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Doctoral Thesis
DOI
10.11606/T.43.1985.tde-13122013-162137
Document
Author
Full name
Hugo Reuters Schelin
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1985
Supervisor
Committee
Pessoa, Elizabeth Farrelly (President)
Carlson, Brett Vern
Coutinho, Francisco Antonio Bezerra
Gomes, Luiz Carlos
Qualifik, Paul
Title in Portuguese
Um estudo das reações 10,11B (p,n)10,11C entre Ep=13,7 e 14,7 MeV
Keywords in Portuguese
Modelos de dois canais acoplados
Reações nucleares
Abstract in Portuguese
Usando as facilidades do sistema de tempo de vôo do Acelerador Pelletron 8UD da USP, foram medidas seções de choque diferenciais absolutas para os grupos 'n IND. 0', 'n IND. 1', 'n IND. 2', 'n IND. 3', ('n IND. 4'+'n IND. 5'), 'n IND. 6' e 'n IND. 7' na reação 'ANTPOT. 11 B' (p, 'n IND. 0') 'ANTPOT. 11 C' e para os grupos de nêutrons 'n IND. 0' e 'n IND. 1' na reação 'ANTPOT. 10 B' (p, 'n IND. 0') 'ANTPOT. 10 C' nas energias de próton incidente de 14.0, 14.3 e 14.6 MeV no intervalo angular de 20 a 160 graus. Foram também medidas funções de excitação em 'teta IND. lab' = 30 graus de 'E IND. p' = 13.7 e 14.7 MeV em intervalos de 100 keV. A análise teórica foi conduzida no sentido de se determinar as contribuições relativas dos processos de mecanismo direto e de núcleo composto. Para este fim, foi assumido um modelo de dois canais acoplados, e os modelos DWBA para o processo direto e de Hauser-Feshbach para o núcleo composto foram usados de maneira a simularem os cálculos exatos de canais acoplados via escolha do termo de absorção W no potencial óptico. Os resultados indicam que aproximadamente a metade da seção de choque é devida ao mecanismo de núcleo composto. A análise teórica visou ainda obter o fator de "enhancement elástico para o canal 'ANTPOT. 11 B' (p, 'n IND. 0') 'ANTPOT. 11 C' em 'E IND. p' = 14.3 MeV. Este fator foi demonstrado a aparecer em reações de troca de carga que seguem via núcleo composto por Harney, Weidenmüller e Richter e predito a atingir o valor de 2 quando há conservação de isospin. Os nossos resultados mostram um fator de enhancement maior do que 1, indicando que a mistura de isospin é fraca nessa reação.
Title in English
Study of reactions 10,11 B (p,n) 10,11 C between Ep= 13.7 and 14.7 MeV.
Keywords in English
Models of two coupled channels
Nuclear reactions
Abstract in English
Using the time-of-flight facilities of the são Paulo 8UD Pelletron Accelerator, absolute differential cross sections for the 'n IND. 0', 'n IND. 1', 'n IND. 2', 'n IND. 3', ('n IND. 4'+'n IND. 5'), 'n IND. 6' and 'n IND. 7' groups for the reaction 'ANTPOT. 11 B' (p, 'n IND. 0') 'ANTPOT. 11 C' and the 'n IND. 0' and 'n IND. 1' neutron groups for the reaction 'ANTPOT. 10 B' (p, 'n IND. 0') 'ANTPOT. 10 C' have been measured at incident proton energies of 14.0, 14.3 and 14.6 MeV in the angular interval of 20 to 160 degrees. Excitation functions at 'teta IND. lab' = 20 deg from 'E IND. p' = 13.7 to 14.7 MeV in intervals of 100 keV were also measured. The theoretical analysis was conducted to determine the relative contributions of the direct and compound nucleus processes in the differential cross sections. To this end, a two coupled channel model for the reactions was assumed. The DWBA model for the direct and the Hauser-Feshbach for the compound nucleus processes were used in such a way as to simulate the exact coupled channels calculation through an appropriate choice of the absorption term W in the optical potential. The results indicate that about half of the cross section is due to the compound nucleus mechanism. The theoretical analysis aimed at obtaining the elastic enhancement factor for the channel 'ANTPOT. 11 B' (p, 'n IND. 0') 'ANTPOT. 11 C' at 'E IND. p' = 14.3 MeV. This factor has been demonstrated to appear in compound nucleus charge exchange reactions by Harney, Weidenmüller and Richter and predicted to attain the value 2 when isospin is conserved. Our results show an enhancement factor larger than 1 indicating that isospin mixing is weak in this reaction.
 
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Publishing Date
2014-02-21
 
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