Détermination par réaction de transfert de largeurs alpha dans le fluor 19. Applications à l'astrophysique

Abstract : The nucleosynthesic origin of fluorine is not known. Several astrophysical models predict the alpha radiative capture reaction onto nitrogen fifteen as the main fluorine producing reaction. In the expression of the reaction rate, one parameter is missing : the alpha width of the resonance on the E = 4,377 MeV level in fluorine. A direct measure is excluded due to the very low cross section expected. We determined this alpha width using a transfer reaction followed by analyses with FR-DWBA (Finite Range Distorted Wave Born Approximation) in a simple cluster alpha model. This experiment was carried out with a lithium seven beam et E = 28 MeV onto a nitrogen fifteen gas target. The 16 first levels were studied. Spectroscopic factors were extracted for most of them. Alpha widths for unbound levels were determined. Many alpha widths were compared with known values from direct reaction and the differences lie within the uncertainty range (factor 2). The alpha width for the E = 4,377 MeV level was determined, its value is about 60 times weaker than the used value. The influence of our new rate was studied in AGB (Asymptotic Giant Branch) stars during thermal pulses. In this model the alteration is sensitive.
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F. de Oliveira Santos. Détermination par réaction de transfert de largeurs alpha dans le fluor 19. Applications à l'astrophysique. Astrophysique stellaire et solaire [astro-ph.SR]. Université Paris Sud - Paris XI, 1995. Français. ⟨tel-01009384⟩

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