This work presents a study of high-spin states in the nucleus ¹⁹⁶Tl via γ-spectroscopy. ¹⁹⁶Tl was produced via the ¹⁹⁷Au(⁴He,5n) ¹⁹⁶Tl reaction at a beam energy of 63 MeV. The γ-γ coincidence measurements were performed using the AFRODITE γ-spectrometer array at iThemba LABS. The previous level scheme of ¹⁹⁶Tl has been extended up to an excitation of 4071 keV including 24 new γ-ray transitions. The spin and parity assignment to levels was made from the directional correlation of oriented nuclei (DCO) and linear polarization anisotropy ratios. An analysis of the B(M1)/B(E2) ratios was found to be consistent with the configuration of πh₉/₂♁vi₁₃/₂ for the ground state band. Although no chiral band was found in ¹⁹⁶TI and ¹⁹⁸TI.

Bibliography: p. 156-162. Chronological list of the author's works: p. 155.

Bibliography: p. 156-162. / Chronological list of the author's works: p. 155. / viii, 162 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2002

Several chiral macrocyclic crown ethers and related analogues have shown to be capable of / Thesis (PhD-Chemistry)-University of KwaZulu-Natal, Durban, 2004

Made available in DSpace on 2016-01-13T13:27:34Z (GMT). No. of bitstreams: 0 Previous issue date: 1994. Added 1 bitstream(s) on 2016-01-13T13:33:01Z : No. of bitstreams: 1 000524316.pdf: 3132245 bytes, checksum: cdfd47a27f819ee95d467ba02ef476d7 (MD5) / Este trabalho consiste no estudo do papel das simetrias quiral e de calibre eletromagnético, da constante 'g IND. A' e do tipo de acoplamento pion-núcleon em três processos: fotoprodução de um píon e de dois píons e interação fóton-núcleon. Os dois primeiros processos são tratados na aproximação em árvore, enquanto que no último são considerados também diagramas envolvendo um loop. O papel das simetrias é analisado investigando-se a existência de relações entre os vários diagramas de um dado processo. Já o papel do tipo de acoplamento pion-núcleon é analisado, comparando-se os resultados obtidos por meio de dois modelos de implementação da simetria quiral: o sigma linear e o não linear de Weinberg. Analogamente, o papel de 'g IND. A' é avaliado pela inspeção direta das expressões obtidas para os vários processos. Este estudo mostrou que, apenas no processo envolvendo dois píons externos a simetria quiral é relevante. Em particular, a simetria quiral é irrelevante para o fator de forma eletromagnético devido à nuvem piônica do núcleon, pelo menos no contexto das correções de um loop consideradas. Estes resultados constituem pontos de partida para o estudo mais abrangente do papel da simetria quiral em abordagens não perturbativas, tais como a do modelo de Skyrme / In this Work we study the role played by chiral and electromagnetic gauge symmetries, the weak constant 'g IND. A' and pion-nucleon couplings in three processes; single and double pion photo production and photon-nucleon interaction. The first two of them are treated at tree levei, whereas the last one includes one loop corrections. The role of the symmetries is analyzed considering the existence of relationships among various diagrams contributing to a given process. The influence of the way pions couple to nucleons is studied by comparing results obtained by means of the linear sigma model and the non linear model proposed by Weinberg. Finally, the role of 'g IND. A' is assessed by direct inspection of formal expressions. Our study showed that chiral symmetry is relevant only for double pion photo production. In particular, chiral symmetry does not influence the pion cloud contribution to the electromagnetic nucleon form factor, at least within the one loop approximation considered. These results pave the way for more comprehensive studies of the role of chiral symmetry in non perturbative approaches, such as the Skyrme model

Orientador: Manoel Roberto Robilotta / Banca: Fernando Silveira Navarro / Banca: Bruto Max Pimentel Escobar / Resumo: Este trabalho consiste no estudo do papel das simetrias quiral e de calibre eletromagnético, da constante 'g IND. A' e do tipo de acoplamento pion-núcleon em três processos: fotoprodução de um píon e de dois píons e interação fóton-núcleon. Os dois primeiros processos são tratados na aproximação em árvore, enquanto que no último são considerados também diagramas envolvendo um loop. O papel das simetrias é analisado investigando-se a existência de relações entre os vários diagramas de um dado processo. Já o papel do tipo de acoplamento pion-núcleon é analisado, comparando-se os resultados obtidos por meio de dois modelos de implementação da simetria quiral: o sigma linear e o não linear de Weinberg. Analogamente, o papel de 'g IND. A' é avaliado pela inspeção direta das expressões obtidas para os vários processos. Este estudo mostrou que, apenas no processo envolvendo dois píons externos a simetria quiral é relevante. Em particular, a simetria quiral é irrelevante para o fator de forma eletromagnético devido à nuvem piônica do núcleon, pelo menos no contexto das correções de um loop consideradas. Estes resultados constituem pontos de partida para o estudo mais abrangente do papel da simetria quiral em abordagens não perturbativas, tais como a do modelo de Skyrme / Abstract: In this Work we study the role played by chiral and electromagnetic gauge symmetries, the weak constant 'g IND. A' and pion-nucleon couplings in three processes; single and double pion photo production and photon-nucleon interaction. The first two of them are treated at tree levei, whereas the last one includes one loop corrections. The role of the symmetries is analyzed considering the existence of relationships among various diagrams contributing to a given process. The influence of the way pions couple to nucleons is studied by comparing results obtained by means of the linear sigma model and the non linear model proposed by Weinberg. Finally, the role of 'g IND. A' is assessed by direct inspection of formal expressions. Our study showed that chiral symmetry is relevant only for double pion photo production. In particular, chiral symmetry does not influence the pion cloud contribution to the electromagnetic nucleon form factor, at least within the one loop approximation considered. These results pave the way for more comprehensive studies of the role of chiral symmetry in non perturbative approaches, such as the Skyrme model / Mestre

A strong argument can be made that physics is, at its core, the study of symmetries. Nonlinear optics is certainly no exception, with an enormous number of distinct processes each depending in its own way on the underlying symmetries of the physical system, the light, or of nature itself. Restricting ourselves to optical harmonic generation, we will explore three unique physical systems as well as three symmetries. In each case, the controlled breaking of that symmetry will lead to optical enhancements, novel nonlinearities, or deep physical insights. Beginning with silicon metasurfaces, we will explore the effects of even and odd spatial symmetries in optical systems. The periodic breaking of this symmetry will lead us to the highly engineerable physics of bound states in the continuum. By studying the harmonic emission from an atomic gas in the volume surrounding the metasurface, we will come to understand that significant nonlinear optical enhancements can be engineered with any linewidth and at any wavelength. In the context of the two-dimensional material hexagonal boron nitride, we will investigate and break crystal inversion symmetries. Using an intense laser tuned to the phonon resonance of hexagonal boron nitride, large amplitude anharmonic ionic motions will provide us a powerful degree of control over the internal symmetries of the system at an atomic level. Breaking this symmetry, we measure short-lived even-order nonlinearities that would otherwise be forbidden in equilibrium. Our observations for second- and third- harmonic generation are confirmed by time-dependent density functional theory. Those simulations further extend the understanding of this symmetry-breaking effect to even higher order processes. Lastly, single-crystal graphene and graphite provide an ideal platform through which to explore time-reversal symmetry. Chiral photons, or optical beams with ellipticity and handedness, are well known to break time-reversal symmetry. While applying high-power, chiral light to graphene, the breaking of time-reversal lifts a degeneracy of the K and K’ valleys in the momentum space Brillouin zone. Lifting this degeneracy, we unveil underlying spatial symmetry properties of graphene in odd-order third- and fifth- harmonic generation which should otherwise be unobservable. We also show experimentally, for the first time, that valley polarization and population can be extracted using our technique.

No description available.

Orientador: Gastão Inácio Krein / Banca: Vicente Pleitez / Banca: Manoel Roberto Robilotta / Resumo: Consideramos modelos de quarks quirais para estudar o espalhamento 'PI-PI' a baixas energias. A quebra dinâmica da simetria quiral é estudada através do método variacional de Bogoliubov-Valatin. Dentro deste esquema, a estrutura de quarks dos pions considerados como bosons de Goldstone é obtida. Através do formalismo Fock-Tani obtemos um Hamiltoniano efetivo em termos dos graus de liberdade piônicos e a partir deste obtemos a amplitude de espalhamento 'PI-PI' no limiar. Usando a propriedade de "crossing" da matriz de espalhamento, o resultado é estendido para energias além do limiar. O resultado concorda com aquele obtido por Weinberg no contexto da álgebra de correntes / Abstract: We consider chiral quark models to study 'PI-PI' scattering at low energies. The dynamical chiral symmetry breaking is studied by means of the Bogoliubov-Valatin variational method. Within such a scheme, the quark structure of the pions considered as Goldstone bosons is obtained. By means of the Fock-Tani formalism we obtain an effective Hamiltonian in terms of pion degrees of freedom and from this we obtain the 'PI-PI' scattering matrix at threshold. Using the crossing property of the scattering matrix, the result is extended to energies beyond threshold. The result agrees with the one obtained by Weinberg in context of current algebra / Mestre