A study has been made of the external conversion spectrum of gamma-rays of less than 200 kev. A set of semi-empirical curves relating the photoelectric peak height to the gamma-ray intensity has been established using antimony radiators. These results will be discussed. A method of preparing thin beta sources will also be described. / Thesis / Master of Science (MSc)

As the world's nuclear reactors approach the end of their originally planned lifetimes and seek license extensions, which would allow them to operate for another 20 years, accurate information regarding neutron radiation exposure is more important than ever. Structural components such as the reactor pressure vessel (RPV) become embrittled by neutron irradiation, reducing their capability to resist crack growth and increasing the risk of catastrophic failure. The current dosimetry approaches used in these high flux environments do not provide real-time information. Instead, radiation dose is calculated using computer simulations, which are checked against dose readings that are only available during refueling once every 1.5-2 years. These dose readings are also very expensive, requiring highly trained technicians to handle radioactive material and operate specialized characterization equipment. This dissertation describes the development of a novel neutron radiation dosimeter based on carbon nanotubes (CNTs) that not only provides accurate real-time dosimetry, but also does so at very low cost, without the need for complex instrumentation, highly trained operators, or handling of radioactive material. Furthermore, since this device is based on radiation damage rather than radioactivation, its readings are time-independent, which is beneficial for nuclear forensics. In addition to development of a novel dosimeter, this work also provides insight into the particularly under-investigated topic of the effects of neutron irradiation of carbon nanotubes. This work details the fabrication and characterization of carbon nanotube based neutron and gamma radiation dosimeters. They consist of a random network of CNTs, sealed under a layer of silicon dioxide, spanning the gap between two electrodes to form a conductive path. They were fabricated using conventional wafer processing techniques, making them intrinsically scalable and ready for mass production. Electrical properties were measured before and after irradiation at several doses, demonstrating a consistent repeatable trend that can be effectively used to measure dose. Changes to the microstructure were investigated using Raman spectroscopy, which confirmed that the changes to electrical properties are due to increasing defect concentration. The results outlined in this dissertation will have significant impacts on both the commercial nuclear industry and on the nanomaterials scientific community. The dosimeter design has been refined to the point where it is nearly ready to be deployed commercially. This device will significantly improve accuracy of RPV lifetime assessment while at the same time reducing costs. The insights into the behavior of CNTs in neutron and gamma radiation environments is of great interest to scientists and engineers studying these nanomaterials. / Ph. D.

Proton Compton scattering has been studied from 220 to 330 MeV at 90 degree center of mass scattering angle with the polarized photon beam at LEGS. Compton scattering is an important probe of the nucleon structure and its excited states. Polarization degrees of freedom reveal more information than unpolarized observables. This experiment measured, for the first time, the polarized cross sections of proton Compton scattering up to the Δ resonance. The parallel and perpendicular cross sections were measured at the same time. All the photons were tagged so that the energy dependent systematic errors are small. The measured unpolarized cross section is above the lower bound from unitary at all energies. The cross section asymmetry is obtained as a function of energy for the first time. The unpolarized cross section is compared with previous data and with calculations from the fixed-t dispersion model, the isobar model and the finite energy dispersion model. Although all these calculations agree fairly well with unpolarized cross section data, the photon asymmetry data show that the isobar model contains serious defects. The ratio of polarized cross sections, dσ_⫫/dσ_⟂, is compared with a model independent result. The results from the present experiment can be used in the calculation of the E2/M1 ratio in the N — Δ transition, which is an important signature of the tensor interaction between quarks. / Ph. D.

This thesis summarizes a senior project on the Active Galactic Nucleus (AGN) Markarian 421 (Mrk 421). Observations of Gev and TeV flux with Fermi Large Area Telescope (LAT) and High Energy Stereoscopic System (H.E.S.S.) were compared with previous reports and publications of flux analyses of the gamma-ray emission from Mrk 421. Power laws with exponential cutoffs made consistent fits to most SEDs in the GeV and TeV bands.

Title: Study of Cosmic-Ray Acceleration in Extragalactic Objects Author: Stanislav tefnik Department: Institute of Particle and Nuclear Physics Supervisor: RNDr. Dalibor Nosek, Dr. Abstract: This thesis deals with production processes of cosmic γ-rays in astro- physical objects and methods of their detection. Possible interactions leading to the emission of high energy γ-rays in the active galaxy Centaurus A are discussed in this context. Cherenkov Telescope Array is presented as a new experiment fo- cused on the detection of air showers initiated by cosmic γ-rays. Cherenkov light of air showers is studied in the simulations done by CORSIKA simulation tool. Method of data analysis within the framework of Cherenkov telescopes is descri- bed and performed on the dataset of the active galaxy PKS 2155-304. The results include statistical tests of γ-ray source presence and its time variability. Keywords: Cosmic rays, gamma rays, astroparticle physics, high energy astro- physics, acceleration, CTA experiment

A radiação gama é uma das tecnologias aplicadas para a esterilização de sistemas de embalagens contendo produtos para a saúde. No processo de esterilização, é fundamental que as propriedades das embalagens sejam mantidas. Neste estudo, duas amostras de embalagens comerciais, no formato de envelope compostas por papel grau cirúrgico de um dos lados e filme plástico laminado do outro, foram irradiadas com raios gama com doses de 25 kGy (taxa de dose de 1,57 kGy/h) e 50 kGy (taxa de dose de 1,48 kGy/h). Uma das amostras de embalagem era constituída por papel de fibras de coníferas e filme plástico laminado de poli(tereftalato de etileno) (PET)/polietileno (PE) e a outra por papel de fibras de coníferas e de folhosas e filme plástico laminado de poli(tereftalato de etileno) (PET)/polipropileno (PP). Os efeitos da radiação nas propriedades físicas e químicas dos papéis e dos filmes plásticos, assim como nas propriedades da embalagem foram estudados. O papel foi o material mais sensível à radiação, sendo a alvura, o pH e as resistências ao rasgo, ao arrebentamento e à tração os parâmetros nos quais foram observadas maiores modificações, em ambas as amostras. Todavia, dos dois tipos de papel, o efeito foi mais pronunciado para a amostra com fibras de conífera e de folhosas. A porosidade dos papéis foi alterada com 50 kGy. No caso dos filmes plásticos, a propriedade com maior modificação foi a resistência à tração, em ambas as amostras. No caso das embalagens, a irradiação diminuiu a resistência da selagem. Os efeitos observados para a dose de 50 kGy foram em média mais pronunciados quando comparados com as modificações nos valores das amostras tratadas com 25 kGy, que é a dose usualmente empregada para esterilização de produtos para a saúde. A dosimetria deste estudo foi realizada nos materiais irradiados com 25 kGy, 40 kGy e 50 kGy, demonstrando sua importância à medida que a variação média para as três doses estudadas foi de 20 %. / Gamma radiation is one of the technologies applied for the sterilization of packaging systems containing products for health. During sterilization process it is critical that the properties of packages are maintained. In this study two samples of commercial pouch packaging comprised of surgical grade paper on one side and the other side multilayer plastic film were irradiated with gamma rays. The following doses were applied 25 kGy (1,57 kGy/h) and 50 kGy (1,48 kGy/h). One packaging sample was paper formed by softwood fibers and multilayer plastic film based on poly(ethylene terephthalate) (PET)/polyethylene (PE). The second type of paper sample was made by a mixture of softwood and hardwood fibers and multilayer plastic film based on polyethylene terephthalate (ethylene) (PET)/polypropylene (PP). The effects of radiation on the physical and chemical properties of papers and multilayer plastic films, as well as the properties of the package were studied. The paper was the more radiation sensitive among the studied materials and radiation effects were more pronounced at brightness, pH, tearing resistance, bursting strength and tensile strength. Nonetheless, worst comparatively effects were noted on the sample made by a mixture of softwood and hardwood fibers. The porosity of paper was enhanced by 50 kGy. In the case of plastic films, radiation effects on tensile strength was the most pronounced property for both samples. In the case of the packaging the sealing resistance decreased with radiation. The effects observed for the treatment at 50 kGy were more pronounced when compared to 25 kGy. This last is the dose which is usually applied to sterilize health products. A dosimetry study was performed during irradiation at 25 kGy, 40 kGy and 50 kGy and its importance may be reported by the average dose variation 20 %.

A engenharia de tecidos e a medicina regenerativa possuem como objetivo principal o restabelecimento morfológico/funcional de tecidos e órgãos lesionados com a utilização de células, matrizes celulares e células tronco, controlando as respostas imunológicas/bioquímicas promovidas pelo organismo. Adicionalmente, a ciência dos materiais busca desenvolver biomateriais biocompatíveis que não promovam reações imunológicas indesejadas e proporcionem o reestabelecimento das funções do tecido/órgão. Polímeros de origem natural destacam-se como biomateriais por assemelharem-se a macromoléculas biológicas, similaridade com a matriz extracelular, menor possibilidade de estimulação de inflamação crônica e baixa ou ausência de toxicidade. O presente trabalho teve como objetivo desenvolver matrizes macromoleculares originadas do óleo de soja epoxidado (OSE), analisando a relação estrutura química/atividade biológica das matrizes macromoleculares para uso como biomaterial na engenharia de tecidos. A síntese do OSE foi efetuada pela rota oleoquímica, cuja eficiência foi determinada por espectroscopia de infravermelho e o rendimento da reação de 85% determinado por ressonância magnética nuclear de prótons. A partir da análise por calorimetria exploratória diferencial, detectou-se uma diminuição da temperatura de transição vítrea do polímero do óleo de soja (POSE) em relação ao OSE, sugerindo aumento do crescimento das cadeias poliméricas do POSE. Através da análise termogravimétrica, foi possível definir o perfil de degradação do OSE, com degradação em duas etapas, e do POSE, que degrada em apenas uma etapa e demonstra maior estabilidade térmica do POSE pelo aumento das interações moleculares. A reticulação e a hidrofilicidade do POSE foram promovidas com a adição de metacrilato de 2-hidroxietila (HEMA) à formulação por enxertia do monômero pela irradiação gama. Os resultados obtidos identificaram aumento da estabilidade mecânica, da gelificação e da absorção de água com o aumento do conteúdo de HEMA. Por fim, o grau de cristalinidade estimado para esses polímeros enxertados com HEMA de 27,5% foi definido através da difratometria de raios-X. A segunda etapa caracterizou-se pelo (i) desenvolvimento de POSEs com a enxertia de HEMA nas proporções OSE/HEMA 90:10 e 65:35 com irradiação por raios gama nas doses de 50 e 100kGy, (ii) caracterização físico-química dos POSE-HEMA e (iii) análise biológica desses materiais. Através da espectroscopia de infravermelho, pode-se detectar as regiões epoxidadas do POSE, assim como o sucesso da enxertia do monômero HEMA em todas as concentrações e doses de radiação utilizadas. Através da calorimetria exploratória diferencial, calculou-se a energia de ativação (Ea) dos polímeros. A cristalinidade dos materiais foi definida por difratometria de raios-X, mostrando caráter amorfo do material, bem como um pequeno incremento na porcentagem da cristalinidade com o aumento da intensidade das doses de radiação durante a síntese e um decréscimo dessa cristalinidade com o aumento na concentração de HEMA. A análise da citotoxicidade das amostras mostrou a ausência de toxicidade dos POSE-HEMA, confirmando a eficiência das lavagens dos polímeros para retirada de resíduos do processamento. A análise da hemocompatibilidade mostrou ausência de adesão de plaquetas e os testes de crescimento celular nas matrizes foram positivos. Através dos resultados obtidos nesta pesquisa, pôde-se concluir pelo potencial de utilização dos POSE-HEMA na engenharia de tecidos. / Tissue engineering and regenerative medicine have as main objective the morphologic/functional reestablishment of injured tissues and organs using cells, scaffolds, stem cells and control of immunological/biochemical responses promoted by the body. In addition, materials science seeks to develop biocompatible biomaterials that do not promote unwanted immune responses and provide the re-establishment of the functions of the tissue/organ. Polymers of natural origin stand out as biomaterials to resemble biological macromolecules, similarity to the extracellular matrix, reduced chance of inflammation and chronic pacing low or no toxicity. This study aimed the development of macromolecular arrays originated from epoxidized soybean oil (OSE), analyzing the relationship between the chemical structure/biological activity of the macromolecular arrays for use as biomaterials in tissue engineering. The synthesis of OSE was performed through the oleochemical route, whose efficiency was determined by infrared spectroscopy and the reaction yield of 85%, determined by nuclear magnetic resonance spectroscopy. From the analysis by differential scanning calorimetry, it was detected a decrease of the glass transition temperature of the epoxidized soybean oil polymer (POSE) compared with OSE, suggesting an increase of the growth of polymer chains of POSE. Thermogravimetric analysis was performed to define the OSE degradation profile, which degrades in two steps. The POSE degrades in just one step and shows higher thermal stability by the increased molecular interactions. The hydrophilicity and crosslinking of POSE was promoted by the addition of 2-hydroxyethyl methacrylate (HEMA) with the monomer grafting by gamma irradiation. The results showed an increased mechanical stability, gelation and water absorption with the HEMA content increasing. Finally, the degree of crystallinity for such polymers grafted with HEMA was 27.5%, estimated by X-ray diffractometry. The second stage was characterized by (i) developing POSEs with the grafting of HEMA in the proportions OSE / HEMA 90:10 and 65:35 irradiated by gamma rays at doses of 50 and 100kGy, (ii) physico-chemical characterization of POSE-HEMA and (iii) analysis of biological materials. By infrared spectroscopy, it was detect the epoxidized regions of POSE, as well as the successful grafting of the monomer HEMA concentrations with all radiation doses. By differential scanning calorimetry, the activation energy was calculated (Ea) of the polymers. The crystallinity of the material was defined by X-ray diffraction, showing tendency of amorphous material as well as a small percentage of the increase in crystallinity with increasing intensity of radiation doses during this synthesis and a decrease in crystallinity with the increasing concentration of HEMA. The analysis of the samples did not show cytotoxicity on POSE-HEMA and confirmed the efficiency of polymer washings to remove the processing waste. The analysis of hemocompatibility showed any platelet adhesion and the cell growth on the scaffolds was positive. From the results obtained in this research, we concluded by the potential use of POSE-HEMA in tissue engineering.

A engenharia de tecidos e a medicina regenerativa possuem como objetivo principal o restabelecimento morfológico/funcional de tecidos e órgãos lesionados com a utilização de células, matrizes celulares e células tronco, controlando as respostas imunológicas/bioquímicas promovidas pelo organismo. Adicionalmente, a ciência dos materiais busca desenvolver biomateriais biocompatíveis que não promovam reações imunológicas indesejadas e proporcionem o reestabelecimento das funções do tecido/órgão. Polímeros de origem natural destacam-se como biomateriais por assemelharem-se a macromoléculas biológicas, similaridade com a matriz extracelular, menor possibilidade de estimulação de inflamação crônica e baixa ou ausência de toxicidade. O presente trabalho teve como objetivo desenvolver matrizes macromoleculares originadas do óleo de soja epoxidado (OSE), analisando a relação estrutura química/atividade biológica das matrizes macromoleculares para uso como biomaterial na engenharia de tecidos. A síntese do OSE foi efetuada pela rota oleoquímica, cuja eficiência foi determinada por espectroscopia de infravermelho e o rendimento da reação de 85% determinado por ressonância magnética nuclear de prótons. A partir da análise por calorimetria exploratória diferencial, detectou-se uma diminuição da temperatura de transição vítrea do polímero do óleo de soja (POSE) em relação ao OSE, sugerindo aumento do crescimento das cadeias poliméricas do POSE. Através da análise termogravimétrica, foi possível definir o perfil de degradação do OSE, com degradação em duas etapas, e do POSE, que degrada em apenas uma etapa e demonstra maior estabilidade térmica do POSE pelo aumento das interações moleculares. A reticulação e a hidrofilicidade do POSE foram promovidas com a adição de metacrilato de 2-hidroxietila (HEMA) à formulação por enxertia do monômero pela irradiação gama. Os resultados obtidos identificaram aumento da estabilidade mecânica, da gelificação e da absorção de água com o aumento do conteúdo de HEMA. Por fim, o grau de cristalinidade estimado para esses polímeros enxertados com HEMA de 27,5% foi definido através da difratometria de raios-X. A segunda etapa caracterizou-se pelo (i) desenvolvimento de POSEs com a enxertia de HEMA nas proporções OSE/HEMA 90:10 e 65:35 com irradiação por raios gama nas doses de 50 e 100kGy, (ii) caracterização físico-química dos POSE-HEMA e (iii) análise biológica desses materiais. Através da espectroscopia de infravermelho, pode-se detectar as regiões epoxidadas do POSE, assim como o sucesso da enxertia do monômero HEMA em todas as concentrações e doses de radiação utilizadas. Através da calorimetria exploratória diferencial, calculou-se a energia de ativação (Ea) dos polímeros. A cristalinidade dos materiais foi definida por difratometria de raios-X, mostrando caráter amorfo do material, bem como um pequeno incremento na porcentagem da cristalinidade com o aumento da intensidade das doses de radiação durante a síntese e um decréscimo dessa cristalinidade com o aumento na concentração de HEMA. A análise da citotoxicidade das amostras mostrou a ausência de toxicidade dos POSE-HEMA, confirmando a eficiência das lavagens dos polímeros para retirada de resíduos do processamento. A análise da hemocompatibilidade mostrou ausência de adesão de plaquetas e os testes de crescimento celular nas matrizes foram positivos. Através dos resultados obtidos nesta pesquisa, pôde-se concluir pelo potencial de utilização dos POSE-HEMA na engenharia de tecidos. / Tissue engineering and regenerative medicine have as main objective the morphologic/functional reestablishment of injured tissues and organs using cells, scaffolds, stem cells and control of immunological/biochemical responses promoted by the body. In addition, materials science seeks to develop biocompatible biomaterials that do not promote unwanted immune responses and provide the re-establishment of the functions of the tissue/organ. Polymers of natural origin stand out as biomaterials to resemble biological macromolecules, similarity to the extracellular matrix, reduced chance of inflammation and chronic pacing low or no toxicity. This study aimed the development of macromolecular arrays originated from epoxidized soybean oil (OSE), analyzing the relationship between the chemical structure/biological activity of the macromolecular arrays for use as biomaterials in tissue engineering. The synthesis of OSE was performed through the oleochemical route, whose efficiency was determined by infrared spectroscopy and the reaction yield of 85%, determined by nuclear magnetic resonance spectroscopy. From the analysis by differential scanning calorimetry, it was detected a decrease of the glass transition temperature of the epoxidized soybean oil polymer (POSE) compared with OSE, suggesting an increase of the growth of polymer chains of POSE. Thermogravimetric analysis was performed to define the OSE degradation profile, which degrades in two steps. The POSE degrades in just one step and shows higher thermal stability by the increased molecular interactions. The hydrophilicity and crosslinking of POSE was promoted by the addition of 2-hydroxyethyl methacrylate (HEMA) with the monomer grafting by gamma irradiation. The results showed an increased mechanical stability, gelation and water absorption with the HEMA content increasing. Finally, the degree of crystallinity for such polymers grafted with HEMA was 27.5%, estimated by X-ray diffractometry. The second stage was characterized by (i) developing POSEs with the grafting of HEMA in the proportions OSE / HEMA 90:10 and 65:35 irradiated by gamma rays at doses of 50 and 100kGy, (ii) physico-chemical characterization of POSE-HEMA and (iii) analysis of biological materials. By infrared spectroscopy, it was detect the epoxidized regions of POSE, as well as the successful grafting of the monomer HEMA concentrations with all radiation doses. By differential scanning calorimetry, the activation energy was calculated (Ea) of the polymers. The crystallinity of the material was defined by X-ray diffraction, showing tendency of amorphous material as well as a small percentage of the increase in crystallinity with increasing intensity of radiation doses during this synthesis and a decrease in crystallinity with the increasing concentration of HEMA. The analysis of the samples did not show cytotoxicity on POSE-HEMA and confirmed the efficiency of polymer washings to remove the processing waste. The analysis of hemocompatibility showed any platelet adhesion and the cell growth on the scaffolds was positive. From the results obtained in this research, we concluded by the potential use of POSE-HEMA in tissue engineering.

Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate. One of the most interesting scenarios is the creation of monochromatic gamma-rays from the annihilation or decay of these particles. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. In this thesis, the search for spectral lines with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi) is presented. The satellite was successfully launched from Cape Canaveral in Florida, USA, on 11 June, 2008. The energy resolution and performance of the detector are both key factors in the search and are investigated here using beam test data, taken at CERN in 2006 with a scaled-down version of the Fermi-LAT instrument. A variety of statistical methods, based on both hypothesis tests and confidence interval calculations, are then reviewed and tested in terms of their statistical power and coverage. A selection of the statistical methods are further developed into peak finding algorithms and applied to a simulated data set called obssim2, which corresponds to one year of observations with the Fermi-LAT instrument, and to almost one year of Fermi-LAT data in the energy range 20–300 GeV. The analysis on Fermi-LAT data yielded no detection of spectral lines, so limits are placed on the velocity-averaged cross-section, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%3C%5Csigma%20v%3E_%7B%5Cgamma%20X%7D" />, and the decay lifetime, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ctau_%7B%5Cgamma%20X%7D" />, and theoretical implications are discussed. / QC20100525 / GLAST

Recently, the Oak Ridge National Laboratory (ORNL) successfully encapsulated a new generation of medical grade Cf-252 sources having intensities and size comparable to that of the widely used high-dose-rate (HDR) Ir-192 brachytherapy sources. Advent of the new sources, therefore, marked a new era for Cf-252-based neutron brachytherapy (NBT). As part of source calibration and characterization process, a study has been conducted at Georgia Tech lately on determining the neutron and gamma dose rates in water surrounding the new Cf-252 source. A Lucite-walled water phantom was built for this study. The neutron and gamma dose rates were determined both by ion chamber measurements and by Monte Carlo code MCNP. The results show that the measured neutron absorbed dose rates were approximately 25% lower than that predicted by MCNP for all dose positions in water, suggesting that the Cf-252 content of the new source is actually 25% lower than the ORNL's estimate. The measured gamma absorbed dose rates in water, on the contrary, are higher than that predicted by MCNP. The differences between the measured and MCNP-predicted gamma doses are not uniform for all dose positions; they are most pronounced (~a factor of two) at the distance of 1 cm, and fall to approximately 30% at distances 2 cm and beyond. These results suggest that the spectrum of gamma rays emitted from the new Cf-252 source may contain significantly more low-energy gamma rays than the previously published spectrum used in MCNP.