• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 44
  • 11
  • 8
  • 5
  • Tagged with
  • 94
  • 94
  • 66
  • 63
  • 17
  • 14
  • 14
  • 14
  • 14
  • 14
  • 12
  • 12
  • 11
  • 10
  • 10
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Otimização do feixe de irradiação na instalação para estudos em BNCT junto ao reator IEA-R1 / Optimization of the irradiation beam in the bnct research facility at IEA-R1 reactor

CASTRO, VINICIUS A. de 09 June 2015 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-06-09T18:28:55Z No. of bitstreams: 0 / Made available in DSpace on 2015-06-09T18:28:55Z (GMT). No. of bitstreams: 0 / A Terapia por Captura de Nêutrons pelo Boro (BNCT) é uma técnica radioterapêutica, que visa o tratamento de alguns tipos de câncer, em que sua energia útil é proveniente da reação nuclear promovida pela incidência de nêutrons térmicos no isótopo de 10B. No Brasil existe uma instalação, localizada junto ao canal de irradiação número 3 do Reator de Pesquisas IEA-R1 do IPEN, que foi projetada para o desenvolvimento de pesquisas em BNCT. Para uma aplicação adequada da técnica é necessário que o feixe de irradiação na posição de amostra, seja composto predominantemente por nêutrons térmicos com reduzida contaminação dos componentes do feixe, correspondente aos nêutrons epitérmicos e rápidos e à radiação gama. Este trabalho tem como objetivo monitorar e avaliar o feixe de irradiação na posição de irradiação de amostras, através do uso de detectores de ativação (folhas de ativação), e a partir de simulações utilizando o código de transporte de radiação, MCNP, avaliar mudanças na instalação, mais especificamente no conjunto de filtros e moderadores, para que se aprimore as condições de irradiação na instalação. O trabalho propos uma nova metodologia de cálculo para estudos de otimização do feixe a partir do recurso de redução de variância presente no MCNP, o wwg (weight window generation). Com os resultados obtidos através da adoção de um conjunto maior de folhas de ativação, foi possível a discriminação experimental do feixe de nêutrons em 5 faixas de energia e concluir que a instalação para estudos em BNCT do IPEN possui fluxo de nêutrons térmicos de 108 n/cm2.s, intensidade suficiente para que os estudos na área possam ser realizados com grande potencial de alteração de suas componentes conforme demanda experimental. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
72

Padrões de abundâncias entre estrelas muito pobres em metais no halo da galáxia / Abundance patterns among very metal-poor stars in the halo of the Galaxy: a statistical approach

Vinicius Moris Placco 31 August 2007 (has links)
Um dos maiores desafios da Astrofísica é tentar compreender a complexidade da composição química das estrelas. Elementos com massas atômicas acima de A>60 são formados pelos chamados processos de captura de nêutrons (processo-s e processo-r). A presença destes em espectros de estrelas de baixa massa (longo período de vida) e com pouco conteúdo metálico sugere episódios de enriquecimento por estrelas massivas nos primórdios da Galáxia. Portanto, o estudo das estrelas chamadas \"pobres em metais\" enriquecidas por elementos formados por captura de nêutrons pode reproduzir as condições físicas dominantes à época de sua formação. O objetivo deste trabalho é explorar os padrões de abundâncias das estrelas muito pobres em metais observadas no survey HERES. Através deste estudo, é possível inferir correlações entre elementos químicos e restringir a operação dos processos de captura de nêutrons na Galáxia. Para tanto, utiliza-se técnicas estatísticas como a análise de conglomerados, que permite o estudo da formação de grupos naturais baseado na relação entre as abundâncias elementais. Este estudo fornece uma análise compreensiva de uma amostra de 382 estrelas pobres em metais, além de introduzir duas novas subclasses para estrelas pobres em metais enriquecidas em elementos formados por captura de nêutrons. / One of the most challenging subjects of Astrophysics is trying to understand the complexity of the chemical composition of stellar objects. Spectroscopic observations are widely used nowadays in order to achieve these goals, as they provide the chemical composition of the atmosphere of the stars. Elements with atomic masses above A>60 are formed by the so called neutron capture processes (r-process and s-process). Its presence on low-mass star spectra (which have long life-time) and low metal content suggests episodes of enrichment by high-mass stars that took place in the early times in the Galaxy formation. Then, the study of those \"metal-poor\" stars enriched by neutron-capture elements may help reproduce the physical conditions of the environment from where they were formed. The main goal of this project is to explore the abundance patterns of the very metal-poor stars observed by the HERES survey. This study allows the analysis of the correlations between chemical elements and place some constraints on the operation of the neutron capture processes in the early Galaxy. This approach made use of statistical tools, such as agglomerative nesting, which can identify the formation of natural groups based on relations among elemental abundances. In this context, this study provides a comprehensive analysis of a 382 metal-poor stars sample, and introduces two new subclasses for metal-poor stars with determined abundances of neutron-capture elements.
73

Development of a detector for the simultaneous measurement and for the study of uranium-233 capture and fission yields at the CERN n_TOF neutron source / Développement d'un détecteur pour la mesure simultanée et l’étude des rendements de capture et de fission de l’uranium-233 auprès de la source de neutrons n_TOF au CERN

Bacak, Michael 25 October 2019 (has links)
Des perspectives énergétiques sobres en carbone pour atténuer le changement climatique nécessitent le remplacement des combustibles fossiles par des sources produisant peu de CO2, par exemple l’énergie nucléaire. L'une des options discutées par le Forum international Gen-IV pour la prochaine génération de réacteurs nucléaires consiste à utiliser le cycle du thorium. L'isotope fissile 233U est l'un des isotopes les plus importants du cycle du thorium et est directement responsable du bilan neutronique. L'une des particularités de ce noyau est d'avoir une section efficace de capture qui est inférieure d'un ordre de grandeur à celle de fission. Cette circonstance rend très difficile la mesure de sa section efficace de capture, comme l'atteste seulement deux jeux de données à haute résolution disponibles depuis les années 1960. Dans cette thèse, une nouvelle mesure auprès de la source de neutrons n_TOF est décrite utilisant une nouvelle chambre à fission compacte insérée au centre d'un détecteur de rayons gamma, le calorimètre à absorption totale. La chambre à fission permet d’identifier et de soustraire les rayons gamma de la réaction de fission dans le but d’améliorer la précision de la section efficace de capture de 233U. La chambre à fission est conçue dans cet objectif. Son excellente performance est décrite en détail et permet d'extraire des informations sur les rayons gamma de fission. Une discussion détaillée du processus de réduction des données et des éléments clés de l’analyse, est présentée et aboutit au calcul du rapport alpha de 233U, le rapport entre la section efficace de capture et celle de fission. / A low-carbon energy outlook to mitigate the climate change requires the replacement of fossil fuel by sources with low CO2 emissions, like nuclear energy.. One of the options discussed in the Gen-IV International Forum for the the next generation of nuclear reactors is to use the thorium cycle. The fissile isotope 233U is among the most important isotopes in the thorium cycle and directly responsible for the neutron economy. One of the particularities of this nucleus is to have a capture cross section which is one order of magnitude lower than fission, making the measurement of the 233U capture cross section very challenging as indicated by only two high resolution data sets available since the 1960s. In this thesis, a new measurement at the n_TOF neutron source is described employing a novel compact fission chamber inserted in the center of the Total Absorption Calorimeter g-ray detector. The fission chamber allows to tag and subsequently subtract the gamma rays from the fission reaction aiming to improve the accuracy of the 233U capture cross section.The performance of the custom tailored fission chamber is described in detail and allows to extract information about the prompt fission g-rays. A detailed discussion of the data reduction process and the key elements in the analysis is given resulting in the calculation of the 233U-alpha-ratio, the ratio between the capture and fission cross-section.
74

L-phenylalanine preloading reduces the 10B(n,α)7Li dose to the normal brain by inhibiting the uptake of boronophenylalanine in boron neutron capture therapy for brain tumours. / L-フェニルアラニンの前投与はホウ素中性子捕捉療法に用いるボロノフェニルアラニンの正常脳の取り込みを抑制する

Watanabe, Tsubasa 23 March 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20227号 / 医博第4186号 / 新制||医||1019(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 増永 慎一郎, 教授 宮本 享, 教授 伊佐 正 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM
75

Enlargement of a Modular System—Synthesis and Characterization of an s-Triazine-Based Carboxylic Acid Ester Bearing a Galactopyranosyl Moiety and an Enormous Boron Load

Kellert, Martin, Lönnecke, Peter, Riedl, Bernd, Koebberling, Johannes, Hey-Hawkins, Evamarie 11 April 2023 (has links)
The amount of boron accumulated in tumor tissue plays an important role regarding the success of the boron neutron capture therapy (BNCT). In this article, we report a modular system, combining readily available starting materials, like glycine, 1,3,5-triazine and the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12), as well as alpha-d-galactopyranose for increased hydrophilicity, with a novel boron-rich tris-meta-carboranyl thiol.
76

Peptide-Drug Conjugates and Their Targets in Advanced Cancer Therapies

Hoppenz, Paul, Els-Heindl, Sylvia, Beck-Sickinger, Annette G. 03 April 2023 (has links)
Cancer became recently the leading cause of death in industrialized countries. Even though standard treatments achieve significant effects in growth inhibition and tumor elimination, they cause severe side effects as most of the applied drugs exhibit only minor selectivity for the malignant tissue. Hence, specific addressing of tumor cells without affecting healthy tissue is currently a major desire in cancer therapy. Cell surface receptors, which bind peptides are frequently overexpressed on cancer cells and can therefore be considered as promising targets for selective tumor therapy. In this review, the benefits of peptides as tumor homing agents are presented and an overview of the most commonly addressed peptide receptors is given. A special focus was set on the bombesin receptor family and the neuropeptide Y receptor family. In the second part, the specific requirements of peptide-drug conjugates (PDC) and intelligent linker structures as an essential component of PDC are outlined. Furthermore, different drug cargos are presented including classical and recent toxic agents as well as radionuclides for diagnostic and therapeutic approaches. In the last part, boron neutron capture therapy as advanced targeted cancer therapy is introduced and past and recent developments are reviewed.
77

Fractionnement isotopique de l'Erbium et de l'Ytterbium dans le système Terre-Lune / Er and Yb isotope fractionation in Earth-Moon System

Albalat, Emmanuelle 20 December 2012 (has links)
Nous avons développé une méthode pour analyse isotopique de Yb et Er, deux terres rares aux propriétés chimiques identiques et aux températures de condensation différentes, avec comme objectifs (1) de déterminer la variabilité isotopique de ces éléments dans les processus pétrologiques terrestres, et (2) de comparer leurs compositions isotopiques dans les chondrites, la Terre et la Lune afin de déterminer le rôle potentiel de la condensation à haute température à partir de vapeurs qui a suivi l’impact géant à l’origine de la formation de la Lune. Les résultats obtenus montrent une plus grande variabilité des fractionnements isotopiques de Yb par rapport à ceux d’Er. Deux effets contribuent à cette différence : un effet oxydo-réducteur et un effet de température. La corrélation positive obtenue entre la composition isotopique en Yb, et le rapport La/Yb dans les échantillons terrestres, peut être interprétée par la présence d’une faible fraction d’ Yb(2+), Yb étant majoritairement présent sous la forme Yb(3+). La kimberlite (liquide magmatique formé par un faible taux de fusion partielle) est enrichie en isotopes lourds et les grenats, résidus de fusion partielle, sont isotopiquement légers, tandis que les basaltes de ride ou d’îles ont des compositions isotopiques intermédiaires.La composition isotopique en Yb de la Lune est enrichie en isotopes légers par rapport à celle de la Terre et des chondrites. Dans le disque proto-lunaire, les frictions entre les phases fondues et gazeuses favorisent la migration des premiers condensats très réfractaires et enrichis en isotopes lourds vers la Terre, et celle de la vapeur enrichie en isotopes légers, vers l’extérieur, au-delà de la limite de Roche à partir de laquelle la Lune s’accrète. Ceci est un nouvel argument en faveur de la condensation de la Lune à partir de vapeur générée par un impact géant. La mesure de la composition isotopique d’Er dans les échantillons lunaires reflète pour la première fois la capture par 167Er des neutrons produits par interaction du rayonnement cosmique galactique avec la surface lunaire. L’apport de Er aux systèmes communément utilisés pour déterminer le spectre d’énergie des neutrons d’un matériau peut permettre de couvrir une gamme énergétique plus large et de disposer ainsi d’un proxy plus complet pour l’étude des histoires des irradiations des matériaux planétaires. / Er and Yb are two refractory rare-earth elements that have overall similar crystallochemical properties but differ in their temperatures of condensation from the nebular gas. We developed an analytical protocol for the measurement of Er and Yb isotope compositions 1) to establish their isotopic variability in terrestrial magmatic processes 2) to compare their isotopic composition in chondrites, Earth and Moon in order to study fractionation during the high temperature condensation of vapor formed by the giant impact that generated the Moon. The range of mass-dependent isotope fractionation obtained is larger for Yb than Er isotopes. Two effects contribute to the difference between Er and Yb : a redox effect and a temperature effect.First, for terrestrial rocks, the presence of a small fraction of Yb(2+) together with the most common Yb(3+) is inferred from the positive corre- lation between δYb and the La/Yb ratio. Yb(3+) fractionates favorably into tighter bonds and, at the same time, is much more compatible than Yb(2+). Small-degree melts (kimberlite) tend to be enriched in the heavy Yb isotopes, whereas the opposite is true for residual garnets. Second, the stronger volatility of Yb with respect to Er is demonstrated by the apparent deficit of heavy Yb isotopes in the Moon with respect to the Earth, chondrites, and eucrites. Separation of vapor from melt and of heavy from light isotopes is first expected during the adiabatic expansion of the initial vapor plume. Subsequently, friction between melt and gas tends to further enrich the Moon feeding zone in silicate vapor to compensate the inward migration of melt out of the pre-lunar disk. The lighter isotope composition of Yb in lunar samples provides new evidence that the Moon formed by condensation of silicate vapor in the aftermath of the giant lunar impact.Erbium isotope ratios in lunar samples reflect for the first time the capture by 167Er of secondary neutrons produced by interactions of galactic cosmic rays with the lunar surface. The cross section of 167Er for neutron capture being particularly strong and its first resonance standing out at energies poorly covered by other nuclides, 167Er anomalies may help refine the knowledge of the neutron energy spectrum on the Moon and other planetary bodies.
78

Avaliação da atividade antitumoral do composto DM-1 e da terapia de captura de nêutrons por boro em associação ao quimioterápico dacarbazina no tratamento de melanoma / Antitumor evaluation of DM-1 compound and boron neutron capture therapy associated to dacarbazine chemotherapeutic in melanoma treatment

Flores, Fernanda Faião 19 February 2013 (has links)
O melanoma maligno é a forma mais agressiva dos tumores cutâneos. Sendo o responsável por mais de 75% das mortes relativas á este tipo de câncer. O principal quimioterápico utilizado no tratamento do melanoma é a dacarbazina (DTIC), entretanto, as taxas de resposta são insatisfatórias. O composto DM-1 é um análogo estrutural da curcumina, e por esta razão possui propriedades biológicas semelhantes, como agente antiproliferativo e próapoptótico. A terapia de captura de nêutrons por boro (BNCT) atua por meio da deposição do isótopo 10Boro nas células tumorais e após a irradiação de nêutrons térmicos há produção de partículas alfa e lítio que destroem a célula. Neste trabalho estudou-se o mecanismo de ação destas três terapias, DTIC, DM-1 e BNCT no tratamento do melanoma e seus efeitos em células normais in vitro com a finalidade de obtenção de modalidades terapêuticas diferentes para o tratamento desta neoplasia. A IC50 foi obtida pela metodologia de MTT, além da análise da progressão do ciclo celular e marcadores de morte celular por citometria de fluxo. O composto DM-1 e a BNCT apresentaram efeito citotóxico seletivo para as linhagens de melanoma, com alta produção de radicais livres peroxidados. Nas mesmas condições, estes efeitos foram mínimos em células normais, diferente do tratamento com DTIC. Houve diminuição da proporção de matriz extracelular e colágeno solúvel sintetizado em células de melanoma tratadas com DM-1, BNCT e DTIC, entretanto, o quimioterápico ocasionou isoladamente diminuição também em células normais. O potencial elétrico mitocondrial das células de melanoma foi diminuído nos três protocolos de tratamento, assim como houve aumento na quantidade de DNA fragmentado. Este efeito não foi encontrado em células normais tratadas com DM-1 e BNCT. O composto DM-1 foi capaz de induzir apoptose via intrínseca e extrínseca, avaliado pela Anexina V e por marcadores de cinética e de morte celular. A terapia de BNCT induziu apoptose e necrose, indicando que esta terapia atua por diferentes vias em cada linhagem celular. BNCT e DM-1 induziram aumento na expressão dos marcados próapoptóticos, como Bax, citocromo c, caspase 3 e 8 clivadas, além de diminuir os valores na expressão de ciclina D1 e Ki-67, relacionados com a progressão do ciclo celular e proliferação. O quimioterápico DTIC apresentou alguns indícios de apoptose em células de melanoma, mas seus efeitos em células normais foram extensivos, ocasionando morte e parada do ciclo celular em melanócitos, células endoteliais e fibroblastos. O composto DM-1 apresentou formação de corpos apoptóticos, modificações no citoesqueleto e clivagem de caspase 9 e Parp em linhagens de melanoma humano. Desta forma, o composto DM-1 e a BNCT mostraram-se ferramentas terapêuticas mais eficazes no controle da progressão e no aumento da morte celular em células de melanoma. O poder efetivo da terapia de BNCT e do composto DM-1 faz com que a possibilidade de terapias combinatórias tenha resultados extremamente favoráveis na modulação da resposta proliferativa desses tumores. / Malignant melanoma is the most aggressive skin cancer. It is responsible for more than 75% of deaths. The main and most active chemotherapy in the melanoma treatment is represented by dacarbazine (DTIC), however, response rates are disappointing. The DM-1 compound is a curcumin structural analogue and it has similar biological properties, such as an antiproliferative and pro-apoptotic agent. Boron Neutron Capture Therapy (BNCT) works through the deposition of the isotope 10Boron in tumor cells, with subsequent irradiation of thermal neutrons, which produce alpha particles and lithium that destroy the cell. In this study, the action mechanism of these three therapies, DTIC, DM-1 and BNCT in the melanoma treatment and its effects in vitro on normal cells were studied in order to obtain different therapeutic modalities for cancer treatment. The IC50 was obtained by MTT method, besides the analysis of cell cycle progression and cell death markers by flow cytometry. The DM-1 and BNCT showed selective cytotoxic in melanoma cell lines, with high of free radicals production. In the same conditions, these effects were minimal in normal cells, unlike the treatment with DTIC. There was a decrease in the proportion of extracellular matrix and soluble collagen synthesized in melanoma cells treated with DM-1, BNCT and DTIC, however, only DTIC also resulted in decreased in normal cells. The mitochondrial electrical potential of melanoma cells was decreased in the three treatment protocols, as there was an increase in the amount of fragmented DNA. This effect was not found in normal cells treated with DM-1 and BNCT. The compound DM-1 was able to induce apoptosis by the intrinsic and extrinsic pathways, as assessed by Annexin V, cell death and kinetic markers. BNCT induced apoptosis and necrosis, indicating that this therapy acts through different pathways in each cell line. DM-1 and BNCT induced an increase of pro-apoptotic markers, such as Bax, cytochrome c, cleaved caspase 3 and 8 expression, and they reduced cyclin D1 and Ki-67, expression related to the progression of the cell cycle and proliferation. The DTIC has shown some signs of apoptosis in melanoma cells, but its effect on normal cells were extensive, causing death and cell cycle arrest in melanocytes, fibroblasts and endothelial cells. The DM-1 showed apoptotic bodies formation, cytoskeleton changes and caspase 9 and Parp cleavage in human melanoma cell lines. Thus, the DM-1 and BNCT showed as therapeutic tools more with high effectiveness in controlling the cell cycle progression and cell death increase in melanoma cells. The effectiveness of BNCT and DM-1 makes the possibility of combinatorial therapies, with extremely favorable results in the modulation of the proliferative response of these tumors.
79

Dosimetria "in vitro" em BNCT com o uso de filmes finos de boro e detectores PADC / "In vitro" dosimetry in BNCT using boron thin films and PADC detectors

Smilgys, Bárbara, 1986- 26 May 2017 (has links)
Orientadores: Sandro Guedes de Oliveira, Jörg Kobarg / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-02T02:16:09Z (GMT). No. of bitstreams: 1 Smilgys_Barbara_D.pdf: 17430152 bytes, checksum: 82ba0350f1128e5f264b9ee314a4fef6 (MD5) Previous issue date: 2017 / Resumo: BNCT (do inglês, Boron Neutron Capture Therapy) é uma terapia para tratamento de cânceres que tem se mostrado efetiva em casos de metástases e tumores inoperáveis. Sua base física é a reação de captura de nêutrons pelo boro resultando na produção de uma partícula 'alfa' e de um íon de recuo de lítio: 10B(n,'alfa')7Li. O objetivo principal deste trabalho foi verificar a viabilidade de monitoração de taxa de reações de interesse em BNCT e estimar, a partir das taxas de reações medidas, quantidades probabilísticas que descrevam o campo de irradiação, utilizando-se filmes finos de boro e detectores plásticos de traços nucleares (PADC). Além disto, pretendia-se realizar estudos biológicos de sobrevivência celular, para então, com a descrição detalhada do campo de irradiação e medidas de efeitos radiobiológicos, avaliar possíveis correlações entre os efeitos de heterogeneidade de deposição de energia (quantidades probabilísticas) e as frações de sobrevivência celular. Assim, o trabalho foi dividido em três partes experimentais fundamentais: a calibração do conjunto de filmes finos de boro acoplados a detectores PADC, cuja importância é a quantificação de átomos de 10B presentes nos filmes finos utilizados para a medida da taxa da reação 10B(n,'alfa')7Li, a realização de experimentos in vitro com irradiações com partículas 'alfa' que visavam o desenvolvimento da metodologia de quantificação de sobrevivência celular, que seriam utilizadas posteriormente, quando realizados os experimentos in vitro com nêutrons, os quais unem os resultados obtidos das calibrações dos filmes finos de boro e os métodos aplicados nas análises de resposta biológica de irradiações de células com partículas 'alfa'. A partir das fluências de partículas 'alfa' e das taxas da reação 10B(n,'alfa')7Li, calculou-se as médias da distribuição de eventos poissonianos em uma célula de área A e com estas médias foram feitas simulações de distribuição de eventos em uma matriz de células, para quantificação da formação de clusters de células (primeiras vizinhas) atingidas. Por se tratar de um problema de muitas variáveis (sobrevivência celular, média de eventos, eventos por célula, células por cluster e total de clusters), escolheu-se fazer uma análise de componentes principais, na tentativa de se determinar quais destas variáveis introduzem as maiores variabilidades no problema. Mostrou-se que a formação de clusters de células vizinhas influencia a inativação das células, embora não tenha sido possível estabelecer modelos quantitativos. Portanto, com este trabalho, foi possível estabelecer uma metodologia segura para a quantificação da taxa de reação de interesse na BNCT, e a partir desta, calcular descritores que levam em conta a heterogeneidade da distribuição de energia durante as irradiações. A partir de dados de experimentos in vitro, tanto de irradiações com partículas 'alfa' quanto com nêutrons térmicos, foi possível encontrar correlações com estes descritores de heterogeneidade e conclui-se, então, que eles podem ser usados como descritores de efeitos biológicos / Abstract: BNCT (Boron Neutron Capture Therapy) is a therapy for the treatment of cancers that has been proven to be effective in cases of metastases and inoperable tumors. Its physical basis is the boron neutron capture reaction resulting in the production of an 'alpha' particle and a lithium recoil ion: 10B(n,'alpha')7Li. The main objective of this work was to verify the feasibility of monitoring the main reactions rates in BNCT using boron thin films and nuclear tracks plastic detectors (PADC) and to estimate, from the reactions rates measured, probabilistic quantities that describe the irradiation field. In addition, it was intended to carry out biological studies of cell survival, and with the detailed description of the field of irradiation and measurements of radiobiological effects, to evaluate possible correlations between the effects of heterogeneity of energy deposition (probabilistic quantities) and fractions of cell survival. Thus, the work was divided into three fundamental experimental parts: the calibration of the setup of boron thin films coupled to PADC detectors (whose importance is the quantification of the 10B atoms present in the thin films used for the measurement of 10B(n,'alpha')7Li reaction rate), the in vitro experiments carried out with irradiations with particles 'alpha' aiming to develop the methodology for cell survival quantification, which would later be used when performing the in vitro experiments with neutrons, which combine the results obtained from the calibrations of the boron thin films and the methods applied for cell survival quantification. From the 'alpha' particles fluences and the 10B(n,'alpha')7Li reaction rates, it was possible to calculate the mean of the Poisson distribution for events happening inside a cell of area A. Simulations were performed for quantifying the number of clusters formed by neighbor cells that were hit by an incident particle. Since this is a problem of many variables (cell survival, poissonian mean, events per cell, cells per cluster and total number of clusters), it was performed a principal components analysis in an attempt to determine which of these variables introduce the greatest variabilities to the problem. It was shown that the cells clusters formation influences cell inactivation, though it was not possible to establish quantitativy models. Therefore, with this work, it was possible to establish a safe methodology for the quantification of the reaction rate of interest in BNCT, and from this, to calculate descriptors that take into account the heterogeneity of energy distribution during irradiation. From data from both in vitro experiments of cells irradiation with 'alpha' particles and with thermal neutrons, it was possible to find correlations with these descriptors of heterogeneity and it is concluded, then, that they can be used as descriptors for biological effects / Doutorado / Física / Doutora em Ciências
80

Développement et caractérisation d’une cible active scintillante pour l’étude de la fission et étude des possibilités de calorimétrie de la fission avec le détecteur CARMEN / Development and characterization of an active scintillating target for fission study, and fission calorimetry study possibilities avec the CARMEN detector

Vayre, Sylvain 27 March 2015 (has links)
La désexcitation des fragments de fission reste mal comprise et les modèles théoriques ne permettent pas de prédire et d’expliquer toutes les corrélations observées dans le processus de fission. Il y a un besoin important de données simultanées sur les émissions de neutrons et de rayonnements gamma et sur l’énergie cinétique des fragments de fission. Dans ce contexte, l’utilisation d’un détecteur de fragments de fission avec le détecteur CARMEN permettrait de fournir des données contraignantes pour les modèles grâce à la mesure simultanée de la multiplicité neutronique, de l’énergie totale gamma rayonnée, de l’énergie cinétique totale des fragments et potentiellement de l’énergie totale neutron. L’objectif de ce travail de thèse a consisté à développer un détecteur de fragments de fission et à l’utiliser en association avec CARMEN pour réaliser des mesures calorimétriques de la fission. Dans un premier temps, nous avons développé un nouveau détecteur pour l’étude de la fission dont le principe est de mettre un actinide en solution dans un scintillateur organique. Des simulations Monte Carlo et différentes expériences sous faisceau de neutrons ont permis de caractériser et d’optimiser les performances de ce détecteur qui peut être utilisé comme trigger fission pour différentes mesures de sections efficaces de fission, de taux de fission spontanée ou encore comme veto fission. Dans un second temps, nous avons étudié les possibilités de mesure de l’énergie totale gamma et neutron rayonnée dans la fission avec CARMEN grâce à la caractérisation expérimentale de ses performances et à la simulation Monte Carlo et l’analyse de sa réponse « prompte » aux neutrons et aux rayonnements gamma / Still, the nuclear fission process and the de-excitation of the fission fragments is not fully understood. Current theoretical models can not predict and explain correctly every experimentally observed correlations, and new correlated data upon neutron emission, gamma-ray emission and kinetic energy of the fission fragments are needed. In this context, coincident use of a fission fragment detector and the CARMEN detector would provide compelling data for these models by measuring both neutron multiplicity, total gamma-ray energy, total kinetic energy and possibly total neutron energy. The work presented here consists in developing a fission fragment detector and using it together with CARMEN in order to perform fission calorimetry measurements. Initially, we developed a new detector for fission studies whose principle is dissolving the actinide of choice into an organic liquid scintillator. Monte Carlo simulations and neutron induced experiments were used to fully characterize its performances and shown it can be used as a fission trigger for various measurements, such as fission cross section or spontaneous fission rate measurements, and used as a fission veto. The second part of this work was dedicated to the study of CARMEN’s ability to measure the total gamma-ray energy and total neutron energy released in fission. For this purpose, lab characterization of the detector’s performances and Monte Carlo simulation and analysis of its “prompt” response to neutrons and gamma-rays were performed

Page generated in 0.0459 seconds