The PAMELA space experiment is scheduled for launch towards the end of 2004 on-board a Russian Resurs DK1 satellite, orbiting Earth at an altitude of 300– 600 km. The main scientific goal is a study of the antimatter component of the cosmic radiation. The semipolar orbit (70.4◦) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV–190 GeV) and positrons (50 MeV– 270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio He/He below 10−7. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield built at KTH. The anticounter scintillators are used to aid in the rejection of background from particles not cleanly entering the acceptance of the tracker. Information from the anticounter system will be included as a veto in a second level trigger, to exclude the acquisition of events generated by false triggers. An LED-based monitoring system has been developed for the anticounter system. The LEDs mimic the light signal produced in the scintillator by an ionising particle. This allows the functionality of the AC system to be verified in-orbit. The development and testing of the monitoring system are presented and comparisons have been made with independent radioactive source-based calibration methods. The anticounter system has also been extensively tested with cosmic rays and particle beams. Most of these tests have been performed with the anticounters integrated with the other PAMELA subdetectors in a flight-like configuration.

As our understanding of ceramic processing methods for the purpose of fabricating polycrystalline optical materials has increased over the past few decades, the race is on to bring ceramic technology to markets where single crystalline materials have traditionally been used. One such market is scintillators. This Master’s thesis focuses specifically on a class of materials attractive for use as gamma-ray scintillators. These barium based halides can potentially be utilized in applications ranging from ionizing radiation detection in the field to high-energy physics experimentation. Barium bromide iodide and barium chloride single crystals have already showed high light yield, fast scintillation decay, and high energy resolution, all desirable properties for a scintillator. This work attempts to show the likelihood of moving towards polycrystalline scintillators to take advantage of the lower processing temperature, higher manufacturing output, and overall reduced cost. The experiments begin with identifying appropriate sintering conditions for hot pressed ceramics of BaBrI and BaCl2. Possible sources of optical loss in the first phase of hot pressed samples are investigated using a wide range of characterization tools. Preliminary luminescence and scintillation measurements are reported for a translucent sample of BaBrI. Recommendations are made to move toward highly transparent ceramics with scintillation properties approaching those measured in single crystal samples

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.

Es werden die Entdeckung der organischen Szintillatoren durch Hartmut Kallmann und seine anderen Arbeiten, insbesondere die Entwicklung der flüssigen Szillitatoren beschrieben. / The discovery of organic scintillators by Hartmut Kallmann and his further work, especially the development of liquid scintillators are described.

A new class of scintillation detector has emerged that combines columnar scintillators and CCD/CMOS sensors for high-resolution imaging. Originally developed for single-photon gamma-ray imaging, these detectors provide better than an order-of-magnitude improvement in spatial resolution compared to conventional photomultiplier tube (PMT)-based gamma cameras; sub-100 micron detector resolutions have been achieved. This work reviews the several detector configurations developed in recent years, with a specific emphasis on a type of CCD/CMOS detector developed at the Center for Gamma-Ray Imaging, which we call BazookaSPECT, that amplifies scintillation light using an image intensifier to achieve both high spatial resolution and high event-rate capability.Ongoing research into scintillator deposition techniques has led to a new form of scintillation material where crystallites are organized into columns. Similar to optical fibers, this columnar structure helps to channels scintillation light towards an exit face while restricting lateral light spread. However, because they are not perfect optical fibers, light spreads laterally and is absorbed by an amount relating to the interaction depth. Taking advantage of this phenomenon, we discuss the use of maximum-likelihood methods to estimate the 3D position and energy of gamma-ray interactions in columnar CsI(Tl)/EMCCD-based detectors.Finally, we present new imaging applications that have arisen from BazookaSPECT. These include the the development of a gamma-ray microscope using micro-coded apertures, feasibility studies for photon-counting digital mammography and eventually X-ray CT, and FastSPECT III -- a third generation small animal stationary SPECT imager. FastSPECT III system design, fabrication methods, data acquisition system, system calibration procedure, and initial tomographic reconstructions are presented.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016. / Plastic scintillators play a key role in reconstructing the energy and tracks of hadronic particles that impinge the Tile Calorimeter of the ATLAS detector as a result of high energy particle collisions generated by the Large Hadron Collider of CERN. In the detector, plastic scintillators are exposed to harsh radiation environments and are therefore susceptible to radiation damage. The radiation damage effects to the optical properties and structural damage were studied for PVT based commercial scintillators EJ200, EJ208, EJ260 and BC408, as well as PS based UPS923A and scintillators manufactured for the Tile Calorimeter. Samples of dimensions 5x5x0.3 mm were subjected to irradiation using 6 MeV protons to doses of approximately 0.8 MGy, 8 MGy, 25 MGy and 25 MGy using the 6 MV tandem accelerator of iThemba LABS. Results show that damage leads to a reduced light output and loss in transmission character. Structural damage to the polymer base and the formation of free radicals occur for doses ≥ 8 MGy leading to reduced scintillation in the base and re-absorption of scintillation light respectively. Scintillators containing a larger Stokes shift, i.e. EJ260 and EJ208 exhibit the most radiation hardness. EJ208 is recommended as a candidate to be considered for the replacement of Gap scintillators in the TileCal for the 2018 upgrade. / LG2017

A dissertation submitted to the Faulty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. April 2017. / Plastic scintillators, situated in the Tile Calorimeter (TileCal) of the ATLAS detector at the Large Hadron Collider (LHC), play an integral part in the detection of diffractive, energetic hadronic particles that result from high energy proton-proton collisions. As these particles traversetheplastic, theresultantdecayofthepolymerbaseemitsluminescentlightwhichacts as a signature of this interaction. However, the deleterious radiation environment in which the plastics are situated ultimately degrade the plastic through the formation of free radicals which initiate chemical reactions and alter the structure of the plastic. Radical formation was studied using electron paramagnetic resonance (EPR) spectroscopy in six plastic scintillator types of either polystyrene (PS) or polyvinyl toluene (PVT) base, and computational EPR studies were conducted on two small monomer structures and two large polymer, plastic-like computer models. Damage was simulated in the computational models by removing an increasing number of hydrogen atoms. Plastic samples, of volume 500 ⇥500 ⇥ 250 µm, were to subjected protons accelerated to 6 MeV using the tandem accelerator at iThemba LABS, Gauteng, to increasing target doses of 0.8 MGy, 2.5 MGy, 8.0 MGy, 25 MGy, 50 MGy, and 80 MGy. The experimental EPR data taken after two weeks of the sample exposure to air indicate the presence of peroxy-type radicals that initiate chemical reactions, discolour the plastic, and decrease the efficiency of the plastic. Furthermore, the data suggests that damaged PS and PVT samples are susceptible to different mechanisms of radiation damage. However, results pertaining to the decrease in the g-factor and the increase in normalised EPR intensity suggest that all plastics behave similarly using an EPR analysis as a function of dose. Thus, the EPR analysis could not identify a specific plastic that would perform better than the existing plastics used in the TileCal. The computational chemical potential results indicate that electron transfer between damaged pristine and damaged models is possible. In the two small damaged models, the computational EPR data indicate the presence of a various stable akyl-like radicals depending on the site from which the hydrogen atoms are removed. In the two large damaged models, these results indicate a number of alkyl-, benzyl-, and cyclohexadienyl-like radicals. / LG2017

Orientador: Marian Rosaly Davolos / Co-orientador: Marco Aurélio Cebim / Banca: Luiz Antonio de Oliveira Nunes / Banca: Lucas Carvalho Veloso Rodrigues / Banca: Marli Leite de Moraes / Banca: Renata Danielle Adati / Resumo: L uminescência é a emissão de luz decorrente da excitação de átomos, íons, moléculas ou materiais. Quando a excitação é realizada por radiações ionizantes, o material luminescente é denominado cintilador e possui aplicações tecnológicas relacionadas à detecção dessas radiações de alta energia . A conformação desses materiais tem impacto direto em seu custo e aplicabilidade e atualmente, há uma busca por novas conformações de materiais luminescentes para aplicação em diversos dispositivos. S istemas bidimensionais, como filmes finos nanoestruturados, possuem potencial aplicação em nanotecnologia e os processos de auto - organização desses sistemas tê m sido crescentemente estudados e empregados. Neste trabalho, as propriedades luminescentes do polioxometalato [Eu(W 5 O 18 ) 2 ] 9 - foram estudadas em função de sua conformação em s ólido estendido, filmes de Langmuir e de Langmuir - Blodgett, com ênfase em medidas de luminescência com excitação por radiação ultravioleta ou raios X. O sólido Na 9 [Eu(W 5 O 18 ) 2 ].14H 2 O foi preparado pela mistura de soluções de tungstato de sódio e nitrato de európio em pH e temperatura adequados. Medidas de espectroscopia de fotoluminescência do sólido evidenciam a presença de íons Eu 3+ ao menos em dois sítios não - centrossimétricos, sendo um deles de menor simetria com relação ao outro . Com o aumento da temper atura, as distorções provocadas pelas vibrações térmicas e pela saída das moléculas de água de hidratação diminuem a simetria local ao redor dos íons Eu 3+ em ambos os sítios. As mudanças n as propriedades luminescentes decorrentes do aumento da temperatura são irreversíveis a partir de 100 o C, temperatura na qual inicia - se a desidratação do sólido. A excitação via transferência de carga dos ligantes para os metais favorece a emissão proveniente dos íons Eu 3+ no s sítio s me... / Abstract: Luminescence is the emission of light resulting from the excitation of atoms, ions, molecules or materials . When ionizing radiation is used in the excitation, the luminescent material is called scintillator and h as technological applications related to the detection of these high energy radiations. The conformation of the se materials has direct impact on theirs cost and applicability and currently, there is a search for new conformations of luminescent materials f or application in several devices. Two - dimensional systems, as nanostructured thin films, have potential applications in nanotechnology and the self - assembly processes of these systems have been increasingly studied and employe d . In this work, the luminesc ent properties of the polyoxometalate [ Eu (W 5 O 18 ) 2 ] 9 - were studied as a function of its conformation in solid bulk, Langmuir and Langmuir - Blodgett films, with emphasis on X - ray - and UV - excited luminescence measurements . Solid Na 9 [Eu(W 5 O 18 ) 2 ].14H 2 O was prepa red by mixing sodium tungstate and europium nitrate solutions in suitable temperature and pH. Photoluminescence measurements of the solid sample evidence the presence of Eu 3+ ions at leas t two non - centrosymmetric sites . With increasing temperature, the dis tortions caused by thermal vibration and de hydration process decrease th e local symmetry around the Eu 3+ at both sites. Changes in the luminescent properties are irreversible after temperature s above 100°C, temperature at which it begins the solid dehydrat ion. Ligand to metal charge transfer excitation promotes the emission from the Eu 3+ ions at less distorted site while the direct excitation in intraconfigurational levels of Eu 3+ ions promote the emission from the Eu 3+ ions at more distorted site. The scin tillation mechanism of this solid has significant contribution of the energy transfer process from charge transfer states to... / Doutor

Orientador: Marco Aurélio Cebim / Banca: Ana Maria Pires / Banca: Renata Danielle Adati / Resumo: Neste trabalho foi realizada a síntese do hidroxinitrato de lutécio (Lu2(OH)5NO3 n.H2O) nominalmente puro e dopado com Eu3+. Esse composto foi sintetizado via síntese hidrotérmica para a obtenção de um hidróxido lamelar de terra rara com cristais em formato de agulha. O composto foi então utilizado como precursor para obtenção do óxido de lutécio, puro e dopado com Eu3+, com a intenção de se levar as propriedades desse composto lamelar para o óxido, objetivo que foi verificado através de imagens MEV que mostraram que ambos os compostos, precursor lamelar e óxido, tinham cristais em formato de agulha, ou bastões. Ambos compostos foram caracterizados e foi possível verificar que além do composto lamelar ter sido obtido e suas características terem permanecido no óxido o mesmo apresentou bons resultados quando ativado por raios X indicando a possibilidade de ser utilizado como cintilador. Tanto óxido quando composto lamelar foram obtidos através das técnicas de Difração de Raio-X, Espectroscopia de absorção na região do Infra-vermelho, Espectroscopia de reflectância difusa no UV-Vis, Espectroscopia de Luminescência com excitação UV-Vis, Espectroscopia de luminescencia por raios X (XEOL) e Microscopia eletrônica de varredura. / Abstract: In this work the synthesis of lutetium hydroxynitrate (Lu2(OH)5NO3 n.H2O) and Eu3+ pure and doped was performed. This compound was synthesized via hydrothermal synthesis to obtain a rare earth lamellar hydroxide with needle-shaped crystals. The compound was then used as a precursor to obtain the pure lithium oxide and Eu3+ doped with the intention of bringing the properties of this lamellar compound to the oxide, which was verified through MEV images which showed that both compounds, lamellar precursor and oxide, had needle-shaped crystals, or rods.Both compounds were characterized and it was possible to verify that besides the lamellar compound was obtained, its characteristics remained in the oxide what showed good results when activated by X rays indicating the possibility of being used as a scintillator. Both oxide and lamellar compounds were characterized by the techniques of X-ray Diffraction, Infra-red absorption spectroscopy, UV-Vis diffuse reflectance spectroscopy, UV-Vis excitation luminescence spectroscopy, light-ray spectroscopy X (XEOL) and Scanning Electron Microscopy. / Mestre

Inorganic scintillators are playing an ever increasing role in the search for rare events. Progress in the use of cryogenic phonon-scintillation detectors (CPSD) has allowed for a rapid increase in sensitivity and resolution of experiments using this technique. It is likely that CPSD will be used in future dark matter searches with multiple scintillator materials. Further improvements in the performance of CPSD can be expected if the amount of light collected is increased. In this thesis, two approaches are used to look at ways of maximising the amount of light collected in CPSD modules. The first approach is to obtain a detailed understanding of the spectroscopic properties in the crystal to identify ways of increasing their scintillation intensity. The second is to simulate the light collection properties using a Monte-Carlo simulation program. This requires a detailed understanding of the optical properties of inorganic scintillators and obtaining this information is the focus of the current work. Two new methods have been developed to evaluate the scintillation decay time and the intrinsic light yield of scintillators. These methods are tested on CRESST CaWO₄ crystals so that all the input parameters necessary for the simulation of CRESST modules is available. These input parameters are used to successfully explain features of the light collection in CRESST CPSD modules and to suggest possible improvements to the design of the modules. In summary, the current work has contributed to the development of a standardised method to maximise the light yield that can be obtained from CPSD for application to rare event searches.