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1
Дядечко, Алла Миколаївна, Алла Николаевна Дядечко, Alla Mykolaivna Diadechko, and A. Velytchenko. "Nuclear reactions." Thesis, Вид-во СумДУ, 2009. http://essuir.sumdu.edu.ua/handle/123456789/16936.
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Shaw, Martin. "Laser induced nuclear reactions." Thesis, University of the West of Scotland, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545857.
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Pavel, Hans-Peter. "Nuclear reactions ar ultrarelativistic energies." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258355.
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Field, G. M. "Pre-equilibrium processes in nuclear reactions." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233509.
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Providencia, M. C. "Theory of nuclear structure and reactions." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235048.
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Chamon, Luiz Carlos. "ESTUDO EXPERIMENTAL DA DEPENDENCIA ISOTOPICA NA FUSAONUCLEAR E NO ESPALHAMENTO ELASTICO NOS SISTEMAS 16,18O + 63,65 Cu." Universidade de São Paulo, 1990. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-31082012-131325/.
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Fizemos medidas de fusao nuclear e de espalhamento elastico nos sistemas ANTPOT.16,18 O+ANTPOT.63,65 CU. Os dados foram obtidos entre as energias 39 e 64 mev. Observamos significativas diferencas entre sistemas com ANTPOT. 63 CU e com ANTPOT.65 CU como nucleos-alvos, em contraposicao a uma insensibilidade em relacao ao projetil. Propusemos um modelo teorico que explica os resultados experimentais tanto em relacao ao espalhamento elastico como em relacao a fusao nuclear. Tal modelo esta fundamentado no incremento da absorcao suprficial devido aos dois neutrons extras do ANTPOT.65 CU (em relacao ao ANTPOT.63 CU)Experimental study of the isotopic dependence on nuclear fusion and elastic scattering systems
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Gomes, Luiz Carlos. "Estudo dos primeiros estados coletivos de isótopos pares de rutênio." Universidade de São Paulo, 1993. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-04122013-162039/.
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Parâmetros de deformação nuclear de massa, inéditos, e de carga, associados aos primeiros estados 2 POT.+ dos isótopos ANTPOT.100 Ru, ANTPOT.102 Ru e ANTPOT.104 Ru, foram extraídos simultaneamente a partir da análise de espalhamentos inelásticos de dêuterons e partículas alfa. Foram obtidas distribuições angulares, com dêuterons incidentes de 13,2 MeV, detalhando a região de máxima interferência nuclear-coulombiana, utilizando-se emulsões nucleares no plano focal de um espectrógrafo magnético tipo Enge. As medidas de espalhamento elástico e inelástico de partículas alfa forma realizadas, com a utilização de detetores de barreira de superfície, compreendendo funções de excitação, em = 172,8 POT. 0, entre 9 MeV e 17 MeV (incluindo regiões de excitação coulombiana pura e de interferência nuclear-coulombiana), e também distribuições angulares a 22 MeV para o ANTPOT.100 Ru. Ajustes das distribuições angulares e funções de excitação dos espalhamentos inelásticos, com previsões DWBA calculadas com fator de forma coletivo, permitiram a extração dos parâmetros de deformação, através de metodologia criticamente estabelecida no presente trabalho. A informação original de estrutura nuclear obtida refere-se a um aumento da deformação nuclear de massa com acréscimo do número de nêutrons, que entretanto, definitivamente não acompanha o aumento da deformação de carga. A coerência entre os resultados com os dois projéteis e a ótima concordância com os dados de excitação coulombiana da literatura convalidam o método de medida e de análise.Nuclear deformation parameters characterizing separately the mass and the charge contributions to the excitation of the first 2 POT.+ states of ANTPOT.100 Ru, ANTPOT.102 Ru and ANTPOT.104 Ru were simultaneously extracted in the analysis of inelastic scattering of both deuterons and alpha-particles. Angular distributions detailing the region of maximal coulomb-nuclear interference were recorded for deuterons of 13.2 MeV incident energy, with nuclear emulsions at the focal plane of an Enge split-pole magnetic spectrograph. Elastic and inelastic alpha-particle scattering was observed with surface barrier detectors, both as excitation functions at = 172,8 POT. 0, for alpha energies between 9 MeV and 17 MeV (covering pure coulomb excitation and interference), and as an angular distribution for ANTPOT.100 Ru at 22 MeV. The deformation parameters were extracted by means of DWBA fits to these data, employing a collective form factor within an analysis method critically established in the present work. The original nuclear structure information thus obtained gives evidence for an increase of the nuclear mass deformation as one or two neutrons pairs are added, but in a definitely less pronounced way than that of the charge deformation. The very good agreement between our results obtained with both deuterons and alphas, and with coulomb excitation experiments, validates the method of measurement and analysis.
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Silva, Cely Paula da. "Fusão nuclear e processos periféricos nos sistemas 16,18O + 58,60,64Ni." Universidade de São Paulo, 1996. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-16122013-145825/.
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Com o objetivo de investigar os processos de fusão nuclear e espalhamento elástico entre íons pesados, fizemos medidas para a seção de choque de fusão dos sistemas ANTPOT.16,18 O + ANTPOT.58,60,64 Ni, no intervalo de energias de bombardeio abrangido por 38.0 E IND. LAB 72.0 MeV, e medidas para a seção de choque de espalhamento elástico dos sistemas 18O+ 58,60,64Ni, no intervalo compreendido entre 35.1 E IND.LAB 55.1 MeV. As distribuições angulares do processo de fusão foram obtidas em ângulos entre 2 IND.LAB 18 graus, enquanto que para o de espalhamento elástico a variação ocorreu para 17.5 IND.CM M 170.0 graus. Nossos resultados, para as medidas das funções de excitação dos resíduos de evaporação indicam que, na região de energias logo abaixo da barreira coulombiana, o sistema ANTPOT.18 O + ANTPOT.58 Ni apresenta um favorecimento da seção de choque de fusão bastante significativo, quando comparado A sistemática dos isótopos pares do níquel, obtida de nossos dados e da literatura. O desvio padrão do raio de interação, extraído dos sistemas ANTPOT.16,18 O + ANTPOT.58,60,64 Ni para a fusão, na faixa de energias abaixo da barreira, é comparado aqueles associados a modos de vibrações superficiais de núcleos em estados de baixas energias de excitação e de emparelhamento. Efeitos não locais também foram investigados para as referidas medidas. Neste trabalho encontra-se a análise, via modelo óptico, dos resultados experimentais do processo de espalhamento elástico para vinte e sete distribuições angulares. Por último é apresentada uma conexão entre o aumento da fusão e a anomalia de limiar na região em tomo da barreira coulombiana.With the objective of investigating the heavy-ion fusion and elastic scattering processes, we performed measurements of fusion cross sections for the 16,18O + 58,60.64Ni systems in the bombarding energy range 38.0 ELAB 72.0 MeV and of elastic scattering cross sections for the 18O+ 58,60,64Ni systems in the interval 35.1 I EL- I 55.1 MeV. The fusion process angular distributions were obtained for angles between 2 .0 LAB 18.0 degrees, whereas for the elastic scattering the angles varied in the interval 17.5 CM M 170.0 degrees. Our results for the evaporation residues excitation functions indicate that, for energies right below the coulomb barrier, the 18 O+ 58Ni system presents a significant enhancement of the fusion cross section when compared to systematics for even nickel isotopes, obtained from our data and data in the literature. The interaction radius standard deviation extracted from the fusion data for the 16,18O + 58,60,64Ni systems at energies below the barrier, is compared to those associated to surface vibration modes of nuclei at low excitation and pairing energies. Non local effects were also investigated for these measurements. In this work, we also performed for the elastic scattering data, an optical model analysis for twenty seven angular distributions. Finally, a connection between the fusion enhancement and the threshold anomaly at energies close to the barrier is also presented.
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Silva, Cely Paula da. "Estudo experimental da fusão nuclear 16O + 60Ni." Universidade de São Paulo, 1990. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-19062015-164639/.
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Com o objetivo de estudar o processo de fusão entre íons pesados, realizamos medidas da seção de choque do processo de fusão nuclear para o sistema 16O + 60Ni no intervalo de energia de bombardeio ao redor da barreira coulombiana (ELAB -> 40 - 72 mEv). A técnica utilizada para a detecção dos resíduos de evaporação do núcleo composto, foi a da medida do tempo de voo, associada a um sistema de deflexão eletrostática para separar esses resíduos, das partículas com massa perto da do feixe incidente. As distribuições angulares dos resíduos de evaporação foram medidas no intervalo angular de 2° <= ? <= 18°. A função de excitação de fusão foi analisada inicialmente via modelo de penetração de barreira unidimensional que mostrou subestimar a seção de choque de fusão em energias em torno e abaixo da barreira coulombiana; desta forma procuramos ajustar os dados desta região, através do modelo de canais acoplados, que não se mostrou totalmente satisfatório. Em energias acima da barreira (na região de anomalia) também foram detectados desvios dos dados experimentais com relação às previsões teóricas do modelo unidimensional, que são explicados através de considerações de potenciais ópticos. Com o objetivo de se obter uma melhor compreensão de efeitos de estrutura nuclear nos processos de reação envolvidos, comparamos o sistema até aqui citado com o sistema 18O + 58Ni (que leva ao mesmo núcleo composto do sistema 16O + 60Ni). A comparação revelou que o primeiro sistema possui um aumento significativo na seção de choque de fusão na região subcoulombiana, em relação ao 16O + 60Ni. Isto pode estar relacionado com o fato de que as estruturas internas dos núcleos são diferentes, mas não nos foi possível confirmar esta afirmação.With the objective to study the process of fusion between heavy ions, we measured the nuclear fusion cross section for the system 16O + 60Ni, at an energy range around the Coulomb barrier (ELAB -> 40 - 72 mEv). In order to detect the evaporation residues following the fusion process, the time of flight method was adopted in conjunction with an electrostatic deflector capable of separating the evaporations residues from the beam particles. The angular distributions of the evaporation residues were measured in the angular range of 2° <= ? <= 18°. The excitation function was analyzed using the unidimensional barrier penetration model. Theoretical fusion cross sections obtained from this analysis were smaller than our measured values, in the energy region near and below the Coulomb barrier. In order to discover which channels enhance the fusion cross section in this region, a coupled channel calculation was performed, but did not lead to satisfactory results. Theoretical predictions for the unidimensional model were compared to the experimental fusion cross section (anomaly region). We compared the systems 18O + 58Ni and 16O + 60Ni (which lead to the same compound nucleus) to understand the nuclear structure effects in the reaction process. This comparison showed that the cross section of the first system is larger than for 16O + 60Ni, at energies below the Coulomb barrier. This could be possibly to the different internal structures of the nuclei, but it was not possible to confirm this affirmation.
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Cruz, João Duarte Neves. "Experimental study of proton induced nuclear reactions in 6,7 Li." Doctoral thesis, FCT - UNL, 2006. http://hdl.handle.net/10362/1139.
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This work presents the results of the experimental study of proton induced nuclear reactions
in lithium, namely the 7Li(p,α)
4He, 6Li(p,α)
3He and 7Li(p,p)7Li reactions.
The amount of 7Li and 6Li identified as primordial and observed in very old stars of the
Milky Way galactic halo strongly deviates from the predictions of primordial nucleosynthesis
and stellar evolution models which depend, among other factors, on the cross sections of reactions
like
7Li(p,α)
4He and 6Li(p,α)
3He. These discrepancies have triggered a large amount
of research in the fields of stellar evolution, cosmology, pre-galactic evolution and low energy
nuclear reactions.
Focusing on nuclear reactions, this work has measured the 7Li(p,α)
4He and 6Li(p,α)
3He reactions
cross sections (expressed in terms of the astrophysical S -factor) with higher accuracy,
and the electron screening effects in these reactions for different environments (insulators and
metallic targets). The 7Li(p,α)
4He angular distributions were also measured. These measurementstook
place in two laboratory facilities, in the framework of the LUNA (Laboratory for Undergroud
Nuclear Astrophysics) international collaboration, namely the Laboratorio ´ de Feixe de
Ioes ˜ in ITN (Instituto Tecnologico ´ e Nuclear) Sacavem, ´ Portugal, and the Dynamitron-TandemLaboratorium
in Ruhr-Universitat¨ Bochum, Germany. The ITN target chamber was modified
to measure these nuclear reactions, with the design and construction of new components, the
addition of one turbomolecular pump and a cold finger. The 7Li(p,α)
4He and 6Li(p,α)
3He reactions
were measured concurrently with seven and four targets, respectively. These targets were
produced in order to obtain adequate and stable lithium depth profiles.
In metallic environments, the measured electron screening potential energies are much
higher than the predictions of atomic-physics models. The Debye screening model applied
to the metallic conduction electrons is able to explain these high values. It is a simple model,
but also very robust. Concerning primordial nucleosynthesis and stellar evolution models, these results are very important as they show that laboratory measurements are well controlled, and
the model inputs from these cross sections are therefore correct.
In this work the 7Li(p,p)7Li differential cross section was also measured, which is useful to
describe the 7Li(p,α)
4He entrance channel.
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Leistenschneider, Erich. "Reações induzidas por protons em 8Li a baixas energias e espectroscopia do 9Be altamente excitado." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26092014-025439/.
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Reações induzidas por prótons são importantes no estudo do consumo de 8Li em alguns cenários astrofísicos. Neste trabalho, as seções de choque para as reações 8Li(p,p), 8Li(p,α) e 8Li(p,d) foram medidas em cinemática inversa entre Ecm=0.7 e 2.2 MeV. Foi usado um feixe de 8Li de alta pureza selecionado pelo Sistema RIBRAS no Laboratório Pelletron (IF-USP), São Paulo, que colidia com um alvo grosso de polietileno ((CH2)n, 7.7(8) mg/cm2), um plástico rico em prótons. Os produtos de reação foram medidos por um telescópio formado por detectores de barreira de superfície de silício posicionados em um ângulo dianteiro. As funções de excitação medidas foram analisadas através da metodologia de matriz-R e puderam fornecer informações sobre ressonâncias pouco conhecidas do núcleo composto 9Be a altas energias de excitação. A importância de outros canais de decaimento e consequências das reações estudadas na nucleossíntese também são discutidas.Proton-induced reactions are important in the study of the destruction of 8Li in some astrophysical scenarios. In this work, the cross sections for the reactions 8Li(p,p), 8Li(p,α) and 8Li(p,d) were measured in inverse kinematics between Ecm = 0.7 and 2.2 MeV. A highly pure 8Li beam selected by RIBRAS System in the Pelletron Laboratory (IF-USP), São Paulo, was used impinging on a thick polyethylene target ((CH2)n , 7.7(8) mg/cm2), a proton-rich plastic. The reaction products were detected by a telescope formed by silicon surfasse barrier detectors placed at a foward angle. The measured excitation functions were analysed through the R-matrix methodology and could provide information about poorly known high-lying resonances of the 9Be compound nucleus. The importance of other decay channels and the consequences of the studied reactions on nucleosynthesis are also discussed.
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Foglia, Graciela Alicia. "Teoria de reações para análise de processos de produção e decaimento de ressonâncias gigantes nucleares." Universidade de São Paulo, 1991. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-04102012-150340/.
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É apresentada uma teoria de reações que inclui consistentemente a formação e o decaimento das Ressonâncias Multipolares Gigantes. Achamos uma expressão teórica para parâmetros de mistura, dependentes da energia, que regem os diferentes tipos de decaimento. A formulação é aplicada à reação ANTPOT. 208 Pb(,n) e são obtidas estimativas para as larguras de decaimento semi-direto,We present a theory of reactions wich includes consistently the formation and decay of Giant Multipole Resonances. We find an energy dependent theoretical expression for the mixture parameters which govern the different types of decay. The formulation is applied to the reaction 208 Pb(,n) and we obtain estimates for the semi-direct widths for the first five states of ANTPOT 207 Pb.
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Terremoto, Luis Antonio Albiac. "Experimento de coincidência 26Mg (e,e\'c)." Universidade de São Paulo, 1993. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-11032014-165807/.
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O objetivo deste trabalho consiste em estudar as ressonâncias gigantes no \'ANTPOT. 26 MG\' por intermédio de reações nucleares de eletrodesintegração em que o elétron espalhado inelasticamente e a partícula carregada c emitida (onde c designa um próton ou uma partícula alfa) são medidos em coincidência. Durante o experimento foi utilizado o feixe contínuo de elétrons do acelerador Microtron-A2, instalado no Instituto de Física Nuclear da Universidade de Mainz (Alemanha). Os elétrons espalhados foram medidos nos ângulos de \'22 GRAUS\' e \'35 GRAUS\', correspondentes a momentos transferidos de 0,35 e 0,54 \'fm POT. -1\', respectivamente, uma vez que a energia cinética dos elétrons incidentes era de 183,5 MeV. O experimento abrangeu uma faixa de energia de excitação do núcleo-alvo compreendida entre 10,6 MeV 31,8 MeV e tornou possível a investigação do decaimento das ressonâncias gigantes em um estado final definido dos núcleos-produto. Os elétrons espalhados inelasticarnente foram detectados por um espectrômetro magnético de \'180 GRAUS\' bifocal e as partículas carregadas c por um sistema compostos por detectores de barreira de superfície, ambos conectados por uma eletrônica de coincidência. O processo de redução e análise dos dados experimentais constitui a ênfase deste trabalho, uma vez que não houve participação direta na realização do experimento. Foram obtidas as seções de choque e distribuições angulares para as reações \'ANTPOT. 26 MG\'(e, e\' \'alfa IND. 0\') \'ANTPOT. 22 NE\', \'ANTPOT. 26 MG\'(e, e\' \'alfa IND. 1\') \'ANTPOT. 22 NE\', \'ANTPOT. 26 MG\'(e, e\' \'p IND. 01\') \'ANTPOT. 25 NA\' e \'ANTPOT. 25 MG\'(e, e\' \'p IND. 2\') \'ANTPOT. 25 NA\'. No caso específico do decaimento \'alfa IND. 0\' , foi efetuada uma separação independente de modelo das componentes multipolares da seção de choque. Um estudo da influência de efeitos de isospin e deformação nuclear nas ressonâncias gigantes do \'ANTPOT. 26 MG\' foi realizado com base em comparações com resultados de outros experimentos que abrangem a faixa de energia de excitação localizada entre 10 Me V e 40 MeV.Measurements of the ANTPOT 26 MG\'(e, e\' c) reaction (c standing for p or alfa) have been performed at electron energy of 183.5 Me V and scattering angles of \'22 GRAUS\' and \'35 GRAUS\' (momentum transfer of 0.35 and 0.54 \'fm POT. -1\', respectively). Excitation energy of the target nucleus ranged from 10.6 MeV to 31.8 MeV and cross sections and angular distributions were determined for the following decay channels: \'alfa IND. 0\', \'alfa IND. 1\', \'p IND. 01\' and \'p IND. 2\'. The multi polar composition of the \'alfa IND. 0 channel was determined by means of a model independent analysis. A simple model based on effects of isospin, nuclear deformation and configurational splitting was used to explain the observed behaviour of the strength distribution of the giant resonances as a function of energy.
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Dell'aquila, Daniele. "Clustering dans les noyaux légers : une approche multi-méthodique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS093/document.
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Les phénomènes de clustering caractérisent plusieurs domaines des sciences naturelles et de la sociologie. Ils consistent en l'auto-organisation de groupes d'objets en sous-groupes corrélés, en introduisant des symétries et, dans certains cas, un certain degré d'ordre dans le système global. En physique nucléaire, ces aspects représentent l'un des effets les plus fascinants induits par le principe de Pauli dans les noyaux. Leur investigation est un outil extrêmement puissant pour comprendre le comportement des forces nucléaires dans les systèmes d’N corps avec interactions les unes les autres. Dans ce thèse, je discute des résultats d'une campagne expérimentale qui explore les aspects de clustering dans les systèmes nucléaires légers à partir d'une approche multi-méthodique et en utilisant des techniques différentes et complémentaires. Le travail commence avec le noyau 10Be, prévu pour être constitué par une structure de cluster moléculaire de deux particules alpha liées par les deux neutrons de valence supplémentaire. L'expérience a été réalisée avec des faisceaux de 10Be produits au laboratoire INFN-LNS avec la technique de fragmentation des projectiles FRIBs. À travers des techniques de corrélation particule-particule, des signaux d'un nouvel état appartenant possiblement à la bande de rotation moléculaire de 10Be ont été observés. Autres noyaux appartenants à la chaîne isotopique du carbone ont également été étudiés pour comprendre comment les phénomènes de clustering évoluent avec l'excès de neutrons. Pour 11C et 13C, nous avons utilisé les réactions nucléaires 10B(p,a) et 9Be(a,a), respectivement, à basse énergie. Ces mesures ont été conduites à l'accélérateur TANDEM de Naples. Les sections efficaces différentielles et les distributions angulaires, ainsi que autres données disponibles dans la littérature, ont été reproduites par des calculs R-matrix, ce qui nous a permis d'affiner la structure de ces noyaux et de suggérer l'existence d'états à cluster.Le noyau 16C a été étudié avec la même configuration expérimentale utilisée dans le cas du 10Be mais avec un faisceau secondaire très intense. J'ai observé des contributions non négligeables dans les voies de désintégration à deux et à trois corps pour le 16C, voies qui représentent des désintégrations extrêmement rares. Enfin, l'état de Hoyle dans 12C (7.654 MeV,0+) a été étudié avec une expérience de haute précision en utilisant la réaction 14N(d,a) à 10,5 MeV à INFN-LNS. L'étude a fourni un limite supérieure pour la voie de désintégration directe en trois alpha avec une précision sans précédent. Ce résultat, qui améliore d'un facteur 5 l'état actuel de la technique, fournit une contrainte importante aux modèles de structure théorique ainsi qu'aux calculs de nucléosynthèse stellaire responsables de l'origine des éléments dans l'univers. Les phénomènes de clustering ont également été étudiés dans les noyaux 19F et 20Ne avec la réaction 19F(p,a) à très basse énergie à l'accélérateur AN-2000 de l'INFN-LNL. Une analyse par R-matrix de la section efficace intégrée a été utilisée pour fournir des informations sur la structure du noyau composé 20Ne avec des implications astrophysiques sur le cycle CNO dans les étoiles. J'ai également étudié les collisions entre les ions lourds à des énergies intermédiaires pour explorer les phénomènes de clustering dans la matière nucléaire diluée et chaude. J'ai développé un modèle thermique des corrélations particules-particules pour décrire la population d'états non liés produits lors de l'évolution des collisions Ar+Ni violentes à 32-95 MeV par nucléon. Les limites d'une approche purement thermique dans un tel système dynamique ont été discutées, avec des idées possibles pour expliquer le mécanisme qui peuplent les états internes dans les noyaux 8Be en discutant l'interconnexion entre la thermodynamique et les effets d'interaction d’état final. Ces études sont importants pour décrire la formation de clusters dans la matière nucléaireClustering phenomena characterise several fields of natural sciences and sociology. They consist on the self-organisation of groups of objects in correlated sub-groups, introducing symmetries and, in some cases, a certain degree of order in the overall system. In nuclear physics, these aspects represent one of the most fascinating effects induced by the Pauli principle in nuclei. Their investigation is an extremely powerful tool to understand the behaviour of nuclear forces in N-body interacting systems. In this thesis, I discuss the results of an experimental campaign that explores clustering aspects in light nuclear systems from a multi-methodic approach and by using different and complementary techniques.The work start with the 10Be nucleus, predicted to be constituted by a molecular cluster structure of two alpha particles kept bound by the two extra valence neutrons. The experiment has been performed with 10Be beams produced at the INFN-LNS laboratory with the FRIBs projectile fragmentation technique. By means of particle-particle correlation techniques, signals of a new state possibly belonging to the 10Be molecular rotational band were observed. Other nuclei along the carbon isotopic chain were also investigated to understand how clustering phenomena evolve with neutron excess. For 11C and 13C we used 10B(p,alpha) and 9Be(alpha,alpha) nuclear reactions, respectively, at low energies. These measurements were made at the tandem accelerator in Naples. Measured Differential cross sections and angular distributions, together with other data available in the literature, were reproduced by R-matrix calculations, which allowed us to refine the spectroscopy of such nuclei and suggest the existence of cluster states, possibly members of molecular rotational bands. The 16C nucleus was investigated with the same setup used in the 10Be case with a very intense secondary beam. I have observed non vanishing yields in both two-body and three-body cluster disintegration channels for 16C which represent extremely rare decays. Finally, the Hoyle state in 12C (7.654 MeV, 0+) was investigated in a high-precision experiment by using the 14N(d,a) reaction at 10.5 MeV at INFN-LNS. The study has provided an upper limit to the direct three-alpha decay process of such state with an unprecedented precision. This result, which improves of a factor 5 the existing state of the art, provides important constraint to theoretical structure models as well as to stellar nucleosynthesis calculations aiming at revealing the origin of elements in the universe. Clustering phenomena have also been studied in 19F and 20Ne nuclei with the 19F(p,a) reaction at very low energies at the AN-2000 accelerator of the INFN-LNL. An R-matrix analysis of the integrated cross-section was used to provide information on the structure of the 20Ne compound nucleus with its astrophysical implications on the CNO cycle in stars.I have also used heavy ion collisions at intermediate energies to explore clustering phenomena in dilute and hot nuclear matter. I have developed a thermal model of particle-particle correlations whit the aim of describing the population of decaying unbound states produced during the evolution of violent Ar+Ni collisions at 32-95 MeV per nucleon. The limitations of a purely thermal approach in such a dynamical system have been discussed, with possible ideas to explain the mechanism which populate internal states in 8Be cluster states accounting for the interplay of thermodynamics with final state interaction effects. Such studies are relevant to model cluster formation in nuclear matter
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Nieminen, John Matti. "Superdeformation : a tool to study fusion-evaporation reactions /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/NQ42868.pdf.
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Granados, Carlos G. "QCD Structure of Nuclear Interactions." FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/447.
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The research presented in this dissertation investigated selected processes that involve baryons and nuclei in hard scattering reactions. These processes are characterized by the production of particles with large energies and transverse momenta. Through these processes, this work explored both, the constituent (quark) structure of baryons (specifically nucleons and ∆-Isobars), and the mechanisms through which the interactions between these constituents ultimately control the selected reactions.
The first of such reactions is the hard nucleon-nucleon elastic scattering, which was studied here considering the quark exchange between the nucleons to be the dominant mechanism of interaction in the constituent picture. In particular, it was found that an angular asymmetry exhibited by proton-neutron elastic scattering data is explained within this framework if a quark-diquark picture dominates the nucleon’s structure instead of a more traditional SU(6) three quarks representation. The latter yields an asymmetry around 90o center of mass scattering with a sign opposite to what is experimentally observed.
The second process is the hard breakup by a photon of a nucleon-nucleon system in light nuclei. Proton-proton (pp) and proton-neutron (pn) breakup in 3He, and ∆∆-isobars production in deuteron breakup were analyzed in the hard rescattering model (HRM), which in conjunction with the quark interchange mechanism provides a QCD description of the reaction. Through the HRM, cross sections for both channels in 3He photodisintegration were computed without the need of a fitting parameter. The results presented here for pp breakup show excellent agreement with recent experimental data.
In ∆∆-isobars production in deuteron breakup, the HRM angular distributions for the two ∆∆ channels were compared to the pn channel and to each other. An important prediction from this study is that the ∆++∆- channel consistently dominates ∆+∆0, which is in contrast with models that unlike the HRM consider a ∆∆ system in the initial state of the interaction. For such models both channels should have the same strength. These results are important in developing a QCD description of the atomic nucleus.
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Ni, QingWen. "A New Method for Measuring the Nuclear Hexadecapole Interaction in Some Solids." Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc332505/.
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A new method for measuring the nuclear hexadecapole interaction (HDI) in solids based on NMR quadrupole echoes is described. Theoretical values of the shifts of the quadrupole echo times caused by the HDI are given for two pulse and three pulse echoes in a nuclear spin 5/2 system. The method is applied to 1271 in an almost strain free crystal of KI and a hexadecapole coupling frequency (e2M16m16/h) of 630 Hz was found. Here e is the electronic charge, em16 is the fourth gradient of the external electric potential at the nuclear site, eM16 is the hexadecapole moment and h is the Planck constant. This HDI is smaller than previously measured values in solids (42.6 MHz for 1 81 Ta in TaF 5, 66.6 MHz for 175Lu in Lu(NO3 )3*4H 20), but not as small as an atomic beam result of 151 Hz for 165Ho in atomic Ho. The method described here may be used to search for the HDI in other cubic crystals. A double resonance (1151n, 31P) multiple pulse method was unsuccessfully used to search for the 1151n HDI in a single crystal of InP.
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Windham, Gordon. "Spin dependence in heavy ion induced nuclear reactions." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/843452/.
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The interest of this work is to explore the spin dependent effects of projectile structure in nuclear heavy ion induced reactions. The projectiles are considered to consist of two clusters which remain inert, the intercluster wavefunctions are obtained by the use of the orthogonality condition model. Excitation to the low lying projectile states is included by the use of coupled channels calculations. The projectile excited states are included by allowing excitation in the inter cluster wavefunctions. Coupling to the excited states is performed by multipole terms arising from a single folding model, which is used consistently throughout the work. The effects of projectile excitation are considered in two areas, elastic and inelastic scattering, and transfer reactions. It is found that the inclusion of the projectile excited states has a very strong effect on the spin dependent elastic observables, in particular the vector analysing powers. In contrast to earlier analysis it is found that projectile excitation plays a dominant role in reproducing the experimentally observed vector analysing powers for the elastic scattering of 6Li from 16O and 28Si at 22.8 MeV. Projectile excitation is also seen to produce strong spin dependent effects in the elastic scattering of Li from 120Sn at 44 MeV and of 19Ffrom 28Si at 60 MeV. The inclusion of projectile excitation via CCBA calculations produces changes in the transfer cross section for the 28Si (19F, 16O)31P(1/2+ ,g.s.) reaction. The observed changes can be understood in terms of the effects of spin dependence in the reaction path. The inclusion of projectile excitation however does not significantly improve the quality of the agreement with experimental data.
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Pass, Christopher Neil. "Recoil product analysis of low energy nuclear reactions." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329995.
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MASHA, ELIANA. "ASTROPHYSICAL NUCLEAR REACTIONS ON NEON ISOTOPES AT LUNA." Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/899089.
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This thesis reports the direct measurements of the 22Ne(α,γ)26Mg and 20Ne(p,γ)21Na
reactions at astrophysical energies of interest.
The 22Ne(α,γ)26Mg reaction competes with the 22Ne(α,n)25Mg reaction which is the main source of neutrons for the s-process in low-mass Asymptotic Giant Branch and massive stars. At temperatures T < 300 MK where the (α,γ) channel becomes dominant, the rate of the 22Ne(α,γ)26Mg reaction is influenced by several resonances studied only indirectly. The first part of this thesis concerns the direct measurement of one of these resonances, Er = 334 keV, which so far was studied only indirectly leading to six orders of magnitude range of possible values for its resonance strength. The experiment has been performed at LUNA (Laboratory for Underground Nuclear Astrophysics) using the intense alpha beam of the LUNA 400 kV accelerator and a windowless gas target combined with a high-efficiency BGO detector. In the present study, an upper limit of 4.0·10−11 eV has been determined for the resonance strength. Taking into account these results, an up-dated 22Ne(α,γ)26Mg thermonuclear reaction rate was obtained and its role on the predicted 25Mg/26Mg ratio of a 5M⊙ AGBs was investigated. The data show a decrease by a factor of 15 of the intershell 25Mg/26Mg ratio.
The 20Ne(p,γ)21Na is the slowest reaction of the NeNa cycle. It determines the velocity of the cycle and defines the final abundances of the isotopes synthesized in this cycle. The uncertainties on the NeNa cycle are affected by the 20Ne(p,γ)21Na reaction rate. The main goal of the second part of this thesis was the direct measurement of the Ecm = 366 keV resonance which dominates the total rate in the temperature range between 0.2 GK and 1 GK. The measurement has been performed at LUNA using the windowless gas target and two high-purity germanium detectors placed at different positions. This measurement allowed to reduce the uncertainty on the strengths of the 366 keV resonance from 18% to 7%. These results were used to update the 20Ne(p,γ)21Na reaction rate.
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Shorto, Julian Marco Barbosa. "Mecanismos de Reação nos Sistemas 16,18O + 63,65Cu." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-02102007-121454/.
Full textAbstract:
Foram medidas as funções de excitação quase-elásticas para os sistemas 16,18O + 63,65Cu, no ângulo de 161ºe em energias compreendidas entre 30 e 48MeV, no referencial do laboratório. O termo quase-elástico aqui significa a soma do espalhamento elástico, dos espalhamentos inelásticos e das reações de transferência. Todos os cuidados foram tomados para se obter dados de alta precisão em pequenos passos de 0,5MeV de energia, pois o objetivo primeiro deste trabalho era realizar operações matemáticas (derivadas) sobre os pontos experimentais a fim de deduzir as distribuições de barreiras quase-elásticas desses sistemas. O ângulo de detecção escolhido, o maior possível com o arranjo experimental utilizado, objetivava estudar diretamente a competição entre a fusão e os processos diretos quando ambos os processos são alimentados pelas mesmas ondas parciais. Nessa situação, as representações das distribuições de barreiras de fusão e quase-elástica devem ser equivalentes devido à conservação do fluxo. O intervalo de energia foi escolhido para cobrir a região em torno da barreira coulombiana onde as distribuições de barreiras constituem um bom instrumento para o estudo dos mecanismos de reação. Além das medidas quase-elásticas inclusivas, a resolução em carga do detector permitiu que as funções de excitação de alguns canais de transferência fossem também medidas no mesmo ângulo e energias citados acima. A análise teórica dos dados foi realizada no âmbito do modelo de Canais de Reações Acoplados através do programa FRESCO. Outro objetivo deste trabalho foi a utilização de núcleos ímpares como alvos, pois os seus spins não nulos introduzem fenômenos adicionais ao mecanismo de reação que, eventualmente, podem se detectados pelas distribuições de barreiras. Um novo procedimento de cálculo foi empregado pela eliminação de qualquer potencial imaginário na região de interação, substituindo-o pela inclusão do maior número possíveis de canais de reação no cálculo de canais acoplados. Dessa maneira, elimina-se um problema muito comum nos cálculos de canais acoplados, que é o de misturar canais de reação com potencial imaginário deduzido a partir do ajuste de espalhamento elástico, o qual já contém o efeito desses canais. Além disso, e esse é um ponto importante desta análise, foi utilizada a parte real do Potencial de São Paulo, um potencial de dupla-convolução sem parâmetros livres, para simular a interação nuclear entre projéteis e alvos. Uma vez que todos os parâmetros nucleares necessários aos cálculos de canais acoplados advieram da literatura, nossa análise apresenta previsões teóricas que devem ser comparadas com os dados experimentais, o que é muito diferente dos ajustes aos dados através da variação de vários parâmetros livres. Outra característica importante da análise teórica empreendida neste trabalho é a utilização de todos os dados disponíveis na literatura para esses sistemas nas energias em torno da barreira. Assim, as previsões teóricas puderam ser comparadas com um grande conjunto de dados e ganharam grande consistência e amplitude. Os resultados obtidos com essas análises revelaram uma forte coletividade dos núcleos 63Cu e 65Cu, sendo que os três primeiros estados vibracionais quadrupolares 1/2-, 5/2- e 7/2- predominam sobre os demais estados excitados. As reações de transferência têm pequeno efeito sobre os demais processos, mas sofrem forte influência deles.Uma exceção é a transferência de dois nêutrons do 18O para o 63Cu, cuja importância nesse sistema é considerável. Além disso, foi constatado que, mesmo nesses sistemas de peso médio, o mecanismo de reorientação do spin do estado fundamental, de ambos os alvos, tem grande efeito em todos os processos nucleares analisados, mas é particularm ente forte no espalhamento elástico em ângulos traseiros. Finalmente, as distribuições de barreiras quase-elásticas se mostraram sensíveis a todos esses mecanismos de reação e constituem, de fato, uma excelente ferramenta para o estudo de reações nucleares.The quasi-elastic excitation functions for the systems 16,18O + 63,65Cu have been measured, at the angle 161º and at energies between 30 and 48MeV, in the laboratory reference system. The quasi-elastic term refers to the sum of the elastic scattering, the inelastic scattering and the transfer reactions. Care has been taken in order to obtain high precision data in small energy steps of 0,5MeV, because the aim of this work was to perform mathematics operations (derivates)on the experimental points, to deduce the quasi-elastic barrier distributions of these systems. The choice of this angle of detection, the largest possible, allows the direct study of the competition between the fusion and the direct processes, as both are fed by the same partial waves. The energy interval has been chosen to cover the region around the Coulomb barrier, where the barrier distributions constitute a good instrument for the study of the reaction mechanisms at these energies. Beyond the inclusive quasi-elastic, measurements of some transfer channels, at the same angle and energies mentioned above, were possible due to the charge resolution of the detector. The theoretical analysis of the data has been done on the scope of the coupled reaction channel model, with the code FRESCO. Another aim of this work was the utilization of odd-mass nuclei as targets, as their non-vanishing spins introduce additional phenomena to the reaction mechanisms, that might, eventually, be detected by the barrier distributions. A new calculation procedure has been used by the elimination of any imaginary potential at the interaction region, and it\'s substitution by the inclusion of the largest number as possible of channels at the coupled reaction channel calculation. Another important feature of the theoretical analysis is the utilization of many data available in the literature for these systems at energies around the barrier. Thus, the theoretical forecast could be compared with a great set of data and earned consistency and amplitude. The results obtained with this analysis revealed a strong collective behaviour of the 63Cu and 65Cu nuclei, and the first three quadrupolar vibrational states 1/2-, 5/2- and 7/2- prevail over the other excited states. The transfer reactions have small effect over the others processes, but are greatly influenced by them. There is an exception, the two neutron transfer from 18O to 63Cu, whose importance on this system is considerable. Besides, it was revealed that even on these medium weight systems, the ground state reorientation mechanism, of both targets, have large effect on all the analysed nuclear processes, but is strongest on the elastic scattering at back angles. Finally, the quasi-elastic barriers distributions showed up to be sensible to all of these reaction mechanisms and constitute an excellent tool for the study of nuclear reactions.
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Faria, Pedro Neto de. "Estudo do espalhamento elástico e reações de feixes secundários de núcleos exóticos." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26032009-103941/.
Full textAbstract:
Foram medidas distribuições angulares do espalhamento elástico 7Be+51V em Elab=26.6 MeV, 8Li+58Ni em Elab=20.2 e 22.0 MeV e 6He+120Sn em 17.4, 18.05, 19.8, 20.5 MeV e 8Li+120Sn em Elab=20.3 MeV. Os feixes radioativos foram produzidos no sistema RIBRAS (Radioactive Ion Beams in Brasil) a partir das reações de produção 9Be(7Li,8Li), 9Be(7Li,6He), 3He(7Li,7Be), 3He(6Li,7Be). No caso dos projéteis 7Be e 8Li e alvos de massas intermediárias, realizamos uma análise de modelo óptico das distribuições angulares e obtivemos a secção de choque total de reação. A secção de choque de reação reduzida foi comparada com outros sistemas estáveis fortemente ligados e fracamente ligados. Uma alta produção de partículas alfa foi detectada no espalhamento 6He+120Sn com velocidades próximas a do 6He espalhado. Foram determinadas distribuições angulares do espalhamento elástico e das alfas produzidas. Análises teóricas de quebra (CDCC), fusão-evaporação, transferência para o contínuo e para estados ligados indicam que a transferência é o que melhor explica os dados.Measurements of the elastic angular distributions of 7Be+51V at Elab=26.6 MeV, 8Li+58Ni at Elab=20.2 e 22.0 MeV and 6He+120Sn at 17.4, 18.05, 19.8, 20.5 MeV and 8Li+120Sn at Elab=20.3 MeV have been performed. The radioactive beams have been produced at the system RIBRAS (Radioactive Ion Beams in Brasil) using the production reactions 9Be(7Li,8Li), 9Be(7Li,6He), 3He(7Li,7Be), 3He(6Li,7Be). The 7Be e 8Li scattering on intermediate mass targets have been analysed by optical model and the total reaction cross section has been obtained. The reduced reaction cross section has been compared to other stable, tightly bound and weakly bound systems. A high yield of alpha particles has been detected in the 6He+120Sn collision with velocities around the velocity of the scattered 6He. Angular distributions of these alpha particles have been obtained. Theoretical calculations of the breakup of the 6He (CDCC), fusion-evaporation and neutron transfer to bound states and to the continuum indicate that the neutron transfer is the process which best explains the data.
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Zhao, Song 1964. "Defect reactions and impurity control in silicon." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/8635.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1997.Includes bibliographical references (p. 225-234).
This Ph.D. thesis has covered the scientific issues of defect reactions involving dopants and impurities in Si, and the applications of this knowledge to reactive ion etching (RIE) and Fe gettering processes. The reactions among self-interstitials (Sii), vacancies (V), impurities (C, 0), and dopants (B, P) in Si produce undesirable defects which affect device operation and control transport processes such as dopant diffusion. Electron beam irradiation has been used to generate Sii and V to initiate the defect reactions. Deep level transient spectroscopy (DLTS) has been used to identify specific defects and to measure defect concentrations. The experimental results can be summarized in terms of a complex hierarchy diagram of defect reactions. We describe the defect reactions as a three-step process: (i) the displacement reaction to generate Sii and V, (ii) the Watkins replacement reaction to generate C and B interstitials (Ci, Bi), and (iii) the diffusion limited pairing and clustering processes to generate defect pairs and clusters. On the basis of reaction kinetics, we have simulated the reaction processes. The interstitial migration enthalpy (Him) and capture radius (r,) are two parameters used in the model to describe the long range migration and the near neighbor capture of mobile interstitials. The calculated defect reaction rates are in good agreement with the experimental data. We conclude that the diffusion limited pairing reactions are the predominant processes in the defect reactions. The reaction kinetics are determined by Him, r,, and the background dopant and impurity concentrations. The model supports the defect assignments by DLTS. The model can be improved by including pair breakup processes and large interstitial clusters.
(cont.) RIE causes substrate surface contamination, substrate damage, and induces defect reactions at depths extending to um range. We have applied the defect reaction model to RIE and developed a model describing interstitial injection for the defect reaction region to evaluate the defect depth profile. The reaction kinetics is formulated as a series of coupled 1-D interstitial diffusion-reaction partial differential equations (PDEs) with a moving boundary. The model predicts the profiles which are consistent with that measured in the photoluminescence (PL) experiments. We conclude that the depth profile is determined by the interstitial diffusion coefficient, the etch rate, the etch time, the interstitial defect reaction rate, and the background dopant and impurity concentrations in the Si substrate. The um range depth profile can be explained as: (i) fast diffuser Sii injection to ,um depth range; (ii) the generation of Bi and Ci by the Watkins replacement reactions, and (iii) the formation of Bi- and Ci-related defects through diffusion limited pairing reactions. The injection of Bi or Ci is extremely shallow during a typical RIE process. Fe is incorporated into Si as a highly mobile and soluble interstitial species (Fei) during device processing or in the starting materials. Fei and Group III impurities (B, Al, Ga, In) form Fe-acceptor (FeiAs) pairs in Si. Both Fei and the FeiAs pairs introduce deep levels in the bandgap which act as recombination centers. The long range Coulomb interaction between Fei and As is the driving force for the FeiAs pair formation. The short range near neighbor interactions determine the specific FeiAs pair energetics and structures. We have studied the FeiAs pairs within the framework of an ionic model. ...
by Song Zhao.
Ph.D.
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Hashim, Hasnita. "Heavy ion transfer reactions." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306004.
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Van, Zyl Johannes Jacobus. "The role of a direct knock-out mechanism in the inclusive (p, \03B1) reaction /." Link to the online version, 2008. http://hdl.handle.net/10019/797.
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Glossop, Michael William. "Calorimetry of 'red-oil reactions'." Thesis, London South Bank University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299211.
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Souza, Francisco de Assis. ""Identificação de mecanismos em reações induzidas por núcleos fracamente ligados"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-22012007-153428/.
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Neste trabalho, a significativa importância dos processos de breakup, fusão incompleta e transferência para o sistema de massa intermediaria 'ANTPOT.6 Li' + 'ANTPOT.59 Co', envolvendo o núcleo estável e fracamente ligado 'ANTPOT.6 Li', é investigada em energias próximas à barreira Coulombiana. Foram realizadas medidas das distribuições angulares das partículas leves nas energias 'E IND.lab' = 18, 22, 26 e 30 MeV, espalhamento elástico nas energias 'E IND.lab' = 12, 18, 22, 26 e 30 MeV e medidas de fusão total (completa+incompleta), por meio do método de espectroscopia 'gama', nas energias 12 MeV < 'E IND.lab' < 26 MeV. As previsões para evaporação do núcleo composto por partículas leves foram baseadas no modelo estatístico, e uma descrição simultânea dos processos de espalhamento elástico, fusão e breakup foi obtida por meio de cálculos de canais acoplados com discretização do contínuo (CDCC). Com base nestes resultados, realizamos a separação das contribuições dos processos de breakup, fusão incompleta e transferência. Por meio de medidas de coincidência entre d e 'alfa', obtivemos as distribuições angulares para o breakup seqüencial do 6Li. Os processos de espalhamento elástico e fusão total do sistema 'ANTPOT.7 Li' + 'ANTPOT.59 Co', e suas descrições sob o formalismo de CDCC também foram estudadasIn the present work, the relative importance of breakup, incomplete fusion and transfer processes is investigated in the vicinity of the Coulomb barrier for the intermediate mass target 6Li + 59Co reaction involving the weakly bound 6Li. Measurements for light particle angular distributions were performed at energies Elab = 18, 22, 26 e 30 MeV,elastic scattering at energies Elab = 12, 18, 22, 26 e 30 MeV and total fusion (complete+incomplete), by the -ray spectroscopy method, at energies 12 MeV < Elab < 26 MeV. The compound nucleus decay by light particles was predicted using the statistical model, and a simultaneous description of scattering, fusion and breakup was obtained by means of continuum discretized coupled-channels calculations (Cdcc). Based on these results, the contribution of non-capture breakup, incomplete fusion and transfer were disentangled. The 6Li sequential breakup cross sections were obtained by means of ´alfa´-d coincidence measurements. The Cdcc descriptions of 7Li + 59Co elastic scattering and fusion processes were also subject of study.
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Murata, Jiro. "Nuclear Calorimetry on GeV Proton Induced Target Multifragmentation Reactions." 京都大学 (Kyoto University), 1999. http://hdl.handle.net/2433/181434.
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Oliver, Pam 1949. "Young people's reactions to nuclear issues : a constructivist analysis." Thesis, University of Auckland, 1992. http://hdl.handle.net/2292/1998.
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The 1980s saw an increasing interest amongst psychologists, both as researchers and as practitioners, in the ways in which people react to nuclear weapons issues, especially the perceived threat of nuclear war. Much of the research in relation to "nuclear threat", undertaken either within the United States or by United States psychiatrists in collaboration with European colleagues, and using extensive questionnaire surveys, focused on the fears of children and teenagers. Some researchers concluded that large proportions of young people were at risk of impaired psychological development because of nuclear threat which resulted in a pervasive sense of futurelessness and a distrust of .adults. This research has been widely criticised since because of apparent researcher bias in the methods used, interpretations offered, and general paradigm. I also found much of the research ethically objectionable. My research has involved 52 interviews with young New Zealanders and administration of a questionnaire to more than 2000 others, including ages nine to 18 and three ethnocultural groups, as well as interviews with some teachers. The objectives of these studies were: (1) to produce detailed information about how young New Zealanders react to nuclear weapons issues which might be used by educationalists, mental health professionals, parents, and young people themselves in dealing with those issues; (2) to make specific recommendations about young New Zealanders' apparent needs and preferences for learning about and dealing with nuclear weapons and related issues; (3) to provide a detailed methodological comparison of interview and questionnaire approaches to this research topic, and discuss issues of theory and paradigm; and (4) to comment on ethical and practical issues for both the researcher and the researched in undertaking research on emotive and potentially distressing topics, especially with young people. As a result Chapter 1 of my thesis contains a comprehensive critical review of the international research and theory relating to young people's perceptions of nuclear weapons, examining the problems of method, interpretation and paradigm associated with this area of research. Both interview and survey data are presented in relation to: (a) young people's levels of awareness and sources of information about nuclear issues; (b) their emotional, cognitive and behavioural reactions to nuclear issues, including coping strategies and activism: (c) their perceptions of the future; (d) comparisons across gender, age and ethnocultural group; (e) the role of adults; and (f) differences between New Zealanders and other national groups. The data are discussed in terms of: (i) their patterns, contexts and meanings; (ii) their implications for peace and global issues education; and (iii) their implications for research method, including ethical issues. Recommendations are made for how psychologists and others can help young people and adults in dealing with global and social threats, including how to undertake research which is empowering as well as valid and useful.
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Chadwick, Mark Benjamin. "The theory of pre-equilibrium processes in nuclear reactions." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257655.
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Lotay, Gavin James. "Gamma-ray spectroscopy measurements for nuclear reactions in novae." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3893.
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The 23Mg(pγ)24Al and 26Al(pγ)27Si astrophysical reactions are expected to be of considerable importance in the nucleosynthesis of A≥20 nuclei in classical novae. Previous studies have indicated that both reactions are dominated by resonant capture to excited states, above the proton-emission thresholds, in the proton-rich nuclei 24Al and 27Si, respectively. Consequently, by determining the nuclear properties of such resonant states it is possible to estimate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. In this thesis work, excited states in 24Al and 27Si were populated via the 10B(16O, 2n) and 12C(16O, n) heavy-ion fusion-evaporation reactions, respectively. The beams of 16O ions were produced by the Argonne Tandem Linear Accelerator System and prompt electromagnetic radiation was detected using the GAMMASPHERE detector array, which, in the case of the 24Al experiment, was used in coincidence with recoil selection provided by the Argonne Fragment Mass Analyzer. The two γray spectroscopy studies performed in this work allowed level structure determinations below the respective proton-emission thresholds of 24Al and 27Si nuclei, with improved precision on previous work. In addition to this, these studies also allowed a determination of the nuclear properties of proton-unbound astrophysically important γ decaying states, which, in turn, were used to re-evaluate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. The improved precision of the level energies and unambiguous assignments of resonant states has reduced the relative uncertainties in both the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates, constraining the production of A≥20 nuclei in classical novae.
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Guo, Fanqing. "Nuclear reactions with 11C and 14O radioactive ion beams." Berkeley, Calif. : Oak Ridge, Tenn. : Lawrence Berkeley National Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/840236-JlqxbQ/native/.
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Thesis (Ph.D.); Submitted to the UNIVERSITY OF CALIFORNIA, BERKELEY, CA (US); 9 Dec 2004.Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56744" Guo, Fanqing. USDOE Director. Office of Science. Office of Nuclear Physics (US) 12/09/2004. Report is also available in paper and microfiche from NTIS.
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Smith, Barry. "Naturally occurring nuclear reactions in rock formations and groundwaters." Thesis, University of Bath, 1989. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235804.
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Denke, Robson Zacarelli. "Fator S astrofisico para a reação de captura 4He(t,g)7Li pela investigação da reação de transferência elástica no sistema 7Li + 4He." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-30052007-170452/.
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Neste trabalho obtivemos o coeficiente de normalização da parte não ressonante da reação de captura 3H(alpha,gama)7Li (ou alternativamente, o fator S astrofísico) aplicando o método indireto ANC (Coeficientes de Normalização Assintótica) para a reação de transferência elástica do sistema 7Li + 4He. Essa reação de captura é de suma relevância na nucleosíntese de elementos leves no Universo primordial. Nesse método, o fator espectroscópico (ou alternativamente, o ANC) é obtido pela investigação de uma reação de transferência periférica que contenha como vértice a correspondente reação de captura. Reações de transferência têm normalmente dois vértices e um deles deve ser conhecido para que possamos obter o outro. No caso de uma transferência elástica, cuja característica é que o canal de saída elástico e de transferência são os mesmos, existe a vantagem da necessidade de consideração de apenas um vértice. Assim, uma análise combinada da distribuição angular para o espalhamento elástico 4He(7Li,7Li)4He, e para a reação de transferência 4He(7Li,4He)7Li, permitiu a extração do fator espectroscópico e consequentemente do ANC para o estado ligado <3He|4He>=7Li de uma forma única. As distribuições angulares para esses processos foram medidas no Laboratório Pelletron de São Paulo em duas energias de centro de massa 9.67 MeV e 10.62 MeV. Utilizamos nessas medidas feixes de 7Li obtidos no acelerador Pelletron com as energias de laboratório de 26.6 e 29.2 MeV. Empregamos um alvo gasoso de 4He e um sistema de colimadores de dupla-fenda na detecção. As partículas de 7Li espalhadas elasticamente e as partículas alfa da reação de transferência foram ambas detectadas em ângulos de laboratório diânteiros por um sistema de telescópios delta E - E com detectores de silício. Um código de simulação de Monte Carlo foi desenvolvido para calcular o ângulo sólido para esse sistema de fendas em ângulos próximos de zero grau. Um conjunto de parâmetros globais do Modelo Óptico foi obtido da análise das distribuições angulares do espalhamento elástico do sistema 7Li + 4He, juntamente com outras distribuições angulares obtidas da literatura em diferentes energias (~ 7-32 MeV). Os parâmetros do potencial óptico encontrados foram usados em uma análise de DWBA (Aproximação de Born de Ondas Distorcidas) para descrever a contribuição da reação de transferência de um tritio nas distribuições angulares. O fator espectroscópico obtido para o sistema ligado <3He|4He>=7Li foi S = 0.55+-0.03 e o coeficiente ANC C2 = 17.5 +- 1.0 fm-1. Com estes resultados, a seção de choque de captura para a reação 3H(alpha,gama)7Li e o respectivo fator S astrofísico foram calculados.The normalization coefficient for the non-resonant part of the 3H(alpha,gama)7Li capture reaction (or alternately, the astrophysical S-factor) was obtained with the indirect method ANC (Asymptotic Normalization Coefficients). In this method the spectroscopic factor (or alternately, the ANC) is extracted from the investigation of a peripheral transfer reaction, which involves the same vertex as the corresponding capture reaction. Usually transfer reactions have two vertexes and the spectroscopic factor for one of them has to be known to obtain the other. In this work we investigate the 4He(7Li,4He)7Li elastic transfer reaction to obtain the spectroscopic factor and ANC for the 4He + t = 7Li bound system. The elastic transfer process, where the elastic and transfer exit channels are the same, has the advantage of having only one unknown vertex. Thus, the combined analysisof the angular distribution for elastic 4He(7Li,7Li)4He, and transfer process 4He(7Li,4He)7Li, allowed the extraction of the spectroscopic factor (and ANC) for the <3H|4He>=7Li bound system in an unique way. Angular distributions for these processes were measured at the Pelletron Laboratory at the center of mass energies of 9.67 MeV and 10.62 MeV. In these measurements, the 7Li beams with 26.6 MeV and 29.2 MeV were obtained from the Sao Paulo Pelletron accelerator. A 4He gas target and a double-slit collimator system were used. The 7Li scattered particles and alpha particles from transfer reaction were both detected at forward angles by a set of delta E - E silicon detectors telescopes. A Monte Carlo simulation code was developed to calculate the solid angle for the collimator system near the zero degree. A global optical potential parameters set for the 7Li + 4He system were defined using the measured elastic scattering angular distribution and other angular distributions obtained from the literature at different energies (from ~ 7-32 MeV). These optical potential parameters were used in the DWBA (Distorted Wave Born Approximation) analysis to describe the tritium transfer reaction contribution in the angular distributions. The obtained spectroscopic factor for the <3H,4He>=7Li bound system is S = 0.55+-0.03 and the ANC coefficient C2 = 17.5+-1.0 fm-1. With these results, the 3H(alpha,gama)7Li direct capture cross sections and astrophysical S-factor were calculated.
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Gouffon, Philippe. "Verificação experimental do espectro de fótons virtuais de quadrupolo elétrico." Universidade de São Paulo, 1986. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-20022014-153207/.
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O presente trabalho apresenta uma tentativa de teste experimental do cálculo do espectro de fótons virtuais de quadrupolo elétrico, medindo a função de excitação (e, ) de um nível isolado 2+ do 24Mg situado em 20.14 MeV. Os resultados são comparados com as previsões dos cálculos mais recentes. A seção de choque duplamente diferencial d2 /ddE foi medida a 48°, 90° e 132° no sistema de laboratório, para energias de excitação do 24Mg entre 19 e 23 MeV. Esta seção de choque foi medida nas energias totais de elétron incidente de 20.0, 20.8, 21.5, 24.0, 26.0, 28.0, 30.0, 32.0, 36.0, 40.0 MeV. São apresentados as medidas experimentais e os valores calculados usando a aproximação de ondas distorcidas (DWBA) para núcleo puntiforme e finito. Como resultado secundário, extraiu-se a intensidade do nível, através do elemento reduzido de matriz de transição B(E2).To test experimentally the quadrupole virtual photon spectrum calculation, the (e,) excitation function of an isolated 2+ level at 20.14 MeV in 24Mg was measured. The most recent calculations in DWBA, including nuclear size effects, are compared to this experimental curve. The differential cross section d2 /d dE was measured at 48°, 90°, and 132° in the laboratory system, for total electron energies of 20.0, 20.8, 21.5, 24.0, 26.0, 28.0, 30.0, 32.0, 36.0, and 40.0 MeV. The reduced matrix element B(E2) of the 20,14 MeV level is extracted as a secondary product of this work.
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Coley, David A. "Deuteron stripping reactions at 80MeV." Thesis, University of Surrey, 1989. http://epubs.surrey.ac.uk/804935/.
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Rozier, Robert. "A study of the kinetics of lithium-oxygen reactions." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14896.
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Condori, Ruben Pampa. "Medidas de espalhamento ressonante 6He+p e da reação 3He(7Be,)6 Be." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27032013-132712/.
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A espectroscopia de núcleos leves como ANTPOT. 6,7 Li e outros no contínuo é ainda um campo relativamente pouco explorado, e a possibilidade de se produzir esses núcleos a partir de canais de entrada envolvendo núcleos exóticos é relativamente recente. Em particular, o estudo do ANTPOT. 7 Li em energias de excitação em torno do limiar ANTPOT. 6 He+p é interessante pois corresponde a uma região próxima ao estado fundamental do exótico análogo isobárico ANTPO. 7 He. Neste trabalho, apresentamos resultados de um estudo do espalhamento ressonante ANTPOT. 6 He+p utilizando feixe de ANTPOT. 6 He. As medidas da função de excitação ANTPOT. 6 He+p foram realizadas no sistema RIBRAS (\"Radioactive Ion Beams in Brasil\") do Instituto de Física da Universidade de São Paulo. O feixe secundário foi produzido mediante a reação primária ANTPOT. 9 Be(ANTPOT. 7 Li, ANTPOT. 6 He). Fez-se pela primeira vez, uso do conjunto de dois solenóides do sistema RIBRAS para purificar o feixe secundário de ANTPOT. 6 He, que incide em um alvo sólido de CH IND. 2, grosso o bastante para parar o feixe incidente de ANTPOT. 6 He. Assim, somente as partículas leves de recuo foram detectados, as quais levam a informação do sistema composto ANTPOT. 7 Li. Dessa forma foram analisados os espectros obtidos das reações p(ANTPOT. 6 He,p) e p(ANTPOT. 6 He,). Além disso realizamos um estudo da reação ANTPOT. 3 He(ANTPOT. 7 Be, )ANTPOT. 6 Be. A experiência foi realizada no CRIB-RIKEN fazendo uso de um feixe puro de ANTPOT. 7 Be e um alvo gasoso de ANTPOT. 3 He. O feixe de ANTPOT. 7 Be tem uma energia de laboratório de E IND. lab= 53.4 MeV e foi produzido pela reação primária de ANTPOT. 7 Li(p, n)ANTPOT. 7 Be usando um alvo criogênico H IND. 2. Existem na literatura estados excitados identificados nos núcleos ANTPOT. 6 Li e ANTPOT. 6 He, mas apenas poucos estados no ANTPOT 6 Be. Além do interesse na estrutura nuclear, a importância destes estados no ANTPOT. 6 Be próximos ao limiar de ANTPOT. 3 He ANTPOT. 3 He a 11.48MeV está principalmente na astrofísica. A possível existência de ressonâncias perto deste limiar poderia trazer fortes implicações na queima próton-próton em estrelas.The spectroscopy in the continuum of light nuclei such as 6,7 Li and others still remains a relatively unexplored field, and the ability to produce these nuclei from entrance channels involving exotic nuclei is relatively recent. In particular, the study of 7Li at excitation energies around the 6He+p threshold is interesting since it corresponds to a region near to the ground state of the exotic analog isobaric 7He. In this work we present the results of the study of the resonant scattering p+6He. The measurements of the excitation function of the system p+6He have been performed in the RIBRAS system (\"Radioactive Ion Beams in Brasil\") of the Institute of Physics of the University of São Paulo. The secondary beam has been produced by the primary reaction 9Be(7Li,6 He). For the first time, the two solenoids of the RIBRAS system have been used to purify the secondary 6He beam, which collides into a solid CH2, thick enough to stop the incident 6He beam. Only the light recoil particles have been detected, which provide information of the compound system 7Li. We analyzed the spectrum obtained from the p(6He,p) and p(6He,) reactions. In addition, we performed a study of the 3He(7Be, )6Be reaction. The experiment has been performed at the CRIB-RIKEN laboratory (Japan), using a pure 7Be beam and a 3He gas target. The 7Be beam had an energy of Elab = 53.4MeV and has been produced by the 7Li(p, n)7Be primary reaction, using a H2 cryogenic target. There are in the literature, excited states identified in the nuclei 6Li and 6He but only a few states in 6Be. Besides the interest in nuclear structure, the importance of these states at 6Be near the threshold of 3He3He at 11.48MeV lies mainly in astrophysics. The possible existence of resonances near this threshold could bring strong implications for proton-proton burning in stars.
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Buthelezi, E. Z. (Edith Zinhle). "Near-target and other heavy residues in the interaction of ¹²C and ¹⁶O with ¹⁰³Rh." Thesis, Stellenbosch : University of Stellenbosch, 2004. http://hdl.handle.net/10019.1/15939.
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Dissertation (PhD)--University of Stellenbosch, 2004.175 Leaves printed single pages, preliminary pages i-xiii and 147 numberd pages. Includes bibliography. List of figures, List of tables.
ENGLISH ABSTRACT: This study forms part of a larger investigation which has as a primary objective the development of a comprehensive theoretical description of all the processes which contribute to the continuum in the interaction of 12C and 16O with nuclei. Previous investigations of 12C and 16O induced reactions on targets with mass close to A = 100 have shown that the experimental excitation functions and recoil range distributions of heavy residues can be reproduced satisfactorily by means of a theoretical model which takes relatively few dominant reaction mechanisms into account. These include the complete fusion of the projectile with the target, the incomplete fusion of break-up α-type fragments (i.e. single α particles, 8Be fragments and for the 16O induced reactions also 12C fragments) with the target and single-nucleon transfer at incident energies above about 15 MeV/nucleon. The mean-field interaction is mainly responsible for these interactions. The thermalization of the intermediate excited nuclei produced in this first stage of the reaction is described by an intranuclear interaction cascade, during which pre-equilibrium emission of particles and clusters may occur, followed by evaporation after statistical equilibrium has been attained. The model also included the probability that break-up α particles may escape with a large fraction of their initial energy after only a few interactions with individual target nucleons following their initial incomplete fusion. The theory also predicted an enhanced isobaric yield for residues with mass similar or near to that of the target. The subsequent analysis of the emission spectra of intermediate mass fragments in these reactions, however, indicated that two additional aspects need to be considered as well in order to reproduce the experimental data. The first is that the projectile may lose a substantial amount of energy in an initial-state interaction before breaking up, which can be described as a friction dissipative process. The second is that several other incomplete fusion channels of “non-α-cluster”- type fragments should also be included in a more complete description of these reactions as their contributions are not negligible. The present study has two main objectives. Firstly, to investigate the isobaric yield in the neartarget mass region by measuring production cross sections for 103Pd, 103mRh and 103Ru. Previous studies only provided data for 103Ag, which constitute only a few percent of the A = 103 isobaric yield. The new data constitute more than 80% of the A = 103 isobaric yield, which provide experimental confirmation of the enhanced isobaric yield in the near-target mass region. The second objective is to perform extensive new calculations of the excitation functions and recoil ranges in order to investigate the predictive power of the extended model in a priori calculations for the entire available data set.
AFRIKAANSE OPSOMMING: Hierdie studie maak deel uit van ‘n meer omvattende ondersoek wat as ‘n primêre doelwit die beskrywing van al die bydraende prosesse tot die kontinuum in die interaksie van 12C en 16O met kerne behels. In vorige ondersoeke van 12C en 16O geïnduseerde reaksies op skywe met massa naby A = 100 kon die eksperimentele opwekkrommes van swaar reskerne en reikwydte distribusies van terugslagkerne bevredigend gereproduseer word met behulp van ‘n teoretiese model wat slegs enkele dominante reaksiemeganismes in berekening bring. Hierdie sluit in die volledige versmelting van die projektiel met die skyfkern, die onvolledige versmelting van opbreek α-tipe fragmente (d.w.s. α- deeltjies, 8Be fragmente, en in die geval van 16O geïnduseerde reaksies ook 12C fragmente) met die skyfkern, en enkel-nukleon oordrag by invalsenergië wat hoër is as ongeveer 15 MeV/nukleon. Die gemiddelde-veld interaksie is hoofsaaklik verantwoordelik vir bogenoemde reaksie meganismes. Die oorgang na termiese ewewig van die opgewekte tussenkerne wat in hierdie eerste stadium van die reaksie gevorm word, word beskryf deur ‘n intrakern interaksie kaskade wat gekenmerk word deur die voorewewigs emissie van deeltjies en klonte van deeltjies, gevolg deur verdamping nadat statistiese ewewig bereik is. Dié model sluit ook die waarskynlikheid in dat opbreek α-deeltjies kan ontsnap met ‘n betekenisvolle fraksie van hul aanvanklike energie na slegs enkele interaksies met individuele skyfnukleone nadat hulle aanvanklik onvolledig versmelt het. In latere studies van die emissiespektra van intermediêre massa fragmente in hierdie reaksies het dit egter geblyk dat twee addisionele aspekte ook in berekening geneem moet word om die eksperimentele data te reproduseer. Eerstens kan die projektiel ‘n substansiële hoeveelheid energie verloor in ‘n aanvangstoestand interaksie voordat dit opbreek, wat beskryf kan word as ‘n wrywingdissipatiewe proses. Tweedens kan verskeie ander onvolledige versmeltingskanale van fragmente met ‘n nié-α-karakter ook betekenisvol bydra en kan hulle dus nie verwaarloos word in ‘n meer volledige beskrywing van hierdie reaksies nie. Die huidige studie het twee hoofdoelwitte. Eerstens word die isobariese opbrengs in die nabyskyfgebied ondersoek deur die produksie kansvlakke van 103Pd, 103mRh en 103Ru te meet. In vorige studies is slegs data verkry vir 103Ag, wat net ‘n klein persentasie van die A = 103 isobariese opbrengs verteenwoordig. Die nuwe data verteenwoordig meer as 80% van die A = 103 isobariese opbrengs, wat eksperimetele bevestiging verleen dat ‘n verhoging in die isobariese opbrengs in die nabyskyfgebied bestaan. Die tweede doelwit is om ‘n volledige stel nuwe a priori berekeninge te doen vir al die opwekkrommes van reskerne en reikwydte distribusies van terugslagkerne wat tans beskikbaar is om sodoende die voorspellings van die nuwe uitgebreide teoretiese model te toets.
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Barros, Cristian Javier Caniu. "Alpha Particles in Effective Field Theory." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-13012015-131131/.
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In this thesis we work on the problem of the two-alpha-particle system using a halo/- cluster effective field theory (EFT). Our goal is to address the alpha-alpha scattering observables and its low-energy resonance identified as the ground state of Beryllium-8. In this work we start with an EFT in which the degrees of freedom are the alpha particles interacting via momentum-dependent contact forces. These, in contrast to forces that are energy-dependent, are more useful in extending the theory to systems with more than two alpha particles. Additionally, momentum-dependent forces allow us to address causal restrictions on scattering observables, known as the Wigners causality bound. We present our EFT calculations for the alpha-alpha system.Nesta tese, nós trabalhamos sobre o problema do sistema de duas partículas alfa utilizando uma teoria de campos efetiva. O nosso objetivo é abordar os observáveis e a ressonância do sistema alfa-alfa de baixa energia identificada como o estado fundamental do berílio-8. Neste trabalho nós começamos com uma teoria de campo efetiva em que os graus de liberdade são as partículas alfa interagindo via forças de contato dependentes do momento. Estes, em contraste com as forças que são dependentes da energia, são mais úteis na extensão da teorias para sistemas com mais de duas partículas alfa. Além disso, forças dependentes do momento nos permitem abordar restrições causais nos observáveis, conhecidas como causalidade de Wigner. Nós apresentamos nossos cálculos para o sistema alfa-alfa.
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Wiedemann, Kenia Teodoro. "Estudo da distribuição angular na emissão de partículas carregadas como ferramenta em espectroscopia nuclear." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-16042009-114144/.
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Técnicas de espectroscopia gama associadas ao estudo de mecanismos de reação têm sido alvo de estudos desenvolvidos em física nuclear. O sistema Saci-Perere (Sistema Ancilar de Cintiladores e Pequeno Espectrômetro de Radiação Eletromagnética com Rejeição de Espalhamento) foi utilizado para esse tipo de estudo a partir de três experiências de fusão-evaporação, sendo elas: 11B+100Mo, utilizando um alvo de 100Mo de 16 mg/cm2 e com Efeixe = 43 MeV , 10B+51V , utilizando três alvos de 51V de 0.2 mg/cm2 e com Efeixe = 33 MeV e 16O+51V , utilizando um alvo de 4.4 mg/cm2 em um backing evaporado de 197Au de 7.7mg/cm2 e com Efeixe = 70 MeV . Foram estudadas as relações entre as energias das transições gama, associadas a diferentes isótopos produzidos nessas reações, com a distribuição angular de partículas carregadas detectadas. Para esse fim, foram construídas e analisadas matrizes em coincidência temporal com partículas carregadas detectadas seletivamente em diferentes ângulos. Foram obtidas razões entre as intensidades dos picos de transições gama em coincidência com partículas carregadas a ângulos dianteiros com aqueles em coincidência com partículas detectadas a ângulos traseiros, em função da energia dos raios gama. Essas razões apresentam-se em faixas nitidamente distintas, de acordo com o isótopo analisado numa mesma reação. O aparecimento de razões distintas para diferentes isótopos foi inicialmente associada à presença de fusão incompleta na população de determinados núcleos residuais. Neste trabalho é demonstrado que, embora desejável, por favorecer a anisotropia na distribuição de partículas emitidas, a presença de fusão incompleta não é uma condição necessária para a obtenção de razões distintas. Foram estimadas as seções de choque experimentais e comparadas com os valores fornecidos pelo programa PACE ( Projection Angular Momentum Coupled Evaporation ), baseado no método de Monte Carlo, que prevê somente o caso de fusão completa. Para as reações 11B+100Mo e 16O+51 V foram feitas simulações para estimar os valores esperados das razões. As simulações foram feitas através do espectro de distribuição de partículas, previsto pelo programa PACE, transferido para o referencial de laboratório e integrado em ângulos restritos. Na reação 10B+51V, a utilização de alvos finos permitiu a determinação da contribuição de fusão incompleta através da análise do deslocamento Doppler das energias das transições gama, de onde foi possível obter a velocidade de recuo dos núcleos residuais e, consequentemente, a velocidade de recuo do sistema composto, comparando-a com o esperado nos casos de população através de fusão completa e incompleta. Os resultados apresentam a possibilidade de utilização das razões obtidas para as áreas das transições gama em função das energias dos raios gama, como ferramenta na identificação de transições canditadas como pertencentes a determinado isótopo emissor deste raio gama.Techniques in gamma-ray spectroscopy, associated with reaction mechanism studies have been developed in nuclear physics. The Saci-Perere array (Sistema Ancilar de Cintiladores e Pequeno Espectrômetro de Radiação Eletromagnética com Rejeição de Espalhamento) was used for this kind of research in three fusion-evaporation reactions: 11B+100Mo (Eb = 43MeV ), with a target of 16mg/cm2 of 100Mo, 10B+51V (Eb = 33MeV), with three targets of 200ug/cm2 foils of 51V, and 16O+51V (Eb = 70MeV), with a target of a 4.4mg/cm2 foil of 51V on a evaporated 7mg/cm2 gold backing. There was studied the relationship between the energies of gamma transitions, associated to different isotopes produced in these reactions, with the angular distribution of emmited particles. For this purpose, there were constructed and analyzed gamma-gamma matrices in coincidence with selected charged particles at different angles. There were measured ratios of gamma-transitions intensities in coincidence with charged particles detected in forward and backward angles, as a function of the gamma-ray energy. These yield ratios are located in clearly different values according with the isotope analyzed in the same reaction. The obtainment of different yield ratios for different isotopes was initially associated with the presence of incomplete fusion in the production of determined residual nuclei. In this work is shown that, even if the presence of incomplete fusion increases the anisotropy in the angular distribution of emmited particles, it is not a necessary condition to obtain different yield ratios. The experimental cross-sections were estimated and compared with the values given by the Monte Carlo code PACE (Projection Angular Momentum Coupled Evaporation), which describe the case of complete fusion. For the reactions 11B+100Mo and 16O+51V, simulations to estimate the expected values of the yield ratios were made. The simulations were made using the spectrum of the angular distribution of emmited particles, given by code PACE, transferred to the laboratory frame and integrated in restrict angles. In the reaction 10B+51V, there were used thin targets, which enable us to determinate the contribution of incomplete fusion throught the analysis of the Doppler shift in the gamma transitions energies, making possible to obtain the recoil velocity of the residual nuclei and, as a consequence, the recoil velocity of the compound system, comparing with the expected in the case of population by complete and incomplete fusion. The results show it\'s possible to use the yield ratios obtained to differentiate candidate gamma transitions, as a useful tool for assigning individual transitions to specific isotopes produced in heavy-ion reactions.
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Alvarez, Marcos Aurelio Gonzalez. "Um método para determinação experimental da densidade da matéria nuclear." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-19022014-141107/.
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Neste trabalho foi proposto um método de deconvolução para extrair experimentalmente a densidade da matéria nuclear no estado fundamental a partir de dados de espalhamento elástico entre íons pesados em energias baixas (abaixo da barreira de fusão) e intermediárias. A consistência dos resultados foi totalmente verificada. O método se mostrou uma poderosa ferramenta para a determinação experimental da densidade da matéria de núcleos no estado fundamental, particularmente em uma região superficial, onde a diferença entre a densidade de núcleos exóticos e núcleos estáveis vizinhos é muito enfatizada. Foram realizadas medidas de seções de choque de espalhamento elástico para os sistemas 16O + 40Ca, 120Sn, com o objetivo de ajudar na construção de uma sistemática experimental para a parte real da interação nuclear, e para obter a densidade experimental da matéria nuclear no estado fundamental para o núcleo 16O. Como complemento, o trabalho apresenta: i-) uma sistemática teórica das densidades nucleares, realizada para toda região de massa da tabela periódica; ii-) o modelo não-local, desenvolvido para descrever a dependência com a energia da parte real da interação nuclear; e iii-) uma nova representação para a absorção de fluxo, devido aos canais de reação. Com isso, foi desenvolvida uma sistematização para o potencial ótico a partir de uma análise consistente de dados de espalhamento elástico de íons pesados em energias baixas e intermediárias. Esta análise resultou em uma previsão extremamente satisfatória para as seções de choque de espalhamento elástico experimentais, para um vasto conjunto de dados, utilizando um modelo bastante fundamental e global para o potencial ótico e, mais importante, sem a utilização de parâmetros livres.An unfolding method is proposed to extract ground-state nuclear matter densities from heavy-ion elastic scattering data analyses at low (sub-barrier) and intermediate energies. The consistency of the results was fully checked. The method is a powerful tool to obtain ground-state nuclear matter densities, particularly at the surface region where the difference between densities of exotic and stable neighbor nuclei is very emphasized. Precise elastic scattering cross sections were measured for the systems 16O + 40Ca, 120Sn, with the aim of helping the construction of an experimental systematics for the real part of the nuclear interaction, and to obtain the experimental ground-state nuclear matter density for the 16O nucleus. As a complement, this work presents: i-) A theoretical systematics for nuclear densities which was performed for the whole mass region throughout the periodic table, ii-) the non-local model, developed to describe the energy dependence of the real part of the nuclear interaction; iii-) a new representation for the absorption of flux due to the reaction channels. This framework has allowed us to obtain a systematization of the optical potential from a consistent heavy-ion elastic scattering data analysis at low and intermediate energies. This analysis resulted a remarkable prediction for a very large elastic scattering cross section data set using a global and fundamental parameter-free model for the optical potential.
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Laid, Abdallah. "Polarisation transfer and breakup effects in deuteron induced nuclear reactions." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/842772/.
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Optical model studies of low energy (d,d) data show that deuteron-nucleus tensor potentials differ from theoretical model predictions. This suggests that measurement of additional observables, such as Polarization Transfer Coefficients (PTC), are needed to complement the existing data. Whether PTCs can clarify the experimental/theoretical ambiguity has been a matter of controversy. The first part of this thesis addresses this problem. We began by investigating whether the PTC, yields new information concerning the deuteron-nucleus tensor potential. We then examined the extent to which this coefficient can distinguish between the two types of tensor forces, Tr and Tp. We showed that Kyzz is strongly affected by tensor force effects, and that the origin of this sensitivity is the bi-linear combination of scattering amplitudes, Im(Q00Q*21). We also found that, for realistic optical mode parameters, T21 and particularly Kyzz discriminate between the effects of both tensor forces. In the second part of this thesis we study the Weinberg State Expansion model (WSE) for (d,p) reactions. The weakly bound structure of the deuteron suggests the relevance of 3-body effects in the dynamics of deuteron stripping. At intermediate energies, the DWBA provides a much less reliable description of particle transfer reactions. Although the adiabatic theory (ADIA) has provided improvements over the conventional DWBA, recent experimental data suggest that it needs to be refined. The WSE method, in which the dominant contributions from the 3-body channels are explicitly included, is a way to systematically improve ADIA which appears as the lowest order solution in the WSE theory. In implementing the WSE model, we found that as the Weinberg basis size N increases more c.m. n-p relative energies are simulated and readily included into the (d,p) calculations. We also showed that, when performing zero-range WSE calculations for 66Zn(d,p)67Zn (G.S.;5l2-;1 =3) at 25 and 88.2 MeV, the results for dsigma/dO and iT11 converge for N=35. Although 35 Weinberg states were used in constructing the new basis, the reaction calculation reduced to a three coupled channels problem. Our calculations are therefore more efficient than the CDCC methods. The WSE results for dsigma/dO and iT11 were also compared against those of equivalent ADIA and Quasi-ADiabatic (QAD) methods. Our findings reveal that: a) the WSE model provides significant corrections to ADIA's predictions and as such constitutes an elegant mathematical justification of ADIA's ideas; b) the WSE results are overall in good agreement with those obtained using QAD.
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Mountford, David James. "Investigations of nuclear reactions relevant to stellar γ-ray emission." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8238.
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The detection of γ-rays from explosive astrophysical scenarios such as novae provides an excellent opportunity for the study of on-going nucleosynthesis in the Universe. Within this context, this work has addressed an uncertainty in the destruction rate of the 18F nucleus, thought to be the primary source of 511 keV γ-rays from novae. A direct measurement of the 18F(p,α )15O cross section has provided the opportunity to extract resonance parameters through the R-Matrix formalism. The inferred parameters of populated states in 19Ne include the observation of a broad 1/2+ state, consistent with a recent theoretical prediction, which will have a significant impact on the rate of destruction of this γ-ray producing radioisotope. The 18O(p,α )15N reaction follows similar nuclear and kinematic processes and is expected to occur in the hydrogen burning layers of AGB stars. Resonance widths have been extracted from a direct measurement in the region around a poorly constrained broad state close to the Gamow window. This has produced a new parameter set for future reference and provides new information on the reaction rate. The complex R-Matrix formalism used in these analyses is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the complex mathematics. This thesis presents a comparison of two publicly available codes from the JINA collaboration and a code used extensively by the University of Edinburgh. For this, the recent results of the 18F destruction reaction, presented here, have been used. A minor error was found within one of the codes, and corrected. The final parameters extracted, and the resulting cross sections calculations, are shown to be consistent between the three codes. A further γ-ray line of interest at 1.809 MeV, characteristic of 26Al decay, has been observed throughout the interstellar medium. If, however, this isotope is formed in a known isomeric state, its decay bypasses the emission of this γ-ray, thus complicating the interpretation of observed γ-ray fluxes. To this end, an experiment has been carried out, providing proof of principle of a direct measurement of the 26mAl(p,γ)27Si reaction. The calculation of the isomeric intensity is presented here.
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Clasie, Benjamin Michael Patrick. "Measurement of nuclear transparency from A(e,e'[pi]⁺) reactions." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/39564.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.In title on t.p., "[pi]" appears as the lower-case Greek letter.
Includes bibliographical references (p. 161-165).
The color transparency phenomenon refers to the suppression of final-state interactions of a hadron propagating through the nuclear medium at large momentum transfer when the hadron is produced with small transverse size. The pion electroproduction cross section from 1H, 2H,12C, 63Cu and 197Au targets from Q2 = 1.1 to 4.8 (GeV/c)2 was measured in Jefferson Laboratory Experiment E01-107. The nuclear transparency was formed by the ratio of ([sigma]A/[sigma]H) from the data and ([sigma]A/[sigma]H) from a model of electroproduction from nuclei that does not include [pi]-N final state interactions. A signature of color transparency is the enhancement of the nuclear transparency at large Q2 compared with predictions based on Glauber multiple scattering theory. This experiment represents the first nuclear transparency data from (e,e'[pi]+) reactions.
by Benjamin Michael Patrick Clasie.
Ph.D.
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McFarland, Eric W. (Eric Wesley). "Nuclear spin transfer studies of chemical reactions in living systems." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/17215.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Harvard-MIT Division of Health Sciences and Technology Program in Medical Engineering and Medical Physics, 1987.Bibliography: leaves 212-227.
by Eric W. McFarland.
Ph.D.
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Luis, Hélio Fernandes. "Study of nuclear reactions relevant for astrophysics by Micro-AMS." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/11274.
Full textAbstract:
Dissertação para obtenção do Grau de Doutor em
FísicaThis work of this thesis was dedicated to the application of the Micro-AMS(Accelerator Mass spectrometry with micro-beam) to the study of nuclear reactions relevant to Astrophysics, namely reactions involving the radioisotope 36Cl. Before this could be done, the system had to be installed, tested and optimized. During the installation and testing phase, several isotopes were measured, principally lead and platinum isotopes, which served to show the potential of this technique for applications to Material science and archeology. After this initial stage, the work with 36Cl began. 36Cl is one of several short to medium lived isotopes (as compared to the earth age) whose abundances in the earlier solar system may help to clarify its formation process. There are two generally accepted possible models for the production of this radionuclide: it originated from the ejecta of a nearby supernova (where 36Cl was most probably produced via the s-process by neutron irradiation of 35Cl) and/or it was produced by in-situ irradiation of nebular dust by energetic particles(mostly, p, a, 3He -X-wind irradiation model). The objective of the present work was to measure the cross section of the 35Cl(n,γ)36Cl nuclear reaction which opened the possibility to the future study of the 37Cl(p,d)36Cl and 35Cl(d,p)36Cl nuclear reactions, by measuring the 36Cl content of AgCl samples with Micro-AMS, taking advantage of the very low detection limits of this technique for chlorine measurements. For that, the micro-AMS system of the CTN-IST laboratory had to be optimized for chlorine measurements, as to our knowledge this type of measurements had never been performed in such a system (AMS with micro-beam). This thesis presents the results of these developments, namely the tests in terms of precision and reproducibility that were done by comparing AgCl blanks irradiated at the Portuguese National Reactor with standards produced by the dilution of the NIST SRM 4943 standard material. With these results the cross section of the 37Cl(n,γ)36Cl was calculated.
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Cresswell, Alan James. "Studies of nuclear structure using heavy ion-induced transfer reactions." Thesis, University of Liverpool, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240215.
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Lombardo, Ivano. "N/Z Effects on Nuclear Reactions Near the Fragmentation Threshold." Thesis, Universita' degli Studi di Catania, 2011. http://hdl.handle.net/10761/123.
Full textAbstract:
Effects due to the neutron to proton ratio (N/Z) degree of freedom in nuclear reactions involving calcium beams at 25 MeV/nucleon have been investigated. For central collisions, we found that the competition between evaporation residue emission and binary-like phenomena is related to the neutron richness of the total system. The described experimental findings open the way for further investigations with radioactive beams.
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Zhao, Xianfeng 1971. "Micro-heterogeneous thorium based fuel concepts for pressurized water reactions." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8680.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001.Includes bibliographical references (p. 139-143).
The purpose of this work is to evaluate the potential for enhancing the performance of the once-through PWR fuel cycle by appropriate design of thorium containing fuel with concurrent consideration of neutronics, thermal-hydraulics, and proliferation resistance. CASMO-4 is employed to model a fuel assembly consisting of a homogeneously fueled ThO2-UO2 lattice of conventional design. It is found that homogeneously mixed ThO2-UO2 fuel in general has better physics behavior than all-UO2 fuel, e.g. more negative MTC and less reactivity swing. The H/HM ratio can be optimized to extend the burnup of both ThO2-UO2 and all-UO2 fuel about 10% and 5% respectively. However, it is found that the all-UO2 fuel provides higher potential energy generation (or achievable burnup) than the homogeneously mixed ThO2-UO2 fuel. MOCUP (MCNP+ORIGEN) is used to model unit cells of the micro-heterogeneous fuel. The key findings for the best micro-heterogeneous configurations are as follows: (1) For a given U-235 inventory, a 20% to 30% increase in fuel cycle achievable bumup above the homogeneous case is possible, therefore 10% to 15% above the all-UO2 fuel; (2) For certain axially heterogeneous configurations, a "burnable poison" reactivity suppression effect appears at the beginning of irradiation. Analysis of the possible mechanisms behind these effects shows that they are due to a combination of changes in self-shielding, local fissile worth, and conversion ratio.
(cont.) Economic evaluations show that the homogeneous ThO2-UO2 fuel is 20%-30% more expensive than the equivalent all-U fuel but micro-heterogeneous fuel can be comparable to or even cheaper than the all-UO2 fuel. In terms of the plutonium content, the micro-heterogeneous Th/U fuel is more proliferation-resistant than the homogeneous Th/U fuel, and the homogeneous Th/U fuel is more proliferation-resistant than the all-UO2 fuel. However, the uranium produced in the ThO2 zone of any undenatured micro-heterogeneous design should be considered of proliferative concern. Adding natural or depleted uranium to the ThO2 zone can make the material not weapon-usable at the expense of degrading the neutronic performance. Placing some enriched uranium within the thorium zone may be needed to reduce local thermal peaking to a manageable level.
by Xiaofeng Zhao.
Ph.D.