The s-process is responsible of the synthesis of most of the nuclei in the mass range 90 <= A <= 208. It consists in a series of neutron capture reactions on seed nuclei followed by beta-decays, since the neutron accretion rate is slower than the beta-decay rate. Such small neutron flux is supplied by the C-13(alpha,n)O-16 reaction. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures <= 10(8) K, corresponding to an energy interval of 140 - 230 keV. In this region, the astrophysical S(E)-factor is dominated by the -3 keV sub-threshold resonance due to the 6.356 MeV level in O-17. In this work, we have applied the Trojan Horse Method (THM) to the C-13(Li-6,n(16)O)d quasi-free reaction to extract the 6.356 MeV level resonance parameters, in particular the asymptotic normalization coefficient (ANC) ((C) over tilde O-17(alpha 13C)(1/2+))(2). A preliminary analysis of a partial data set has lead to ((C) over tilde O-17(alpha 13C)(1/2+))(2) = 6.7(-0.6.)(+0.9) fm(-1), slightly larger than the values in the literature. However, the deduced C-13(alpha,n)O-16 reaction rate is in agreement with most results in the literature at similar to 10(8) K, with enhanced accuracy thanks to our innovative approach merging together ANC and THM.
Reaction rate of the C-13(alpha, n)O-16 neutron source using the ANC of the-3 keV resonance measured with the THM
Sparta, R
2016-01-01
Abstract
The s-process is responsible of the synthesis of most of the nuclei in the mass range 90 <= A <= 208. It consists in a series of neutron capture reactions on seed nuclei followed by beta-decays, since the neutron accretion rate is slower than the beta-decay rate. Such small neutron flux is supplied by the C-13(alpha,n)O-16 reaction. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures <= 10(8) K, corresponding to an energy interval of 140 - 230 keV. In this region, the astrophysical S(E)-factor is dominated by the -3 keV sub-threshold resonance due to the 6.356 MeV level in O-17. In this work, we have applied the Trojan Horse Method (THM) to the C-13(Li-6,n(16)O)d quasi-free reaction to extract the 6.356 MeV level resonance parameters, in particular the asymptotic normalization coefficient (ANC) ((C) over tilde O-17(alpha 13C)(1/2+))(2). A preliminary analysis of a partial data set has lead to ((C) over tilde O-17(alpha 13C)(1/2+))(2) = 6.7(-0.6.)(+0.9) fm(-1), slightly larger than the values in the literature. However, the deduced C-13(alpha,n)O-16 reaction rate is in agreement with most results in the literature at similar to 10(8) K, with enhanced accuracy thanks to our innovative approach merging together ANC and THM.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.