A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016. / This study investigates the e ect of nuclear deformation on both the broad and ne structure of the Isovector Giant Dipole Resonance (IVGDR) in the rareearth region. The IVGDR is strongly excited at and close to zero degrees by virtual-photon Coulomb excitation. As such, the Zero-degree Facility of the K600 magnetic spectrometer of iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) was used with an incident proton beam energy of 200 MeV to measure high energy-resolution (p,p0) scattering on a range of neodymium isotopes from spherical 142 60Nd82 to the permanently deformed 150 60Nd90 and the correspondingly deformed 152 62Sm90 in the region of the IVGDR. It is important to note that for nuclei with 88 N 92, a detailed study of the IVGDR is of speci c interest since it is here that a transition from spherical to permanently deformed nuclei occurs. An extensive data analysis procedure was performed, which included cross section extraction and conversion to equivalent photo-absorption spectra for comparison with existing photo-absorption data and theoretical predictions. For the more deformed 150Nd and 152Sm nuclei, however, the data from this study lack the expected double-peaked structure resulting from the splitting of the IVGDR into K = 0 and K = 1 components, and display a signi cant reduction in the strength of the K = 0 component of the IVGDR in comparison to previously published photo-absorption spectra. This reduced strength near the neutron threshold agrees very well with recent photo-neutron experiments. A ne structure analysis was performed on all of the measured isotopes, that is, 142;144;146;148;150Nd and 152Sm through the use of techniques associated with ii the continuous wavelet transform. Characteristic energy scales for the present high energy-resolution data are extracted using the complex Morlet motherwavelet and compared to those obtained for the theoretically predicted B(E1) strength functions. Finally, conclusions regarding the suitability of the model predictions to the current data are drawn. / GR 2016

High angular momentum states in $\sp{79}$Rb were populated via the $\sp{63}$Cu($\sp{19}$F,2pn)$\sp{79}$Rb $\sp{65}$Cu($\sp{18}$O,4n)$\sp{79}$Rb reactions. The 65 MeV $\sp{19}$F and 65 MeV $\sp{18}$O beams were provided by the Florida State University FN Tandem accelerator. Prompt $\gamma$-$\gamma$ coincidences were measured for both reactions. Two additional $\gamma$ cascades have been assigned to $\sp{79}$Rb, including a new high-excitation structure dominated by dipole transitions. Firm spin assignments were made for the first time for a number of states by means of directional correlation ratios and an angular distribution measurement using the $\sp{63}$Cu($\sp{19}$F,2pn) reaction. The Doppler-shift attenuation method was used to determine lifetimes for states and their respective side-feeding times in both the yrast positive-parity and yrast negative-parity states. Transition quadrupole moments were deduced from the transition strengths and compared with those predicted by Woods-Saxon cranking calculations. The energy spacings and mixing ratios were compared with particle-rotor calculations. A recoil distance apparatus has also been developed as part of this project. Software has been written to analyze the results from a $\sp{\rm nat}$Ni($\sp{19}$F,2pn)$\sp{74}$Br reaction. The 62 MeV $\sp{19}$F beam was also provided by the FN Tandem accelerator. Singles events were taken for a number of drift distances. Lifetimes of states in $\sp{74}$Br have been measured and compared with previously known values with excellent agreement. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6268. / Major Professor: Samuel L. Tabor. / Thesis (Ph.D.)--The Florida State University, 1993.

Source: Dissertation Abstracts International, Volume: 35-02, Section: B, page: 0724. / Thesis (Ph.D.)--The Florida State University, 1974.

Source: Dissertation Abstracts International, Volume: 35-09, Section: B, page: 4384. / Thesis (Ph.D.)--The Florida State University, 1974.

Foram medidas as funções de excitação de fusão de 14N+ 27Al, 14N + 28Si e 14N + 29Si por detecção dos resíduos de evaporação com um telescópio proporcional E-E. Com o objetivo de determinar se a origem da limitação da seção de choque total de fusão em energias intermediárias era devido a propriedades do núcleo composto ou do canal de entrada os resultados experimentais foram interpretados do ponto de vista do: modelo de Horn-Ferguson, modelo de Lozano-Madurga, modelo de Glas-Mosel, modelo da linha de yrast, modelo da linha estatística de yrast, modelo da superposição de níveis, modelo das etapas intermediárias. Foi feita uma discussão da origem destes modelos e um estudo comparativo dos valores que seus parâmetros assumem numa larga faixa de massa inclusive os calculados neste trabalho. Para estes concluímos que existem indicações de que o canal de entrada pode ter influência na limitação da seção de choque de fusão, mas que é necessário medir as reações periféricas nos três sistemas para assegurar esta hipótese. / Fusion excitation functions were measured for the systems 14N + 27Al, 14N + 28Si and 14N + 29Si by detecting the evaporation residues with a E-E proportional telescope. Since the principal objective of this work was to determine the roles which the formation of the compound nucleus and the specific properties of entrance channel play in the observed limitations of the total fusion cross section, the experimental results were analyzed in the light of the following models: Horn-Ferguson, Lozano-Madurga, Glas-Mosel, Yrast Line, Statistical Yrast Line, Superposition of Levels, Intermediate Step. The results of these theoretical analyses indicate that the entrance channel exerts some influence on the fusion cross section, but to secure this conclusion it is suggested that measurements on direct reaction mechanisms for these systems be made.

Estudo do espalhamento elástico do ANTPOT.16O pelo ANTPOT.27 AL / Study of elastic scattering of \'ANTPOT.16O\' by \'ANTPOT.27 AL\'

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.

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.

Estudo dos movimentos atômicos do t-Butanol do Espalhamento de nêutrons lentos / Study of the atomic motions of the slow neutron scattering t-Butanol

Este trabalho apresenta medidas do efeito de reorientação nos núcleos de \'ANTPOT. 122 Te\', \'ANTPOT. 128 Te\' e \'ANTPOT. 136 Ba\'. O método utilizado é o do espalhamento elástico e inelástico de várias partículas carregadas (\'ANTPOT. 4 He\', \'ANTPOT. 14 N\', \'ANTPOT 16 O\' e \'ANTPOT. 18 O\'). As partículas espalhadas foram detectadas em ângulos traseiros por detectores de estado sólido de alta resolução. A comparação das probabilidades experimentais de excitação do primeiro estado \'2 POT. +\' com aquelas calculadas na aproximação semi-clássica de múltipla excitação Coulombiana possibilitou, para cada núcleo; uma determinação dos valores da probabilidade reduzida B(E2; \'O POT. +\'\'SETA\'\'2 POT. +\') e do momento de quadrupolo estático \'Q IND. 2 POT. +\' do primeiro estado excitado. São discutidas as limitações do método adotado, e os resultados obtidos são comparados com os de outros autores. Faz-se também uma comparação dos valores de B(E2; \'O POT. +\'\'SETA\'\'2 POT. +\') e \'Q IND. 2 POT. +\' previstos por modelos nucleares com os determinados experimentalmente. / Measurements of the reorientation effect in Coulomb excitation were carried out in 122 Te, 128 Te e 136 Ba. The experimental method adopted is the elastic and inelastic backscattering of several projectiles (4He, 14N, 16O and 18O). The scattered particles were detected by high resolution solid state detectors. The determination of the static quadrupole moment for the 1st. 2+ excited state, Q2+ and of the reduced transition probability B(E2; O+ 2+) was accomplished by comparing the measured probabilities of excitation with calculations based on the semi-classical theory for multiple Coulomb excitation. The limitations of the method are discussed and the results obtained are compared with existing data from other authors. Calculated values for B(E2; O+ 2+) and Q2+ predicted by nuclear models are compared with experiment.