Dissertations / Theses on the topic 'Scintillation material'

L'ion ytterbium trivalent présente la particularité de pouvoir donner lieu à deux émissions aux propriétés spectroscopiques différentes : l'une, de durée de vie courte, dans l'ultraviolet (émission de transfert de charge) employée au sein de détecteurs tels que les scintillateurs, et l'autre, de durée de vie longue, dans l'infrarouge (émission de type 4f x 4f) pour des applications de type laser.La relation étroite qui existe entre structure et propriétés de la matière est illustrée au travers de l'étude de la luminescence de l'ytterbium, dans l'ultraviolet et l'infrarouge, inséré dans le borate Li6Y(BO3)3 ainsi que deux oxyborates : LiY6O5(BO3)3 et Y17,33B8O38. Pour la première fois dans des oxyborates une émission de transfert de charge de l'ytterbium a été observée. Une approche théorique a permis le calcul des courbes à une seule coordonnée de configuration des niveaux d'énergie de la liaison ytterbium - oxygène, ainsi que la simulation de l'extinction thermique de cette émission. L'étude de la spectroscopie infrarouge de l'ytterbium dans ces composés a été réalisée et une attribution des niveaux d'énergie est proposée dans le cas du borate Li6Y(BO3)3 : Yb3+. Une approche originale est également introduite avec l'étude des états de transfert de charge pour les trois composés via l'émission dans l¤infrarouge. Les premiers tests portant sur les performances lasers dans trois régimes de fonctionnement (continu, déclenché et blocage de modes) d¤un cristal de Li6Y(BO3)3 : Yb3+ (Yb-LYB) sont reportés.

First part of this thesis is a theoretical essay which deals with the basics of scanning electron microscopy, with structure and function of a scanning electron microscope, its’ special case of an various pressure scanning electron microscope, electron interaction with surrounding environment and with a scintillation detector. The applied part of the thesis is focused on evaluation of material contrast on Cu-W specimen. Material contrast is evaluated for different pressures of water vapors in the microscope specimen chamber and for different detection conditions.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2010.
Thesis Advisor(s): Smith, Craig F. ; Second Reader: Bowden, Nathaniel S. "June 2010." Description based on title screen as viewed on July 16, 2010. Author(s) subject terms: Antineutrino detection, Inverse Betad Decay, neutron capture, lithium gadolinium borate. Includes bibliographical references (p. 71-73). Also available in print.

This research explores the synthesis of anthracene and stilbene-based metal-organic framework (MOF) structures as potential scintillating (radioluminescent) materials for use in the detection of gamma radiation. The organic molecules 9,10-anthracenedicarboxylic acid (ADCH2) and trans-4,4’-stilbenedicarboxylic acid (SDCH2), were each used as a linker, in combination with a range of lanthanide metal ions, to synthesize novel three dimensional MOF structures under hydrothermal conditions. With ADCH2, the early period lanthanides yield isostructures with the metal ion in higher coordination (nine) than for those with late period metals (seven). The ADC-MOFs show linker-based photoluminescence properties with well defined vibronic peaks in their emission profile and their emission (λmax~435 nm) blue shifting from that of the ADCH2 powder (~500 nm) and closer to the organic molecule in monomer arrangement (λmax ~ 420 nm). The structures also show photoluminescence lifetimes between 1 and 2 ns, which is similar to the reported value for monomeric anthracene units. The blue-shift and reduction in lifetime, compared to ADCH2, are indicative of minimal π-π interactions amongst the aromatic moieties, thereby limiting the non-radiative relaxation pathways. On exposure to ionizing radiation (protons and g- rays), the ADC-MOFs demonstrated scintillation properties, with a radioluminescence lifetime of ~ 6 ns which is similar to that of the ADCH2 powder. A combination of SDCH2 and lanthanide metal ions produced two isostructured MOFs containing Tm3+ and Er3+, under the hydrothermal synthesis conditions explored. The 3-D structure contained ultra large diamond-shaped pores with dimensions of 16 Å x 30 Å. A blue-shift of fluorescence spectra was observed for the SDC-MOF structures (λmax ~ 425 nm) compared to that of bulk SDCH2 powder (λmax ~475 nm), and closely resembling that of monomeric isolated SDC units (λmax~475 nm). Their photoluminescence lifetime is ~0.76 ns, about half of that observed for SDCH2 powder. The blue shift and reduction in lifetime (compared to SDCH2) is attributed to minimal π-π interactions between SDC units in the MOF structure, thus minimizing associated non-radiative relaxation pathways. The isolation of anthracene and stilbene in MOF structures therefore has the potential to improve their performance as scintillators.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Neste trabalho avaliou-se o efeito da microestrutura na cintilação de nanopartículas de Y2O3:Eu3+. Neste contexto utilizam-se dois métodos de síntese, o método Pechini, que apresenta matéria orgânica remanescente de síntese, assim como, aglomerados micrométricos constituídos de partículas nanométricas com variação da forma e tamanho. Utilizando o método de precipitação homogênea modificado, estudou-se a influência de partículas com estreita distribuição de tamanho e morfologia esférica. A estrutura apresenta simetria cubica (grupo espacial Ia3) e com os estudos espectroscópicos caracterizou-se a presença de pelo menos dois sítios de simetria sendo eles C2 e S6. Avaliou-se o efeito da temperatura de tratamento térmico de 700 a 1100 ºC na cristalinidade do material através de difratometria de raios x do pó. Por meio da espectroscopia de luminescência com excitação de raios X, avaliou-se o efeito da microestrutura do material na cintilação. Por meio da área integrada da transição 5D0→7F2 observou-se a relação da intensidade de emissão com as temperaturas de tratamento térmico e com o tamanho de cristalito, calculados pela equação de Scherrer. Observou-se o efeito de defeitos na cintilação das partículas, pois, em menores temperaturas de tratamento térmico e/ou menores tamanhos de cristalitos os defeitos presentes no material se apresentam em maiores proporções, deste modo proporcionando mecanismos não radiativos de recombinação. Utilizando as curvas de danos de radiação pode-se caracterizar algumas etapas envolvidas na cintilação, como a criação de defeitos, que apresentaram dependência com o tamanho de cristalito obtido para o método Pechini. Após longos períodos sob radiação X os materiais apresentam intensidade de emissão inalterada ou até mesmo um aumento significativo, comportamento que depende dos mecanismos de...
In this work one consider the effects of microstructure in the scintillations properties of Y2O3:Eu3+. Two preparation methods were used; the Pechini method, which exhibits remaining organic matter derived from the synthesis, and tends to form agglomerates of nanoparticles with variable shape and size. By using a modified method of homogeneous precipitation one studied the effects of spherical particles with narrow distribution of particle size in its scintillation properties. The Y2O3 presents cubic symmetry (Ia3 space group) and with spectroscopy results at least two Y3+ symmetry sites were identified, a C2 and a S6 site. The firing temperature of the samples (700- 1100oC) was correlated with its crystallinity by X-ray diffractometry data. The relation between the integrated emission intensity of 5D0 ® 7F2 transition and the firing temperature or the Scherrer crystallite size were analyzed, and from these results were observed the influence of defects in the scintillation of particles, since in lower firing temperatures and/or lower crystallite sizes defects are presented in higher concentrations, leading to non-radiactive paths of pairs recombination. By using radiation damage measurements it was possible to identify the steps involved in the scintillation process, as the creation of defects, which presents a direct relation with the particles characteristics. After a long exposition time to the incoming ionizing radiation, the materials present constant scintillation intensity or a linear growth by means of recovery processes. Samples prepared by the homogeneous precipitation presented higher scintillation intensity and a higher recovery ability when fired at high temperatures. A comparison between the two methods in relation to crystallinity (firing temperature of 1100oC) revels similar results, however spherical particles presented higher scintillation intensity and... (Complete abstract click eletronic access below)

Resumo: Neste trabalho avaliou-se o efeito da microestrutura na cintilação de nanopartículas de Y2O3:Eu3+. Neste contexto utilizam-se dois métodos de síntese, o método Pechini, que apresenta matéria orgânica remanescente de síntese, assim como, aglomerados micrométricos constituídos de partículas nanométricas com variação da forma e tamanho. Utilizando o método de precipitação homogênea modificado, estudou-se a influência de partículas com estreita distribuição de tamanho e morfologia esférica. A estrutura apresenta simetria cubica (grupo espacial Ia3) e com os estudos espectroscópicos caracterizou-se a presença de pelo menos dois sítios de simetria sendo eles C2 e S6. Avaliou-se o efeito da temperatura de tratamento térmico de 700 a 1100 ºC na cristalinidade do material através de difratometria de raios x do pó. Por meio da espectroscopia de luminescência com excitação de raios X, avaliou-se o efeito da microestrutura do material na cintilação. Por meio da área integrada da transição 5D0→7F2 observou-se a relação da intensidade de emissão com as temperaturas de tratamento térmico e com o tamanho de cristalito, calculados pela equação de Scherrer. Observou-se o efeito de defeitos na cintilação das partículas, pois, em menores temperaturas de tratamento térmico e/ou menores tamanhos de cristalitos os defeitos presentes no material se apresentam em maiores proporções, deste modo proporcionando mecanismos não radiativos de recombinação. Utilizando as curvas de danos de radiação pode-se caracterizar algumas etapas envolvidas na cintilação, como a criação de defeitos, que apresentaram dependência com o tamanho de cristalito obtido para o método Pechini. Após longos períodos sob radiação X os materiais apresentam intensidade de emissão inalterada ou até mesmo um aumento significativo, comportamento que depende dos mecanismos de... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: In this work one consider the effects of microstructure in the scintillations properties of Y2O3:Eu3+. Two preparation methods were used; the Pechini method, which exhibits remaining organic matter derived from the synthesis, and tends to form agglomerates of nanoparticles with variable shape and size. By using a modified method of homogeneous precipitation one studied the effects of spherical particles with narrow distribution of particle size in its scintillation properties. The Y2O3 presents cubic symmetry (Ia3 space group) and with spectroscopy results at least two Y3+ symmetry sites were identified, a C2 and a S6 site. The firing temperature of the samples (700- 1100oC) was correlated with its crystallinity by X-ray diffractometry data. The relation between the integrated emission intensity of 5D0 ® 7F2 transition and the firing temperature or the Scherrer crystallite size were analyzed, and from these results were observed the influence of defects in the scintillation of particles, since in lower firing temperatures and/or lower crystallite sizes defects are presented in higher concentrations, leading to non-radiactive paths of pairs recombination. By using radiation damage measurements it was possible to identify the steps involved in the scintillation process, as the creation of defects, which presents a direct relation with the particles characteristics. After a long exposition time to the incoming ionizing radiation, the materials present constant scintillation intensity or a linear growth by means of recovery processes. Samples prepared by the homogeneous precipitation presented higher scintillation intensity and a higher recovery ability when fired at high temperatures. A comparison between the two methods in relation to crystallinity (firing temperature of 1100oC) revels similar results, however spherical particles presented higher scintillation intensity and... (Complete abstract click eletronic access below)
Orientador: Marian Rosaly Davolos
Coorientador: Marco Aurélio Cebim
Banca: Flávio Maron Vichi
Banca: Vera Regina Leopoldo Constantino
Mestre

The design of biomaterials, historically initiated and developed by physicians and engineers, in the last decades has slowly shifted toward a more biochemical based approach. For the replacement, repair and regeneration of tissues scientists are now focusing on materials that stimulate specific biological response at the molecular level. These biomaterials have already shown interesting applications in cell proliferation, differentiation, and extracellular matrix production and organization when the material modifications are designed to elicit specific interactions with cell integrins. In the present work we propose the application of this strategy for the development of blood-compatible materials. We first identified, in the coagulation cascade a key enzyme that constitute a valuable biological target for the development of anti-thrombogenic compounds. Piperazinyl-amide derivatives of N-alfa-(3-trifluoromethyl-benzenesulfonyl)-L-arginine were synthesized as graftable thrombin inhibitors. These inhibitors provided a spacer arm for surface grafting and a fluorine tag for XPS (X-ray photoelectron spectroscopy) detection. The possible disturbance of biological activity due to a variable spacer-arm fixed on the N-4 piperazinyl position was evaluated in vitro against human alfa-thrombin, in silico by molecular modelling and via X-ray diffraction study. Selected inhibitors, having inhibition potency in the mM range, were grafted on polyesters surface via wet chemistry and photochemical activation treatments. Wet chemistry surface grafting was performed by specific hydroxyl chain-ends activation and resulted in bioactive molecules fixation of 20-300pmol/cm2. The photochemical grafting was performed using a molecular clip providing an aromatic azide, for nitrene insertion into a polymer, and an activated ester for grafting of tag compounds. This grafting technique resulted in a dramatic increase in fixed bioactive signals (up to nmol/cm2). The material blood-compatibilization induced by the surface fixation of the inhibitors, was measured by a static blood clot weight measurement test. The wet chemistry grafting technique resulted in moderate blood-compatibilization while by the photochemical grafting method important decrease in surface blood clot formation was observed. In the latter case, the blood response to material contact was found to be strongly affected by the polyester surface photo-degradation induced by the activation treatment.

Els materials escintil·ladors són àmpliament utilitzats com a detectors en els sistemes de detecció de diverses aplicacions, com la imatge mèdica, la física d’alta energia, l’astrofísica i en proves no destructives (seguretat aeroportuària, control industrial, etc.). Hi ha diversos requisits importants per avaluar favorablement el rendiment d’un escintil·lador. Donat que no existeix el escintil·lador ideal, s’estan dedicant molts esforços a buscar nous escintil·ladors inorgànics amb millors propietats que els dels escintil·ladors existents. En aquesta tesi, es creixen monocristalls amb alta qualitat cristal·lina de KGd(PO3)4 tipus III dopats amb Ce3+ i Pr3+, i també nanocristalls de Pr:KGd(PO3)4 tipus III per posteriorment caracteritzar-los estructuralment i òpticament com a possibles nous materials escintil·ladors. Aquests monocristalls es creixen a partir de solucions d’alta temperatura mitjançant la tècnica Top Seeded Solution Growth-Slow Cooling (TSSG-SC) i els nanocristalls es sintetitzen mitjançant el mètode de Pechini. La caracterització estructural inclou la morfologia cristal·lina, estabilitat i expansió tèrmiques, distribució de mida de les partícules, entre altres. S’estudia amb detall l’espectroscòpia de les transicions 4f–5d, sobre les quals es basa el mecanisme d’escintil·lació. Inclou mesures d'absorció òptica, mesures de luminescència i del temps de decaiguda d’aquesta excitant amb llum de sincrotró en el rang espectral des de l'ultraviolat de buit fins l'ultraviolat (VUV-UV), mesures de radioluminescència excitant amb raigs X, entre altres. A més, es proporcionen les dades espectroscòpiques bàsiques dels monocristalls de Pr:KGd(PO3)4 tipus III per aplicacions làser en la gamma de longitud d'ona visible basades en les transicions electròniques 4f-4f. També, es determina la regió de cristal·lització primària del KYP4O12 tipus B i del KY(PO3)4 tipus IV en el sistema ternari K2O–Y2O3–P2O5, ja que són candidats interessants per actuar com a matriu per ions lantànids actius en aplicacions de centelleig.
Los materiales centelleadores son ampliamente utilizados como detectores en los sistemas de detección de diversas aplicaciones, como la imagen médica, la física de alta energía, la astrofísica y en pruebas no destructivas (seguridad aeroportuaria, control industrial, etc.). Hay varios requisitos importantes para evaluar favorablemente el rendimiento de un centelleador. Dado que no existe el centelleador ideal, se están dedicando muchos esfuerzos para buscar nuevos centelleadores inorgánicos con mejores propiedades que los de los centelleadores existentes. En esta tesis, se crecen monocristales con alta calidad cristalina de KGd(PO3)4 tipo III dopados con Ce3+ y Pr3+, y también nanocristales de Pr:KGd(PO3)4 tipo III para posteriormente caracterizarlos estructuralmente y ópticamente como posibles nuevos materiales centelleadores. Estos monocristales se crecen a partir de soluciones de alta temperatura mediante la técnica Top Seeded Solution Growth-Slow Cooling (TSSG-SC) y los nanocristales se sintetizan mediante el método de Pechini. La caracterización estructural incluye la morfología cristalina, estabilidad y expansión térmicas, distribución de tamaño de las partículas, entre otros. Se estudia con detalle la espectroscopia de las transiciones 4f-5d, sobre las que se basa el mecanismo de centelleo. Incluye medidas de absorción óptica, medidas de luminiscencia y del tiempo de decaída de ésta excitando con luz de sincrotrón en el rango espectral desde el ultravioleta de vacío hasta el ultravioleta (VUV-UV), medidas de radioluminiscencia excitando con rayos X, entre otros. Además, se proporcionan los datos espectroscópicos básicos de los monocristales de Pr:KGd(PO3)4 tipo III para aplicaciones láser en la gama de longitud de onda visible basadas en las transiciones electrónicas 4f-4f. También, se determina la región de cristalización primaria de KYP4O12 tipo B y de KY(PO3)4 tipo IV en el sistema ternario K2O-Y2O3-P2O5, ya que son candidatos interesantes para actuar como matriz para iones lantánidos activos en aplicaciones de centelleo.
Scintillators materials are widely used as detectors in the detection systems of a variety of applications, such as medical imaging, high energy physics, astrophysics and non-destructive testing (airport security, industrial control, etc.). There are several important requirements to evaluate favourably the performance of a scintillator. Since the ideal scintillator does not exist, many efforts are dedicated to find new inorganic scintillators with better properties than those of the existing scintillators. Here, Ce3+- and Pr3+-doped type III KGd(PO3)4 bulk single crystals with high crystalline quality and type III Pr:KGd(PO3)4 nanocrystals are grown and structurally and optically characterized as possible new scintillator materials. These bulk single crystals are grown from high temperature solutions by the Top Seeded Solution Growth-Slow Cooling (TSSG-SC) technique, while the nanocrystals are synthesized by the Pechini method. The structural characterization includes the crystal morphology, thermal stability, thermal expansion, particle size distribution, among others. The spectroscopy of the 4f–5d transitions, on which the scintillation mechanism is based, is studied in detail. The spectroscopic characterization includes optical absorption measurements, luminescence and decay time measurements under synchrotron vacuum ultraviolet-ultraviolet (VUV-UV) excitation, radioluminescence measurements after synchrotron X-ray irradiation, among others. In addition, the basic spectroscopic data of the type III Pr:KGd(PO3)4 crystal for lasing applications in the visible wavelength range based on the 4f–4f electronic transitions is provided. Moreover, the primary crystallization region of type B KYP4O12 and type IV KY(PO3)4 in the K2O–Y2O3–P2O5 ternary system is determined, since these are interesting candidates as hosts for active lanthanide ions in scintillation applications.

This thesis contains both physics analysis and hardware studies. It consists of two primary sections: the results of a search for heavy Majorana mass neutrinos, using the event signature of same (like) sign charged electron pairs ($e^{\pm} e^{\pm}$ ) and two jets, and the results of studies to upgrade the Hadronic Forward (HF) and Hadronic Endcap (HE) subdetectors in the Compact Muon Solenoid (CMS) detector in response to the high intensity proton-proton collisions generated at the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN, Conseil Europ\'{e}en pour la Recherche Nucl\'{e}aire). In this search for Majorana mass neutrinos, same sign dielectron ($e^{\pm} e^{\pm}$) + dijet events in the final state have been considered as a signature for neutrino particles. The analyzed data corresponds to an integrated luminosity of 19.7 fb\textsuperscript{-1} of proton-proton collisions at a center of mass energy of \begin{math}\sqrt{s} = 8\ TeV \end{math}, collected using the CMS detector during the 2012 operation at the LHC. Monte Carlo simulations accounting for the theoretical expectations of the Standard Model (SM) and the detector limitations are used to prototype the experiment and to test proposed analysis steps. No excess of events is observed in the data beyond the expected SM background. Upper limits are set on the mixing element squared, $|{V}_{eN}|^{2}$, of the heavy Majorana neutrino with standard model neutrinos, as a function of Majorana neutrino mass for masses in the range of 40-500 $GeV/c^2$. The detector upgrade search comprises three sections of this thesis. The first section describes the test results of 1785 multianode Hamamatsu R7600U-200-M4 photomultiplier tubes (PMT) in numerous parameters such as gain, dark current, and timing characteristics, which provide insights on the expected performance of the upgraded CMS-HF detector. These PMTs replaced the previous single anode R7525 PMTs because the glass windows of previous PMTs are the source of Cherenkov radiation, which causes a background noise in the experiment. The second section reports characterization results of two types of PMTs in a novel operation mode for Secondary Emission (SE) Ionization Calorimetry, which is a novel technique to measure electromagnetic shower particles in extreme radiation environments. The third section presents the test results of novel scintillating materials for CMS experiment in specific and future particle accelerators in general. These materials are Polyethylene Naphthalate (PEN), Polyethylene Terephthalate (PET), high efficiency mirror (HEM) and quartz plates with various organic and inorganic coating materials such as p-Terphenyl (pTp), Anthracene and Gallium-doped Zinc Oxide (ZnO:Ga). We have investigated them for radiation hardness, light yield, timing characteristics, and scintillation and transmission properties.

In recent years, the United States Departments of Homeland Security (DHS) and Customs and Border Protection (CBP) have been charged with the task of scanning every cargo container crossing domestic borders for illicit radioactive material. This is accomplished by using gamma-ray detection systems capable of discriminating between non-threatening radioisotopes, such as Cs-137, which is often used in nuclear medicine, and fissile material, such as U-238, that can be used to make nuclear weapons or "dirty" bombs. Scintillation detector systems, specifically thallium-doped sodium iodide (NaI(Tl)) single crystals, are by far the most popular choice for this purpose because they are inexpensive relative to other types of detectors, but are still able to identify isotopes with reasonable accuracy. However, increased demand for these systems has served as a catalyst for the research and development of new scintillator materials with potential to surpass NaI(Tl). The focus of a majority of recent scintillator materials research has centered on sintered transparent ceramics, phosphor-doped organic matrices, and the development of novel single crystal compositions. Some of the most promising new materials are glass-ceramic nanocomposites. By precipitating a dense array of nano-scale scintillating crystals rather than growing a single monolith, novel compositions such as LaBr₃(Ce) may be fabricated to useful sizes, and their potential to supersede the energy resolution of NaI(Tl) can be fully explored. Also, because glass-ceramic synthesis begins by casting a homogeneous glass melt, a broad range of geometries beyond the ubiquitous cylinder can be fabricated and characterized. Finally, the glass matrix ensures environmental isolation of the hygroscopic scintillating crystals, and so glass-ceramic scintillators show potential to serve as viable detectors in alpha- and neutron-spectroscopy in addition to gamma-rays. However, for the improvements promised by glass-ceramics to become reality, several material properties must be considered. These include the degree of control over precipitated crystallite size, the solubility limit of the glass matrix with respect to the scintillating compounds, the variation in maximum achievable light yield with composition, and the peak wavelength of emitted photons. Studies will focus on three base glass systems, sodium-aluminosilicate (NAS), sodium-borosilicate (NBS), and alumino-borosilicate (ABS), into which a cerium-doped gadolinium bromide (GdBr₃(Ce)) scintillating phase will be incorporated. Scintillator volumes of 50 cubic centimeters or greater will be fabricated to facilitate comparison with NaI(Tl) crystals currently available.

Cette thèse étudie la détection de matière nucléaire avec la technique de la particule associée pour l’inspection de bagages abandonnés ou de conteneurs maritimes dans le domaine de la sécurité. Le principe consiste à mesurer, avec des scintillateurs plastique, les coïncidences entre particules de fissions induites par des neutrons de 14 MeV produits par un générateur basé sur la réaction 2H(3H,n)4He et équipé d’un détecteur alpha à localisation pour déterminer le temps d’émission et la direction du neutron opposé. La détection d’au moins trois particules de fission en coïncidence avec la particule qui permet de discriminer les matières nucléaires des matériaux bénins. Le système d’acquisition et les outils de simulation ont été qualifiés en passif avec des sources radioactives puis en actif avec le générateur et diverses cibles, validant les estimations de performances de systèmesd’inspection de bagages abandonnés ou de conteneurs maritimes réalisées par simulation numérique avec le code MCNP-PoliMi. Il est ainsi possible de détecter en quelques minutes, quelques kg d’uranium au centre d’un container rempli d’une matrice fer mêmesi l’échantillon est masqué par du plomb, à l’aide du signal des neutrons prompts de fission. La détection est plus difficile dans les matrices organiques en raison de la diffusion des neutrons interrogateurs et de fission sur les noyaux d’hydrogène. Par ailleurs, l’utilisation de scintillateurs plastiques à la place des compteurs gazeux à 3He a été évaluée pour caractériser le plutonium dans les colis de déchets radioactifs par mesure passive des coïncidences. La détection des neutrons de fission est beaucoup plus rapide,ce qui permet de minimiser le bruit accidentel dû aux réactions (,n). Les scintillateurs sont cependant plus sensibles aux rayonnements gamma et à la diaphonie entre détecteurs voisins, ce qui nécessite d’exploiter les coïncidences de multiplicité 3 avec un traitement des données spécifique pour limiter la diaphonie
This thesis investigates the detection of Special Nuclear Materials (SNM) by neutroninterrogation with the Associated Particle Technique (APT). 14 MeV neutrons areproduced from the 3H(2H,n)α fusion reaction in a sealed tube neutron generatorembedding a position-sensitive alpha detector. The alpha detector determines thedirection of the nearly opposite neutron and its time of flight. The detection of at leastthree prompt fission particles in coincidence with the tagged neutron signs the presenceof SNM. The acquisition system and simulation tools have been qualified in passive modewith radioactive sources and active mode with the generator and various targets,validating the simulation of inspection systems with MCNP-PoliMi. Calculations showthat the detection of a few kilograms of shielded SNM with the ATP is possible in ironcargo container, with the prompt fission neutrons signal. Detection is more difficult inorganic matrices due to tagged- and prompt fission neutrons scattering on hydrogennuclei. Furthermore, the use of plastic scintillators instead of 3He counters was studied tocharacterize the plutonium in the radioactive waste by passive coincidences measurement.Measurements at fast time scales of fast-neutrons instead of the long time scales ofthermal-neutrons reduce random coincidences that can occur with high (,n) reactionrate. The scintillators are however sensitive to gamma rays and cross-talk betweenadjacent detectors. Therefore, we used data-analysis algorithms to minimize cross-talkcontribution to measured three-fold coincidences

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Neste trabalho foi desenvolvido um Espectrômetro de Correlação Angular Gama- Gama Perturbada Diferencial em Tempo (CAP) constituído por seis detectores cintiladores de BaF2, para realização de medidas de interações hiperfinas (campo hiperfino magnético e gradiente de campo elétrico) em diversos materiais e propiciar estudos na área da física da matéria condensada. O espectrômetro desenvolvido possui um sistema de aquisição não convencional em comparação aos demais equipamentos destinados a medidas de CAP. Ao invés do tradicional Analisador Multicanal (MCA), este espectrômetro utiliza um sistema de aquisição de dados constituído, basicamente, por um Conversor Analógico Digital (ADC) rápido, uma placa digital (I/O) convencional e um roteador construído no laboratório de Interações Hiperfinas (LIH) do IPEN. Este versátil e eficiente sistema, controlado por um software também criado no LIH em LabVIEW, permite a geração simultânea de 30 espectros de coincidências γ - γ atrasadas, número superior em comparação aos 12 espectros do antigo espectrômetro de quatro detectores. Além de medidas de linearidade, resolução em tempo e tempo morto, o funcionamento e o desempenho do espectrômetro foram comprovados através de medidas de CAP utilizando os núcleos de prova 111In -> 111Cd e 181Hf -> 181Ta, cujos resultados são bem conhecidos da literatura. Foram feitas medidas de interação quadrupolar do 181Ta em háfnio metálico e do 111Cd em cádmio metálico, e de campo hiperfino magnético do 111Cd e do 181Ta em níquel. Os resultados destas medidas se mostraram em concordância com a literatura. Adicionalmente foram realizadas medidas inéditas de interações hiperfinas magnéticas no composto intermetálico LaMnSi2 utilizando os núcleos de prova 111Cd e 140Ce. As medidas foram realizadas na faixa de temperatura de 10 K a 400K. No caso das medidas utilizando a sonda 111In -> 111Cd, os resultados mostram uma variação do campo magnético com a temperatura que segue a função de Brillouin. Já no caso das medidas com o núcleo de prova 140La -> 140Ce, o resultado apresentou um comportamento anômalo do campo hiperfino em função de temperatura. Os resultados evidenciam uma forte hibridização da banda 4f do Ce com a banda 3d do Mn, fato verificado e estudado em trabalhos anteriores com compostos semelhantes.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Cintiladores inorgânicos com tempo de decaimento de luminescência rápido, densidade alta e boa produção de luz têm sido objeto de estudos para aplicações em física nuclear, física de energias altas, tomografia nuclear e outros campos da ciência e da engenharia. Cristais de cintilação baseados em iodeto de césio (Csl) são materiais que apresentam higroscopia relativamente baixa, número atômico alto, fácil manuseio e custo baixo, características que favorecem o seu uso como detectores de radiação. Neste trabalho descreve-se a obtenção de cristais Csl puro, Csl:Br e Csl:Pb, utilizando-se a técnica de Bridgman. A concentração do elemento dopante bromo (Br) foi estudada no intervalo de 1,5x10-1 M a 10-2 M e o elemento chumbo (Pb) no intervalo de 10-2 M a 5x10-4 M. Para avaliar os cintiladores desenvolvidos foram efetuadas medidas sistemáticas de emissão de luminescência e tempo de decaimento de luminescência para a radiação gama, ensaios de transmitância óptica, ensaios de microdureza Vickers, determinações da distribuição dos dopantes ao longo dos cristais crescidos e análise da resposta dos cristais à radiação gama no intervalo de energia de 350 keV a 1330 keV e partículas alfa provenientes de fonte de 241Am com energia de 5,54 MeV. Os resultados obtidos de tempo de decaimento de luminescência para os cristais CsI:Br e CsI:Pb, no intervalo de 13 ns a 19 ns, mostraram-se promissores para medidas de alta energia. O estudo de microdureza mostrou um aumento significativo em função da concentração dos elementos dopantes, quando comparado ao cristal Csl puro, melhorando desta forma a resistência mecânica dos cristais crescidos. A validade de utilização desses cristais como sensores de radiação para medidas de radiação gama e partículas alfa, pode ser demonstrada pelos resultados da resposta à radiação.
Inorganic scintillators with fast luminescence decay time, high density and high light output have been the object of studies for application in nuclear physics, high energy physics, nuclear tomography and other fields of science and engineering. Scintillation crystals based on cesium iodide (CsI) are matters with relatively low higroscopy, high atomic number, easy handling and low cost, characteristics that favor their use as radiation detectors. In this work, the growth of pure CsI crystals, CsI:Br and CsI:Pb, using the Bridgman technique, is described. The concentration of the bromine doping element (Br) was studied in the range of 1,5x10-1 M to 10-2 M and the lead (Pb) in the range of 10-2 M to 5x10-4 M. To evaluate the scintillators developed, systematic measurements were carried out for luminescence emission and luminescence decay time for gamma radiation, optical transmittance assays, Vickers micro-hardness assays, determination of the doping elements distribution along the grown crystals and analysis of crystals response to the gamma radiation in the energy range of 350 keV to 1330 keV and alpha particles from a 241Am source, with energy of 5.54 MeV. It was obtained 13 ns to 19 ns for luminescence decay time for CsI:Br and CsI:Pb crystals. These results were very promising. The results obtained for micro-hardness showed a significant increase in function of the doping elements concentration, when compared to the pure CsI crystal, increasing consequently the mechanical resistance of the grown crystals. The validity of using these crystals as radiation sensors may be seen from the results of their response to gamma radiation and alpha particles.

The development and application of a combinatorial sputtering thin film technique to screen potential scintillation material systems was investigated. The technique was first benchmarked by exploring the binary lutetium oxide-silicon oxide material system, which successfully identified the luminescence phases of the system, Lu2SiO5 (LSO) and Lu2Si2O7 (LPS). The second application was to optimize the activator concentration in cerium doped LSO. The successfully optimized cerium concentration in the thin film LSO of 0.34 atomic percent was much greater than the standard cerium concentration in single crystal LSO. This lead to an intensive study based on temperature dependent steady-state and lifetime photoluminescence spectroscopy to understand the different concentration quenching mechanisms involved in the bulk single crystal versus the thin film LSO. The results were used to develop configuration coordinate models which were employed to explain the observed concentration dependent behavior. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer, and ultimately self-absorption. For the thin films it was found self-absorption was not a dominant factor due to the thin dimension of the film and also its nano-crystalline nature. Instead, the photoluminescence excitation and emission spectra as a function of concentration demonstrated the concentration quenching behavior was due to an increase in defect-mediated non-radiative transitions with increasing cerium. The final application of the thin film screening technique was the exploration of the ternary Lu2O3-SiO2-Al2O3 material system doped with cerium. It was found that the presence of aluminum and silicon hindered LSO and Al5Lu3O12 (LuAG) emission, respectively. However, the presence of aluminum was found to increase LPS emission intensity. The percent of aluminum in the LPS phase was estimated at 2.5 atomic percent.

For the application as a transverse ion beam diagnostics device, various scintillation screen materials were analysed. The properties of the materials such as light output, image reproduction and radiation stability were investigated with the ion beams extracted from heavy ion synchrotron SIS-18. The ion species (C, Ne, Ar, Ta and U) were chosen to cover the large range of elements in the periodic table. The ions were accelerated to the kinetic energies of 200 MeV/u and 300 MeV/u extracted with 300 ms pulse duration and applied to the screens. The particle intensity of the ion beam was varied from 1E4 to 1E9 particles per pulse. The screens were irradiated with typically 40 beam pulses and the scintillation light was captured using a CCD camera followed by characterization of the beam spot. The radiation hardness of the screens was estimated with high intensity Uranium ion irradiation. In the study, a linear light output for 5 orders of magnitude of particle intensities was observed from sensitive scintillators and ceramic screens such as Al2O3:Cr and Al2O3. The highest light output was recorded by CsI:Tl and the lowest one by Herasil. At higher beam intensity saturation of light output was noticed from Y and Mg doped ZrO2 screens. The light output from the screen depends not only on the particle intensity but also on the ion species used for irradiation. The light yield (i.e. the light intensity normalised to the energy deposition in the material by the ion) is calculated from the experimental data for each ion beam setting. It is shown that the light yield for light ions is about a factor 2 larger than the one of heavy ions. The image widths recorded exhibit a dependence on the screens material and differences up to 50 % were registered. On radiation stability analysis with high particle intensity of Uranium ions of about 6E8 ppp, a stable performance in light output and image reproduction was documented from Al2O3:Cr screen over 1000 pulses while slight saturation effects was noticed from some other screens. No considerable radiation induced damage for an irradiation by maximal fluence of 1.7×1E11 cm-2 Uranium ions was seen in the samples except the formation of point defects and color centers. Among the investigated screens P43 (Gd2O2S:Tb) powder seems to be a good candidate up to certain energy deposition threshold while for very high intensity measurements Al2O3:Cr screens are recommended.

Single crystals with composition Lu3Al5O12 were synthesized using Czochralski and micro-pulling-down melt growth techniques. Polycrystalline ceramics of the same composition were synthesized by vacuum annealing of powders prereacted using a citrate-nitrate combustion technique and by spark-plasma-sintering of powders prereacted using a flame-spray-pyrolysis technique. Single crystals and polycrystalline ceramics are activated with Ce3+ or Pr3+ or doubly activated with Ce3+ and Tb3+ ions. Cerium-doped Czochralski-grown single crystals were compared to cerium-terbium codoped Czochralski-grown and micro-pulling down single crystals. Cerium-terbium codoped single crystals are also compared to similarly-activated polycrystalline ceramics sintered under vacuum using combustion-synthesized prereacted powders. X-ray diffraction analysis and fluorescence characterization were used to determine successful formation of single-phase LuAG and successful incorporation of doping species. Absorbance, fluorescence, radioluminescence, and scintillation decay analyses were used to compare synthesis processes and activator selection.

Lutetium oxide doped with europium (Lu2O3:Eu3+) has been established as a promising scintillator material with properties that are advantageous when compared to other scintillators such as cesium iodide doped with thallium (CsI:Tl). Due to high X-ray attenuation characteristics, Lu2O3:Eu3+ is an attractive material for use in high resolution digital X-ray imaging systems. However, challenges still remain especially in the area of light output for Lu2O3:Eu3+. Processing by physical vapor deposition (PVD) and manipulation of oxygen defect structure was explored in order to better understand the effect on the scintillation phenomena. PVD results were obtained using high temperature radio frequency sputtering (RF) and pulsed laser deposition (PLD) systems. Characterization of light output by radial noise power spectrum density measurements revealed that high temperature RF films were superior to those obtained using PLD. Optimization of sputtered films based on light output over a range of process parameters, namely temperature, power, pressure, and substrate orientation was investigated. Parameterization of deposition conditions revealed that: 75 watts, 10.00 mtorr, and 800°C were optimum conditions for Lu2O3:Eu3+ films. Manipulation of anionic defect structure in similar material systems has been shown to improve scintillation response. Similar methods for Lu2O3:Eu3+ were explored for hot pressed samples of Lu2O3:Eu3+; via controlled atmosphere annealing, and use of extrinsic co-doping with calcium. The controlled atmosphere experiments established the importance of oxygen defect structure within Lu2O3:Eu3+ and showed that fully oxidized samples were preferred for light output. The second method utilized co-doping by the addition of calcium which induced oxygen vacancies and by Frenkel equilibrium changed the oxygen interstitial population within the Lu2O3:Eu3+ structure. The addition of calcium was investigated and revealed that scintillation was improved with a maximum response occurring at 340ppm of calcium. PVD optimization and co-doping experimental results provided a template for the use of calcium co-doped Lu2O3:Eu3+ targets for deposition of films. Preliminary deposition results were promising and revealed that small additions (around 550 ppm) of calcium resulted in better activator efficiency. Calcium co-doped films have a predicted increase in the light yield greater than 14% when compared to analogous un-doped Lu2O3:Eu3+ films at 60keV.

In recent years, there have been several research endeavors to increase the ability to identify and quantify special nuclear material in field measurements. These have included both gamma spectroscopy and neutron coincidence systems that are portable and work in a variety of environments. In this work, a Monte Carlo Neutral Practicle X (MCNPX) model was used to design an instrument that includes four gamma detection slabs placed within four neutron detection slabs. The combination of gamma spectroscopy and neutron coincidence counting in a single instrument allows for direct measurement of plutonium (Pu) mass without need for assumptions or operator declarations. A combined neutron-gamma instrument was designed for use in characterizing and quantifying Pu in field samples. This detector consists of a plastic scintillator containing LaBr3 nanoparticles and a polyethylene slab containing four 3He tube detectors. The system was tested via simulation with MCNPX for four Pu samples of known quality and quantity. These samples had masses ranging from 100-300 g of Pu. It was found that the designed detector system could be used to determine 240Pu-effective mass to within 3.5% accuracy and to characterize the isotopic content of the Pu to within 2% accuracy for all isotopes except for 238Pu and 242Pu. The system could determine 238Pu isotopic content to within 14% accuracy but is completely unable to determine 242Pu content. This system has the ability to Four Plutonium (Pu) samples of known quantity were modeled and tested to determine what data was available from each individual signature. Each model included a separate MCNPX deck for each individual isotope that contributes to the gamma signature in photon mode and a spontaneous fission and (alpha,n) deck for the neutron signature. The first three samples were used to create spectrums and efficiency curves for each odd isotope as well as for a Pu effective mass for the neutron signature. The data from these simulations were then used to identify the isotopics in the fourth sample to within acceptable accuracy. From this data, a total Pu mass was obtained as well as an ability to determine the ratio of (alpha,n) to spontaneous fission neutrons without additional simulations. This provides a new method to detect and identify the Pu content within a sample without producing requiring supplemental additional information since isotopics can be determined with the combined use of the gamma and neutron systems.

This work focuses on discovery and development of novel binary halide scintillation materials for radiation detection applications. A complete laboratory for raw materials handling, ampoule preparation, material rapid synthesis screening, single crystal growth, sample cutting, polishing and packaging of hygroscopic halide scintillation materials has been established. Ce3+ and Eu2+ activated scintillators in three binary systems: Alkali Halide – Rare Earth Halide (AX–REX3), Alkali Halide – Alkaline Earth Halide (AX–AEX2) and Alkalin Earth Halide – Rare Earth Halide (AEX2–REX3) were systematically studied. Candidates for new scintillation materials in the three systems were selected based on a set of selection rules. A total of 42 Ce3+ or Eu2+ activated binary halide scintillation material candidates were synthesized and characterized. Among all synthesized candidates, 10 - 15 candidate materials were found to be highly promising in terms of high scintillation light output, fast scintillation decay or desirable emission wavelength. Three most promising candidates, Cs3EuI5, CsGd2Cl7:Ce3+ and CsSrI3:Eu2+ were selected for single crystal growth and further evaluation. Technologies for single crystal growth of hygroscopic halide scintillation materials were developed. Detailed design of experimental apparatuses was discussed. Single crystals were successfully grown via Bridgman or Vertical Gradient Freeze techniques. Study on optical and scintillation properties was performed. Possibility of using CsGd2Cl7:Ce3+ as a neutron detector was confirmed. CsSrI3:Eu2+ shows extraordinary scintillation light output (73,000 ph/MeV), excellent energy resolution (3.9%) and ease for crystal growth. A scaled-up crystal growth was carried out. A bulk crystal of 1” diameter CsSrI3:Eu2+ was successfully grown. Energy level structure and charge carrier traps in CsSrI3:Eu2+ were investigated. Potential of CsSrI3:Eu2+ in various radiation detection applications were evaluated.