Made available in DSpace on 2014-10-09T12:47:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:11Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Made available in DSpace on 2014-10-09T12:47:05Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:11Z (GMT). No. of bitstreams: 0 / Radiação gama com energias maiores que 1,25 MeV são usualmente encontradas em ambientes de reatores, aceleradores de partículas e campos de radiação de origem cósmica. Nestas energias, a resposta de um dosímetro varia fortemente com a espessura de material absorvedor, até atingir um valor máximo conhecido como espessura de equibl^rio de partículas carregadas. O objetivo principal do presente trabalho foi a determinação experimental do perfil de dose absorvida por uma amostra de alumínio, para várias energias de feixes de raios gama, de forma a obter uma relação entre a energia média do campo de radiação gama e a espessura de equilíbrio de partículas carregadas para o alumínio. Os dosímetros foram irradiados com radiação gama produzida pela captura de neutrons térmicos em 23 materiais alvos no arranjo experimental montado no canal tangencial do reator do IPEN-CNEN/SP. Na determinação da camada de equilíbrio de partículas carregadas, foi ajustada aos dados experimentais uma função semi-empirica que permitiu obter a espessura de ETPC (Equilíbrio Transitório de Partículas Carregadas) para cada espectro de radiação gama utilizado neste trabalho, com energia média variando no intervalo de 3,26 a 7,85 MeV. Os resultados experimentais do presente trabalho permitiram obter uma relação entre a energia média do campo de radiação gama e a espessura de ETPC, que apresenta uma excelente concordância com o alcance corrigido dos elétrons gerados naquela energia. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Radiação gama com energias maiores que 1,25 MeV são usualmente encontradas em ambientes de reatores, aceleradores de partículas e campos de radiação de origem cósmica. Nestas energias, a resposta de um dosímetro varia fortemente com a espessura de material absorvedor, até atingir um valor máximo conhecido como espessura de equibl^rio de partículas carregadas. O objetivo principal do presente trabalho foi a determinação experimental do perfil de dose absorvida por uma amostra de alumínio, para várias energias de feixes de raios gama, de forma a obter uma relação entre a energia média do campo de radiação gama e a espessura de equilíbrio de partículas carregadas para o alumínio. Os dosímetros foram irradiados com radiação gama produzida pela captura de neutrons térmicos em 23 materiais alvos no arranjo experimental montado no canal tangencial do reator do IPEN-CNEN/SP. Na determinação da camada de equilíbrio de partículas carregadas, foi ajustada aos dados experimentais uma função semi-empirica que permitiu obter a espessura de ETPC (Equilíbrio Transitório de Partículas Carregadas) para cada espectro de radiação gama utilizado neste trabalho, com energia média variando no intervalo de 3,26 a 7,85 MeV. Os resultados experimentais do presente trabalho permitiram obter uma relação entre a energia média do campo de radiação gama e a espessura de ETPC, que apresenta uma excelente concordância com o alcance corrigido dos elétrons gerados naquela energia. / Gamma radiation with energies greater than 1.25 MeV are usually produced in reactor environments, particle accelerators and in cosmic radiation fields. For these energies, the response of a dosimeter heavily vary with the absorber material thickness, up to attain a maximum value named as charged particle equilibrium thickness. The main gol of this paper was the experimental determination of the absorbed dose profile in an aluminum sample for several energies of gamma ray beam, in order to obtain a relationship between the average energy of the gamma radiation field and the charged particle equilibrium thickness. The dosimeters were irradiated with gamma radiation produced by thermal neutron capture in 23 target materials in the experimental arrangement mounted at the tangential beam hole of the BPEN-CNEN/SP reactor. For the determination of the charged particle equilibrium thickness, it was fitted to the experimental data a semi-empirical fimction which allowed to obtain the thickness of CTPE ( Charged Particle Transient Equilibrium ) for each gamma radiation spectrum used in this work, with average energy varying in the interval from 3.26 to 7.85 MeV. The experimental results of the present paper allowed to obtain a relationship between average energy of the radiation field and the CTPE thickness, which presents an excellent agreement with the corrected range for electrons produced in that energy.

Radiação gama com energias maiores que 1,25 MeV são usualmente encontradas em ambientes de reatores, aceleradores de partículas e campos de radiação de origem cósmica. Nestas energias, a resposta de um dosímetro varia fortemente com a espessura de material absorvedor, até atingir um valor máximo conhecido como espessura de equibl^rio de partículas carregadas. O objetivo principal do presente trabalho foi a determinação experimental do perfil de dose absorvida por uma amostra de alumínio, para várias energias de feixes de raios gama, de forma a obter uma relação entre a energia média do campo de radiação gama e a espessura de equilíbrio de partículas carregadas para o alumínio. Os dosímetros foram irradiados com radiação gama produzida pela captura de neutrons térmicos em 23 materiais alvos no arranjo experimental montado no canal tangencial do reator do IPEN-CNEN/SP. Na determinação da camada de equilíbrio de partículas carregadas, foi ajustada aos dados experimentais uma função semi-empirica que permitiu obter a espessura de ETPC (Equilíbrio Transitório de Partículas Carregadas) para cada espectro de radiação gama utilizado neste trabalho, com energia média variando no intervalo de 3,26 a 7,85 MeV. Os resultados experimentais do presente trabalho permitiram obter uma relação entre a energia média do campo de radiação gama e a espessura de ETPC, que apresenta uma excelente concordância com o alcance corrigido dos elétrons gerados naquela energia. / Gamma radiation with energies greater than 1.25 MeV are usually produced in reactor environments, particle accelerators and in cosmic radiation fields. For these energies, the response of a dosimeter heavily vary with the absorber material thickness, up to attain a maximum value named as charged particle equilibrium thickness. The main gol of this paper was the experimental determination of the absorbed dose profile in an aluminum sample for several energies of gamma ray beam, in order to obtain a relationship between the average energy of the gamma radiation field and the charged particle equilibrium thickness. The dosimeters were irradiated with gamma radiation produced by thermal neutron capture in 23 target materials in the experimental arrangement mounted at the tangential beam hole of the BPEN-CNEN/SP reactor. For the determination of the charged particle equilibrium thickness, it was fitted to the experimental data a semi-empirical fimction which allowed to obtain the thickness of CTPE ( Charged Particle Transient Equilibrium ) for each gamma radiation spectrum used in this work, with average energy varying in the interval from 3.26 to 7.85 MeV. The experimental results of the present paper allowed to obtain a relationship between average energy of the radiation field and the CTPE thickness, which presents an excellent agreement with the corrected range for electrons produced in that energy.

Luminescence measurements have been applied to three different structures namely, sulphate, fluorides and YAG. In all cases the RE doping suppresses the intrinsic emission and results in intense luminescence characteristic of the RE dopant. Additionally, in double doped samples, or contaminated ones, the TL data show that each dopant defines a glow peak, which is displaced in temperature relative to the others. Examples of this were discussed for CaS04:Ce,Mn; YAG:Nd,Tb,Cr,Mn; BaF2:Ho,Ce and BaF2:Tm,Ce. The data are discussed in terms of an energy transfer model between different parts of extended defect complexes which encompass the RE ion and the lattice defects. Calcium sulphate doped with Dy define a TL peak near 200°C suitable for radiation measurements, but when co-doped with Ag the TL peak move to higher temperatures with minor effects on the peak sensitivity. In Ce,Mn double doped samples, the peak temperatures differ by -7°C between the Ce and Mn sites. The TL glow curves from alkaline earth fluorides are complex and contain several overlapping peaks. Curve fitting show that the peak maxima below room temperature are insensitive to the RE dopant. Additionally the host material has a modest effect on the peak positions. Above room temperature each dopant provides a TL curve specific to the added RE ion and do not show common peaks. Concentration has many effects on the resultant glow curve, and even at the lowest concentration used here (0.01%) there is evidence of cluster formation. Samples with high RE content show low values of the frequency factor consistent with the energy transfer model in that the emission from RE-RE cluster dominates over the emission from direct charge recombination within the defect complex. The effect of concentration and the TL mechanism operating below room temperature are also discussed. Luminescence signals from the near surface of YAG:Nd (via CL) were contrasted with those from the bulk material via RL. Results indicate that the outer few micron layers differ significantly in luminescence response from the bulk crystal. The differences were ascribed to result from solvents that enter the YAG lattice during the growth stage or subsequently from cleaning treatments via the dislocations caused by cutting and polishing. Additionally, the growth stage may include gases from the residual air in the growth furnace trapped into the YAG lattice. In each case there is a discontinuity in luminescence intensity and/or emission wavelengths at temperatures which mach the phase transitions of the contaminants. At the transition temperature there will be a sudden pressure change and this will induce surface expansion or bulk compression. The differences between the two cases were detected by the alternatives of CL and RL excitation, where the Nd or Er lines have moved in opposite directions. The detection of such low concentrations of solvents/trapped gases by luminescence is extremely difficult due to experimental limitations. Hence their role in luminescence generation is normally ignored.

Made available in DSpace on 2014-10-09T12:35:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:49Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:42:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:42Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP