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Made available in DSpace on 2014-10-09T12:50:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:47Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:50:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:47Z (GMT). No. of bitstreams: 0 / Neste trabalho são apresentados os estudos das condições de resposta de um diodo de Si, com estrutura de múltiplos anéis de guarda, na detecção e espectrometria de partículas alfa. Este diodo foi fabricado por meio do processo de implantação iônica (Al/p+/n/n+/Al) em um substrato de Si do tipo n com resistividade de 3 kohm•cm, 300 mícrons de espessura e área útil de 4 mm2. Para usar este diodo como detector, a face n+ deste dispositivo foi polarizada reversamente, o primeiro anel de guarda aterrado e os sinais elétricos extraídos da face p+. Estes sinais eram enviados diretamente a um pré-amplificador desenvolvido em nosso laboratório, baseado no emprego do circuito híbrido A250 da Amptek, seguido da eletrônica nuclear convencional. Os resultados obtidos com este sistema na detecção direta de partículas alfa do Am-241evidenciaram excelente estabilidade de resposta com uma elevada eficiência de detecção (= 100 %). O desempenho deste diodo na espectrometria de partículas alfa foi estudado priorizando-se a influência da tensão de polarização, do ruído eletrônico, da temperatura e da distância fonte-detector na resolução em energia. Os resultados mostraram que a maior contribuição para a deterioração deste parâmetro é devida à espessura da camada morta do diodo (1 mícron). No entanto, mesmo em temperatura ambiente, a resolução medida (FWHM = 18,8 keV) para as partículas alfa de 5485,6 keV (Am-241) é comparável àquelas obtidas com detectores convencionais de barreira de superfície freqüentemente utilizados em espectrometria destas partículas. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Doctor Educationis / The progressive development of scintillator detectors has made it possible to perform direct electronic lifetime determination up to a few hundred nanoseconds. The 2” by 2” LaBr3:Ce detectors provide a combination of excellent time resolution and good energy resolution. Recently a fast timing array has been commissioned at iThemba LABS, Cape Town consisting of eight 2” by 2” LaBr3:Ce detectors. Test measurements using radioactive sources produced at the laboratory were conducted. Six 2” by 2” LaBr3:Ce detectors were coupled to the AFRODITE array as their first in-beam experiment. AFRODITE consisted of eight HPGe clover detectors as well as two 3.5” x 8” LaBr3:Ce detectors. A particle telescope was used to select the desired reaction channels. The reactions of interest 45Sc(p,d)44Sc and 45Sc(p,α) 42Ca were carried out at a beam energy of 27 MeV. The current analysis also investigates the rare earth nucleus 150Gd which was populated through 150Sm(α,4n)150Gd at a beam energy of 48 MeV. Through these reactions, excited states that have lifetimes which are apt for the characterization of the 2” by 2” LaBr3:Ce detectors were populated. Various techniques such as the slope method and the centroid shift method have been employed to extract the lifetimes of excited states. Lifetimes that were previously measured for 44Sc and 42Ca were measured again in this work. New lifetimes were obtained 44Sc and 150Gd. Shell Model calculation were done to compare experimental and theoretical results. All these endeavours will seek to unveil the quadrupole moment of nuclei and their intrinsic behaviour.

Spectral computed tomography with energy-resolving detectors has a potential to improve the detectability of images and correspondingly reduce the radiation dose to patients by extracting and properly using the energy information in the broad x-ray spectrum. A silicon photon-counting detector has been developed for spectral CT and it has successfully solved the problem of high photon flux in clinical CT applications by adopting the segmented detector structure and operating the detector in edge-on geometry. The detector was evaluated by both the simulation and measurements. The effects of energy loss and charge sharing on the energy response of this segmented silicon strip detector with different pixel sizes were investigated by Monte Carlo simulation and a comparison to pixelated CdTe detectors is presented. The validity of spherical approximations of initial charge cloud shape in silicon detectors was evaluated and a more accurate statistical model has been proposed. A photon-counting energy-resolving application specific integrated circuit (ASIC) developed for spectral CT was characterized extensively by electrical pulses, pulsed laser and real x-ray photons from both the synchrotron and an x-ray tube. It has been demonstrated that the ASIC performs as designed. A noise level of 1.09 keV RMS has been measured and a threshold dispersion of 0.89 keV RMS has been determined. The count rate performance of the ASIC in terms of count loss and energy resolution was evaluated by real x-rays and promising results have been obtained. The segmented silicon strip detector was evaluated using synchrotron radiation. An energy resolution of 16.1% has been determined with 22 keV photons in the lowest flux limit, which deteriorates to 21.5% at an input count rate of 100 Mcps mm−2. The fraction of charge shared events has been estimated and found to be 11.1% for 22 keV and 15.3% for 30 keV. A lower fraction of charge shared events and an improved energy resolution can be expected by applying a higher bias voltage to the detector. / <p>QC 20121123</p>

著者名別形の記述を修正（2022-04-21） / 京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第16850号 / 工博第3571号 / 新制||工||1540(附属図書館) / 29525 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 河合 潤, 教授 酒井 明, 教授 大塚 浩二 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM