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.

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.

Foi investigada a produção de isótopos ricos em nêutrons a partir do decaimento de projéteis de \'ANTPOT.28 Si\' com momento de \'P IND.lab\'= 14.6 GeV/c por nucleon seguindo a excitação eletromagnética por alvos de Al, Cu, Sn e Pb. A busca foi feita selecionando fragmentos ricos em nêutrons (\'ANTPOT.6 He\', \'ANTPOT.8 He\',\'ANTPOT.8 Li\', \'ANTPOT.9 Li\', \'ANTPOT.10 Be\', \'ANTPOT.11 Be\' e \'ANTPOT.13 B\') detectados no espectrômetro do Experimento 814 do AGS de Brookhaven. Foi estabelecido um limite superior de 54 ub (a um Nível de Confiança de 95%) para a seção de choque de dissociação eletromagnética para um único canal, baseado num conjunto com ~3x \'10 POT.7\' partículas de feixe. Foram medidas seções de choque de produção de isótopos ricos em nêutrons por fragmentação nuclear e obtidas as distribuições de energia transversal e energia a zero graus associadas à produção destes fragmentos. As distribuições de momento transversal para o \'ANTPOT.6 He\' e para o \'ANTPOT.9 Li\' foram medidas experimentalmente e os resultados comparados ao modelo estatístico de Goldhaber para a fragmentação. A comparação fornece um valor médio de 229±9 MeV/c para o momento de Fermi do projétil. / The production of neutron-rich isotopes from the decay of 28Si projectile at Plab = 14.6 GeV/c per nucleon following the electromagnetic excitation by Al, Cu, Sn and Pb targets was investigated. The search was made triggering on neutron-rich ions (6He, 8He, 8Li, 9Li, 10Be, 11Be and 13B) detected in the BNL-AGS-E814 spectrometer. An upper limit of 54 ub (at the Confidence Level of 95%) for the electromagnetic dissociation cross-section for an individual channel is set, based on a data sample of ~ 3 x 107 beam particles. Inclusive cross section for the nuclear fragmentation production of those isotopes were measured and forward and transverse energy distribuitions were determined. From a comparison of the experimental momentum distributions for 6He and 9Li with the Goldhaber statistical fragmentation model an average value of 229±9 MeV/c for the Fermi momentum of the 28Si projectile was obtained.

Neste trabalho, foram estudadas as reações envolvendo núcleos pesados e prótons no regime de energias intermediárias e altas através de simulações computacionais com o modelo Monte Carlo CRISP (Colaboração Rio - Ilhéus - São Paulo). Os principais processos nucleares investigados foram a cascata intranuclear e a competição evaporação-fissão. Em estudos preliminares, determinou-se que o CRISP reproduz satisfatoriamente a multiplicidade de nêutrons de evaporação (E < 20 MeV) da reação p (1200 MeV) + Pb-208 e a produção de resíduos de spallation para p (1000 MeV) + Pb-208. Já o estudo da relação entre multiplicidade de nêutrons e fissão para a reação de prótons com energia até 85 MeV com Th-232 indicou que o CRISP superestimou as emissões, enquanto subestimou a seção de choque de fissão dessa reação - reflexo das limitações do modelo de cascata nuclear para baixas energias (da ordem de 50 MeV). A reação p (1200 MeV) + Pb-208 foi escolhida para o estudo de uma fonte de nêutrons de spallation. A cascata intranuclear foi responsável pela emissão dos nêutrons energéticos da reação (E > 20 MeV), enquanto que a evaporação foi responsável pelo maior número de nêutrons emitidos. A seção de choque de fissão encontrada foi de 209 mb, enquanto que a de spallation foi de 1788 mb - ambas comparáveis aos valores experimentais. A distribuição de massa dos fragmentos indicou fissão simétrica. Finalmente, foi utilizado outro código Monte Carlo, o MCNP, para o transporte de radiação, a fim de compreender o papel da fonte de nêutrons de spallation em um reator nuclear ADS (Accelerator Driven System). Simulou-se um reator PWR, inicialmente, para estudar a produção de nuclídeos no processo de queima do combustível nuclear. Em seguida, simulou-se uma primeira tentativa de adaptação de uma fonte de spallation a um reator térmico de dimensões industriais. Constatou-se que não houve redução da concentração de elementos transurânicos com o modelo de reator adotado e alterações foram propostas. / In the present work, intermediate- and high-energy nuclear reactions involving heavy nuclei and protons were studied with the Monte Carlo CRISP (Rio - Ilhéus - São Paulo Collaboration) model. The most relevant nuclear processes studied were intranuclear cascade and fission-evaporation competition. Preliminary studies showed fair agreement between CRISP model calculation and experimental data of multiplicity of evaporated neutrons (E < 20 MeV) from the p (1200 MeV) + Pb-208 reaction and of spallation residues from the p (1000 MeV) + Pb-208 reaction. The investigation of neutron multiplicity from proton-induced fission of Th-232 up to 85 MeV showed that it was being overestimated by CRISP model; on the other hand, fission cross section were being underestimated. This behavior is due to limitations of the intranuclear cascade model for low-energies (around 50 MeV). The p (1200 MeV) + Pb-208 reaction was selected for the study of a spallation neutron source. High-energy neutrons (E > 20 MeV) were emitted mostly in the intranuclear cascade stage, while evaporation presented larger neutron multiplicity. Fission cross section of 209 mb and spallation cross section of 1788 mb were calculated - both in agreement with experimental data. The fission process resulted in a symmetric mass distribution. Another Monte Carlo code, MCNP, was used for radiation transport in order to understand the role of a spallation neutron source in a ADS (Accelerator Driven System) nuclear reactor. Initially, a PWR reactor was simulated to study the isotopic compositions in spent nuclear fuel. As a first attempt, a spallation neutron source was adapted to an industrial size nuclear reactor. The results showed no evidence of incineration of transuranic elements and modifications were suggested.

This study gives the details about several experiments done in Eugene Mallove Laboratory for New Energy Research. Three experiments are presented and discussed in detail with different type of microscopes and mass spectrometry techniques. Also inspired by work done by Rolison and O'Grady [1], the other part of this study presents the variation of isotopic abundance after experiments on palladium cathode immersed in a heavy water electrolyte. This original inspiring paper has been published through proceedings of the first edition of International Conference on Cold Fusion held in Washington D.C. in 1989. In other words, both works provides similar evidence of an isotopic variation before and after low energy nuclear experiments. By measuring the variation in isotopic concentration, before and after electrolysis, these measurements provide insight for how the low energy nuclear phenomenon occurs. Scanning electron microscopes are used in the first part to provide high resolution, high magnification images of the electrodes. They show the morphology the topology of the cathode after experiment. An energy dispersive mass spectrometer is used to provide elemental composition of the cathode and provide a second independent measurement of elemental composition of the cathode. The presented isotopic measurements are made with a secondary ion mass spectrometer. [1]: D. Rolison & W. O'Grady - Mass/Charge Anomalies in Pd after electrochemical loading with deuterium - Section 10 in Proceedings: EPRI-NSF Workshop on Anomalous Effects in Deuterided Metals - (October 16-18, 1989) Washington, D.C.

The principal goal of this thesis is to highlight a possible "neutron skin" effect in the nuclear reaction mechanisms between heavy ions at energies around 6 MeV/nucleon. To this end, the reactions 58Ni+122Sn at 354 and 375.5 MeV and 64Ni+116Sn at 382.5 MeV were carried out at the CYCLONE accelerator in Louvain-la-Neuve. The projectile Ni and the target Sn were selected because of their magicity in proton. This characteristic implies the existence of a proton core more bound and of a neutron peripheral distribution in the isotopes 64Ni and 122Sn, rich in neutrons. The first goal was, to observe the possible influence of these neutrons on the fusion probability between the projectile and the target. In addition, the two types of reactions were selected in order to produce the same compound nucleus (180Pt) with the same excitation energy or with the same angular momentum. Thus, the effect of a neutron skin could be observed from the point of view of the production as from the point of view of the de-excitation of the compound nucleus. This de-excitation can proceed by evaporation of light particles or by fission. So, on the one hand, the fusion, fusion-evaporation and fusion-fission cross sections, and, on the other hand, the multiplicities of the light particles (neutrons, protons or alpha) emitted by the compound nucleus or by the fission fragments should have been compared. The experimental realization of this project required the use of the neutron detection system DEMON made up of 90 liquid scintillators laid out on a 4 m in diameter sphere which contain an aluminium chamber under vacuum. The chamber contained two multi-wire proportionnal counters XY intended for the detection of the fission fragments, two systems of Silicon junctions coupled with microchannels intended for the detection of evaporation residues and finally six triple Silicon telescope intended for the detection of the light charged particles (protons and alpha). At the end of the analysis, it was shownthat the cross sections of fusion are identical, within the error bars (about 10 %), for the two types of studied reactions.Also, it was observed that the possible compound nucleus de-excitations are independent of its production, as well on the competition between fission and evaporation as on the light particle emission. No effect of neutron skin was thus highlighted in the nuclear reaction mechanisms leading to fusion of the target and the projectile at energy around 6 MeV/nucleon. An effect seems nevertheless to appear in the nucleons transfer reactions in which the compound nucleus does not amalgamate. ------------------------------------------------ L'objectif principal de cette thèse est de mettre en évidence un éventuel effet de "peau de neutrons" dans les mécanismes des réactions nucléaires entre ions lourds à des énergies de l'ordre de 6 MeV/nucléon. Dans ce but, les réactions 58Ni+122Sn à 354 et à 375.5 MeV et 64Ni+116Sn à 382.5 MeV ont été réalisées auprès de l'accélérateur CYCLONE de Louvain-la-Neuve. Le projectile Ni et la cible Sn ont été choisis en raison de leur magicité en proton. Cette caractéristique implique l'existence d'un coeur de protons plus liés et d'une distribution plus périphérique des neutrons dans les isotopes 64Ni et 122Sn, riche en neutrons. Il s'agissait donc, dans un premier temps, d'observer l'influence possible de ces neutrons excédentaires sur la probabilité de fusion du projectile et de la cible. D'autre part, les deux types de réactions ont été choisis afin de produire le même noyau composé 180Pt de même énergie d'excitation ou de même moment angulaire. Ainsi, l'effet de peau de neutrons pouvait être observé tant du point de vue de la production que du point de vue de la désexcitation du noyau composé. Cette désexcitation peut se faire par évaporation de particules légères ou par fission. Plus précisement, il s'agissait de comparer, d'une part, les sections efficaces de fusion, de fusion-évaporation et de fusion-fission, et, d'autre part, les multiplicités des particules légères (neutrons, protons ou alpha) émises par le noyau composé ou les fragments de fission. La réalisation expérimentale de ce projet a nécessité l'utilisation du système de détection de neutrons DEMON constitué de 90 scintillateurs liquides disposés sur une sphère de 4 m de diamètre au centre de laquelle une chambre en aluminium était mise sous vide. Celle-ci contenait deux chambres à gaz et à multi-fils XY destinés à la détection des fragments de fission, deux systèmes de jonctions au Silicium couplées à des galettes à micro-canaux destinés à la détection de résidus d'évaporation et enfin six triple-téléscopes au Silicium destinés à la détection des particules chargées légères (protons et a). Au terme de l'analyse des données récoltées, il s'avère que les sections efficaces de fusion du projectile et de la cible sont identiques, dans une barre d'erreur de l'ordre de 10 %, pour les deux types de réactions étudiées. De même, il a été observé que les désexcitations possibles du noyau composé sont indépendantes de sa production, tant sur la compétition entre fission et évaporation que sur l'émission de particules légères. Aucun effet de peau de neutrons n'a donc été mis en évidence dans les mécanismes des réactions nucléaires impliquant la fusion du projectile et de la cible. Un effet semble néanmoins apparaître dans les réactions d'échanges de nucléons dans lesquelles les noyaux ne fusionnent pas.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Adam J. Sarty, Florida State University, College of Arts and Sciences, Dept of Physics. Title and description from dissertation home page (viewed Apr. 08, 2004). Includes bibliographical references.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Kirby W. Kemper, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Nov. 20, 2003). An arrow pointed to the right over the Li in title. Includes bibliographical references.

No description available.

A study has been made of the 90 Zr(n,d) 89 Y reactlion at an incident neutron energy of 22 MeV. The experimental aspect of the study was performed at the Van der Graaf facility at the National Accelerator Centre, using a particle spectrometer developed by K Bharuth-Ram and W R McMurray for the study of neutron-induced charged-particle emissions. The spectrometer, which consists of a telescope of three multiwire proportional counters and a curved plastic scintillator, permits the simultaneous accumulation of data over an angular range of 80°. Solid-angle- calculations have been performed to correct for the effect of the geometry of the system on the angular distribution of the cross-sections. A review has been made of the shell model of the nucleus, the optical potential model and the distorted waves method (or DWBA) for the analysis of direct nuclear reactions. A distorted-waves method analysis of the reaction is performed with the code DWUCK 4 and the resulting angular distribution of the various cross-sections are compared with the experimentally obtained data. ThIs comparison produces spectroscopic factors which are used to perform some analysis of the nuclear structure of the 90 Zr nucleus. / Thesis (M.Sc.)-University of Durban-Westville, 1986.