Made available in DSpace on 2014-10-09T12:51:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:30Z (GMT). No. of bitstreams: 1 11253.pdf: 7162286 bytes, checksum: 8c317086ceb03e1882b7946a3ddefe94 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:52:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:17Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:51:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:30Z (GMT). No. of bitstreams: 1 11253.pdf: 7162286 bytes, checksum: 8c317086ceb03e1882b7946a3ddefe94 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:52:24Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:17Z (GMT). No. of bitstreams: 0 / Muitos materiais termoluminescentes têm sido desenvolvidos e utilizados para a monitoração individual externa de fótons, mas nenhum tem todas as características desejadas sozinho. Estas características incluem robustez, alta sensibilidade, independência de resposta quanto à energia do fóton, larga faixa de detecção de energia, boa reprodutibilidade, evanescência pequena e curva de emissão termoluminescente simples, com picos abaixo de 150oC. O dosímetro de sulfato de cálcio dopado com disprósio CaSO4:Dy) tem sido usado por muitos laboratórios, principalmente no Brasil e na Índia. Outro fósforo interessante é o fluoreto de cálcio (CaF2). As vantagens destes fósforos começam a ser mais requisitadas e suas desvantagens mais aparentes, no mercado globalizado mais e mais competitivo. Estes fósforos são utilizados em monitoração de área e ambiental devido à sua maior sensibilidade do que outros fósforos, como o LiF:Mg. A sua maior desvantagem é a forte dependência energética da resposta, que deve ser corrigida para suas aplicações em campo, onde o fóton é desconhecido a priori. Um modo interessante de fazer esta correção numa incidência ortogonal da radiação no fósforo é a interposição de um filtro plano vazado entre o feixe e o fósforo. Com o objetivo de reduzir a dependência energética sob incidência em qualquer ângulo, reduzindo a incerteza de medição da dose em campo também, este trabalho apresenta um estudo de simulação em geometrias de filtro esféricas. Foram simuladas irradiações de fótons com raios gama do cobalto 60, com raios-X de 33, 48 e 118 keV, em vários ângulos de incidência de zero a noventa graus. Estas simulações computacionais semi-empíricas, utilizando diferenças finitas em três dimensões, foram feitas em coordenadas esféricas. Os resultados indicaram as melhores espessuras e larguras para a otimização da correção da dependência energética. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

Foram estudadas as respostas de 76 detectores Geiger-Müller, 4 detectores semicondutores e 34 câmaras de ionização. Muitos deles foram calibrados em feixes de radiação gama (37Cs e 60Co) e alguns foram testados em feixes de radiação beta (90Sr+90Y e 204Tl) e X (N-60, N-80, N-100, N-150). Para os três tipos de radiação, foram obtidos os fatores de calibração dos instrumentos e foi estudada a dependência tanto energética como angular destes detectores. Para radiação gama e beta foi estudada a dependência angular para ângulos de 00 e ± 450. Foram ainda obtidas as curvas da resposta dos instrumentos em relação a uma varredura angular de 00 e ± 900, para radiação gama, beta e X. Também foram analisados os fatores de calibração obtidos para radiação beta em relação à radiação gama. Para radiação gama, dos 66 detectores Geiger-Müller estudados, 24 apresentaram resultados para a dependência energética de acordo com a recomendação internacional da ISO 4037-2 e 56 estão de acordo com a recomendação brasileira da ABNT 10011. As câmaras de ionização e os semicondutores estão de acordo com as recomendações nacional e internacional. Todos os instrumentos apresentaram dependência angular menor que 40%. Para radiação beta, os instrumentos apresentaram resultados insatisfatórios para a dependência energética e angular; Para radiação X, as câmaras de ionização apresentaram resultados para dependência energética de acordo com a recomendação nacional, e a dependência angular foi menor que 40%. / The response of 76 Geiger-Müller detectors, 4 semiconductor detectors and 34 ionization chambers were studied. Many of them were calibrated with gamma radiation beams (37Cs and 60Co), and some of them were tested in beta radiation (90Sr+90Y e 204Tl) and X radiation (N-60, N-80, N-100, N-150) beams. For all three types of radiation, the calibration factors of the instruments were obtained, and the energy and angular dependences were studied. For beta and gamma radiation, the angular dependence was studied for incident radiation angles of 00 and ± 450. The curves of the response of the instruments were obtained over an angle interval of 00 to ± 900, for gamma, beta and X radiations. The calibration factors obtained for beta radiation were compared to those obtained for gamma radiation. For gamma radiation, 24 of the 66 tested Geiger-Müller detectors presented results for the energy dependence according to international recommendation of ISO 4037-2 and 56 were in accordance with the Brazilian ABNT 10011 recommendation. The ionization chambers and semiconductors were in accordance to national and international recommendations. All instruments showed angular dependence less than 40%. For beta radiation, the instruments showed unsatisfactory results for the energy dependence and angular dependence; For X radiation, the ionization chambers presented results for energy dependence according to the national recommendation, and the angular dependence was less than 40%.

Foram estudadas as respostas de 76 detectores Geiger-Müller, 4 detectores semicondutores e 34 câmaras de ionização. Muitos deles foram calibrados em feixes de radiação gama (37Cs e 60Co) e alguns foram testados em feixes de radiação beta (90Sr+90Y e 204Tl) e X (N-60, N-80, N-100, N-150). Para os três tipos de radiação, foram obtidos os fatores de calibração dos instrumentos e foi estudada a dependência tanto energética como angular destes detectores. Para radiação gama e beta foi estudada a dependência angular para ângulos de 00 e ± 450. Foram ainda obtidas as curvas da resposta dos instrumentos em relação a uma varredura angular de 00 e ± 900, para radiação gama, beta e X. Também foram analisados os fatores de calibração obtidos para radiação beta em relação à radiação gama. Para radiação gama, dos 66 detectores Geiger-Müller estudados, 24 apresentaram resultados para a dependência energética de acordo com a recomendação internacional da ISO 4037-2 e 56 estão de acordo com a recomendação brasileira da ABNT 10011. As câmaras de ionização e os semicondutores estão de acordo com as recomendações nacional e internacional. Todos os instrumentos apresentaram dependência angular menor que 40%. Para radiação beta, os instrumentos apresentaram resultados insatisfatórios para a dependência energética e angular; Para radiação X, as câmaras de ionização apresentaram resultados para dependência energética de acordo com a recomendação nacional, e a dependência angular foi menor que 40%. / The response of 76 Geiger-Müller detectors, 4 semiconductor detectors and 34 ionization chambers were studied. Many of them were calibrated with gamma radiation beams (37Cs and 60Co), and some of them were tested in beta radiation (90Sr+90Y e 204Tl) and X radiation (N-60, N-80, N-100, N-150) beams. For all three types of radiation, the calibration factors of the instruments were obtained, and the energy and angular dependences were studied. For beta and gamma radiation, the angular dependence was studied for incident radiation angles of 00 and ± 450. The curves of the response of the instruments were obtained over an angle interval of 00 to ± 900, for gamma, beta and X radiations. The calibration factors obtained for beta radiation were compared to those obtained for gamma radiation. For gamma radiation, 24 of the 66 tested Geiger-Müller detectors presented results for the energy dependence according to international recommendation of ISO 4037-2 and 56 were in accordance with the Brazilian ABNT 10011 recommendation. The ionization chambers and semiconductors were in accordance to national and international recommendations. All instruments showed angular dependence less than 40%. For beta radiation, the instruments showed unsatisfactory results for the energy dependence and angular dependence; For X radiation, the ionization chambers presented results for energy dependence according to the national recommendation, and the angular dependence was less than 40%.

<p>The energy dependent response of silicon diodes in photon beams is a known problem. A new approach to solve this problem is by correcting the response, a response model was suggested by Yin et al. (2002, 2004), and later refined by Eklund and Ahnesjö (2009). In this work a prototype software was developed to calculate correction factors for arbitrary measurement points in MLC shaped fields using fluence pencil beam kernels to calculate the spectra used by the model of Eklund and Ahnesjö (2009). This work investigate this approach for large field sizes. It was found that the relative dose measurements of the corrected unshielded diode agreed with ionization chamber measurements within 1% at the central axis. Measurements made off axis (square and irregular fields) agreed within 2%, better results were achieved within the fields when the off axis beam softening were taken into consideration. This work has also shown that this new approach is an alternitive to shielded diodes and that corrected diodes will in some cases provide more reliable results.</p>

The energy dependent response of silicon diodes in photon beams is a known problem. A new approach to solve this problem is by correcting the response, a response model was suggested by Yin et al. (2002, 2004), and later refined by Eklund and Ahnesjö (2009). In this work a prototype software was developed to calculate correction factors for arbitrary measurement points in MLC shaped fields using fluence pencil beam kernels to calculate the spectra used by the model of Eklund and Ahnesjö (2009). This work investigate this approach for large field sizes. It was found that the relative dose measurements of the corrected unshielded diode agreed with ionization chamber measurements within 1% at the central axis. Measurements made off axis (square and irregular fields) agreed within 2%, better results were achieved within the fields when the off axis beam softening were taken into consideration. This work has also shown that this new approach is an alternitive to shielded diodes and that corrected diodes will in some cases provide more reliable results.

In-vivo dosimetry with diode detectors is used in radiation therapy as a quality assurance tool. The diode sensitivity under radiation depends upon temperature, dose rate and SDD (source-to-detector distance), field size, beam angle, and energy. This dissertation presents the first systematic and quantitative study of dosimetric characteristics for most of the commercial radiation diodes (n-type and p-type) under different radiation beams.In the temperature dependence study, the systematic study on the dose rate dependence of svwt (sensitivity variation with temperature) was performed. It was concluded that sufficient preirradiation can eliminate dose rate dependence of svwt. However, preirradiation cannot eliminate dose rate dependence of the diode sensitivity, S, itself. In the dose rate and SDD dependence study, it was shown that the p-type diodes do not always show less dose rate dependence than the n-type diodes. Preirradiation does not always reduce diode dose rate dependence. SDD dependence of diode sensitivity can be explained by the instantaneous dose rate dependence if sufficient buildup is provided to eliminate electron contamination. An empirical formula was proposed to fit the dose rate dependence of diode sensitivity. In the energy dependence study, the energy dependence diode detectors are quantified. The empirical theory to quantify this effect was developed. Monte Carlo simulation and the cavity theory are used to predict the energy dependence. It was concluded that the energy dependence does not depend on whether the diode is n- or p- type but rather depends mainly on the material around the die (buildup and its geometry). A systematic study of the correction factors for accurate diode dosimetry is presented in this dissertation.This dissertation has established a theoretical foundation for the modeling of the transient electric and radiation properties of the diode detectors, separately. We believe that the Monte Carlo simulations code for radiation transport should be coupled with the continuity equations to describe the charge transport in the diode detector, and thus provides a complete quantitative description of dosimetric characteristics of the diode detectors. The ultimate goal is to use the diode detector as an absolute dosimeter, rather than as a relative dosimeter.