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Doctoral Thesis
DOI
10.11606/T.43.1999.tde-20072011-110522
Document
Author
Full name
Alexandre Alarcon do Passo Suaide
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1999
Supervisor
Committee
Carlin Filho, Nelson (President)
Carlson, Brett Vern
Gomes, Paulo Roberto Silveira
Martins, Marcos Nogueira
Pereira, Dirceu
Title in Portuguese
Escalas Temporais de Processos Binários Envolvendo Íons-Pesados Leves
Keywords in Portuguese
Física nuclear
Fusão nuclear
Ions pesados
Reações nucleares
Abstract in Portuguese
Foram realizadas medidas de seções de choque para processos onde ocorre a emissão binária de fragmentos complexos, utilizando técnicas de coincidência cinemática, para o sistema 16O + 10B no intervalo de 22 MeV < EC.M. < 24.5 MeV com EC.M. ~ 20 KeV e 17 MeV < EC.M. < 25 MeV com EC.M. ~ 190 KeV e para o sistema 19F + 12C em 22 MeV < EC.M. < 24.5 MeV com EC.M. ~ 20 KeV. As funções de excitação obtidas apresentam fortes flutuações. As larguras médias destas flutuações foram obtidas através da análise das funções de correlação em energia. Para o sistema 16O + 10B foram obtidas larguras da ordem de 25 KeV e 350 KeV. Para o sistema 19F + 12C obteve-se larguras da ordem de 40 KeV. As larguras menores, para ambos os sistemas, apresentam comportamento aproximadamente constante, tanto em função da energia de excitação dos fragmentos no canal de saída quanto em função do ângulo de emissão destes fragmentos. Estas larguras sugerem que o tempo de vida do sistema intermediário, da ordem de 2 x 10-20 s, seja muito superior ao seu tempo de rotação, condizente com o previsto para um mecanismo de fusão-fissão. A largura maior obtida para o sistema 16O + 10B apresenta, no canal de espalhamento elástico, uma dependência clara com o ângulo de espalhamento. Esta largura, assim como a dependência angular observada, sugere que o tempo de vida do sistema intermediário seja levemente superior ao tempo de revolução do mesmo. Estes fatos sugerem que o mecanismo responsável por estas flutuações seja o "orbiting" nuclear. Foram feitas comparações com modelos onde há a formação de núcleo composto e "orbiting" nuclear e os resultados obtidos são consistentes com os dados experimentais.
Title in English
Scales of processes involving binary light-heavy ions
Keywords in English
Heavy ions
Nuclear physics
Abstract in English
Binary decay cross section measurements have been performed for the system 16O + 10B at 22 MeV < EC.M. < 24.5 MeV (EC.M. ~ 20 KeV) and 17 MeV < EC.M. < 25 MeV (EC.M. ~ 190 KeV ) and for the system 19F + 12C at 22 MeV < EC.M. < 24.5 MeV (EC.M. ~ 20 KeV). The binary fragments were identified by the kinematic coincidence technique. The excitation functions for these systems show strong fluctuations and their average widths were obtained through the analysis of energy correlation functions. The small widths observed for the 16O + 10B (about 20 KeV) and 19F + 12C (about 40 KeV) systems show a constant behavior with the fragments excitation energy and scattering angle. These widths correspond to an intermediate system time scale of about 2 x 10-20 s which is larger than its revolution time. These features suggest the presence of the fusion-fission mechanism, where the compound nucleus spends a lot of time to acquire a relaxed form and thermal equilibrium. For the 16O + 10B system, larger widths (about 350 KeV) were also observed which are related to a faster process. These widths show a clear dependence with the scattering angle in the elastic scattering channel. These aspects are expected for a process where the time scale is comparable to the intermediate system revolution time, like an orbiting mechanism. Theoretical predictions for fusion-fission and orbiting mechanisms were compared to the experimental results and a good agreement was observed.
 
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Publishing Date
2011-09-12
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • MOURA, M M de, et al. Light heavy-ion reactions: time scales and emission order of light products. Nuclear Physics A, 2001, vol. 696, p. 64-84.
  • SUAIDE, A A P, et al. Time scales for binary processes from light heavy-ion reactions. Physical Review. C, Nuclear Physics, 2002, vol. 66, p. 14607.
  • MOURA, M M de, et al. A Large area two-dimensional position sensitive multiwire proportional detector. Nuclear Instruments And Methods, 1999, vol. 433, p. 623.
  • MOURA, M M de, et al. A triple telescope for the simultaneous identification of light and heavy reaction products. Nuclear Instruments and Methods in Physics Research, 2001, p. 1-6.
  • SOUZA, F A, et al. Study of the influence of projectile breakup on the fusion cross section of 6,7Li+12C, 59Co. Progress of Theoretical Physics. Supplement, 2004, nº 154, p. 101.
  • TOLEDO, A Szanto de, et al. Fusion of light weakly bound nuclei. World Scientific, 2001, p. 347-358.
  • TOLEDO, A Szanto de, et al. Fusion of light weakly bound nuclei. In International Workshop on Fusion Dynamics at the Extremes, 2001. World Scientific., 2001.
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