Dissertations / Theses on the topic 'Cosmic ray direct detection'

This thesis concentrates on the measurement of cosmic-ray light component (proton + helium) spectrum with the Dark Matter Particle Explorer (DAMPE). In chapter one, an introduction on cosmic-ray history is given together with the acceleration mechanism and some recent experiments. A description on DAMPE system is presented in chapter two, which includes its sub-detectors, scientific targets and parameters. There are various challenges in measuring cosmic ray energy with a limited-size calorimeter (like the BGO of DAMPE). In chapter three, various unfolding methods for reconstructing the primary energy of cosmic ray nuclei are discussed. It turns out that the method based on the Bayes theorem has the best performance on reconstructing the cosmic-ray energy for DAMPE. The test results show that the Bayes method is capable of reconstructing nuclei energy with good accuracy on both MC samples (bias within 2%) and real data that come from the test beams at CERN (bias within 3%). In chapter four, a detailed description on the measurement of cosmic ray protons + helium spectrum is presented, which involves the candidates selection, energy reconstruction and calculation of the statistical and systematic uncertainties. Finally, the proton + helium spectrum with energy 40 GeV to 100 TeV is presented.

Astrophysical observations give convincing evidence for a vast non-baryonic component, the so-called dark matter, accounting for over 20% of the overall content of our Universe. Direct dark matter search experiments explore the possibility of interactions of these dark matter particles with ordinary baryonic matter via elastic scattering resulting in single nuclear recoils. The ZEPLIN-III detector operated on the basis of a dualphase (liquid/gas) xenon target, recording events in two separate response channels { scintillation and ionisation. These allow discrimination between electron recoils (from background radiation) and the signal expected from Weakly Interacting Massive Particle (WIMP) elastic scatters. Following a productive first exposure, the detector was upgraded with a new array of ultra-low background photomultiplier tubes, reducing the electron recoil background by over an order of magnitude. A second major upgrade to the detector was the incorporation of a tonne-scale active veto detector system, surrounding the WIMP target. Calibration and science data taken in coincidence with ZEPLIN-III showed rejection of up to 30% of the dominant electron recoil background and over 60% of neutron induced nuclear recoils. Data taking for the second science run finished in May 2011 with a total accrued raw fiducial exposure of 1,344 kg days. With this extensive data set, from over 300 days of run time, a limit on the spin-independent WIMP-nucleon cross-section of 4.8 10-8 pb near 50 GeV/c2 WIMP mass with 90% confidence was set. This result combined with the first science run of ZEPLIN-III excludes the scalar cross-section above 3.9 10-8 pb. Studying the background data taken by the veto detector allowed a calculation of the neutron yield induced by high energy cosmic-ray muons in lead of (5.8 0.2) 10-3 neutrons/muon/(g/cm2) for a mean muon energy of 260 GeV. Measurements of this kind are of great importance for large scale direct dark matter search experiments and future rare event searches in general. Finally, this work includes a comprehensive measurement of the energy dependent quenching factor for low energy nuclear recoils in a plastic scintillator, such as from the ZEPLIN-III veto detector, increasing accuracy for future simulation packages featuring large scale plastic scintillator detector systems.

The identification of the relic particles which presumably constitute cold dark matter is a key challenge for astroparticle physics. Indirect methods for their detection using high energy astro- physical probes such as cosmic rays have been much discussed. In particular, recent ‘excesses’ in cosmic ray electron and positron fluxes, as well as in microwave sky maps, have been claimed to be due to the annihilation or decay of dark matter. In this thesis, we argue however that these signals are plagued by irreducible astrophysical backgrounds and show how plausible con- ventional physics can mimic the alleged dark matter signals. In chapter 1, we review evidence of, and possible particle candidates for, cold dark matter, as well as our current understanding of galactic cosmic rays and the state-of-the-art in indirect detection. All other chapters contain original work, mainly based on the author’s journal publications. In particular, in chapter 2, we consider the possibility that the rise in the positron fraction observed by the PAMELA satellite is due to the production through (hadronic) cosmic ray spallation and subsequent acceleration of positrons, in the same sources as the primary cosmic rays. We present a new (unpublished) analytical estimate of the range of possible fluctuations in the high energy electron flux due to the discreteness of plausible cosmic ray sources such as supernova remnants. Fitting our result for the total electron-positron flux measured by the Fermi satellite allows us to fix the only free parameter of the model and make an independent prediction for the positron fraction. Our explanation relies on a large number of supernova remnants nearby which are accelerating hadronic cosmic rays. Turning the argument around, we find encouraging prospects for the observation of neutrinos from such sources in km^3-scale detectors such as IceCube. Chapter 3 presents a test of this model by considering similar effects expected for nuclear secondary-to-primary ratios such as B/C. A rise predicted above O(100)GeV/n would be an unique confirmation of our explanation for a rising positron fraction and rule out the dark matter explanation. In chapter 4, we review the assumptions made in the extraction of the `WMAP haze' which has also been claimed to be due to electrons and positrons from dark matter annihilation in the Galactic centre region. We argue that the energy-dependence of their diffusion means that the extraction of the haze through fitting to templates of low frequency diffuse galactic radio emission is unreliable. The systematic effects introduced by this can, under specific circumstances, reproduce the residual, suggesting that the ‘haze’ may be just an artefact of the template subtraction. We present a summary and thoughts about further work in the epilogue.

A novel detector for ultra-high energy cosmic rays, and its prototype are discussed. It detects events with primary energy greater than 100 PeV. (1 PeV = 1000 TeV; 1EeV = 1000 PeV.) The detector operates by sensing the near-ultraviolet scintillation light of ionized nitrogen molecules created by the passage of ionizing particles in extensive air showers. (The concept is loosely based on the highly successful Fly's Eye detector situated at Dugway, Utah.) Typical events should consist of 1 to 100 EeV primary energy showers, with near-vertical cores, passing through the detector's field-of-view at distances of 1 to 20 km. The optical field of view of the hypothetical detector would be 60 degrees wide by several (≈ 3) degrees high and would look in a near-horizontal direction at a distant mountain range or other suitably dark background roughly 20 Ian away. A typical good location would be the rim of a canyon, looking slightly downward at the other side. The field-of-view would be subdivided into 3 or more thinner ''wedges'', 60 degrees wide by, perhaps, 1 degree high. A single detector provides timing and brightness information only. Three widely-separated detectors with overlapping fields-of-view provide sufficient data to determine the core location, the zenith and azinruthal angles of the core axis, and the absolute luminosity of the cascade. Interpretation of the luminosity data would be a challenge, but it should be possible to estimate primary energy from it. The advantage of this new scheme is the enormous effective detector area per relatively low-cost detector module. Each triplet of detectors "sees" 300 square km with a typical core axis acceptance of roughly 1 sr. The construction and testing of a prototype unit has been accomplished. The field-of-view was 41 degrees wide by 2 degrees high. Light was collected by a 4.7 square meter mirror and focused onto a wave-shifter PMT system. 8 events with primary energies in the 0.1 to 1 EeV range were observed in an 8.5 hour period. Representative events are shown and preliminary data analysis is discussed.

Existing inorganic materials for radiation dosimeters suffer from several drawbacks, including their inability to cover large curved areas, lack of tissueequivalence, toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triarylamine) (PTAA)-based devices have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. The device was prepared by sandwiching an active layer of PT AA between a transparent indium tin oxide (ITO) b()ttom contact and a metal top contact. The charge transport properties of the device were assessed using the spectral photo current method. Increased photocurrent sensitivity was observed for samples annealed at 150°C, consistent with solvent loss, which was confirmed by thermogravimetric analysis. A diode with an Al contact shows the highest quality of recti tying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo Ka X-radiation over long timescales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. To optimize the performance of the device, the X-ray stopping power and the charge carrier mobility of the active layer have been modified by the introduction of various concentrations of the high atomic number bismuth oxide nanoparticles and the high mobility TIPS-pentacene organic material, respectively. The increasing of the devices' sensitivity correlates with an increased charge carrier mobility which was measured by a time-of-flight photocurrent measurement. Good stability of Xray sensitivity was found as the dosimeter was exposed to the X-ray beam for a long period of time with no discernible reduction in performance. These results indicate that PTAA is a highly-promising material for the direct detection of X-rays and potentially other types of radiation.

Cosmic rays at energies 10^18 eV and above are known as Ultra High Energy Cosmic Rays (UHECR). UHECR are charged particles that are accelerated by the biggest accelerators in our universe. Candidate accelerators generating these UHECR are super novas, black holes and neutron stars. But where and what these intergalactic accelerators is at large still unknown. One of the experiments in the forefront of research in this eld is JEM-EUSO, a planed space based telescope for detecting UHECR particles as they enter Earth's atmosphere. Made possible by the advances in photon detectors and light weighted Fresnel lenses. A ground based path nder experiment was carried out in 2015 called EUSO-TA to test the optics and photomultiplier technologies. When the UHECR enters the atmosphere it collides with the atoms generating a number of secondary particles which in turn interacts with other atoms in the atmosphere generating a cascade of secondary particles. These trails are known as Extensive Air Showers (EAS). Mostly electrons are generated and in turn they excites the nitrogen atoms in the atmosphere which generate a isotropic characteristic uorescence light. The JEM-EUSO telescope is designed to detect and measure the photon ux. From the photon ux it will be able to estimate the energy of the initial UHECR. JEM-EUSO will cover the largest area of EAS search and increase statistics of UHECR data. This thesis describes the method and development of algorithms made for EAS analysis and detection based on EUSO-TA data. A simulation of EUSO-TA focal surface was developed, simulating background, stars and EAS. The algorithms developed involves a background subtracting lter, line detection using Hough transform and a neural network for decision making. The Hough transform is used in computer vision and is a method used to detect lines in the pictures. It successfully identi ed both simulated and captured UHECR incoming direction with small errors. Neural network are a machine learning method used classi cation and regression problems. With the use of know example data simulated or real captured data a neural network can without explicit programing it, adjust its parameters to t the data. Based on method called supervised learning. The algorithms was programed in Python and using ROOT software to build the neural network. The resulting algorithm was able to successfully detect simulated data. Test on the EUSO-TA captured data shows a promising result but has to be developed and tested further.

This dissertation consists of two parts. They are separate ideas, but both fall into the context of General Relativity using dynamical systems. Part one is titled Cyclic Universes. It is shown that a Friedmann model with positive spatial sections and a decaying dark energy term admits cyclic solutions which is shown graphically by the use of phase planes. Coupling the modified Friedmann model to a scalar field model with cross-sectional terms in order to model the reheating phase in the early universe, it is found that there is a violation of the energy condition, i.e. when the universe is in the contracting phase and re-collapses again. We suspect that the cause for this violation is due to the asymmetry of the solution of w together with the cross-sectional terms at the bounce preceding slow-roll inflation. Part two is titled Thought Experiment to Directly Detect Cosmic Expansion by Holonomy. Two thought experiments are proposed to directly measure the expansion of the universe by the parallel transfer of a vector around a closed loop in a curved spacetime. Generally, expansion would cause a measurable deficit angle between the vector’s initial and final positions. Using the McVittie spacetime (which describes a spherically symmetric object in an expanding universe) as a backdrop to perform these experiments it is shown that the expansion of the universe can be directly detected by measuring changes in the components of a gyroscopic spin axis. We find these changes to be small but large enough (∆S ∼ 10−7 ) to be measured if the McVittie spacetime were a representation of our universe.

We have conducted an extensive experimental study on the subject of near ground atmospheric electricity. The main objective was to gain more understanding of this particular aspect of atmospheric phenomena, while testing the possible application to cosmic ray research. The results in atmospheric electricity show that there are certain patterns in ion grouping such as the size and lifetime. The average lifetime of ion group is 0.7 seconds and the average size is about 10 meters at our experimental site. Ultrahigh energy cosmic ray air showers should create sizable slow atmospheric electric pulses according to our theoretical calculations. Preliminary studies on air showers with total particle number N equal or greater than 10⁵ (10¹⁵ eV) have yielded strong evidence that slow atmospheric current pulses are associated with air showers. The theory and the experiment agree with each other fairly well when we average over large numbers of events. With our current experimental arrangement, when the air shower exceeds a certain size, the system response saturates. Therefore it is extremely desirable in future research that the counter array be designed for a much higher threshold level, since this prototype experiment indicates that interesting data would be obtained. Another reason for further experimental research being directed toward ultrahigh energy, e.g., N ≥ 10⁷ (10¹⁷ eV) and higher, is to establish a calibration of the slow atmospheric electric signals generated by cosmic rays as a function of primary cosmic ray energy and core location. This type of slow atmospheric electric signal, if fully understood and calibrated, offers a new and potentially less expensive technique to observe ultrahigh energy cosmic ray events, which hold some fundamental keys to the knowledge of the universe on a large scale.

Organic small molecules semiconductors are promising in the field of direct ionizing radiation detection. Unlike their inorganic counterpart, these molecules are easy to work with, since they are flexible, soluble and can be deposited on electronic devices with very simple processes, such as drop-casting and spin-casting. Moreover, these materials have good detection properties and very low working voltage. To this day, organic semiconductors have mainly been used in indirect radiation detection, employed both in scintillator and as photodetectors. However, direct detection of ionizing radiation is a far more effective method, since it is performed within a single material and a single conversion, directly from photons to electrical signal; furthermore, it provides a higher signal-to-noise ratio and a faster response time. In this experimental work, I fabricated four direct detectors based on transistors; two different organic solutions were drop-casted onto the transistors, creating a conduction channel between source and drain electrodes. Both these solutions had chlorobenzene as a solvent, with DiF-TES-ADT and DiF-TEG-ADT as solutes, respectively, in a 0.5% concentration. The purpose of this thesis is dual. Firstly, I want to study how the detectors’ sensitivity is influenced by semiconductor molecules with different Z-number; secondly, I want to test a new drop-casting method (SAC method) and compare it to results previously obtained with traditional deposition methods. The results are very promising, with very high values of sensitivity obtained with low voltages.

Les preuves pour l'existence de la matière noire (MN), sous forme d'une particule inconnue qui rempli les halos galactiques, sont issues d'observations astrophysiques et cosmologiques: son effet gravitationnel est visible dans les rotations des galaxies, des amas de galaxies et dans la formation des grandes structures de l'univers. Une manifestation non-gravitationnelle de sa présence n'a pas encore été découverte. L'une des techniques les plus prometteuse est la détection indirecte de la MN, consistant à identifier des excès dans les flux de rayons cosmiques pouvant provenir de l'annihilation ou la désintégration de la MN dans le halo de la Voie Lactée. Les efforts expérimentaux actuels se focalisent principalement sur une gamme d'énergie de l'ordre du GeV au TeV, où un signal de WIMP (Weakly Interacting Massive Particles) est attendu. L'analyse des mesures récentes et inédites des rayons cosmiques chargés (antiprotons, électrons et positrons) et leurs émissions secondaires et les améliorations des modèles astrophysiques sont présentées.Les données de PAMELA sur les antiprotons contraignent l'annihilation et la désintégration de la MN de manière similaire (et même légèrement meilleurs) que les contraintes les plus fortes venant des rayons gamma, même dans le cas où les énergies cinétiques inférieures à 10 GeV sont écartées. En choisissant des paramètres astrophysiques différents (modèles de propagation et profils de MN), les contraintes peuvent changer d'un à deux ordres de grandeur. Pour exploiter la totalité de la capacité des antiprotons à contraindre la MN, des effets précédemment négligés sont incorporés et se révèlent être importants dans l'analyse des données inédites de AMS-02 : ajouter les pertes d'énergie, la diffusion dans l'espace des moments et la modulation solaire peut modifier les contraintes, même à de hautes masses. Une mauvaise interprétation des données peut survenir si ces effets ne sont pas pris en compte. Avec les flux de protons et d'hélium exposé par AMS-02, le fond astrophysique et ces incertitudes du ratio antiprotons sur protons sont réévalués et comparés aux données inédites de AMS-02. Aucune indication pour un excès n'est trouvé. Une préférence pour un halo confinant plus large et une dépendance en énergie du coefficient de diffusion plus plate apparaissent. De nouvelles contraintes sur l'annihilation et la désintégration de la MN sont ainsi dérivés.Les émissions secondaires des électrons et des positrons peuvent aussi contraindre l'annihilation et la désintégration de la MN dans le halo galactique : le signal radio dû à la radiation synchrotron des électrons et positrons dans le champs magnétique galactique, les rayons gamma des processus de bremsstrahlung avec le gas galactique et de Compton Inverse avec le champs radiatif interstellaire sont considérés. Différentes configurations de champs magnétique galactique et de modèles de propagation et des cartes de gas et de champs radiatif interstellaire améliorés sont utilisées pour obtenir des outils permettant le calculs des émissions synchrotrons et bremsstrahlung venant de MN de type WIMP. Tous les résultats numériques sont incorporés dans la dernière version du Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID).Une interprétation d'un possible excès dans les données de rayons gamma de Fermi-LAT au centre galactique comme étant dû à l'annihilation de MN en canaux hadronique et leptonique est analysée. Dans une approche de messagers multiples, le calcul des émissions secondaires est amélioré et se révèle être important pour la détermination du spectre pour le canal leptonique. Ensuite, les limites provenant des antiprotons sur l'annihilation en canal hadronique contraignent sévèrement l'interprétation de cet excès comme étant dû à la MN, dans le cas de paramètres de propagation et de modulation solaire standards. Avec un choix plus conservatif de ces paramètres elles s'assouplissent considérablement
Overwhelming evidence for the existence of Dark Matter (DM), in the form of an unknownparticle filling the galactic halos, originates from many observations in astrophysics and cosmology: its gravitational effects are apparent on galactic rotations, in galaxy clusters and in shaping the large scale structure of the Universe. On the other hand, a non-gravitational manifestation of its presence is yet to be unveiled. One of the most promising techniques is the one of indirect detection, aimed at identifying excesses in cosmic ray fluxes which could possibly be produced by DM annihilations or decays in the Milky Way halo. The current experimental efforts mainly focus in the GeV to TeV energy range, which is also where signals from WIMPs (Weakly Interacting Massive Particles) are expected. Focussing on charged cosmic rays, in particular antiprotons, electrons and positrons, as well as their secondary emissions, an analysis of current and forseen cosmic ray measurements and improvements on astrophysical models are presented. Antiproton data from PAMELA imposes contraints on annihilating and decaying DM which are similar to (or even slightly stronger than) the most stringent bounds from gamma ray experiments, even when kinetic energies below 10 GeV are discarded. However, choosing different sets of astrophysical parameters, in the form of propagation models and halo profiles, allows the contraints to span over one or two orders of magnitude. In order to exploit fully the power of antiprotons to constrain or discover DM, effects which were previously perceived as subleading turn out to be relevant especially for the analysis of the newly released AMS-02 data. In fact, including energy losses, diffusive reaccelleration and solar modulation can somewhat modify the current bounds, even at large DM masses. A wrong interpretation of the data may arise if they are not taken into account. Finally, using the updated proton and helium fluxes just released by the AMS-02 experiment, the astrophysical antiproton to proton ratio and its uncertainties are reevaluated and compared to the preliminarly reported AMS-02 measurements. No unambiguous evidence for a significant excess with respect to expectations is found. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. New stringed constraints on DM annihilation and decay are derived. Secondary emissions from electrons and positrons can also be used to constrain DM annihilation or decay in the galactic halo. The radio signal due to synchrotron radiation of electrons and positrons on the galactic magnetic field, gamma rays from bremsstrahlung processes on the galactic gas densities and from Inverse Compton scattering processes on the interstellar radiation field are considered. With several magnetic field configurations, propagation scenarios and improved gas density maps and interstellar radiation field, state-of-art tools allowing the computaion of synchrotron and bremssttrahlung radiation for any WIMP DM model are provided. All numerical results for DM are incorporated in the release of the Poor Particle Physicist Coookbook for DM Indirect Detection (PPPC4DMID). Finally, the possible GeV gamma-ray excess identified in the Fermi-LAT data from the Galactic Center in terms of DM annihilation, either in hadronic or leptonic channels is studied. In order to test this tantalizing interprestation, a multi-messenger approach is used: first, the computation of secondary emisison from DM with respect to previous works confirms it to be relevant for determining the DM spectrum in leptonic channels. Second, limits from antiprotons severely constrain the DM interpretation of the excess in the hadronic channel, for standard assumptions on the Galactic propagation parameters and solar modulation. However, they considerably relax if more conservative choices are adopted

Des de temps immemorials, dels principis de la humanitat, els éssers humans han mostrat un tremenda curiositat i atracció pel que veien quan enlairaven la vista. Per un motiu o un altra, la recerca d'explicacions de naturalesa mística de tot allò que envoltava la vida humana així com el propi destí es buscava fora de la Terra. Aquest interès místic va fomentar la observació del cel nocturn que al cap del temps junt amb altres canvis de tipus filosòfic i social van donar peu a una interpretació racional del que observaven i per tant, a una primera formulació de models cosmogònics i cosmològics.
Precisament el llegat d'aquests primers observadors del cel ha estat la curiositat per l'espai extraterrestre per buscar-hi respostes a diferents preguntes. Algunes d'aquestes preguntes, que han estat formulades per diversos científics, varen consistir en les llavors per a una nova disciplina cultivada en el camp de la ciència física: La física dels Raigs Còsmics.
Actualment, la física dels Raigs Còsmics consisteix en una disciplina que aixopluga diferents tòpics de l'astrofísica i la física com ara la nucleosíntesi dels raigs còsmics, el procés de injecció, els mecanismes d'acceleració, el procés de propagació i la detecció prop de la Terra dels raigs còsmics.
Durant els anys 80, es van planejar un conjunt d'experiències a bord de satèl·lits amb la finalitat d'estudiar la component hadrònica de la radiació còsmica, en concret, els ions ultrapesants amb càrrega superior a la del Ferro. El present treball està unit a un d'aquest experiments: l'UHCRE (Ultra Heavy Cosmic Ray Experiment). Varis apilaments de detectors sòlids de traces nuclears van ser usats en l'UHCRE. Aquests apilaments han estat analitzats i mesurats en el nostre grup, reconeixent un total de 205 traces originades per ions ultrapesants de la radiació còsmica. La identificació d'aquests ions en l'UHCRE ha estat la primera motivació d'aquest treball, així la primera meitat (capítols 1 i 2) d'aquesta tesi tracta aquest problema. D'altra banda, els capítols 3 i 4, concerneix el procés de propagació de l'abundància d'aquests ions cap a les seves fonts mitjançant el model de Leaky Box.
En el capítol 1, es presenta un mètode d'identificació conegut com Gradient Fraccional de la velocitat d'atac reduïda i es realitza un estudi detallat del seu rang d'aplicabilitat. Finalment, s'efectua la determinació de l'abundància dels raigs còsmics ultrapesants amb Z > 65 vistos per l'UHCRE.
En el capítol 2, s'utilitza un model alternatiu de formació de traça latent basat en el model de pèrdua d'energia restringida en el qual s'inclouen la possible contribució de les diferents correccions per col·lisions properes en l'equació de Bethe-Bloch. Un estudi prenent els resultats de l'UHCRE permet establir relacions entre els paràmetres que intervenen en el procés d'identificació. Finalment, s'obté una estimació d'aquests paràmetres usant dades experimentals d'accelerador.
En el capítol 3, es dedueix l'equació de transport pel model de Leaky Box (MLB) que descriu la variació de la composició química de la radiació còsmica durant el seu viatge a través de la galàxia. L'abundància en les fonts que es dedueix dels resultats de l'UHCRE és estimada resolent les equacions de transport per a tots els elements amb càrrega entre 65 i 92 mitjançant un mètode numèric que cal entendre'l com una primera aproximació al problema.
En el darrer capítol, les equacions del MLB es resolen numèricament usant la Weighted Slab Technique. Es presenta un estudi de la resposta d'aquest model quan es varien les expressions dels diferents paràmetres de propagació que es requereixen. Optimitzant el paràmetre estadístic χ² entre l'abundància calculada la qual és afectada per una indeterminació en la càrrega i l'abundància experimental, ah estat possible determinar aquella combinació de totes les expressions disponibles dels paràmetres de propagació que millor reprodueix l'abundància experimental de l'UHCRE.
Since ancient times, from the beginning of humankind, human beings have shown a great curiosity and attraction for what they saw when looking up. For one reason or another, the quest for explanations of mystical nature (maybe justifications) for what surrounded human life as well as its destiny was searched outside the Earth. This mystical interest encouraged the observation of the night sky which, in time, together with other social and philosophical changes, lead to a rational interpretation of what they observed and, hence the formulation of the first cosmogonical models and then cosmological models.
Precisely, the legacy of these first sky observers, has been the curiosity for the extraterrestial space in search of answers to many different questions. Some of these questions formulated by several scientists, were the seeds for a new discipline sowed in the field of physics science: Cosmic Ray Physics.
Nowadays, Cosmic Ray Physics consist on a discipline allowing to gather several different topics of astrophysics and physics such as the nucleosynthesis of cosmic rays, the injection process, the acceleration mechanisms, the propagation process and the detection of cosmic rays near the Earth.
During the 80's, a set of experiences on board of satellites were planned and carried out with the aim of studying the hadronic component of cosmic rays, specifically ultra heavy ions with charge higher than Iron. The present work is, therefore, linked to one of such experiences; the UHCRE (Ultra Heavy Cosmic Ray Experiment). Several stacks of sheets of solid state nuclear track detectors used in the UHCRE have been analysed and measured by our group, recognizing a total of 205 tracks as originated by ultra heavy cosmic ray ions. The identification of cosmic ray ions recorded in UHCRE has been the first motivation of this work, so the first half (chapter 1 and 2) of the present thesis deals with this problem. On the other hand, chapters 3 and 4 concern to the propagation process of the abundances of such ions back to their sources using the Leaky Box model.
In chapter one, an identification method, known as Reduced Etch Rate Fractional Gradient (RERFG) is presented and a detailed study of its range of applicability is performed. The determination of the abundances of ultra heavy cosmic ray with Z > 65 seen by the UHCRE is realized.
In the second chapter, an alternative track formation model based on a modification of the Restricted Energy Loss model is taken into consideration by introducing the contribution of the close collisions corrections in the Bethe-Bloch formula. A study taking the UHCRE measurements allows to establish relationships between the parameters involved in the identification process. Finally, an estimation of these parameters is made using experimental data from accelerator.
In chapter three, the transport equation for the Leaky Box Model (LBM) which describes the variation of the chemical composition of cosmic rays during their travel through the Galaxy is deduced. The source abundances inferred from the UHCRE results are estimated solving the transport equations, corresponding to all elements with charge 65 < Z < 92, with a numerical method that has to be understood as a first approximation to the problem.
In the last chapter, the LBM transport equations are numerically solved using the Weighted Slab Technique. A study of the response of the LBM is presented when different expressions of the required propagation parameters are taken. By optimizing the χ² statistical parameter between calculated abundances which are effected by a charge uncertainty and experimental abundances, it has been possible to determine which combination of all available expressions of the propagation parameters better reproduces the experimental abunadances of UHCRE.

Der TAIGA Detektor (“Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy”) testet eine neue Nachweismethode der erdgebundenen Cherenkov Gamma Astronomie fuer 10TeV bis einige PeV, und fuer kosmische Strahlung oberhalb 100TeV: die Kombination abbildender und nicht-abbildender Cherenkov Detektoren in einem hybriden System. Im Fokus der Arbeit steht TAIGA-HiSCORE - ein Cherenkov Detektorfeld mit grosser Apertur zur Messung der Zeitstruktur der Cherenkovlichtfront in atmosphaerischen Luftschauern (EAS). Die Praezisonsvermessung der Schauerrichtung basiert auf (1) sub-nsec Zeitsynchronisation aller Detektoren, und (2) einer neuentwickelten Zeitkalibrationsmethode. Die Genauigkeit wird bestimmt mit experimentellen und simulierten EAS-Daten, spezieller LED-Kalibration und dem LIDAR Laserstrahl aus der International Space Station (ISS). Mit den HiSCORE9 Daten (2013-2014) wird die sub-nsec Zeitsynchronisation durch das White Rabbit Zeitsystem unter realen Bedingungen nachgewiesen. Eine neue, auch fuer grosse Cherenkov-Detektorfelder praktikable Zeitoffset-Kalibration aller Detektoren wurde entwickelt, und fuer HiSCORE28 (2015-2018) angewandt. Diese hybride Kalibration basiert auf EAS-Ereignissen und direkter LED-Kalibration fuer lediglich eine begrenzte Zahl von Detektoren. Die Genauigkeit der Luftschauer-Richtungsrekonstruktion wird ueber die “Schachbrett-Methode” MC-unabhaengig bestimmt zu 0.4° an der Energieschwelle (50TeV) und <= 0.2° fuer > 100TeV. Eine wichtige Zufallsentdeckung war mit HiSCORE28 moeglich: der Laser des ISS-CATS-Lidars wurde in richtungsrekonstruierten Daten von HiSCORE28 nachgewiesen. Mit den “ISS Ereignissen” gelang es, sowohl die Rekonstruktionsgenauigkeit von HiSCORE, als auch das “absolute pointing” zu messen (<=0.1°) - besonders wichtig, da eine starke Gamma-Quelle im Datensatz bisher nicht nachgewiesen wurde. Im Schlussteil der Arbeit wird ein Methode zur Punktquellensuche im gesamten Gesichtsfeld von TAIGA-HiSCORE vorgestellt.
The TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy) detector is a new ground-based Cherenkov detection technology for gamma-astronomy from 10TeV up to several PeV, and cosmic rays (CR) above 100TeV. The main topic of this work is TAIGA-HiSCORE, the wide-aperture air Cherenkov timing array. The focus is on precision extensive air shower (EAS) arrival direction reconstruction, achieved by (1) sub-nsec time-synchronization between the array stations, and (2) a newly developed array time calibration procedure. The performance is verified using simulated and experimental data from EAS, dedicated LED calibration, and a LIDAR laser beam from the International Space Station (ISS). The analysis of the HiSCORE 9 data (2013-14), collected with a data acquisition system (DAQ) based on the White Rabbit (WR) timing system, allows to verify the sub-nsec time synchronization between the array stations. The analysis of HiSCORE 28 data (2015-2018) addresses the problem of achieving an easy-to-perform time calibration for large area ground-based Cherenkov array. A new "hybrid" calibration method is developed, which makes use of EAS data, and requires direct LED calibration of only a few array stations. The "chessboard" method is applied on the reconstructed data to obtain a MC-independent estimation of the detector angular resolution, found to be 0.4° at threshold (~50TeV) and <= 0.2° above 100TeV. A serendipitous discovery was made in this work: a signal from the CATS-LIDAR on-board the ISS was found in the HiSCORE 28 data. These "ISS-events" are used to verify the detector performance, in particular the absolute angular pointing (<= 0.1°), particularly important since a strong gamma point source has not yet been detected by the TAIGA-HiSCORE. The final part of the work presents a first preliminary approach to a wide aperture point source analysis, developed for the TAIGA-HiSCORE in stand-alone operation.

Identifying what makes up the Dark Matter is a long-standing problem to which the abundance of gravitational and cosmological evidence fails to answer. Indirect detection techniques have the aim to unveil the nature of Dark Matter by catching and identifying the products of potential decays and/or annihilations. The work exposed in this thesis is in line with this strategy and has for common thread the quest for line(-like) features in the extraterrestrial fluxes of gamma-rays and neutrinos. The motivation behind this specific interest is that, due to the absence of astrophysical counterparts beyond the GeV scale, these features constitute the ultimate probes (also called “smoking guns”) of the existence of Dark Matter.The thesis is organized in three Parts, the first of which is an introduction to the different facets of the Dark Matter conundrum and why it is not a trivial issue. The works involving gamma-ray line considerations are gathered in Part II, and those exclusively focusing on neutrino lines in Part III.Part II focuses on the effective field theory of Dark Matter decay, first in the context of millicharged particles decaying to gamma-ray lines, and then in the context of (neutral and millicharged) Dark Matter decays involving the simultaneous emission of gamma-ray and neutrino lines. In both cases, the simultaneous emission of cosmic rays is unavoidable and the decays are constrained in a multi-messenger fashion. The complementarity of the results obtained is used to derive model-independent constraints on the Dark Matter lifetime, and shows the possibility to exclude or distinguishsome specific scenarios on the basis of an explicit experimental conjecture.After an introduction to the neutrino detection principles and to the operation of the IceCube detector, Part III focuses on two careful searches for spectral features in the neutrino spectrum. The main goal behind these analyses, conducted in two different regions of the energy spectrum but using the same likelihood ratio procedure, is to popularize dedicated energy distribution studies by showing their ability to reach sensitivity levels comparable to—sometimes even going beyond—those obtained with angular distribution studies or even in the context of gamma-ray line searches.
Option Physique du Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Prise en compte des antiprotons pour la propagation des rayons cosmiques. Mise en evidence d'une source d'antineutrinos particuliere: l'ensemble des centrales nucleaires terrestres. Utilisation de ces antineutrinos pour etudier les oscillations de neutrinos dans le vide et dans la matiere. Application aux neutrinos emis par sn 1987a

L’expérience JEM-EUSO (traduction de Observatoire spatial de l’univers extrême à bord du module de l'expérience japonaise) est conçu pour observer les UHECR en détectant la lumière fluorescente UV émise par la gerbe qui se développe lorsque les UHECR interagissent avec l'atmosphère terrestre. Les gerbes atmosphériques sont constituées de dizaines de milliards de particules secondaires ou plus traversant l'atmosphère quasiment à la vitesse de la lumière, excitant les molécules d'azote qui émettent ensuite de la lumière dans la gamme UV. Alors que cette « technique de fluorescence » est habituellement utilisée au sol, en opérant ainsi à partir de l'espace, JEM-EUSO, pour la première fois, fournira des statistiques élevées sur ces événements. Avec un large champ de vue de ± 30 °, JEM-EUSO pourra observer depuis l’espace un volume d'atmosphère beaucoup plus grand que ce qui est possible du sol, en collectant un nombre sans précédent d'événements UHECR aux plus hautes énergies.Pour les quatre prototypes d’expériences construites par la collaboration, nous avons développé un ensemble commun d'électronique, en particulier le système central d'acquisition de données capable de fonctionner au sol, sur des ballons à haute altitude et dans l'espace.Ces expériences utilisent toutes un détecteur composé d'un module de détection de photo (PDM) identique aux 137 qui seront présents sur la surface focale JEM-EUSO. La lumière UV générée par les gerbes atmosphériques à haute énergie passe le filtre UV et frappe les tubes à photomultiplicateurs multi-anodes (MAPMT). Les photons UV sont alors transformés en électrons, qui sont multipliés par les MAPMT et le courant qu’ils créent est amplifié par des cartes ASIC de circuit intégré (EC-ASIC), qui effectuent également le comptage des photons et l'estimation de charge. Une carte FPGA nommé PDM board s'interface avec ces cartes ASIC, fournissant des paramètres d'alimentation et de configuration à ces cartes ASIC, collecte alors les données et exécute le déclenchement d’acquisition de niveau 1.Dans le cadre de ces travaux, je me suis occupée de la conception, du développement, de l'intégration et du test la carte FPGA PDM board pour les missions EUSO-TA et EUSO-Balloon ainsi que des tests d'algorithme de déclenchement autonomes d’acquisitions et j'ai également analysé les données de vol d’EUSO-Balloon et de la campagne sol EUSO-TA d’octobre 2015.Dans cette thèse, je donnerai un bref aperçu des rayons cosmiques à haute énergie, y compris de leur technique de détection et des principales expériences pour les détecter (chapitre 1), je décrirai JEM-EUSO et ses pathfinders (chapitre 2), je présenterai les détails de la conception et de la fabrication du PDM (chapitre 3) et de la carte FPGA PDM board (chapitre 4), ainsi que des tests d'intégration d’EUSO-TA et d’EUSO-Balloon (chapitre 5). Je ferai un rapport sur la campagne EUSO-Balloon de 2014 (chapitre 6) et sur ses résultats (chapitre 7), y compris une analyse spécifique développée pour rechercher des variations globales de l'émissivité UV au sol et j’appliquerai une analyse similaire aux données collectées sur le site de Telescope Array (Chapitre 8). Enfin, je présenterai la mise en œuvre et le test du déclencheur de premier niveau (L1) dans la carte de contrôle FPGA (chapitre 9). Un bref résumé de la thèse sera donné au chapitre 10
The JEM-EUSO (Extreme Universe Space Observatory on-board the Japanese Experiment Module) international space mission is designed to observe UHECRs by detecting the UV fluorescence light emitted by the so-called Extensive Air Shower (EAS) which develop when UHECRs interact with the Earth’s atmosphere. The showers consist of tens of billions or more secondary particles crossing the atmosphere at nearly the speed of light, which excite nitrogen molecules which then emit light in the UV range. While this so-called “fluorescence technique'” is routinely used from the ground, by operating from space, JEM-EUSO will, for the first time, provide high-statistics on these events. Operating from space, with a large Field-of-View of ±30 °, allows JEM-EUSO to observe a much larger volume of atmosphere, than possible from the ground, collecting an unprecedented number of UHECR events at the highest energies.For the four pathfinder experiments built within the collaboration, we have been developing a common set of electronics, in particular the central data acquisition system, capable of operating from the ground, high altitude balloons, and space.These pathfinder experiments all use a detector consisting of one Photo-detection Modules (PDMs) identical to the 137 that will be present on the JEM-EUSO focal surface. UV light generated by high-energy particle air showers passes the UV filter and impacts the Multi-anode Photomultiplier Tubes (MAPMT). Here UV photons are converted into electrons, which are multiplied by the MAPMTs and fed into Elementary Cell Application-Specific Integrated Circuit (EC-ASIC) boards, which perform the photon counting and charge estimation. The PDM control board interfaces with these ASIC boards, providing power and configuration parameters, collecting data and performing the level 1 trigger. I was in charge of designing, developing, integrating, and testing the PDM control board for the EUSO-TA and EUSO-Balloon missions as well as the autonomous trigger algorithm testing and I also performed some analysis of the EUSO-Balloon flight data and data from the EUSO-TA October 2015 run.In this thesis, I will give a short overview of high-energy cosmic rays, including their detection technique and the leading experiments (Chapter 1), describe JEM-EUSO and its pathfinders including a description of each instrument (Chapter 2), present the details of the design and the fabrication of the PDM (Chapter 3) and PDM control board (Chapter 4), as well as the EUSO-TA and EUSO-Balloon integration tests (Chapter 5). I will report on the EUSO-Balloon campaign (Chapter 6) and results (Chapter 7), including a specific analysis developed to search for global variations of the ground UV emissivity, and apply a similar analysis to data collected at the site of Telescope Array (Chapter 8). Finally, I will present the implementation and testing of the first-level trigger (L1) within the FPGA of the PDM control board (Chapter 9). A short summary of the thesis will be given in Chapter 10

In this thesis work, I assess the short- and long-term prospects for the joint detection of BNSs and SGRBs with next-generation γ-ray and GW detectors. I combine the Structured Jet (SJ) model developed by Salafia et al. (2015b; 2019) for SGRB prompt emission with the analytical model by Finn and Chernoff (1993) for the GW signal from the BNS inspiral phase and estimate future GW-SGRB joint detection rates, using the SJ profile inferred for GRB 170817A (Ghirlanda et al., 2019) and assuming that all BNS mergers can in principle produce a SGRB. I show that, despite the strong assumptions and simplifications of the adopted model, it provides realistic and consistent estimates of the detection rates of SGRBs and GWs obtained with current facilities, the Fermi/GBM and Swift/Burst Alert Telescope γ-ray detectors and the aLIGO O3a GW interferometer. I also show that, if the SJ profile of GRB 170817A is a relatively common feature of SGRBs, then there is no realistic probability of another coincident detection in the era of aLIGO at design sensitivity (i.e., when it has reached the best achievable sensitivity, the project sensitivity) and SVOM-type detectors. In the CE era, the expected rate of coincident SGRB prompt emission and GW signal detections is ≈ 21-22 yr−1 and ≈ 53-55 yr−1 for SVOM-like and THESEUS-like detectors, respectively. I discuss future prospects for this model, showing how future SGRB-GW joint detection can help to solve the tension on the Hubble parameter estimation and to provide tighter constraints on the NS EoS.

A search for a diffuse flux of cosmic neutrinos with energies in excess of 10¹⁴ eV was performed using two years of AMANDA-II data, collected in 2003 and 2004. A 20% evenly distributed sub-sample of experimental data was used to verify the detector description and the analysis cuts. A very good agreement between this 20% sample and the background simulations was observed. The analysis was optimised for discovery, to a relatively low price in limit setting power. The background estimate for the livetime of the examined 80% sample is 0.035 ± 68% events with an additional 41% systematical uncertainty.

The total neutrino flux needed for a 5σ discovery to be made with 50% probability was estimated to 3.4 ∙ 10^-7 E^-2 GeV s^-1 sr^-1 cm^-2 equally distributed over the three flavours, taking statistical and systematic uncertainties in the background expectation and the signal efficiency into account. No experimental events survived the final discriminator cut. Hence, no ultra-high energy neutrino candidates were found in the examined sample. A 90% upper limit is placed on the total ultra-high energy neutrino flux at 2.8 ∙ 10^-7 E^-2 GeV s^-1 sr^-1 cm^-2, taking both systematical and statistical uncertainties into account. The energy range in which 90% of the simulated E^-2 signal is contained is 2.94 ∙ 10¹⁴ eV to 1.54 ∙ 10¹⁸ eV (central interval), assuming an equal distribution over the neutrino flavours at the Earth. The final acceptance is distributed as 48% electron neutrinos, 27% muon neutrinos, and 25% tau neutrinos.

A set of models for the production of neutrinos in active galactic nuclei that predict spectra deviating from E^-2 was excluded.

Le but de l'expérience EDELWEISS est la détection directe de matière noire sousforme de WIMPs, par l'étude de leur diffusion élastique sur les noyaux de germanium des détecteurs bolomètriques. Le plus problématique des bruits de fond provient des neutrons pouvant mimer l'interaction d'un WIMP dans un détecteur. Ces neutrons sont notamment produits par les rares muons cosmiques de haute énergie qui atteignent le laboratoire souterrain malgré les 4800 m w.e. de roche. Les muons résiduels sont détectés par un système veto de 46 modules de scintillateur plastique entourant l'expérience, qui permet de rejeter la plupart du bruit de fond associé. La détermination précise du bruit de fond neutron résiduel induit par ces muons dans EDELWEISS-III, essentielle pour l'identification des WIMPs, est le but de cette thèse. Le taux de bruit de fond dépend de la géométrie de l'expérience ainsi que des matériaux utilisés, qui ont subi d'importantes modifications depuis EDELWEISS-II. Des simulations GEANT4 du passage des muons dans la nouvelle géométrie ont été réalisées afin d'extraire le taux d'événements induits par les muons dans les bolomètres. Ce taux est en bon accord avec le taux mesuré extrait des données du Run308. En parallèle, une limite inférieure sur l'efficacité du veto muon a été extraite à partir des données bolomètres. Une nouvelle méthode basée sur l'utilisation d'une source d'AmBe a été développée afin d'extraire l'efficacité de chaque module de la simulation. À partir de ces résultats, il a été montré que le bruit de fond attendu est négligeable pour la recherche de WIMPs avec les données du Run308 et ne limitera pas la sensibilité future d'EDELWEISS-III
The aim of the EDELWEISS-III experiment is to detect the elastic scattering of WIMPs from the galactic dark matter halo on germanium bolometers. The most problematic background arises from neutrons, which can mimic a WIMP interaction in a detector. Neutrons are notably induced by high energy cosmic ray muons reaching the underground laboratory despite the 4800 m w.e. of rock overburdened. Remaining muons are tagged using an active muon-veto system of 46 plastic scintillator modules surrounding the experiment, which allows to reject most of the associated background. The goal of this thesis was to give a precise estimation of the irreducible muon-induced neutron background, needed to identify a potential WIMP signal. The expected background depends on the geometry of the experiment as well as on the used materials, both strongly modified since EDELWEISS-II. Geant4-based simulations of muons through the modified geometry were performed to derive the rate of events induced by muons in the bolometer array. This rate has been shown to be in good agreement with the measured one extracted from the Run308 data. In parallel, a lower limit on the muon-veto efficiency was derived using bolometer data only. A new method based on an AmBe source was developed to extract precisely the detection efficiency of individual modules from the simulation. From these results, it was shown that the expected background is negligible for the WIMP search analyses performed with the Run308 data and won't limit the future sensitivity of the EDELWEISS-III experiment

The lunar Cherenkov technique is a promising method to resolve the mystery of the origin of the highest energy particles in nature, the ultra-high energy (UHE) cosmic rays. By pointing Earth-based radio-telescopes at the Moon to look for the characteristic nanosecond pulses of radio-waves produced when a UHE particle interacts in the Moon’s outer layers, either the cosmic rays (CR) themselves, or their elusive counterparts, the UHE neutrinos, may be detected. The LUNASKA collaboration aims to develop both the theory and practice of the lunar Cherenkov technique in order to utilise the full sensitivity of the next generation of giant radio telescope arrays in searching for these extreme particles. My PhD project, undertaken as part of the collaboration, explores three key aspects of the technique. In the first three chapters, I describe a Monte Carlo simulation I wrote to model the full range of lunar Cherenkov experiments. Using the code, I proceed to calculate the aperture to, and resulting limits on, a UHE neutrino flux from the Parkes lunar Cherenkov experiment, and to highlight a pre-existing discrepancy between existing simulation programs. An expanded version of the simulation is then used to determine the sensitivity of past and future lunar Cherenkov experiments to UHE neutrinos, and also the expected event rates for a range of models of UHE CR production. Limits on the aperture of the Square Kilometre Array (SKA) to UHE CR are also calculated. The directional dependence of both the instantaneous sensitivity and time-integrated exposure of the aforementioned experiments is also calculated. Combined, these results point the way towards an optimal way utilisation of a giant radio-array such as the SKA in detecting UHE particles. The next section describes my work towards developing accurate parameterisations of the coherent Cherenkov radiation produced by UHE showers as expected in the lunar regolith. I describe a ‘thinning’ algorithm which was implemented into a pre-existing electromagnetic shower code, and the extensive measures taken to check its veracity. Using the code, a new parameterisation for radiation from electromagnetic showers is developed, accurate for the first time up to UHE energies. The existence of secondary peaks in the radiation spectrum is predicted, and their significance for detection experiments discussed. Finally, I present the data analysis from three runs of LUNASKA’s on-going observation program at the Australia Telescope Compact Array (ATCA). The unusual nature of the experiment required both new methods and hardware to be developed, and I focus on the timing and sensitivity calibrations. The loss of sensitivity from finite-sampling of the electric field is modelled for the first time. Timing and dispersive constraints are used to determine that no pulses of lunar origin were detected, and I use my simulation software to calculate limits on an UHE neutrino flux from the experiment.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1371947
Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009.

The lunar Cherenkov technique is a promising method to resolve the mystery of the origin of the highest energy particles in nature, the ultra-high energy (UHE) cosmic rays. By pointing Earth-based radio-telescopes at the Moon to look for the characteristic nanosecond pulses of radio-waves produced when a UHE particle interacts in the Moon’s outer layers, either the cosmic rays (CR) themselves, or their elusive counterparts, the UHE neutrinos, may be detected. The LUNASKA collaboration aims to develop both the theory and practice of the lunar Cherenkov technique in order to utilise the full sensitivity of the next generation of giant radio telescope arrays in searching for these extreme particles. My PhD project, undertaken as part of the collaboration, explores three key aspects of the technique. In the first three chapters, I describe a Monte Carlo simulation I wrote to model the full range of lunar Cherenkov experiments. Using the code, I proceed to calculate the aperture to, and resulting limits on, a UHE neutrino flux from the Parkes lunar Cherenkov experiment, and to highlight a pre-existing discrepancy between existing simulation programs. An expanded version of the simulation is then used to determine the sensitivity of past and future lunar Cherenkov experiments to UHE neutrinos, and also the expected event rates for a range of models of UHE CR production. Limits on the aperture of the Square Kilometre Array (SKA) to UHE CR are also calculated. The directional dependence of both the instantaneous sensitivity and time-integrated exposure of the aforementioned experiments is also calculated. Combined, these results point the way towards an optimal way utilisation of a giant radio-array such as the SKA in detecting UHE particles. The next section describes my work towards developing accurate parameterisations of the coherent Cherenkov radiation produced by UHE showers as expected in the lunar regolith. I describe a ‘thinning’ algorithm which was implemented into a pre-existing electromagnetic shower code, and the extensive measures taken to check its veracity. Using the code, a new parameterisation for radiation from electromagnetic showers is developed, accurate for the first time up to UHE energies. The existence of secondary peaks in the radiation spectrum is predicted, and their significance for detection experiments discussed. Finally, I present the data analysis from three runs of LUNASKA’s on-going observation program at the Australia Telescope Compact Array (ATCA). The unusual nature of the experiment required both new methods and hardware to be developed, and I focus on the timing and sensitivity calibrations. The loss of sensitivity from finite-sampling of the electric field is modelled for the first time. Timing and dispersive constraints are used to determine that no pulses of lunar origin were detected, and I use my simulation software to calculate limits on an UHE neutrino flux from the experiment.
Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009.

The detection of ionizing radiation such as X-rays is a constantly growing area of research thanks to its numerous application fields, which span from astrophysics, to industrial and civil security or even medical imaging and diagnostics. In this project, conducted at the University of Bologna (UNIBO), department of physics, one of the most active groups of research in this area, four different molecules (TIPS, TIPGe, diF TES ADT and diF TEG ADT) were studied as the organic semiconductor thin film in a photoconductor. The devices were realized by drop-casting a solution processed of the molecules onto three different substrates (PET, PEN and glass), for a direct approach on the detection of this radi-ation. Different parameters such as resistivity, percentage of active area covered by the molecule, quan-tity and thickness of the crystals, were investigated for their influence on the performance of the X-Ray detector. It was found that in the PET substrate there is a process of discharge that seems to be important to the performance of the detector and that seems to induce a decrease in the current of the diF TES ADT and diF TEG ADT based devices, making them unsuitable for any kind of application. With the PEN substrate it is possible to achieve reliable and reproducible devices with high signal to noise ratios and acceptable sensitivities. The glass substrate with the TIPGe would be the best one because it combines a high sensitivity with a reliable and reproducible device. Nevertheless, glass is not a flexible substrate and therefore is not suitable for many of the applications of interest, for example wearable health diagnostic applications like a personal dosimeter. Finally, it was proved that the molecules with the germanium element show, as it was expected due to the higher atomic number of Ge compared to Si, the highest sensitivities. It was also discovered that this is also due to the high quality crystals achieved with these molecules. Given the results obtained, this line of research seems to be fruitful, with very interesting practical applications expected.
A deteção de radiação ionizante, como os raios-X, é uma área de pesquisa em constante crescimento, graças aos seus vastos campos de aplicação, que abrangem desde a astrofísica, centrais nucleares, segurança industrial e civil, até ao diagnóstico médico. Neste projeto, realizado na Universidade de Bolonha, no departamento de física, um dos grupos de investigação mais ativos nesta área, quatro mo-léculas diferentes (TIPS, TIPGe, diF TES ADT e diF TEG ADT) foram estudadas na forma de filme fino orgânico semicondutor num fotocondutor. Os dispositivos foram preparados através da deposição por drop-casting de uma solução destas moléculas em três substratos (PET, PEN e vidro), para uma abordagem direta na deteção desta radiação. A influência de diferentes parâmetros, como a resistividade, percentagem de área ativa coberta pela molécula, quantidade e espessura dos cristais, foi investigada quanto ao desempenho dos detetores de raios-X. Descobriu-se que, no substrato PET, há um processo de descarga que parece ser importante para o desempenho do detetor e que aparentemente induz uma diminuição na corrente dos dispositivos base-ados em diF TES ADT e diF TEG ADT, tornando-os inadequados para qualquer tipo de aplicação. Com o substrato PEN, é possível obter dispositivos fiáveis e reprodutíveis com baixo ruído e sensibilidades aceitáveis. O substrato de vidro com o TIPGe daria o melhor dispositivo porque combina uma alta sensibilidade com um dispositivo fiável e reprodutível. No entanto, não é um substrato flexível e, portanto, não é adequado para muitas das aplicações de interesse, como por exemplo, aplicações de diagnóstico de saúde, como a dosimetria pessoal. Finalmente, ficou provado que as moléculas com o elemento germânio apresentam, como esperado pelo seu número atómico mais elevado que o do silício, as mais altas sensibilidades. Descobriu-se, ainda, que isso também se deve aos cristais de alta qualidade obtidos nessas moléculas. Em função dos resultados obtidos, a linha de investigação parece profícua, esperando-se aplicações práticas muito interessantes.

Digital imaging systems for medical applications use amorphous silicon thin-film transistor (TFT) technology due to its ability to be manufactured over large areas, making it useful for X-ray imaging, which requires imagers to be the size of the subject, unlike optical imaging. TFT technology is used to make imaging arrays coated with an X-ray detector called amorphous selenium (a-Se), which can be grown easily over large areas by being evaporated on a substrate. However, TFT technology is far inferior to crystalline silicon CMOS technology in terms of the speed, stability, noise susceptibility, and feature size. Where CMOS technology falls short is its inability to be manufactured in large wafers at a competitive cost, allowing TFT technology to continue to be dominant in the medical imaging field, unlike the optical imaging industry. This work investigates the feasibility of integrating an imaging array fabricated in CMOS technology with an a-Se detector. The design of a CMOS passive pixel sensor (PPS) array is presented, in addition to how it is integrated with the amorphous selenium detector. Results show that the integrated Selenium-CMOS PPS array has good responsivity to optical light and X-rays, leaving the door open for further research on implementing CMOS imaging architectures going forward. Demonstrating that the PPS chips using CMOS technology can use a-Se as a detector is thus the first step in a promising path of research which should yield substantial and exciting results for the field. Though area may still prove challenging, larger CMOS wafers can be manufactured and tiled to allow for a large enough size for certain diagnostic imaging applications and potentially even large area applications like digital mammography.