Thèses sur le sujet « Spallation sources »

Questa è una tesi sperimentale riguardante misure di neutroni veloci di interesse per la fusione termonucleare e le sorgenti a spallazione. Alcune tecniche specifiche di spettroscopia ad alti tassi di conteggio ed alta risoluzione sono state studiate e sviluppate per queste applicazioni. In particolare rivelatori al cristallo singolo di diamante (SDD), Telescopi di Protoni di Rinculo (TPR) e scintillatori LaBr3 sono stati studiati con esperimenti presso il tokamak JET (UK), la sorgente a spallazione ISIS (UK) ed altri acceleratori.

As the increasing interest in MeV range neutrons for applied physics studies, the development of dedicated fast neutron-based instruments, which have the capabilities to deal with complex background and to measure high counting rate (MHz), is demanded. This thesis presents the development both on a fast response scintillation detector that has been developed as a neutron emission monitor for deuterium beam diagnostics on large current negative beam test facility (like ELISE or SPIDER), and on the design and test of Telescope Proton Recoil (TPR) neutron spectrometers dedicated for neutron spectrum measurements on the fast neutron beam line ChipIr at ISIS. These instruments have been studied at accelerator-based platforms, tested at the ISIS spallation neutron source, as well as been applied in dedicated experiments on ELISE. Development of the two types of fast neutron-based instruments in applications to fusion and spallation neutron sources are presented in the following two parts: (1). Measurement of the deuterium beam-target neutron emission that occurs when the deuterium beam penetrates in the metallic dump of the NBI (neutral beam injector) prototype has been proposed as a means of diagnostics on beam homogeneity at SPIDER and MITICA. In order to present the deuterium beam profile by measuring the produced neutrons from the DD reactions between the deuterium beam and deuterons previously implanted in the beam dump, a relative model should be built to predict the neutron emission based on understanding the process of deuterium implantation in dump, and to aid the CNESM detection system which is based on the GEM technique for beam profile diagnostics in SPIDER. To this end, a calibrated EJ301 liquid scintillation detector has been developed and used on ELISE to measure the time trace of neutron emission and to benchmark calculations based on the Local Mixing Model (LMM), which has been applied to describe the deuterium implantation in the dump. The scintillation detector shows good capabilities on neutron/gamma-rays discrimination and radioactive resistance. In particular, a similar liquid scintillator will be installed at SPIDER as a neutron emission monitor. (2). On the atmospheric-like fast neutron beam-line ChipIr, which is designed for electronics radiation studies at ISIS, direct measurement of the neutron spectrum and flux distribution could be used for characterizing the neutrons profile and benchmarking the simulations. As the challenges of high intensity neutrons, wide energy range and complex background, TPR neutron spectrometers have been proposed as an effective way by applying the deltaE-E technique and coincidence analysis. In this thesis, two types of TPR spectrometers based on silicon detectors (silicon-based TPR) and a YAP scintillator together with silicon detectors (scintillator-based TPR), respectively, have been designed and tested. Two prototypes of scintillator-based TPR have been designed for long-term measurements as the good radioactive resistance of YAP scintillators. The response of the used YAP scintillator to protons has been studied up to 80 MeV. Two scintillator-based prototypes have been tested on ChipIr and ROTAX beam line, respectively. With the collimator installed on the ROTAX beam line for incident neutrons, the triple coincidence scintillator-based TPR shows a good capability on charged particles discrimination and background suppression. The prototype of silicon-based TPR, which consists of four silicon detectors, has been tested on the ROTAX beam line. The recoil proton spectrum obtained by the two types of TPR prototypes on the ROTAX beam-line have been compared. Results show the possible of high intense neutrons measurements by using the silicon-based TPR.
As the increasing interest in MeV range neutrons for applied physics studies, the development of dedicated fast neutron-based instruments, which have the capabilities to deal with complex background and to measure high counting rate (MHz), is demanded. This thesis presents the development both on a fast response scintillation detector that has been developed as a neutron emission monitor for deuterium beam diagnostics on large current negative beam test facility (like ELISE or SPIDER), and on the design and test of Telescope Proton Recoil (TPR) neutron spectrometers dedicated for neutron spectrum measurements on the fast neutron beam line ChipIr at ISIS. These instruments have been studied at accelerator-based platforms, tested at the ISIS spallation neutron source, as well as been applied in dedicated experiments on ELISE. Development of the two types of fast neutron-based instruments in applications to fusion and spallation neutron sources are presented in the following two parts: (1). Measurement of the deuterium beam-target neutron emission that occurs when the deuterium beam penetrates in the metallic dump of the NBI (neutral beam injector) prototype has been proposed as a means of diagnostics on beam homogeneity at SPIDER and MITICA. In order to present the deuterium beam profile by measuring the produced neutrons from the DD reactions between the deuterium beam and deuterons previously implanted in the beam dump, a relative model should be built to predict the neutron emission based on understanding the process of deuterium implantation in dump, and to aid the CNESM detection system which is based on the GEM technique for beam profile diagnostics in SPIDER. To this end, a calibrated EJ301 liquid scintillation detector has been developed and used on ELISE to measure the time trace of neutron emission and to benchmark calculations based on the Local Mixing Model (LMM), which has been applied to describe the deuterium implantation in the dump. The scintillation detector shows good capabilities on neutron/gamma-rays discrimination and radioactive resistance. In particular, a similar liquid scintillator will be installed at SPIDER as a neutron emission monitor. (2). On the atmospheric-like fast neutron beam-line ChipIr, which is designed for electronics radiation studies at ISIS, direct measurement of the neutron spectrum and flux distribution could be used for characterizing the neutrons profile and benchmarking the simulations. As the challenges of high intensity neutrons, wide energy range and complex background, TPR neutron spectrometers have been proposed as an effective way by applying the deltaE-E technique and coincidence analysis. In this thesis, two types of TPR spectrometers based on silicon detectors (silicon-based TPR) and a YAP scintillator together with silicon detectors (scintillator-based TPR), respectively, have been designed and tested. Two prototypes of scintillator-based TPR have been designed for long-term measurements as the good radioactive resistance of YAP scintillators. The response of the used YAP scintillator to protons has been studied up to 80 MeV. Two scintillator-based prototypes have been tested on ChipIr and ROTAX beam line, respectively. With the collimator installed on the ROTAX beam line for incident neutrons, the triple coincidence scintillator-based TPR shows a good capability on charged particles discrimination and background suppression. The prototype of silicon-based TPR, which consists of four silicon detectors, has been tested on the ROTAX beam line. The recoil proton spectrum obtained by the two types of TPR prototypes on the ROTAX beam-line have been compared. Results show the possible of high intense neutrons measurements by using the silicon-based TPR.

Il problema, rilevato a livello globale, circa la progressiva riduzione di disponibilità di 3He, ha indotto la comunità scientifica ad intraprendere un’intensa fase di ricerca e sviluppo con lo scopo di trovare tecniche di rivelazione di neutroni alternative a quelle standard basate su 3He. Queste nuove tecnologie, oltre ad avere un’efficienza comparabile a quella dei tubi a 3He, devono risultare idonee ad effettuare misure in sorgenti ad alto flusso di neutroni come la futura European Spallation Source (ESS). In questa tesi di dottorato si ripercorre lo sviluppo di un rivelatore a gas per neutroni termici in grado di supportare ratei di conteggio pari ai MHz/mm2. Il rivelatore è basato sulla tecnologia del Gas Electron Multiplier (GEM) ed è dotato di un “convertitore” contenente 10B4C, la cui geometria è stata ottimizzata per rivelare neutroni termici tramite la reazione di cattura nucleare 10B(n,α)7Li. Quattro prototipi, con quattro differenti convertitori, sono stati testati in sorgenti di neutroni a spallazione e in reattori nucleari. L’evoluzione dei convertitori riflette il miglioramento delle performance del rivelatore, in particolare l’efficienza (ε = 40% at λ = 4 Ang) e la risoluzione spaziale (FWHM ~ 6mm). Sulla base dei risultati ottenuti con questa nuova tecnologia si è instaurata una collaborazione con ESS allo scopo di ottimizzare il rivelatore oggetto del presente studio, che verrà quindi installato nel sistema di rivelatori di LoKI, una delle prime linee di fascio ad entrare in funzione a ESS.
Due to the current worldwide 3He-shortage the present neutron scientists are facing the challenge of finding alternative technologies to 3He as a thermal neutron detector with a high-rate capability to profit of the high flux of modern spallation sources like European Spallation Source (ESS). The aim of the presented PhD project is the development of a high-rate thermal neutron gaseous detector for applications in spallation sources. The detector is based on the Gas Electron Multiplier (GEM) technology and is provided with a geometrically optimised "converter", as boron carbide 10B4C layers, in order to detect thermal neutrons through the 10B(n,α)7Li reaction. Four detector prototypes with different converters geometry were constructed and tested in spallation sources. The evolution of the converter technology goes with the improvement of detector performance such as efficiency (ε = 40% at λ = 4 Ang) and spatial resolution (FWHM ~ 6mm). On the base of the performance results obtained with this new technology a collaboration with ESS was established with the aim to develop a thermal neutron detector with a boron-based 3D converter, as a part of the detector system of LoKI, a SANS instrument and one of the first to be constructed.

The research of the neutron induced Single Event Effect (SEE) at aircraft altitudes or at ground level are very important since the neutron radiation is able to cause serious errors or damages on electronic components and system. TheWeapons Neutron Research (WNR) facility at Los Alamos Neutron Science Center (LANSCE), and ANITA (Atmospheric-like Neutrons from thIck TArget) facility at The Svedberg Laboratory (TSL) both provide spallation neutron source for radiation testing of electronic components. A local beam monitoring system was successfully developed by S. Platt and L. Zhang in the University of Central Lancashire for measuring neutron dosimetry during accelerated SEE testing of electronic devices with using silicon photodiode. However, such silicon photodiode is sensitive to gamma-ray as well. For above reasons, characterization of neutron and gamma fields at spallation neutron sources used for accelerated SEE testing has become the purpose of this work. Monte Carlo calculation of radiation fields at spallation neutron source was used to characterize neutron and gamma energy spectra for accelerated single event effect testing. Geant4 (GEometry ANd Tracking version 4) toolkit, using Monte Carlo method, was used to simulate a preliminary model of spallation neutron source at LANSCE (ICE House, WNR) and TSL (ANITA) for understanding physical mechanisms of neutron and gamma interactions with matter. At first, two preliminary spallation neutron sources on basis of WNR (ICE House) and ANITA facilities were modeled with using two intra-nuclear cascade models (bertini, binary) provided by Geant4 reference physics lists. The result of neutron spectrum with binary INC model agrees well with LANSCE measurement data and independent calculation results in each case. In this computation, gamma dose rates at WNR and ANITA were calculated, and gamma dose rate from the simulation is consistent with the ANITA measurement results. The results of photon energy spectra with using Geant4 toolkit presents a continuum between 0.1MeV and 10MeV, and the annihilation peak at 0.5MeV. However, calculation results of neutron spectrum at ANITA facility with using binary INC model match ANITA measurements less well in absolute neutron yield above 20MeV, which is likely due to the missing geometry components in preliminary spallation neutron source simulation. A more complex model of ANITA facility was constructed with adding bending magnet, shielding components, detector system, and collimator, which makes modelling as realistically as possible. The discrepancy in absolute neutron yield between simulation results and measurements data has improved at Standard User Position (SUP) of ANITA facility, in contrast with the preliminary modelling of ANITA neutron source. At the same time, a new position referred as Close User Position (CUP) was investigated in order to compare with ANITA measurement informed by Monte Carlo N-Particle eXtended (MCNPX) simulation results. The neutron spatial distribution, radius effect for neutrons, neutron beam profiles, and time of flight spectra were calculated at the SUP and CUP positions for different collimator apertures of 3 cm, 10.2 cm, and 30 cm, respectively. A comparison of simulated neutron beam profiles folded with 238U (n, f) cross-section with ANITA measurements at the SUP and CUP-TOF positions was used for validating improved ANITA neutron source modelling. The neutron beam profiles in the horizontal direction were predicted with using Geant4, which filled the gap of geometrical limitation at ANITA facility for accelerated single event effect testing. It is the first time to predict gamma dose rate at the SUP and CUP positions for 3 cm, 10.2 cm, and 30 cm collimators with using Geant4 modelling of ANITA neutron source. In addition, the gamma dose rate at the SUP position is consistent with ANITA measurement data. Finally, the gamma yield, photon spatial distribution, dose rate against energy are considered for gamma field at the SUP and CUP positions, which have contributed to understand and analyse gamma interactions with matter.

This thesis concerns the development of fast neutron instrumentation for beam diagnostic. Two kind of detectors have been developed. The first is a diamond detector for fast neutron measurements at the ChipIr beamline of the ISIS spallation neutron source (Didcot, UK). ISIS is a 50Hz-pulsed source in which neutrons are produced by 800 MeV protons interacting on a heavy metal target. The second is a Gas Electron Multiplier (GEM) detector developed for measurements of the neutron emission map in the deuterium beam prototype facility for the ITER fusion reactor under construction at the RFX site (Padova). Measurements of the so-called Single Event Effects (SEE) are the main application of the ChipIr beamline. SEEs are a potential threat to the robustness of integrated circuits featuring dimensions of tens of nanometers. SEEs occur when a highly energetic particle causes a disruption of the correct operation of an electronic component by striking its sensitive regions. Recent studies have shown that the neutron component above 1 MeV of the cosmic ray radiation is the primary contribution to SEEs for heights < 10 km. In order to evaluate the sensitivity of electronic devices to SEEs, fault-tolerant design techniques must be employed, and extensive analyses are needed to qualify their robustness. Experiments with atmospheric neutrons can be carried out but, due to the low intensity, they require very long periods of data acquisition. Neutron sources represent an opportunity due to the availability of high intensity fluxes which allow for accelerated irradiation experiments. Recent experiments performed at ISIS on the VESUVIO beamline demonstrated the suitability of ISIS for this kind of application. The new ChipIr beamline will provide an atmospheric-like neutron spectrum with a multiplication factor around 10^8. A crucial task for ChipIr design is the development of a neutron beam monitor for measurements of the neutron fluence in the MeV energy range. The detector developed in this thesis as a beam monitor for ChipIr is a Single-crystal Diamond Detector (SDD). Neutron detection using diamonds is based on the collection of the electrons/holes pairs produced by the energy deposited in the crystal following neutron reactions with carbon. First tests were performed in 2009 using a prototype SDD. The device features a p-type/intrinsic/metal Schottky barrier structure where the active (intrinsic) detection layer is obtained by chemical-vapour deposition. Both Time of Flight (ToF) only and biparametric (ToF and pulse height) measurements were successfully performed. Measurements were also performed using a Fission Diamond Detector (FDD). A FDD is a device based on a single crystal diamond coupled to a natural uranium converter foil. The biparametric data collection allowed us to distinguish events from 235U, 238U and from carbon break-up reactions inside the diamond. Limitations to quantitative analysis due to the initial choice of detector thickness and instrumental settings were highlighted by the tests. In a new set of experiments performed in July 2010, April 2011 and October 2011 a new fast neutron detector was tested. The measurements showed three characteristics regions in the biparametric spectra: -background events of low pulse heights induced by gamma-rays; -low pulse height events in the neutron ToF region corresponding to En in the range 2.4-5.7 MeV which are ascribed to elastic scattering on 12C; -large pulse height events in the ToF region corresponding to En>6 MeV which are ascribed to 12C(n,α)9Be and 12C(n,n')3α reactions. Neutron energy information was found to be contained both in the pulse height and in the ToF data, which suggests that SDDs are good candidate detectors for spectroscopy in fast neutron irradiation experiments. The use of diamond detectors as beam monitors requires further characterization of their response to monoenergetic neutrons. The second detector developed in this thesis is a nGEM detector able to map the neutron intensity produced in the SPIDER/MITICA beams at the Consorzio RFX in Padova. The ITER neutral beam test facility under construction in Padova will host two experimental devices: SPIDER, a 100 keV negative hydrogen/deuterium beam, and MITICA, a full scale, 1 MeV deuterium beam. A number of diagnostics will be deployed in the two facilities to qualify the beams. The aim of this thesis was to design a neutron diagnostic for SPIDER, as a first step towards the application of this diagnostic technique to MITICA. The proposed detection system is called CNESM which stands for Close-contact Neutron Emission Surface Mapping. CNESM is placed right behind the beam dump, as close as possible to the neutron emitting surface. It shall provide the map of the neutron emission on the surface of the beam dump. The latter is a rectangular panel made of water cooled pipes used to stop the incoming beam. The CNESM diagnostic system uses nGEM as neutron detectors. These are Gas Electron Multiplier detectors equipped with a cathode that also serves as neutron-proton converter. The diagnostic was designed on the basis of simulations of the different steps, from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. The deuteron deposition inside the dump was simulated with the TRIM code in order to provide the deposition profile. Neutron emission occurs via fusion reactions between the deuterium beam and the deuterons implanted in the beam dump surface. Neutron scattering in the beam dump was simulated using the MCNPX code. The nGEM cathode is at about 30 mm from the beam dump front surface. It is composed of two layers (polyethylene + aluminum) each ~50μm thick. The aluminum layer stops all protons that are emitted from the polyethylene at an angle higher than 40° relative to the normal to the cathode surface. This means that most of the detected neutrons at a point of the nGEM surface are emitted from the corresponding 40X22 mm^2 beamlet footprint on the dump front surface. The nGEM readout pads (area 20X22 mm^2) will record a useful count rate of ~5 kHz providing a time resolution of better than 1 s. Each nGEM detector maps the neutron emission from a group of 5X16 beamlets: as many as 16 nGEM detectors would be needed to cover the entire beam dump. The effect of the directional detector response due to the Al foil is to decrease the FWHM value to about 30 mm. This level of spatial resolution is adequate for unfolding the neutron source intensity from the 2D event map in the nGEM detector. The first nGEM detector prototype was tested at the FNG neutron source in Frascati, where the directional response of the nGEM cathode to neutrons was verified. The successful design of the CNESM neutron diagnostic for SPIDER provides the basis for its application to MITICA (X100 larger neutron fluxes expected), where it will be particularly useful to resolve the horizontal beam intensity profile.

Des protons de quelques centaines de mev et au dela interagissant avec une cible nucleaire epaisse de numero atomique eleve emettent un grand nombre de neutrons rapides (de quelques mev) par spallation. Ces neutrons constituent la source de neutrons d'un systeme hybride de production d'energie. Nous montrons que nous pouvons caracteriser avec une parametrisation assez simple, reliee a la physique, les distributions radiales, longitudinales et energetiques de cette source etendue de neutrons. Cette parametrisation a ete testee pour differentes energies de faisceau avec differents codes de spallation et differentes structures de cible. De plus, cette parametrisation permet l'etude de l'influence de la repartition spatiale et energetique de cette source sur la neutronique du milieu multiplicateur sous-critique entourant la cible de spallation. Les resultats obtenus au travers de l'experience feat (first energy amplifier test) qui eut lieu au cern en automne 1994, montrent la validite de cette parametrisation. Cette parametrisation permet d'avoir une bonne representation de la source de neutrons, elle offre la possibilite de faire des benchmarks en cible epaisse, donnant directement a l'utilisateur des informations sur la taille de la source et ses spectres en energie et elle permet d'etudier la sensibilite de la neutronique aux parametres.

In this thesis, the design of a high intensity accumulator ring for the European Spallation Source Neutrino Super Beam (ESSnuSB) is considered. The European Spallation Source (ESS) linear accelerator (Linac), presently being constructed in Lund, Sweden, presents an interesting opportunity to also host an experiment to detect neutrino CP violation. 0.7 ms long H- pulses would be accelerated to 2 GeV and collide with a target, producing pions which then decay into neutrinos. To focus the pions a toroidal magnet (''neutrino horn'') is pulsed with a 350 kA current. The peak current is about 5 μs long, which requires the H- pulses to be shortened to about the same length using an accumulator ring that is located between the linac and the target. The H- would be stripped of their electrons using either a thin carbon foil or a laser beam during injection into the ring. Foil stripping is limited by the lifetime of the foil, which depends on the temperature to which it is heated by the beam. The temperature is simulated in a computer model and the results indicate that it does not rise above the critical temperature (2500 K). The high number of protons (1015) circulating in the ring could cause instabilities due to the collective charge of the particles, known as the space charge effect. The space charge tune shift is calculated for the ESSnuSB and different solutions are discussed. The result of a design accumulator lattice for the ESSnuSB, based on the Spallation Neutron Source, at Oak Ridge National Laboratory, Tennessee, U.S., and made using the computer program Methodical Accelerator Design (MAD), is presented.

Ce mémoire de HDR traite d'une dizaine d'années de travaux autour de la modélisation des réactions de spallation. Ces réactions sont définies comme l'interaction nucléaire entre une particule légère, le plus souvent un nucléon, et un noyau atomique à une énergie de l'ordre de 100 MeV à 2-3 GeV. Deux étapes les caractérisent. Une phase rapide, la réaction directe appelée aussi cascade intra- nucléaire, et une phase plus lente, la désexcitation du noyau issu de la première phase. À partir de l'association du code développé par le groupe pour la cascade, INCL4, et du code de désexcitation Abla, de GSI, sont présentés les différentes facettes des réactions de spallation. D'abord la physique et les codes sont présentés, ce sont ensuite les différents types de validations des modèles qui sont exposés, puis les multiples domaines dans lesquels la modélisation de la spallation joue un rôle, pour enfin, tirant profit de tout ce qui aura été dit et d'autres travaux passés, montrer les différents voies qu'il reste à explorer ou redécouvrir.

Thesis (Ph.D.); Submitted to North Carolina State Univ., Raleigh, NC (US); 6 Apr 2005.
Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-TH-211400" Dashdorj, D. 04/06/2005. Report is also available in paper and microfiche from NTIS.

The neutron Electric Dipole Moment Experiment at the Spallation Neutron Source requires an overall magnetic shielding factor of order 105 to attenuate external background magnetic fields. At present, the shielding design includes an external (room-temperature) multi-layer μ-metal magnetic shield, a cryogenic (4 Kelvin) Pb superconducting shield, and a cryogenic (4 Kelvin) ferromagnetic shield composed of Metglas ribbon. This research determined how to construct a Metglas shield using minimal material that produced axial and transverse shielding factors of ~267 and ~1500. In addition, the μ-metal and Metglas shields were modeled using finite element analysis. The FEA model includes external coils and their effect on the residual magnetic fields. This study will help with the design of the shielding.

Les réacteurs hybrides, bases sur le couplage entre un accélérateur de particules et un coeur sous-critique via une cible
de spallation, présentent des possibilités de réduction de la radiotoxicité des déchets de haute activité et a vie
longue promis au stockage. Les différents concepts proposes ces dernières années dans la communauté scientifique montrent
la nécessite de réaliser un démonstrateur.
Ce travail de thèse a porte sur l'optimisation par simulation Monte Carlo a l'aide du code MCNPX, de la neutronique d'un tel
système dans le but de réaliser un réacteur pilote.
Tout d'abord, nous avons indique les principales caractéristiques neutroniques d'un réacteur hybride avant de présenter le
concept de démonstrateur refroidi au gaz base sur le remontage effectue par la société Framatome ANP. Nous avons
caractérise puis optimise la neutronique a travers la géométrie et les matériaux utilises pour ce démonstrateur.
Dans le cadre de l'incinération des actinides mineurs, nous avons calcule l'évolution des combustibles envisageables suivant
les phases de démonstration prévues. Les grandeurs liées a l'incinération des actinides mineurs sont rapportées. En vue
de la transmutation du 99Tc et de l'129I, nous avons calcule les temps caractéristiques et les taux de transmutation
a l'équilibre.
D'autre part, nous avons analyse le passage du démonstrateur vers un réacteur incinérateur de puissance a partir de
critères physiques tels que les facteurs de forme et les niveaux de flux. A partir de cette analyse, des solutions innovantes sont
proposées pour améliorer les facteurs de forme d'un incinérateur de puissance.
Enfin, dans des perspectives a plus long terme, l'utilisation des réacteurs hybrides dans le cadre de la génération
d'233U pour accélérer le démarrage d'une filière de réacteurs a sels fondus basée sur le cycle
232Th/233U a été explorée et s'avère particulièrement efficace.

Neste trabalho apresentamos um estudo das reações nucleares de alta energia que são fundamentais na definição do termo fonte dos reatores nucleares subcríticos acionados por fonte externa. Estas reações nucleares, também conhecidas como \"spallation\", consistem na interação de hádrons de alta energia com os núcleons do núcleo atômico. A fenomenologia destas reações consiste em duas etapas, sendo que à primeira, o próton interage através de espalhamentos múltiplos, em um processo denominado cascata intra-nuclear seguido da etapa na qual o núcleo excitado oriundo da cascata intranuclear ou evapora partículas de forma a atingir estados energéticos moderados ou fissiona, em um processo conhecido como competição entre evaporação e fissão. Neste trabalho os principais modelos nucleares, os modelos de Bertini e Cugnon, são revistos, pois estes modelos são fundamentais para propósito de projeto devido à falta de dados nucleares avaliados para estas reações. A implementação e validação dos métodos de cálculo para o projeto destas fontes são realizadas. A implementação da metodologia é realizada utilizando o programa MCNPX ( \"Monte Carlo N-Particle eXtended\"), dedicado para cálculos de transporte destas partículas e a validação é realizada mediante uma cooperação internacional junto a um projeto coordenado de pesquisa da Agencia Internacional de Energia Atômica e trabalhos disponíveis. O objetivo é qualificar os cálculos relacionados às reações nucleares e os canais de desexcitação envolvidos. O CRISP, um código nacional para a descrição da fenomenologia das reações envolvidas, também foi estudado e os modelos implementados no código foram revistos e melhorados de forma a dar continuidade ao seu processo de qualificação. Devido às limitações dos principais modelos na descrição de produção de nuclídeos leves, a reação de multi-fragmentação foi estudada. As discrepâncias nos cálculos de produção destes nuclídeos são atribuídas à falta do canal de multi-fragmentação estatística do núcleo. A implementação deste canal foi realizada para a aplicação em reações de altas energias junto ao código CRISP de forma a reproduzir a produção de nuclídeos leves, bem como sua validação mediante a comparação com dados experimentais disponíveis para este fenômeno, obtendo com isso uma melhor reprodução de todo o espectro de produção de nuclídeos do processo.
This work presents a study of high energy nuclear reactions which are fundamental to dene the source term in accelerator driven systems. These nuclear reactions, also known as spallation, consist in the interaction of high energetic hadrons with nucleons in the atomic nucleus. The phenomenology of these reactions consist in two step. In the rst, the proton interacts through multiple scattering in a process called intra-nuclear cascade. It is followed by a step in which the excited nucleus, coming from the intranuclear cascade, could either, evaporates particles to achieve a moderate energy state or ssion. This process is known as competition between evaporation and ssion. In this work the main nuclear models, Bertini and Cugnon are reviewed, since these models are fundamental for design purposes of the source term in ADS, due to lack of evaluated nuclear data for these reactions. The implementation and validation of the calculation methods for the design v of the source is carried out to implement the methodology of source design using the program MCNPX (Monte Carlo N-Particle eXtended), devoted to calculation of transport of these particles and the validation performed by an international cooperation together with a Coordinated Research Project (CRP) of the International Atomic Energy Agency and available jobs, in order to qualify the calculations on nuclear reactions and the de-excitation channels involved, providing a state of the art of design and methodology for calculating external sources of spallation for source driven systems. The CRISP, is a brazilian code for the phenomenological description of the reactions involved and the models implemented in the code were reviewed and improved to continue the qualication process. Due to failure of the main models in describing the production of light nuclides, the multifragmentation reaction model was studied. Because the discrepancies in the calculations of production of these nuclides are attributes to the lack of reaction channel and the implementation of this channel was carried out for applications in high energy reactions with the CRISP code to reproduce the production of light nuclides, as well, as its validation by comparison with experimental data available for this phenomenon. Thus, obtaining a better reproduction of the whole spectrum of production of nuclides in the process.

Welding of duplex stainless steel pipeline material for the oil and gas industry is now common practice. To date, research has been conducted primarily on the parent material and heat affected zones in terms of its susceptibility to various forms of corrosion. However, there has been little research conducted on the degree of sensitisation of the various successive weld layers, namely the root, fill and cap layers. The focus of this research study was to: (i) provide an in-depth microstructural analysis of the various weld passes, (ii) study the mechanical properties of the weld regions; (iii) determine degree of sensitisation of the various weld passes; and (iv) investigate the residual stress levels within the various regions/ phases of the welds. Four test conditions were prepared using manual Gas Tungsten Arc Welding with 'V' and 'U' bevel configuration. Structural analysis consisted of (i) optical microscopy, scanning electron microscopy and magnetic force microscopy; (ii) ferrite determination using Magna-Gauge, Fischer Ferrite-scope and Point Count method. Mechanical testing consisted of Vickers hardness measurements, Charpy impact studies and transverse tensile testing. The degree of sensitisation was determined by three test methods: a modified ASTM A262, ASTM A923 and a modified Double Loop Electrochemical Potentiodynamic Reactivation (DL-EPR) test. Residual stress levels were determined using two neutron diffraction techniques: a reactor source and a time of flight spallation source. Microstructure observed by optical microscopy and magnetic force microscopy shows the formation of both fine and coarse structures within the weld metal. There was no evidence of secondary austenite, being present in any of the weld metal conditions examined. In addition, no detrimental intermetallic phases or carbides were present. The DL-EPR test results revealed that the fill layer regions for all four conditions and the base material showed the highest values for Ir/Ia and Qr/Qa. All four test conditions passed the ASTM A262 and A923 qualitative type tests, even under restricted and modified conditions. Residual stress measurements by neutron diffraction conducted at Lucas Heights Hi-Flux Reactor revealed that the ferrite phase stress was tensile in the heat affected zones and weld, and appeared to be balanced by a local compressive austenite phase stresses in the normal and transverse directions. Residual stress measurements by neutron diffraction conducted at Los Alamos Nuclear Science Centre revealed that in the hoop direction, ferrite (211) and austenite (311) exhibit tensile strains in the weld. In the axial and radial direction, the strains for both phases were more compressive. Correlations between the degree of sensitization and microstructural changes / ferrite content were observed. Higher degrees of sensitization (Ir/Ia and Qr/Qa) were associated with reduced ferrite (increased austenite) content. Correlations between the stresses generated, the evolved microstructures and degree of sensitization were evident. Stresses within the cap region were generally shown to be of a tensile nature in the transverse and longitudinal direction. In summary, the study has shown that correlations exist between the weld microstructure, susceptibility to sensitisation and levels / distribution of internal stresses within the weld regions.

Dans le contexte des études sur les systèmes innovants de production d'énergie, des réacteurs exploitant le combustible thorium sont envisagés. Les sections efficaces de fission induite par neutrons des actinides qui y sont engagés entrent en jeu dans les simulations de scénarios. Pour les alimenter, des bases de données sont produites à partir de résultats expérimentaux et de modèles. Pour certains noyaux, elles présentent des lacunes ou des désaccords. Pour compléter ces bases de données, nous avons construit un dispositif original constitué d'une alternance de PPACs(chambres à avalanches sur plaques parallèles) et des cibles ultra-minces, que nous avons installé auprès de l'installation n_TOF. Nous décrivons les détecteurs, le montage, et le soin apporté à la fabrication et à la caractérisation des cibles. La détection en coïncidence des produits de fission se fait grâce à des mesures de temps très précises et à leur localisation par la méthode de la ligne à retard. Nous avons contribué, au sein de la collaboration n_TOF, à la caractérisation de la nouvelle source intense de neutrons de spallation du CERN, basée sur le temps de vol des neutrons, et nous en décrivons les caractéristiques et les performances. Nous avons pu mener des mesures sur les actinides ^{232}Th, ^{234}U, ^{233}U, ^{237}Np, ^{209}Bi, et ^{nat}Pb relativement aux références ^{235}U et ^{238}U, en utilisant un système d'acquisition innovant. Nous avons pu tirer parti du large domaine d'énergie accessible, de 0,7 eV à 1 GeV, et de l'excellente résolution dans ce domaine. Le traitement des données et l'état d'avancée de l'analyse sont décrits afin d'éclairer les performances et les limites des résultats obtenus.

The hydrocyclone is commonly used to separate oil from water, and particulates from fluid streams in various process industries. Two-fluid hydrodynamic theory is used here to develop a model for hydrocyclone performance in the application of separation of helium bubbles larger than 30 micron in diameter from liquid mercury at system pressure near 1 bar. The application is related to high power liquid metal target development for proton beams used in spallation neutron sources.

This document introduces the planned new search for the neutron Electric Dipole Moment at the Spallation Neutron Source at the Oak Ridge National Laboratory. A spin precession measurement is to be carried out using Ultracold neutrons diluted in a superfluid Helium bath at T = 0.5 K, where spin polarized 3He atoms act as detector of the neutron spin polarization. This manuscript describes some of the key aspects of the planned experiment with the contributions from Caltech to the development of the project.

Techniques used in the design of magnet coils for Nuclear Magnetic Resonance were adapted to the geometry of the experiment. Described is an initial design approach using a pair of coils tuned to shield outer conductive elements from resistive heat loads, while inducing an oscillating field in the measurement volume. A small prototype was constructed to test the model of the field at room temperature.

A large scale test of the high voltage system was carried out in a collaborative effort at the Los Alamos National Laboratory. The application and amplification of high voltage to polished steel electrodes immersed in a superfluid Helium bath was studied, as well as the electrical breakdown properties of the electrodes at low temperatures. A suite of Monte Carlo simulation software tools to model the interaction of neutrons, 3He atoms, and their spins with the experimental magnetic and electric fields was developed and implemented to further the study of expected systematic effects of the measurement, with particular focus on the false Electric Dipole Moment induced by a Geometric Phase akin to Berry’s phase.

An analysis framework was developed and implemented using unbinned likelihood to fit the time modulated signal expected from the measurement data. A collaborative Monte Carlo data set was used to test the analysis methods.

Models for solubility of noble gases in liquid metals are reviewed in detail and evaluated for the combination of mercury and helium for applications at the Spallation Nuetron Source (SNS) at Oak Ridge National Laboratory (ORNL). Gas solubility in mercury is acknowledged to be very low; therefore, mercury has been used in ASTM standard methods as a blocking media for gas solubility studies in organic fluids and water. Models from physical chemistry predict a Henry coefficient for helium in mercury near 3.9x1015 Pa-molHg/molHe, but the models have large uncertainties and are not verified with data. An experiment is designed that bounds the solubility of helium in mercury to values below 1.0x10-8 molHe/molHg at 101.3 kPa, which is below values previously measurable. The engineering application that motivated this study was the desire to inject 10 to 15 micron-radius helium bubbles in the mercury target of the SNS to reduce pressure spikes that accompany the beam energy deposition. While the experiment bounds the solubility to values low enough to support system engineering for the SNS application, it does not allow confirmation of the theoretical solubility with low uncertainty. However, methods to measure the solubility value may be derived from the techniques employed in this study.

Thesis (Ph. D.)--University of Tennessee, Knoxville, 2003.
Title from title page screen (viewed Mar. 24, 2004). Thesis advisor: Peter K. Liaw. Document formatted into pages (xxi, 273 p. : ill. (some col.)). Vita. Includes bibliographical references (p. 163-182).

A new measurement of the neutron electric dipole moment (nEDM) is being developed at TRIUMF, where a high density source of ultra cold neutrons (UCN) is currently under construction. A fast, high-efficiency UCN detector is needed for the experiment, and a 6-Li doped glass scintillation detector is being explored for this purpose. In this work, simulations and test measurements were carried out to optimize the light guide design for the new UCN detector. Acrylic and air-core light guides, the latter with two different reflecting surfaces, were considered. Three prototype light guides were constructed and tested, and results were compared with simulations. The best solution was found to be an acrylic guide, wrapped with mylar foil. For a guide 12 cm in length as required by the experimental layout, a lower limit of approximately 25 photoelectrons per neutron capture was established for the proposed geometry and photomultiplier configuration.
May 2016