Global ETD Search

11	Estrutura de Cluster-alfa em Núcleos da Região do Molibdênio / Alpha-cluster structure in nuclei of the Molybdenum region Souza, Marco Antonio de 30 November 2010 (has links) O modelo de cluster-alfa é aplicado aos núcleos de massa intermediária 90Sr, 92Zr, 94Mo, 96Ru e 98Pd com a Abordagem de Potencial Local. As bandas do estado fundamental dos respectivos sistemas alfa + caroço são calculadas com um único parâmetro variável, fornecendo uma boa descrição geral dos níveis experimentais. Mostra-se que o potencial alfa + caroço é fracamente dependente do momento angular L, e que tal dependência pode ser descrita de forma simples e padronizada para os cinco núcleos. O comportamento do parâmetro radial R do potencial alfa + caroço é discutido em relação ao raio do núcleo total e a soma dos raios do cluster-alfa e do caroço. As taxas de transição B(E2) reproduzem corretamente as ordens de grandeza de quase todos os dados experimentais sem o uso de cargas efetivas. A análise das separações intercluster rms e das larguras-alfa reduzidas nas bandas do estado fundamental sugere que há uma redução da intensidade de aglomeração-alfa com o aumento do spin. Uma análise complementar das bandas de estado fundamental dos núcleos 20Ne, 44Ti e 212Po aponta uma diminuição da intensidade de aglomeração-alfa com o aumento da massa nuclear, e mostra uma condição mais fraca de aglomeração-alfa para os núcleos da região do Mo em comparação com os núcleos leves. Bandas de paridade negativa são calculadas para os núcleos 92Zr, 94Mo, 96Ru e 98Pd e informações não relatadas anteriormente são comparadas a níveis experimentais disponíveis. A avaliação geral dos resultados indica que os núcleos com A par e N=52 na região do Mo possuem estruturas alfa + caroço com características semelhantes. / The alpha-cluster model is applied to the intermediate mass nuclei 90Sr, 92Zr, 94Mo, 96Ru and 98Pd with the Local Potential Approach. The ground state bands of the respective alpha + core systems are calculated with only one variable parameter, giving a good general description of the experimental data. It is shown that the alpha + core potential is weakly dependent on the angular momentum L and such dependence may be described in a simple and standardized form for the five nuclei. The behavior of the radial parameter R of the alpha + core potential is discussed in relation to the radius of the total nucleus and the sum of the radii of the alpha-cluster and the core. The calculated B(E2) transition rates reproduce correctly the orders of magnitude of almost all experimental data without the use of effective charges. The analysis of the rms intercluster separations and the reduced alpha-widths for the ground state bands suggests a reduction of the alpha-cluster intensity with the increasing spin. A complementary analysis of the ground state bands of the nuclei 20Ne, 44Ti and 212Po points to a decrease of the alpha-cluster intensity with the increasing nuclear mass, and shows a weaker alpha-cluster condition for the nuclei of the Mo region in comparison with the light nuclei. Negative parity bands are calculated for the nuclei 92Zr, 94Mo, 96Ru and 98Pd and previously not reported information are compared to available experimental levels. The general evaluation of the results indicates that the N=52 even-A nuclei in the Mo region have alpha + core structures with similar features. 90Sr 90Sr 92Zr 92Zr 94Mo 94Mo 96Ru 96Ru 98Pd 98Pd aglomerado-alfa alpha-cluster cluster model cluster structure cluster-alfa espectroscopia nuclear estrutura de cluster intermediate mass nuclei medium-heavy nuclei modelo de cluster modelo nuclear nuclear model nuclear spectroscopy núcleos de massa intermediária núcleos meio-pesados
12	Estrutura de Cluster-alfa em Núcleos da Região do Molibdênio / Alpha-cluster structure in nuclei of the Molybdenum region Marco Antonio de Souza 30 November 2010 (has links) O modelo de cluster-alfa é aplicado aos núcleos de massa intermediária 90Sr, 92Zr, 94Mo, 96Ru e 98Pd com a Abordagem de Potencial Local. As bandas do estado fundamental dos respectivos sistemas alfa + caroço são calculadas com um único parâmetro variável, fornecendo uma boa descrição geral dos níveis experimentais. Mostra-se que o potencial alfa + caroço é fracamente dependente do momento angular L, e que tal dependência pode ser descrita de forma simples e padronizada para os cinco núcleos. O comportamento do parâmetro radial R do potencial alfa + caroço é discutido em relação ao raio do núcleo total e a soma dos raios do cluster-alfa e do caroço. As taxas de transição B(E2) reproduzem corretamente as ordens de grandeza de quase todos os dados experimentais sem o uso de cargas efetivas. A análise das separações intercluster rms e das larguras-alfa reduzidas nas bandas do estado fundamental sugere que há uma redução da intensidade de aglomeração-alfa com o aumento do spin. Uma análise complementar das bandas de estado fundamental dos núcleos 20Ne, 44Ti e 212Po aponta uma diminuição da intensidade de aglomeração-alfa com o aumento da massa nuclear, e mostra uma condição mais fraca de aglomeração-alfa para os núcleos da região do Mo em comparação com os núcleos leves. Bandas de paridade negativa são calculadas para os núcleos 92Zr, 94Mo, 96Ru e 98Pd e informações não relatadas anteriormente são comparadas a níveis experimentais disponíveis. A avaliação geral dos resultados indica que os núcleos com A par e N=52 na região do Mo possuem estruturas alfa + caroço com características semelhantes. / The alpha-cluster model is applied to the intermediate mass nuclei 90Sr, 92Zr, 94Mo, 96Ru and 98Pd with the Local Potential Approach. The ground state bands of the respective alpha + core systems are calculated with only one variable parameter, giving a good general description of the experimental data. It is shown that the alpha + core potential is weakly dependent on the angular momentum L and such dependence may be described in a simple and standardized form for the five nuclei. The behavior of the radial parameter R of the alpha + core potential is discussed in relation to the radius of the total nucleus and the sum of the radii of the alpha-cluster and the core. The calculated B(E2) transition rates reproduce correctly the orders of magnitude of almost all experimental data without the use of effective charges. The analysis of the rms intercluster separations and the reduced alpha-widths for the ground state bands suggests a reduction of the alpha-cluster intensity with the increasing spin. A complementary analysis of the ground state bands of the nuclei 20Ne, 44Ti and 212Po points to a decrease of the alpha-cluster intensity with the increasing nuclear mass, and shows a weaker alpha-cluster condition for the nuclei of the Mo region in comparison with the light nuclei. Negative parity bands are calculated for the nuclei 92Zr, 94Mo, 96Ru and 98Pd and previously not reported information are compared to available experimental levels. The general evaluation of the results indicates that the N=52 even-A nuclei in the Mo region have alpha + core structures with similar features. 90Sr 92Zr 94Mo 96Ru 98Pd aglomerado-alfa cluster-alfa espectroscopia nuclear estrutura de cluster modelo de cluster modelo nuclear núcleos de massa intermediária núcleos meio-pesados 90Sr 92Zr 94Mo 96Ru 98Pd alpha-cluster cluster model cluster structure intermediate mass nuclei medium-heavy nuclei nuclear model nuclear spectroscopy
13	A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies Eliades, John Alexander 21 August 2012 (has links) A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified. radio frequency quadrupole rf quadrupole accelerator mass spectrometry AMS gas-phase reactions isobar suppression anion negative ion chlorine Cl 36Cl carbon trimer C3 sulphur sulfur sulphur oxide sulfur oxide SO methane CH4 nitrogen dioxide NO2 nitrous oxide N2O oxygen O2 argon Ar strontium Sr 90Sr SrF3 yttrium Y zirconium Zr ZrF3 trace isotope analysis superhalogen anion secondary ion mass spectrometry SIMS Cs sputter ion source rf quadrupole ion trajectory simulation anion gas reactions negative ion gas reactions gas-phase anion reactions S- + NO2 SO- + NO2 S- + N2O S- + O2 S- + Ar Cl- + NO2 Cl- + Ar Cl- + CH4 SrF3- + NO2 YF3- + NO2 ZrF3- + NO2 C3- + NO2 0768 0494 0605
14	A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies Eliades, John Alexander 21 August 2012 (has links) A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified. radio frequency quadrupole rf quadrupole accelerator mass spectrometry AMS gas-phase reactions isobar suppression anion negative ion chlorine Cl 36Cl carbon trimer C3 sulphur sulfur sulphur oxide sulfur oxide SO methane CH4 nitrogen dioxide NO2 nitrous oxide N2O oxygen O2 argon Ar strontium Sr 90Sr SrF3 yttrium Y zirconium Zr ZrF3 trace isotope analysis superhalogen anion secondary ion mass spectrometry SIMS Cs sputter ion source rf quadrupole ion trajectory simulation anion gas reactions negative ion gas reactions gas-phase anion reactions S- + NO2 SO- + NO2 S- + N2O S- + O2 S- + Ar Cl- + NO2 Cl- + Ar Cl- + CH4 SrF3- + NO2 YF3- + NO2 ZrF3- + NO2 C3- + NO2 0768 0494 0605

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