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Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 247-251).

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Foram medidos os \"yields\" de eletrofissão do 236 ANTPOT u e 238 ANTPOT u na faixa de 5 a 30 MeV, bem como as distribuições angulares dos fragmentos de eletrofissão, utilizando o feixe de elétrons do Acelerador Linear do Instituto de Física da Universidade de São Paulo. É apresentado um formalismo para análise das distribuições angulares dos fragmentos de foto e eletrofissão, a partir do qual é estudada a competição entre os canais de quadrupolo na fotofissão do 238 ANTPOT u. Desenvolveu-se um novo método de análise para a obtenção de contribuições multipolares , diferentes de El, no processo da fotofissão, que permite obter o \"yield\" integrado dos multipolos adicionais a partir da análise simultânea da foto e eletrofissão, mais o formalismo dos fótons virtuais em DWBA. Através do \"unfolding\" das secções de choque dos multipolos adicionais foram obtidas ressonâncias gigantes de E2 para 236 ANTPOT u e 238 ANTPOT. U, com picos em (10,7 ± 0,2) MeV e (9,9 ± 0,2) MeV, e larguras de (7,8 ± 0,2) MeV e (8,7 ± 0,2) MeV, respectivamente . As posições das ressonâncias E2 estão em razoável acordo com as previsões de Bohr e Mottelson: Ep = 60. A POT -1/3 MeV. As larguras são compatíveis com um possível \"splitting\" triplo das ressonâncias. Foram mostradas evidências quanto a uma mistura de Ml na faixa 6-7 MeV. / Measurements of electrofission yields of 236u and 238u were perfomed in the energy range of 5 to 30 MeV, as well as angular distribution of electrofission fragments using the electron beam of the Linear Accelerator of the Physics Institute of the University of São Paulo. A formalism for the analysis of angular distribution of photo and electrofission fragments is presented, from which a competition between the quadrupole channels in the photo fission of 238u is studied. A new method of analysis to obtain the multipole contribution, other than El, in the process of photofission was developed, which allows the obtainment of the integrated yield on the additional multipoles, from the simultaneous analysis of photo and electrofission using the formalism of virtual photons in OWBA. Through the unfolding of the additional multipoles cross sections the E2 giant resonances were obtained for the 236u and 238u, presenting peaks at (10.7 ± 0.2) MeV and (9.9 ± 0.2) MeV, and widths of (7.8 ± 0.2) MeV and (8.7±0.2) MeV, respectively. The positions of these E2 resonances are in reasonable agreement with the predictions of Bohr and Mottelson: Ep = 60 A -1/3 MeV. The width are compatible with a possible triple splitting of the resonances. Evidences of a Ml mixture were shown in the energy range of 6 to 7 MeV.

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The independent formation cross-sections of ('84,86)Rb,('116m,117m,117g)In, and ('132,134m,134m+g,136)Cs from ('233)U(p,f) and ('235)U(p,f) reactions, and the independent formation cross-sections of ('72)Ga from ('233)U(p,f) reactions were measured radiochemically in the energy range 35 to 90 MeV. The isotopic distributions of Rb, In, and Cs from ('233)U(p,f) and ('235)U(p,f), and the isotopic distributions of Ga from ('233)U(p,f) were measured in the energy range 40 to 100 MeV using the on-line mass spectrometric technique; their relative yields were normalized to the independent formation cross-sections measured radiochemically. / The variations of the FWHM, mean mass numbers, and mean neutron-to-proton ratios of the isotopic distributions were studied. The experimental results indicate that the mean masses of the distributions vary linearly with their atomic numbers. In conjunction with the fission option of the pre-equilibrium/exciton model, the experimental data were used to estimate average total neutron yields. The results show that there are more neutrons emitted for near-symmetric fissions than for asymmetric fissions. The charge distribution postulates, ECD, MPE, and UCD, were examined. In the energy range studied the results indicate that the MPE postulate accounts for asymmetric fissions, and the UCD postulate accounts for near-symmetric fissions.