dos detectores TLD-600, TLD-700 e SS-1 em campos mistos nêutrongama de uma fonte de Amerício-Berílio e definiu-se um algoritmo para cálculo da dose de nêutrons e de radiação gama. A razão entre as respostas para nêutrons térmicos, de albedo e rápidos permite analisar o espectro ao qual o dosímetro foi submetido e corrigir a resposta do detector de traços para variações no ângulo de incidência da radiação. O novo dosímetro está pronto e apresenta desempenho para ser usado como dosímetro de nêutrons no Brasil. / An individual dosimeter for neutron-gamma mixed field dosimetry was design and developed aiming monitoring the increasing number of workers potentially exposed to neutrons. The proposed dosimeter was characterized to an Americium-Beryllium source spectrum and dose range of radiation protection interest (up to 20 mSv). Thermoluminescent albedo dosimetry and nuclear tracks dosimetry, traditional techniques found in the international literature, with materials of low cost and national production, were used. A commercial polycarbonate, named SS-1, was characterized for solid state tack detector application. The chemical etching parameters and the methodology of detectors evaluation were determined. The response of TLD-600, TLD-700 and SS-1 were studied and algorithms for dose calculation of neutron and gamma radiation of Americium- Beryllium sources were proposed. The ratio between thermal, albedo and fast neutrons responses, allows analyzing the spectrum to which the dosimeter was submitted and correcting the track detector response to variations in the radiation incidence angle. The new dosimeter is fully characterized, having sufficient performance to be applied as neutron dosimeter in Brazil.

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No description available.

No description available.

No description available.

Snow Albedo Feedback (SAF) in response to climate change is a process that can amplify the climate warming response to increases in anthropogenic atmospheric CO2 concentrations from the 20th to the 21st Century. Warmer surface air temperature may induce snowmelt and expose darker underlying surfaces which absorb more incoming solar radiation and further increase the ambient temperature. Springtime SAF in the fully Coupled Model Intercomparison Project Phase 3 (CMIP3) models is associated with summertime circulation. However, no clear physical mechanism explaining this link has been found. Furthermore, there is a large intermodel spread in the projection of SAF among the CMIP3 models which is primarily controlled through the parameterization of snow albedo in each model. Limited work was conducted on assessing the response of SAF to that of an isolated controlling parameter such as snow albedo. Here, the uncoupled Geophysical Fluid Dynamics Laboratory Atmospheric Model 2.1 (AM2.1) was used to diagnose SAF in the CMIP3 models by conducting a set of sensitivity experiments with perturbed snow albedo. This was performed to remove indirect external climate factors that may influence SAF and to use the simplified uncoupled model to understand the behaviours exhibited by the complex coupled models. Snow cover extent (SNC) and snow metamorphosis as a function of temperature (TEM) that influences SAF, as well as the knock-on effects of SAF on soil moisture, snow mass, snow melt and circulation were analyzed using both the CMIP3 and AM2.1 models. In addition, it was hypothesized that summertime Land Sea Contrast response to climate change (dLSC) is a physical mechanism that induces summertime circulation patterns in relation to springtime SAF. It is found that the AM2.1 can similarly reproduce SNC and TEM as well as the spread in SAF exhibited in the CMIP3 models. However, no robust link can be determined between SAF and its knock-on effects. Furthermore, the correlation between SAF and dLSC is not significant and thus dLSC is not a physical mechanism that influences the summertime circulation patterns in response to climate change. It is the expectation that these research results can provide an in-depth understanding of the role of SAF among fully coupled GCMs through tests performed by the uncoupled simulation.

No description available.

No description available.

Snow Albedo Feedback (SAF) in response to climate change is a process that can amplify the climate warming response to increases in anthropogenic atmospheric CO2 concentrations from the 20th to the 21st Century. Warmer surface air temperature may induce snowmelt and expose darker underlying surfaces which absorb more incoming solar radiation and further increase the ambient temperature. Springtime SAF in the fully Coupled Model Intercomparison Project Phase 3 (CMIP3) models is associated with summertime circulation. However, no clear physical mechanism explaining this link has been found. Furthermore, there is a large intermodel spread in the projection of SAF among the CMIP3 models which is primarily controlled through the parameterization of snow albedo in each model. Limited work was conducted on assessing the response of SAF to that of an isolated controlling parameter such as snow albedo. Here, the uncoupled Geophysical Fluid Dynamics Laboratory Atmospheric Model 2.1 (AM2.1) was used to diagnose SAF in the CMIP3 models by conducting a set of sensitivity experiments with perturbed snow albedo. This was performed to remove indirect external climate factors that may influence SAF and to use the simplified uncoupled model to understand the behaviours exhibited by the complex coupled models. Snow cover extent (SNC) and snow metamorphosis as a function of temperature (TEM) that influences SAF, as well as the knock-on effects of SAF on soil moisture, snow mass, snow melt and circulation were analyzed using both the CMIP3 and AM2.1 models. In addition, it was hypothesized that summertime Land Sea Contrast response to climate change (dLSC) is a physical mechanism that induces summertime circulation patterns in relation to springtime SAF. It is found that the AM2.1 can similarly reproduce SNC and TEM as well as the spread in SAF exhibited in the CMIP3 models. However, no robust link can be determined between SAF and its knock-on effects. Furthermore, the correlation between SAF and dLSC is not significant and thus dLSC is not a physical mechanism that influences the summertime circulation patterns in response to climate change. It is the expectation that these research results can provide an in-depth understanding of the role of SAF among fully coupled GCMs through tests performed by the uncoupled simulation.