Apresentamos nesse trabalho as medidas de seção de choque absoluta de eletrodesintegração e da taxa de produção da fotodesintegração para a reação 232Th(e,n) 231Th. A análise dos resultados de eletrodesintegração foi realizada pelo método dos fótons com a finalidade de determinar as multipolaridades das transições nucleares envolvidas nessa reação. As medidas foram realizadas no Laboratório do Acelerador Linear do Instituto de Física da USP, tendo se estendido de 7,5 a 26 MeV no caso das medidas de eletrodesintegração e de 20 a 25 MeV no caso das de fotodesintegração. Essas medidas foram feitas para testar a compatibilidade de nossas medidas com as realizadas com o uso de fótons monocromáticos, utilizadas na análise dos resultados de eletrodesintegração. Mostramos que a eletrodesintegração por emissão de um nêutron no tório se processa exclusivamente através de transições de dipolo elétrico. Nossos dados excluem uma contribuição das transições de quadrupolo elétrico maior do que 0,7% da intensidade das transições de dipolo elétrico. A nossa sugestão sobre o decaimento da ressonância isoescalar de quadrupolo elétrico é que este deve se processar preferencialmente pelo canal de fissão, comportamento similar ao do 238U. / The results of the absolute electro disintegration cross section as well the photodisintegration yield of the reaction 232Th(e,n) 231Th, are reported. We used the virtual photon formalism in the analysis of the electro disintegration data in order to establish the multipolarities of the nuclear transitions involved in the reaction. The measurements have been performed using the electron beam of the Linear Accelerator of the IFUSP, ranging from 7,5 to 26 MeV for the electro disintegration and from 20 to 25 MeV for the photodisintegration data. The photodisintegration yield has been measured to check the agreement between our data and those obtained with monochromatic photons, which are used in the analysis of the electro disintegration data. We show that electro disintegration by one neutron emission in thorium can be explained by a E1 process. Our data set up an upper limit to the E2 contribution of 0,7% of the E1 strength. We suggest that the isoescalar giant electric quadrupole resonance (GQR) decays dominantly through the fission channel, as in the 238U case.

Orientador: Fernando J. da Paixão / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-14T04:11:13Z (GMT). No. of bitstreams: 1 Franca_Adriana_M.pdf: 3043177 bytes, checksum: e3a1e393be91a6b36e817cd3f4acf4b3 (MD5) Previous issue date: 1992 / Resumo:Capítulo 1 Para situar o nosso problema, apresentamos uma revisão bibliográfica sobre os cálculos de seção de choque diferencial da excitação do hélio metaestável. Mostramos os processos que levam à população desses estados e sua importância do ponto de vista tecnológico. Capítulo 2 Fazemos um resumo da Teoria de Muitos Corpos para espalhamento elástico e inelástico a partir do estado fundamental e para espalhamento inelástico a partir de um estado excitado. Obtemos equações desacopladas de spin e tempo, numa forma adequada à implementação numérica das mesmas. Capítulo 3 Apresentamos a Teoria de Fano-Macek para a Experiência de Coincidência Elétron-Fóton. Obtivemos os parâmetros de alinhamento e orientação para excitação entre estados tripletos no acoplamento LS. Mostramos as diferenças para a excitação entre os singletos. Capítulo 4 Mostramos os resultados da aplicação da Teoria de Muitos Corpos em Primeira Ordem às transições entre estados tripletos. Obtivemos os resultados para a seção de choque de excitação 23S ® 23P, 33S e 33p e os par âmetros de alinhamento e orientação para as transições 23S ® n3 / Abstract: We use the First Order Many Body Theory (FOMBT), to study the electron impact excitation of the 23S state of helium. We present results for the differential cross section for the 23S ® 23P, 33S e 33P transitions. We use Fano-Macek Theory to study the a1ignment and orientation for 3S ® 3P transitions. We present FOMBT results for these parameters / Mestrado / Física / Mestre em Física

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No description available.

The suitability of using a Nal crystal as a fast coincidence gamma ray detector was investigated using the multichannel "fast-slow" delayed coincidence method to obtain prompt time resolution curves with a Na²² gamma ray source at Nal temperatures of 170, 185, 200°K. A comparison of the time resolution curve obtained using two NE 102 plastic scintillators (FWHM: 640 psec) with that using a cooled Nal scintillator and a NE 102 scintillator (FWHM: 680-psee) showed that Nal is a satisfactory fast coincidence gamma ray detector at 185°K. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Orientador: Alfredo Pio Noronha Rodrigues Galeão / Banca: Diógenes Galetti / Banca: Francisco Krmpoti'c / Resumo: Neste trabalho nós analisamos a influência da troca de um méson sigma sobre alguns dos principais observáveis do processo de decaimento hipernuclear fraco não-mesônico. Para isso discutimos em detalhe o formalismo baseado no modelo de camadas extremo para tratar as taxas do processo de decaimento fraco não-mesônico. O potencial de transição para o processo com mudança de estranheza ('delta'S =1), 'lâmbda'nü' 'SETA'nü'nü', foi construído a partir de diversos modelos de troca de um méson incluindo, além da troca dos mésosns pseudoescalares ('pi', 'capa', 'eta') e dos mésons vetoriais ('rô', 'ômega', 'capa'*), uma nova contribução devido ao méson escalar-isoescalar 'sigma'. Apresentamos tmbém os resultados numéricos obtidos para a taxa não mesônica total 'gama IND. nm='gama IND.n' + 'gama IND. p' e para a razão 'gama IND. n'/'gama IND. p' no decaimento do 'INTPOT. 5 ANTIND. 'LÂMBDA' He'. Esses resultados comprovam que a influências do méson 'sigma' é significativa e vai na direção de aumentar a razão 'gama IND. n'/'gama IND. p' / Abstract: In this work we investigate the influence of the exchange of a scalar-isoscalar sigma meson on some of the main observables in the nonmesonic hypernuclear weak decay. We discuss in detal the formalism based on the extreme shell model for the computation of the nonmesonic weak decay rates. The weak transition potential for the strangeness changing ('delta'S =1) process 'lâmbda'nü' 'SETA'nü'nü' is constructed based on several one-meson-exchange models, that include, beyond of the pseudoscalar ('pi', 'capa', 'eta') and the vector ('rô', 'ômega', 'capa'*) mesons, a ew contribution due to the scalar-isoscalar 'sigma' meson. We also present the numerical results obtained for the total nonmesonic rate, 'gama IND. nm='gama IND.n' + 'gama IND. p', and for the ration 'gama IND. n'/'gama IND. p' in the decay of 'INTPOT. 5 ANTIND. 'LÂMBDA' He'. We show that the influence of the 'sigma' meson is significant and goes in the direction of increasing the 'gama IND. n'/'gama IND. p'ratio. / Mestre

Orientador: Sergio Valdir Bajay / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-17T09:09:45Z (GMT). No. of bitstreams: 1 Santos_EdmilsonMoutinhodos_M.pdf: 45297516 bytes, checksum: 09658a862495bb284660066fcecae6a6 (MD5) Previous issue date: 1992 / Resumo: Com a crise que abalou a energia nuclear no plano internacional e, igualmente, no Brasil, as iniciativas de trabalhos que pudessem reintroduzir novos pontos de referencia para o setor escassearam. Assim, o objetivo principal deste trabalho é focar as novas perspectivas da energia nuclear e suas possibilidades enquanto fonte de geração de energia elétrica em grande escala, competitiva e segura em seus mais diversos aspectos...Observação: O resumo, na íntegra poderá ser visualizado no texto completo da tese digital / Abstract: As a consequence of the international crisis in the nuclear industry, the accademical works that could contribute to new bases for nuclear energy in Brazil have been scarce. This thesis highlights the nuclear energy perspectives to regain a prominent place in the world energy mix, as a competitive and a safe energy source...Note: The complete abstract is available with the full electronic digital thesis or dissertations / Mestrado / Mestre em Engenharia Mecânica

Governments pursue New Nuclear Build (NNB) projects for different strategic reasons. Many countries are not able to devise a funding model for the excessive costs of a NNB project nor do they have the local skills to construct, operate and maintain a NPP. South Africa's Integrated Resource Plan 2016 indicates that the base case scenario includes a target date of 2037 for the first unit of a NNB programme. This date moves to 2026 when the carbon budget is included in the forecast. The National Nuclear Regulator (NNR) has limited experience in licensing NNB programs as the country's only other commercially operating nuclear power plant was completed in 1984. The Build-Own-Operate (BOO) model is being promoted by Russia as an option to finance, design, supply most of the equipment for, construct and operate, a NPP. The first of this model is being executed at Akkuyu in Turkey. South Africa and specifically the NNR will face many challenges should it pursue the Build-Own- Operate model for its New Nuclear Build programme, given this model's novel and complex demands. This study has concluded that the Nuclear Energy Policy does not support an entity other than Eskom (the South African electricity utility) from owning and operating any new NPP in South Africa. The NNR does not presently have the resources to be able to service a NBB program but should be able to adapt to the increased demands of a NNB programme. The minister responsible for the promotion of nuclear energy also provides oversight of the NNR. This conflict of interest does not appear to have affected NNR decisions thus far; however, a NNB programme will exert undue pressure on all stakeholders which could change the relationship between the NNR and its minister. The National Nuclear Regulator Act (NNRA) needs to be enhanced to change this reporting structure while also enhancing the independence of the NNR. Should the Hinkley Point C model be followed in South Africa, the appointment of a design authority within the licensee which effectively creates an additional layer of verification should warrant strong consideration for the South African NNB model. The Akkuyu BOO model challenges the principles of the Intelligent Customer concept. Should the Akkuyu BOO model be followed, the NNR would require the licensee to show that independent verification is in place. Roles and responsibilities should be clearly described and understood by all stakeholders. The onus remains with the licensee to prove Intelligent Customer capability.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1979. / Bibliography: leaf 66. / by Gordon Spencer Swartz. / Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1979.

Excited nucleon states are established as an important milestone to understand quantum chromodynamics in the non-perturbative region. Even after decades of study, not all of the excited states predicted by different theoretical approaches have been verified. The disparity between the predicted states and the verified states is known as the “missing baryon problem". The verified states were mostly established using pion beam data or through Nπ decay channels, but are not sufficient to address the missing baryon problem. In recent years, new experiments were conducted worldwide at CLAS in Jefferson Lab, ELSA in Bonn, MAMI in Mainz, and so on, using electromagnetic probes that also included the study of multiple channels with different states. Since excited baryon states are broad and overlap, they are difficult to disentangle using cross-section data alone. Thus, polarization observables can play a crucial role in the identification of missing baryons. The current work uses CLAS g12 data, which were obtained from a circularly polarized photon beam incident upon an unpolarized hydrogen target, γp −> K+Λ, from CLAS at Jefferson Lab. Due to the weak decay of the hyperon, it is possible to measure the polarization observables from decay products, particularly pπ−with a 64% branching ratio. We measured the transferred polarization observables Cxand Cz, and the induced polarizationP. The measurement covers the center-of-mass energy range from 1.75 GeV to 3.33 GeV, expanding previous coverage by roughly 500 MeV for the Pobservable and 800 MeV for the Cxand Czobservables. We produced results for polarization observables via two topologies, K+p π−and K+p(π−), and found excellent agreement between them. The current analysis data, along with the previously published photo- and electro- production cross section and polarization observables from CLAS, SAPHIR, and GRAAL, are needed in a coupled-channel analysis to find the predicted excited states. The results at higher energies are important for determining the contributions from non-resonant processes, which is a dominant background in the lower energy baryon resonance region.