The Critical Role of Light Neutron-Rich Nuclei in the <font>r</font>-Process Nucleosynthesis

Terasawa, M.; Sumiyoshi, K.; Kajino, T.; Tanihata, I.; Mathews, G. J.; Langanke, K.

doi:10.1142/9789812791276_0044

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“…These possible implications should be studied in detail by using the present new reaction rate. It is to be clarified quantitatively if the α(αn, γ) 9 Be reaction path still predominates the seed production and to what extent the final r-process yields may change by including the present reaction rate and also newly-identified competing reactions 6,7] in the nuclear reaction network.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The necessary expansion time is determined in comparison with the reaction time scale of the ααn reaction [4]. A more recent study reveals that the reaction flow can go through the neutron-rich region of light elements in the rapidly expanding wind [6,7]. Therefore, the competition of the ααn reaction with other bypass reactions in the short expansion time should be carefully considered.…”

Section: Introductionmentioning

confidence: 99%

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Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

et al. 2002

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We study the astrophysical reaction rate for the formation of 9 Be through the three body reaction α(αn, γ). This reaction is one of the key reactions which could bridge the mass gap at A = 8 nuclear systems to produce intermediate-to-heavy mass elements in alpha-and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable 8 Be, α + α ⇀ ↽ 8 Be(n,γ) 9 Be. Off-resonant and on-resonant contributions from the ground state in 8 Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of 9 Be with laser-electron photon beams, which covers all relevant resonances in 9 Be. Experimental data near the neutron threshold are added with γ-ray flux corrections and a new least-squares analysis is made to deduce resonance parameters in the Breit-Wigner formulation. Based on the photodisintegration cross section, we provide the reaction rate for α(αn, γ) 9 Be in the temperature range from T 9 =10 −3 to T 9 =10 1 (T 9 is the temperature in units of 10 9 K) both in the tabular form and in the analytical form for potential usage in nuclear reaction network calculations.The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate, which is based on the photoneutron cross section for the 1/2 + state in 9 Be by Berman et al., is valid at T 9 > 0.028 due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range T 9 ≥ 0.1. The NACRE rate, which adopted different sources of experimental information on resonance states in 9 Be, is 4-12 times larger than the present rate at T 9 ≤ 0.028, but is consistent with the present rate to within ±20% at T 9 ≥ 0.1. 2

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Section: Summary and Discussionmentioning

confidence: 99%