Current state-of-the-art environmental, clinical, and in-vivo radiation sensing systems utilizing various inorganic and tissue-equivalent plastic scintillators are not user friendly, suffer from electron-beam-generated noise, and are difficult to deploy successfully for real-time dosimetry. A robust, real-time detection system using different scintillating materials coupled to solid-state detectors by optical fibers is developed. This system enables radiation monitors/clinicians to conduct meaningful real-time measurements using different inorganic scintillators or organic, tissue-equivalent plastic scintillators in harsh clinical and environmental environments. Recent solid state photomultiplier (SSPM) technology has matured, reaching a performance level that is suitable for replacement of the ubiquitous photomultiplier tube in selected applications for environmental radiation monitoring, clinical dosimetry, and medical imaging purposes. The objective of this work is laboratory and clinical testing of the Hamamatsu MPPC (S10362-11-050C), Photonique SSPM (0810G1), and Voxtel SiPM (SQBF-EKAA/SQBF-EIOA) SSPMs coupled to different inorganic scintillator crystals (Prelude 420, BGO), inorganic doped glass scintillator material SiO₂: Cu²⁺, and organic BCF-12 plastic scintillating fibers, used as detector elements. Both polymer optical fibers (POFs) and glass optical fibers (GOFs) are used as signal conduits for laboratory and clinical testing. Further, reduction of electron-beam-generated Cerenkov light in optical fibers is facilitated by the inclusion of metalized air-core capillary tubing between the BCF-12 plastic scintillating fiber and the POF. Dose linearity, percent depth dose, and angular measurements for 6 MV/18 MV photon beams and 9 MeV electron beams are compared using the Hamamatsu MPPC with-and without the use of the metalized air-core capillary tubing for BCF-12 plastic scintillating fiber. These same measurements are repeated for SiO₂: Cu²⁺ scintillator material without air-core capillary tubing. / Graduation date: 2012

SuperNEMO est un projet de détecteur de nouvelle génération pour la recherche de la décroissance double bêta sans émission de neutrinos. La technique expérimental déployée est dans la lignée du son prédécesseur NEMO3, combinant un trajectographe et un calorimètre, afin d’identifier non seulement les électrons des décroissances double bêta, mais également pour mesurer l’ensemble des composantes de bruit de fond du détecteur. Le projet vise ainsi une sensibilité de 10^26 ans sur la période du 82Se, ce qui permettrait de sonder une masse effective du neutrino de 50 meV. Pour atteindre cette sensibilité, le projet prévoit notamment de mettre en place un calorimètre composé d’un millier de compteur à scintillation de basse radioactivité, dont la résolution en énergie serait meilleure que 8 % FWHM pour des électrons de 1 MeV.Ce travail de thèse apporte une contribution importante dans les travaux de Recherche et Développements pour améliorer les performances des scintillateurs et photomultiplicateurs, et pour réduire leur radioactivité, avec notamment la conception d’un nouveau photomultiplicateur en collaboration avec Photonis. / SuperNEMO is a next generation double beta decay experiment which will extend the successful “tracko-calo” technique employed in NEMO 3. The main characteristic of this type of detector is to identify not only double beta decays, but also to mesure its own background components. The projet aims to reach a sensitivity up to 1026 years on the half-life of 82Se. One of the main challenge of the Research and Development is to achieve an unprecedented energy resolution for the electron calorimeter, better than 8 % FWHM at 1 MeV.This thesis contributes to improve scintillators and photomultiplicators performances and reduce their radioactivity, including in particular the development of a new photomultiplier in collaboration with Photonis.

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.

Fluorescence technologies have only begun exploiting the transient recording of lifetime-based signals and images for low nanosecond lifetimes, but the method has tremendous potential for scientific and medical applications. Low nanosecond lifetime recording in real-time can enable the tracking of metabolite concentrations in cells and tissues (e.g. cancerous tissues) without introducing foreign substances. It will also enable the tracking of reactive species (e.g. ozone) and intermediate/short-lived states in chemical reactions in the atmosphere. Current techniques all employ laser excitation, but LEDs can also be used which cause considerably less damage to live tissue. We have developed a high speed fluorescence prototype using high intensity LED pulses and novel PMT gating technology. Precision timing circuitry generates tunable width pulse signals which are driven through the LED using a comparator-based push-pull architecture. The timing circuitry also generates PMT gating pulses which are applied to the dynode chain via high voltage operational amplifiers. LED pulses with fall times (99%) as short as 2ns and PMT gating times (10% to 90%) of 3.6ns have been achieved. The prototype has been used to successfully measure the fluorescent lifetimes of Alexa Fluor 610X dye (1.7ns and 4.7ns) and riboflavin (4.5ns). Lifetimes of acridine orange were measured as follows: alone (2ns), in solution with ssDNA (3.7ns), in solution with dsDNA (5.8ns), and in solution with dsRNA (5.9ns). Finally, dsRNA was heated and allowed to cool revealing lifetimes that started at 3.7ns when hot and increased to nearly 5ns when cool.

Η Τομογραφία Εκπομπής Ποζιτρονίων, η οποία συχνά αναφέρεται με βάση το ακρωνύμιό της, PET (Positron Emission Tomography), αποτελεί μία πρωτοποριακή τεχνική απεικόνισης η οποία παρέχει εγκάρσιες τομές της λειτουργίας των διαφόρων δομών του ανθρωπίνου σώματος. Η Τομογραφία PET επιτρέπει την μεταβολική απεικόνιση αυτών των δομών (σε αντίθεση με τις ακτίνες-Χ και την Υπολογιστική Τομογραφία (CT – Computer Tomography) οι οποίες παρέχουν ανατομική απεικόνιση), σε μοριακό επίπεδο, και αυτός είναι ο λόγος που συχνά η Τομογραφία PET αναφέρεται ως μοριακή απεικόνιση. Ειδικότερα, οι τομογράφοι PET για μικρά ζώα (Small Animal PET) οι οποίοι απαιτούν ιδιαίτερα υψηλή διακριτική ικανότητα, διαδραματίζουν σημαντικό ρόλο στην βιολογία και στις in-vivo μελέτες της φαρμακοκινητικής των ιχνηθετών και του μεταβολισμού. Σύμφωνα με τη βιβλιογραφία έχουν αναφερθεί διάφοροι τύποι τομογράφων PET, στους οποίους χρησιμοποιήθηκαν διάφοροι τύποι ανιχνευτικών διατάξεων, με διαφορετικό σχεδιασμό σε κάθε περίπτωση. Η τεχνολογία αυτών των τομογράφων βασίζεται στη χρήση μικρών ανόργανων κρυστάλλων, κυρίς αποτελούμενων από BGO, GSO και LSO, οι οποίοι σχηματίζουν ένα block στο οποίο έχει προσαρτηθεί ένας φωτοπολλαπλασιαστής είτε με ευαισθησία θέσης (PS – PMT: Position Sensitive PhotoMultiplier Tube), είτε με πολλαπλές ανόδους (multianode PMT). To BGO (Bismuth Germanate Oxide) είναι το υλικό που χρησιμοποιείται σε αρκετούς εμπορικούς Τομογράφους, έχοντας πλέον αντικαταστήσει το ιωδιούχο νάτριο (ΝαΙ). Ένα πρότυπο σύστημα small animal PET χαμηλού κόστους βρίσκεται υπό ανάπτυξη, προκειμένου να μελετήσουμε τα επιμέρους σχεδιαστικά χαρακτηριστικά του και να μετρήσουμε την απόδοσή του. Ο βασικός block ανιχνευτής αποτελείται από μία 16×16 διάταξη επιμέρους BGO κρυστάλλων διαστάσεων 3.75×3.75×20 mm3, ο οποίος έχει τοποθετηθεί με ειδική διεργασία στην επιφάνεια ενός Hamamatsu R-2486 PSPMT. Με τη χρήση κατάλληλων ηλεκτρονικών διατάξεων και την ανάπτυξη ειδικού λογισμικού πραγματοποιήθηκαν μετρήσεις της απόδοσης των επιμέρους ανιχνευτών καθώς επίσης και μετρήσεις σχετικές με τους φωτοπολλαπλασιαστές. / Positron Emission Tomography, often referred to by its acronym, PET, is an emerging radiologic modality that yields transverse tomographic images of functioning organs in the human body. PET enables the metabolic imaging of organs (as opposed to the anatomic imaging provided by techniques such as the X-ray imaging or the Computerized Tomography (CT)), in molecular level, and this is the reason why it is characterized as molecular imaging. Especially, small animal PET tomographs which require high spatial resolution can play an important role in biology and studies of in vivo tracer pharmacokinetics and metabolism. Various implementations have been reported in the literature using a variety of detector and design technologies. The basic technology for these scanners is based on small inorganic crystals, mainly from BGO, GSO, and LSO, forming detector blocks read out by position sensitive and multianode PMTs. BGO is the material used in a lot of commercial scanners, having replaced NaI, mainly because BGO has higher stopping power and it is not hygroscopic. We have been developing a low-cost small animal PET prototype, in order to study specific design characteristics and measure its performance. The basic block detector design consists of a 16×16 array of 3.75×3.75×20 mm3 individual BGO crystals coupled to a Hamamatsu R-2486 PSPMT. Measurements of the individual detector performance as well as measurements of the PSPMTs have been performed.

No description available.

Frequency domain functional near infrared spectroscopy (FD-fNIRS) is a tissue optical measurement technique used to measure absolute haemoglobin concentrations in brain tissue. This work is intended to be the first step in the development of a wearable, low-cost FD-fNIRS device for neurofeedback applications. The system requirements were generated from a review of relevant literature. A simplified system architecturewas developed based on the various instrumentation methodologies proposed by various authors. The functional blocks of this system were prototyped and their performance was evaluated. The developed vertical-cavity surface-emitting laser (VCSEL) current source was found to have a span of 10uA which meets the design specifications. Challenges exist in optimally biasing silicon photomultiplier (SiPM), which is susceptible to optical and electronic noise sources.

Ein Messsystem mit potentiellem Einsatz zur Überwachung von Flüssigkeitsbestrahlung wird untersucht. Das Messprinzip basiert auf der Szintillationslichtmessung eines organischen Szintillators über einen Einzelphotonensensor. Die Lichtleitung erfolgt mittels einer optischen Faser. Die Konstanz des Signals dieses Messsystems wird in verschiedenen Strahlungsqualitäten untersucht. Während der Bestrahlung mit Elektronen aus einer 90Sr-Radionuklidquelle kann eine konstante Photonenzählrate gemessen und diese in eine Dosisleistung umgerechnet werden. Bei Messungen im Strahlungsfeld einer Röntgenröhre wird ein deutliches Abfallen der Zählrate während der Bestrahlung beobachtet. Ein zweites Messsystem der gleichen Bauart zeigt ebenfalls dieses Verhalten. Der Photosensor wird als Ursache des Effekts ausgeschlossen. Strahlungsbedingte Änderungen im Absorptionsspektrum des Szintillators werden gefunden. Die Eignung des Systems in der jetzigen Form zur Überwachung der Konstanz von Flüssigkeitsbestrahlung ist aufgrund der schwer korrigierbaren Abnahme des Messsignals in Photonenfeldern nicht gegeben. Verschiedene Einflussfaktoren werden diskutiert.

Silicon photon multipliers, or SiPMs, are single photon detectors that have grown increasing interest in the last decade as an alternative to photomultiplier tubes in many field of physics, engineering and medicine. Compared to PMTs, SiPMs are more compact, rugged and operate at much lower bias voltage, in the order of tens of volts. Moreover they are insensitive to magnetic field and can achieve a very high radiopurity SiPM detectors work on the principle of a diode operated above the breakdown voltage, in Geiger mode. In this condition, the electric field in the depletion region is high enough that the electron-hole pairs, generated by a single photon absorption through photoelectric effect, create secondary charges by impact ionization in a potentially diverging avalanche effect that can be exploited to generate a macroscopical current at the output of the diode. Thanks to this effect, the SiPM is capable of counting the number of impinging photons down to single photon level. Noise sources in the SiPM include dark counts and correlated noise. Dark counts are counts happening when an electron-hole pair is generated in the active volume of the device in absence of photon absorptions. These events are caused either by thermal generation, diffusion from the neutral region or by tunnel effect. Correlated noise events, or counts, on the other hand, are generated when a primary firing cell retriggers after a certain time or cause the triggering of another cell. All these noise sources introduce errors in the photon count by adding fake events to the output signal of the detector.Traditional SiPM application is 511 keV gamma-ray detection in PET machines, using scintillator LYSO crystals to convert a single gamma ray into a flash of visible photons. An application based on the same principle was studied in this thesis by coupling FBK RGB-HD SiPMs with CsI:Tl crystals in order to detect lower energy X and gamma-rays. This setup has proven to be effective in the detection of radiation with energy as low as 5.9 keV with a resolution of 38.3%, which is the minimum value of energy resolution measured with SiPMs coupled to scintillator crystals at such low energy. At the same time it was observed that large area detectors provided a dynamic range wide enough to simultaneously detect radiation ranging from 6.4 keV to 122 keV with minimal saturation. In another activity of this thesis it was developed a simulation software that reproduces the behaviour of a SiPM under different light conditions by taking into account the detector efficiency, the dead time and the recharge behaviour of its cells and theoretical modelizations of the noise parameters that affect the measurement. From a given light profile the simulation generates a waveform that reproduces the one measured during the operation of real SiPMs. This waveform was then analysed using FBK software developed for SiPM characterization and the results showed an excellent agreement between the simulated detector and a reference SiPM. This software will become a useful tool for the design of SiPMs for future experiments because it will allow to tune the properties of the detectors to specific applications and it will reduce the need of layout and process split to find the optimal configuration of the detector parameters.Among all FBK technologies, this work was focused on the position-sensitive LG-SiPM. Unlike standard SiPMs, which have a single output, the LG-SiPM employs a more complex structure that splits the current signal into four output channels with ratios depending on the position of the impinging light on its surface. Center of mass calculations are used to reconstruct the position of the firing cell with precision down to some tens of microns while maintaining the fast time response of SiPMs. An application of the LG-SiPM was studied in the framework of the ARIADNE experiment in collaboration with the university of Liverpool. In this work the LG-SiPM was used to detect scintillation light coming from ionization tracks generated by alpha particles inside a CF4 TPC chamber. The ionized electrons where drifted through the action of a high electric field in the TPC towards a THGEM where they created light with timing depending on the distance of each track segment from the scintillator. The LG detector was able to reconstruct the 3D track particle inside the chamber with an error below 8 mm RMS inside the 40 l chamber and, at the same time, to reconstruct the energy released by the particle as function of time and calculate the total energy of the interacting particle and its linear energy transfer. These results open a novel approach for the TPC position reconstruction that combines the low number of readout channels needed for the LG detector to its time-continuous response which allows to reconstruct the tree-dimensional track of a particle inside the chamber.During the experiment it emerged the presence of an artifact that drifted all the reconstructed tracks towards the centre of the detection area, at the end of the signal. This effect was studied by creating a second simulation software that recreates the electrical behaviour of the LG-SiPM equivalent circuit when one or more cells trigger. It was simulated the output of the circuit with different light conditions and different values of the circuit elements and it was observed that the presence of the artifact was related to low intensity currents flowing through the net of the LG-SiPM metal tracks and quenching resistors. Several simulations were run in order to identify the optimal configuration of parameters for the reduction of this unwanted effect and to implement improvements in future LG-SiPM productions.Another application of the LG-SiPM in the field of radiation detection is the position reconstruction of the scintillation light emitted by gamma-rays in a monolithic crystal. Using a thin CsI:Tl crystal and lowering the detector temperature it was possible to distinguish different positions of interaction on the surface of the detector with an error below 1 mm FWHM. This technology can be effective for the creation of monolithic, position sensitive X and gamma-ray detector with good energy resolution for low energy spectroscopy or medical imaging devices.

L’exérèse des tumeurs cancéreuses est une procédure courante pour le traitement de nombreux cancers. L’enjeu est de réaliser une excision la plus complète possible pour éviter les récidives tout en épargnant le plus possible les tissus sains bordant la tumeur. La détection de positons est une modalité d’imagerie particulièrement adaptée au repérage de résidus tumoraux lors de l'éxerèse car sa forte sélectivité spatiale permet de s'affranchir du bruit provenant de la fixation non spécifique du radiotraceur dans les tissus situés en profondeur, offrant ainsi une meilleur sensibilité et un meilleur rapport signal sur bruit que la détection de photons gamma. L’utilisation pour le contrôle d’exérèse impose cependant une contrainte forte sur les dimensions du détecteur qui doit être manipulable facilement par le chirurgien et pouvoir être inséré dans des plaies opératoires potentiellement étroites. Une nouvelle génération de photodétecteurs appelés photomultiplicateurs silicium (SiPM) est particulièrement adaptée à cette application car ceux-ci allient la compacité et la robustesse des technologies silicium avec d'excellentes performances de détection. Mon travail de thèse porte sur le développement et la caractérisation de nouvelles sondes positon basées sur ces photodétecteurs. Dans un premier temps, un travail de caractérisation des SiPMs a été réalisé pour évaluer leurs performances pour la détection de positons. Deux prototypes de prototypes de détecteurs aux rôles complémentaires ont ensuite été réalisé: le premier est un imageur, basé sur l’assemblage de deux scintillateurs avec une ou deux matrices de SiPMs, qui permet de réaliser rapidement l'image de la distribution de traceur sur une large surface de tissus. Le second détecteur est une sonde de comptage, constituée de fibres scintillantes couplées à des SiPMs individuels via des fibres claires et capable d'être couplée à l'outil d'exérèse. Elle permet de guider l'outil du chirurgien vers les tissus repérés préalablement avec l'imageur. La caractérisation de l’imageur a montré sa capacité à détecter des résidus tumoraux de petite taille (15mg) avec une résolution submillimétrique. La sonde de comptage présente quant à elle, une efficacité de détection de 80%. / Excision of cancerous tumors is a common procedure for the treatment of numerous cancers. The stake is to perform the most complete excision to prevent recurrences while preserving as much as possible surrounding healthy tissues. Positron detection is a well suited imaging modality for detection of tumor remains during excision because its strong spatial selectivity makes it insensitive to the noise coming from the non-specific accumulation of the radiotracer in healthy tissues located far from the detector, leading to a better sensitivity and a better signal-to-noise ratio than gamma photon detection. Its use for the control of excision implies however strong constraints on detector dimensions which must be easy to handle by the surgeon and easy to insert in tight surgical wound. A new generation of photodetectors called Silicon Photmultipliers (SiPMs) is particularly suited for this application because they present the compactness and robustness of silicon technologies and very good detection performances. My thesis aims to develop and characterize a new generation of new positron probes based on these photodetectors. Two prototypes of detectors with complementary roles were realized: the first one is an imaging device based on the assembly of two scintillators with one or two SiPMs arrays which allows to quickly make an image of tracer distribution along a wide surface of tissues. The second detector is a counting probe made of scintillating fibers associated with individual SiPMs through clear optical fibers and can be associated to the excision tool. It guides the surgeon tool to the tissues previously localized with the imaging probe. Characterization of the imaging probe showed its ability to detect small tumor remains (15mg) with a submillimetric resolution. The counting probe showed a detection efficiency of 80%.