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Dispersão de partículas alfa em filmes finos
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Neste trabalho, foi estudada a espessura e a uniformidade de filmes finos (folha de alumínio e película
aderente), usados no nosso quotidiano.
Com vista à determinação da espessura e à análise da uniformidade, recorreu-se ao método de perda de
energia das partículas alfa no atravessamento dos filmes.
Foram adquiridos espetros de energia de partículas alfa de fontes radioativas 226Ra e 232U, usando um
detetor de barreira de superfície. A fonte de 226Ra, sendo de melhor qualidade, foi usada na calibração
do sistema. No entanto, para determinar a espessura de filmes finos, recorreu-se à fonte de 232U,
aproveitando a sua maior atividade, o que permitiu reduzir o tempo de aquisição em cada amostra. A
espessura dos filmes finos foi calculada com base no modelo da perda contínua de energia (CSDA),
utilizando a perda de energia das partículas alfa em relação ao pico do 212Po.
Além das abordagens experimentais, este trabalho incorporou simulações de Monte Carlo com o
programa AlfaMC, possibilitando o estudo da espessura dos filmes e estimativas da (não) uniformidade
desses filmes. Na simulação, foram consideradas as características físicas do detetor e da fonte. As
espessuras dos filmes obtidas foram comparadas com outro método de cálculo (aplicação Eloss) baseado
em CSDA, de modo a validar esta abordagem.
A análise de folhas de alumínio de diferentes marcas comerciais revelou algumas variações no valor da
espessura, embora com diferenças inferiores a 2,3 μm entre marcas. Destaque para a marca Lidl, cuja
espessura se aproximou do valor anunciado pela marca.
No caso das películas aderentes, a ausência de informações por parte do fabricante representou um
desafio maior. Após a realização de uma análise de fluorescência de raio-X dispersiva em energia
(EDXRF), chegou-se à conclusão de que duas das amostras são compostas de material PVC (Silvex e
Continente), enquanto outras duas são compatíveis com polietileno (Dia e Auchan).
Relativamente à uniformidade, foi feito um estudo detalhado de amostras da marca Dia, que globalmente
apresentou uma (não) uniformidade da ordem de 5% relativamente ao valor médio da espessura.
In this work, we studied the thickness and uniformity of thin films (aluminum foil and cling film) commonly used in our daily lives. In order to determine the thickness and analyse uniformity, we employed the method of alpha particle energy loss as it traversed the films. Energy spectra of alpha particles from radioactive sources, in this case 226Ra and 232U, were acquired using a surface barrier detector. The 226Ra source, with higher quality, was utilized for system calibration. However, to determine the thickness of the thin films, we turned to the 232U source, taking advantage of its greater activity, which allowed us to reduce the acquisition time for each sample. The thickness of the thin films was calculated based on the Continuous Slowing Down Approximation (CSDA) model, using the energy loss of alpha particles relative to the 212Po peak. In addition to experimental approaches, our study incorporated Monte Carlo simulations with the AlfaMC program, enabling the examination of film thickness and estimates their (non) uniformity. The simulation considered the physical characteristics of both the detector and the source. The film thicknesses obtained were compared with another calculation method (Eloss application) based on CSDA to validate this approach. The analysis of aluminum foil from different commercial brands revealed some variations in thickness, although differences were less than 2.3 µm between brands. Notably, the Lidl brand closely approximated the thickness value advertised by the manufacturer. For cling films, the absence of information from the manufacturer posed a greater challenge. After conducting an Energy-Dispersive X-ray Fluorescence (EDXRF) analysis, it was concluded that two samples were composed of PVC material (Silvex and Continente), while the other two samples were compatible with polyethylene (Dia and Auchan). Regarding uniformity, a detailed study was conducted on Dia brand samples, which showed an overall (non) uniformity of approximately 5% relative to the average thickness value.
In this work, we studied the thickness and uniformity of thin films (aluminum foil and cling film) commonly used in our daily lives. In order to determine the thickness and analyse uniformity, we employed the method of alpha particle energy loss as it traversed the films. Energy spectra of alpha particles from radioactive sources, in this case 226Ra and 232U, were acquired using a surface barrier detector. The 226Ra source, with higher quality, was utilized for system calibration. However, to determine the thickness of the thin films, we turned to the 232U source, taking advantage of its greater activity, which allowed us to reduce the acquisition time for each sample. The thickness of the thin films was calculated based on the Continuous Slowing Down Approximation (CSDA) model, using the energy loss of alpha particles relative to the 212Po peak. In addition to experimental approaches, our study incorporated Monte Carlo simulations with the AlfaMC program, enabling the examination of film thickness and estimates their (non) uniformity. The simulation considered the physical characteristics of both the detector and the source. The film thicknesses obtained were compared with another calculation method (Eloss application) based on CSDA to validate this approach. The analysis of aluminum foil from different commercial brands revealed some variations in thickness, although differences were less than 2.3 µm between brands. Notably, the Lidl brand closely approximated the thickness value advertised by the manufacturer. For cling films, the absence of information from the manufacturer posed a greater challenge. After conducting an Energy-Dispersive X-ray Fluorescence (EDXRF) analysis, it was concluded that two samples were composed of PVC material (Silvex and Continente), while the other two samples were compatible with polyethylene (Dia and Auchan). Regarding uniformity, a detailed study was conducted on Dia brand samples, which showed an overall (non) uniformity of approximately 5% relative to the average thickness value.
Descrição
Tese de Mestrado, Física (Física Nuclear e Partículas), 2024, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Partículas alfa Filmes finos Espetrometria Alfa AlfaMC Simulações de Monte Carlo Teses de mestrado - 2024