In this work, the antineutrino spectrum as specifically generated by nuclear reactors is studied. The topics covered include corrections and higher-order effects in reactor antineutrino experiments, one of which is covered in Ref. [1] and another contributes to Ref. [2]. In addition, a practical application, antineutrino safeguards for nuclear reactors, as summarized in Ref. [3,4] and Ref. [5], is explored to determine its viability and limits. The work will focus heavily on theory, simulation, and statistical analyses to explain the corrections, their origins, and their sizes, as well as the applications of the antineutrino signal from nuclear reactors. Chapter [1] serves as an introduction to neutrinos. Their origin is briefly covered, along with neutrino properties and some experimental highlights. The next chapter, Chapter [2], will specifically cover antineutrinos as generated in nuclear reactors. In this chapter, the production and detection methods of reactor neutrinos are introduced as well as a discussion of the theories behind determining the antineutrino spectrum. The mathematical formulation of neutrino oscillation will also be introduced and explained. The first half of this work focuses on two corrections to the reactor antineutrino spectrum. These corrections are generated from two specific sources and are thus named the spent nuclear fuel contribution and the non-linear correction for their respective sources. Chapter [3] contains a discussion of the spent fuel contribution. This correction arises from spent nuclear fuel near the reactor site and involves a detailed application of spent fuel to current reactor antineutrino experiments. Chapter [4] will focus on the non-linear correction, which is caused by neutron-captures within the nuclear reactor environment. Its quantification and impact on future antineutrino experiments are discussed. The research projects presented in the second half, Chapter [5], focus on neutrino applications, specifically reactor monitoring. Chapter [5] is a comprehensive examination of the use of antineutrinos as a reactor safeguards mechanism. This chapter will include the theory behind safeguards, the statistical derivation of power and plutonium measurements, the details of reactor simulations, and the future outlook for non-proliferation through antineutrino monitoring. / Ph. D.

Currently, we are in an era of neutrino physics in which neutrino oscillation experiments are focusing on doing precision measurements. In this dissertation, we investigate what is important to consider when doing these precise experiments, especially in light of significant unresolved anomalies. We look at four general categories of considerations: systematic uncertainties, fundamental assumptions, parameterization-dependence of interpretations, and Beyond the Standard Model (BSM) scenarios. By performing a simulation using GLoBES, we find that uncertainties in the fine structure of the reactor neutrino spectrum could be vitally important to JUNO, a reactor neutrino experiment being built in China, so a reference spectrum with comparable energy resolution to JUNO is needed in order to alleviate this uncertainty. In addition, we determine that with their fix of the fine structure problem, JUNO can test the existence of a quantum interference term in the oscillation probability. We also reason that the CP-violating phase is very parameterization dependent, and the Jarlskog invariant is better for talking about amounts of CP violation in neutrino oscillations. Finally, we discover that CP-violating neutrino Non-Standard Interactions (NSIs) could already be affecting the outcomes of T2K and NOνA, two accelerator neutrino experiments, and may be why there is a tension in these two data sets. / Doctor of Philosophy / Neutrinos are very weakly interacting, fundamental particles that are extremely plentiful in the universe. There are three known types (or flavors) of neutrinos, and the fact that they change flavors (or oscillate) informs us that their mass is not zero, but no experiments have been able to put a lower bound on the smallest neutrino mass. Now that experiments measuring neutrino oscillations have become more precise and some significant anomalies remain unresolved, there are considerations that have become important to investigate. In this paper, we look at four of these considerations: • Uncertainties in the finer shapes in the energy spectrum of neutrinos coming from a nuclear reactor (Chapter 2): We find that these uncertainties could destroy the ability of the Jiangmen Underground Neutrino Observatory (JUNO) to meet one of its major goals, unless they measured the spectrum at a spot close to the reactor with a really good energy resolution (comparable to that of JUNO). • An assumption about quantum mechanics being the foundation of particles and their interactions (Chapter 3): We determine that by heeding our warning in Chapter 2, JUNO will be able to test the existence of the term in the oscillation probability arising out of quantum interference. • How the neutrino oscillation parameter known as the CP-violating phase is dependent on the parameterization scheme used for the matrix describing how the flavors mix to make neutrino oscillation possible (Chapter 4): We find that the parameterization dependence is drastic, and if we want to discuss how much CP violation (i.e. a measure of how neutrinos behave differently from their anti-matter counterparts) exists in neutrino oscillations, we should talk about a quantity called the Jarlskog invariant. • The possibility of interactions existing between neutrinos and other particles that are not part of the Standard Model of Particle Physics, i.e. neutrino Non-Standard Interactions (NSIs) (Chapter 5): We discover that NSIs that are CP-violating can actually explain a current discrepancy between two neutrino oscillation experiments: Tokai to Kamioka Nuclear Decay Experiment (T2K) and NuMI Off-axis ν e Appearance (NOνA).

La recherche de neutrinos stériles et légers est, à l’heure actuelle, l’un des enjeux majeurs de laphysique des neutrinos. Une indication de leur existence résulte de l’anomalie des antineutrinosde réacteur, qui découle du déficit de 6% entre les taux prédits et les taux observéspar les expériences à courte distance de réacteurs. Ce déficit peut être interprété comme uneoscillation à courte distance des neutrinos. L’objectif de l’expérience STEREO, situé auprès duréacteur de recherche de l’Institut Laue Langevin (ILL), à Grenoble, France, est d’étudier cetteoscillation. La cible du détecteur de neutrinos est placée entre 8,9 et 11,1m du coeur compactdu réacteur d’ILL. Le détecteur consiste d’environ 2t d’un scintillateur liquide, dopé avec duGd. Le volume actif est séparé dans le sens de la longueur en six cellules. Les antineutrinos sontdétectés par la désintégration bêta inverse, où ils interagissent avec un proton libre (ion H+) etproduisent un positron et un neutron. Les deux particules sont détectées dans le scintillateurpar une coïncidence retardée où le positron crée un signal prompt et le neutron est capturéaprès un temps de modération. La lumière produite par le scintillateur est mesurée par lesphotomultiplicateurs (PM). Le détecteur est complété par un“gamma catcher” qui entoure la cible et par un veto à muons.Ce manuscrit présente des études concernant la préparation et la mise en exploitation del’expérience STEREO. La conception du blindage magnétique des PM a été menée sur la basede simulations par éléments finis afin d’examiner différentes options, d’étudier en détail lesperformances de l’option retenue ainsi que de déterminer la qualité nécessaire des matériauxutilisés. Sur la base de ces études, la collaboration a retenu un plan de blindage en deuxcouches: une couche de fer doux à l’extérieur, couvrant le détecteur et le veto à muons, et unecouche de mu-métal autour de la cible. Ce blindage réduit les champs magnétiques externes à laposition des PM de la cible à moins de 60μT pour toutes les configurations connues de champsexternes. Ceci réduit à moins de 2% une variation de l’amplification des PM induite par deschangements des champs magnétiques.D’autre part, des études du bruit de fond sur le site de STEREO ont été menées. Unecartographie du bruit de fond du rayonnement gamma a été effectuée avec des détecteurs augermanium et un scintillateur NaI, afin de valider l’efficacité du blindage installé. Uneestimation du taux de bruit de fond est présentée et comparée au taux mesuré avec STEREO.Dans l’état actuel de l’analyse des données, le bruit de fond de coïncidences fortuites est inférieurau bruit de fond corrélé induit par les muons cosmiques. Après une première phase d’exploitationde STEREO, un “doigt de gant” en fin de vie situé à l’avant de STEREO a dû être retiré.Un bouchon était adapté à l’extrémité de ce doigt de gant afin de réduire le bruit du fondpour STEREO. Ce dispositif n’ayant pas pu être réinstallé à la suite l’enlèvement du doigt degant, un nouveau blindage a été proposé par l’ILL. Une série des simulations neutroniques etphotoniques (MCNP) a été effectué pour étudier l’effet de ce changement sur le bruit de fondautour de STEREO et pour décider si le blindage proposé était suffisant. Les deux scénariosavant et après l’enlèvement ont été comparés et selon cette simulation, la situation du bruit defond devrait être améliorée.Enfin une procédure a été proposée et appliquée pour analyser les données de calibration del’échelle d’énergie de STEREO. La procédure a été élaborée pour être applicable pour toutes lessources de calibration disponibles et pour minimiser les incertitudes systématiques. Le résultatpeut être utilisé pour ajuster les paramètres de la simulation Geant4 du détecteur développée parla collaboration, par comparaison avec des données mesurées et après pour déterminer l’échellede l’énergie avec la précision requise de < 2%. / Light sterile neutrinos are currently a topic actively discussed in neutrino physics. Oneindication of their possible existence and their participation in neutrino oscillations is the ReactorAntineutrino Anomaly, which states a deficit of about 6% between predicted and observedantineutrino fluxes in short baseline reactor neutrino experiments. The STEREO experimentaddresses this anomaly by searching for neutrino oscillations at baselines of 8.9-11.1m from thecompact core of the research reactor of the Institut Laue Langevin (ILL), Grenoble, France. Forthis purpose a Gd-loaded liquid scintillator detector was designed with an active target massof about 2 t. The target volume is subdivided in six optically separated cells along the line ofpropagation of the neutrinos. The electron antineutrinos emitted from the reactor are detectedvia the inverse beta decay on hydrogen nuclei, where a positron and a neutron are created. Thesetwo particles are detected in the scintillator in delayed coincidence, with the prompt signal fromthe positron and a delayed signal from neutron capture. The scintillation light created in theprocesses is read out by photomultiplier tubes (PMTs) on top of the detector cells. The detectoris completed by a gamma catcher and a muon veto.This manuscript covers parts of the preparation and the commissioning of the STEREOexperiment. As basis for the design process of the magnetic shielding for STEREO’s PMTsa series of finite element simulations was performed. The studies of different general layoutsand required material qualities as well as of details of the final design are summarised. Underconsideration of these studies the collaboration opted for a shielding design, a double layer setupwith an outer soft iron and inner mumetal layer, which has the required shielding efficiency toreduce the magnetic field at the position of the detector PMTs below 60 μT for all known externalmagnetic field configurations. This limits the maximum PMT gain change due to variations ofthe external magnetic fields to < 2%.Furthermore different studies have been performed concerning the on-site background situation.A mapping of the-ray background was conducted with high purity germanium detectorsand a NaI scintillator detector, in order to validate the efficiency of the installed shielding. Thefocus lied on the characterisation of the count rate in the neutron capture energy window. Anestimation of the background rate is presented and compared to the rate obtained in STEREO.At the current state of the analysis the background of accidental coincidences in STEREO is aminor contribution compared to the muon induced correlated background. In addition a seriesof MCNP simulations was performed to determine the impact of a beamtube removal in thevicinity of STEREO on the overall reactor-related background situation. The beamtube wasclosed by a dedicated shielding, optimised for background reduction for STEREO, which couldnot be reinstalled after removal of the tube. A new shielding at the end of the former beamtubewas proposed by the ILL. Its shielding effect was studied with MCNP and compared tothe previous configuration in order to assess whether the new shielding suffices or needs to beimproved. According to these simulations the background situation is expected to improve.Finally a procedure is proposed and applied for the analysis of the energy calibration ofthe STEREO detector. The procedure is designed to be applicable to all available calibrationsources and to minimise systematic uncertainties. It can be used to adjust parameters in theexisting Geant4-based simulation of the detector, developed by the collaboration, by comparisonto measured data and later to determine the energy scale with the required precision of < 2%.

Orientador: Marcelo Moraes Guzzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T20:53:09Z (GMT). No. of bitstreams: 1 Zavanin_EduardoMarcio_M.pdf: 2031044 bytes, checksum: a24fad776402ee2c06c0d5c44baaf4bb (MD5) Previous issue date: 2013 / Resumo: O objetivo desse trabalho é desenvolver um mecanismo que possa servir como solução para as anomalias dos antineutrinos de reatores e do Gálio. Relaxando a hipótese de Pontecorvo, permitindo que os ângulos de mistura que compõem um estado de sabor possuam diferentes valores, conseguimos explicar o fenômeno de desaparecimento de neutrinos/antineutrinos em baixas distâncias, através de um parâmetro livre. Para confrontar o mecanismo desenvolvido também fazemos uma analise criteriosa de alguns limites experimentais obtidos por aceleradores de partículas e identificamos uma possível dependência desse parâmetro livre com a energia. Adotando esse dependência energética para o parâmetro livre, conseguimos acomodar a grande maioria dos dados experimentais em física de neutrinos através de um único modelo / Abstract: This project aims the development of a mechanism that provides a possible solution to reactor antineutrino anomaly and Gallium anomaly. Relaxing the Pontecorvo\'s hypothesis, allowing the mixing angles that compose a flavor state possesses different values, it is possible to explain the phenomenon of desappearance in short-baselines, through a free parameter. To confront the mechanism developed we also perform an analysis of some experimental limits obtained by particle accelerators and identify a possible dependence of this free parameter with the energy. Adopting this energetic dependence for the free parameter, we can¿t almost every experiment in neutrino physics through a single model / Mestrado / Física / Mestre em Física

Orientador: Marcelo Moraes Guzzo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-01T21:05:54Z (GMT). No. of bitstreams: 1 Zavanin_EduardoMarcio_D.pdf: 12290577 bytes, checksum: e37b2af24ec03321ad993ebd98fbc0dc (MD5) Previous issue date: 2017 / Resumo: O objetivo desse trabalho é estudar um mecanismo alternativo à hipótese de neutrino estéril para a solução das anomalias dos antineutrinos de reatores, da anomalia do Gálio e da anomalia dos aceleradores. Vamos também entender como encaixar esse mecanismo na teoria da física de partículas através de interações não padrão. Além disso, vamos estudar o duplo decaimento beta sem a emissão de neutrinos e colocar vínculos para a massa efetiva de Majorana. Não obstante, vamos entender os limites que o experimento ECHo fornecerá para medidas direta da massa dos neutrinos / Abstract: The objective of this work is the study of an alternative mechanism, that is not the hypothesized sterile neutrino, to solve the reactor anti-neutrino anomaly, the Gallium anomaly and the LSND anomaly. We will also understand how to fit this mechanism in the theory of particle physics through non standard interactions. In addition, we will study the neutrino-less double beta decay and set constraints to the effective Majorana neutrino mass. Furthermore we will understand the limits that the ECHo experiment will provide for direct measurements of the neutrino mass / Doutorado / Física / Doutor em Ciências / 2013/02518-7 / 1189631/2013 / FAPESP / CAPES

High precision measurements of a weak interaction decay were conducted to search for possible variation of the decay rate parameter caused by an antineutrino flux. The experiment searched for variation of the ⁵⁴Mn electron capture decay rate parameter to a level of precision of 1 part in ∼10⁵ by comparing the difference between the decay rate in the presence of an antineutrino flux ∼3×10¹² cm^-2sec^-1 and no flux measurements. The experiment is located 6.5 meters from the reactor core of the High Flux Isotope Reactor (HFIR) in Oak Ridge National Laboratory. A measurement to this level of precision requires a detailed understanding of both systematic and statistical errors. Otherwise, systematic errors in the measurement may mimic fundamental interactions. <div><br></div><div>The gamma spectrum has been collected from the electron capture decay of ⁵⁴Mn. What differs in this experiment compared to previous experiments are, (1) a strong, uniform, highly controlled, and repeatable source of antineutrino flux, using a reactor, nearly 50 times higher than the solar neutrino flux on the Earth, (2) the variation of the antineutrino flux from HFIR is 600 times higher than the variation in the solar neutrino flux on the Earth, (3) the extensive use of neutron and gamma-ray shielding around the detectors, (4) a controlled environment for the detector including a fixed temperature, a nitrogen atmosphere, and stable power supplies, (5) the use of precision High Purity Germanium (HPGe) detectors and finally, (6) accurate time stamping of all experimental runs. By using accurate detector energy calibrations, electronic dead time corrections, background corrections, and pile-up corrections, the measured variation in the ⁵⁴Mn decay rate parameter is found to be δλ/λ=(0.034±1.38)×10^-5. This measurement in the presence of the HFIR flux is equivalent to a cross-section of σ=(0.097±1.24)×10^-25cm². These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a 68% confidence level upper limit sensitivity in δλ/λ <= 1.43×10^-5 or σ<=1.34×10^-25cm² in cross-section. The cross-section upper limit obtained in this null or no observable effect experiment is ∼10⁴ times more sensitive than past experiments reporting positive results in ⁵⁴Mn.</div>