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Heil, M.; Detwiler, R.; Azuma, R.E.; Couture, A.; Daly, J.; Käppeler, F.; Reifarth, R.; Tischhauser, P.; Ugalde, C.; Wiescher, M.

doi:10.1103/physrevc.78.025803

Cited by 124 publications

(277 citation statements)

References 36 publications

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“…[29] without allowing the experimentally determined normalization to change. More recently, the (α, n) reaction was measured at low energies in Karlsruhe [31] and this data appears to agree substantially with that of Ref. [28].…”

Section: O System Analysissupporting

confidence: 72%

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Paris

Brown

Hale

et al. 2014

EPJ Web of Conferences

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Abstract. Unitarity, the mathematical expression of the conservation of probability in multichannel reactions, is an essential ingredient in the development of accurate nuclear reaction networks appropriate for nucleosynthesis in a variety of environments. We describe our ongoing program to develop a "unitary reaction network" for the big-bang nucleosynthesis environment and look at an example of the need and power of unitary parametrizations of nuclear scattering and reaction data. Recent attention has been focused on the possible role of the 9 B compound nuclear system in the resonant destruction of 7 Li during primordial nucleosynthesis. We have studied reactions in the 9 B compound system with a multichannel, two-body unitary R-matrix code (EDA) using the known elastic and reaction data, in a four-channel treatment. The data include elastic 6 Li( 3 He, 3 He) 6 Li differential cross sections from 0.7 to 2.0 MeV, integrated reaction cross sections for energies from 0.7 to 5.0 MeV for 6 Li( 3 He,p) 8 Be* and from 0.4 to 5.0 MeV for the 6 Li( 3 He,d) 7 Be reaction. Capture data have been added to the previous analysis with integrated cross section measurements from 0.7 to 0.825 MeV for 6 Li( 3 He,γ) 9 B. The resulting resonance parameters are compared with tabulated values from TUNL Nuclear Data Group analyses. Previously unidentified resonances are noted and the relevance of this analysis and a unitary reaction network for big-bang nucleosynthesis are emphasized.

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Section: O System Analysissupporting

confidence: 72%

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Paris

Brown

Hale

et al. 2014

EPJ Web of Conferences

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“…Nuclear reaction rates were included using the reaclib file provided by the Joint Institute for Nuclear Astrophysics (JINA, Cyburt et al 2010), as of May 2012 (reaclib V2.0). The rates of the neutron source reactions correspond to Heil et al (2008) for the 13 C(α,n) 16 O and to Iliadis et al (2010) for the 22 Ne(α,n) 25 Mg and 22 Ne(α,γ) 26 Mg reactions. For the neutron-capture cross sections, the JINA reaclib database includes the KADoNiS database (Dillmann et al 2006) 2 .…”

Section: The Stellar Nucleosynthesis Sequencesmentioning

confidence: 99%

Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

Buntain

Doherty

Lugaro

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The production of the elements heavier than iron via slow neutron captures (the s process) is a main feature of the contribution of asymptotic giant branch (AGB) stars of low mass (< 5 Msun) to the chemistry of the cosmos. However, our understanding of the main neutron source, the 13 C(α,n) 16 O reaction, is still incomplete. It is commonly assumed that in AGB stars mixing beyond convective borders drives the formation of 13 C pockets. However, there is no agreement on the nature of such mixing and free parameters are present. By means of a parametric model we investigate the impact of different mixing functions on the final s-process abundances in low-mass AGB models. Typically, changing the shape of the mixing function or the mass extent of the region affected by the mixing produce the same results. Variations in the relative abundance distribution of the three s-process peaks (Sr, Ba, and Pb) are generally within +/-0.2 dex, similar to the observational error bars. We conclude that other stellar uncertainties -the effect of rotation and of overshoot into the C-O core -play a more important role than the details of the mixing function. The exception is at low metallicity, where the Pb abundance is significantly affected. In relation to the composition observed in stardust SiC grains from AGB stars, the models are relatively close to the data only when assuming the most extreme variation in the mixing profile.

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“…This means that the cross section at the typical AGB temperatures has to be extrapolated from the data through model predictions. For our calculation, we used the reaction rate derived by Heil et al (2008). The uncertainty at relevant temperatures is up to 50%.…”

Section: Reaction Rate Uncertaintiesmentioning

confidence: 99%

Effects of nuclear cross sections on¹⁹F nucleosynthesis at low metallicities

Cristallo

Leva

Imbriani

et al. 2014

A&A

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Context. The origin of fluorine is a longstanding problem in nuclear astrophysics. It is widely recognized that asymptotic giant branch (AGB) stars are among the most important contributors to the Galactic fluorine production. Aims. In general, extant nucleosynthesis models overestimate the fluorine production by AGB stars with respect to observations. Although those differences are rather small at solar metallicity, low metallicity AGB stellar models predict fluorine surface abundances up to one order of magnitude larger than the observed ones. Methods. As part of a project devoted to reducing the uncertainties in the nuclear physics that affect the nucleosynthesis in AGB stellar models, we review the relevant nuclear reaction rates involved in the fluorine production or destruction. We perform this analysis on a model with initial mass M = 2 M and Z = 0.001. Results. We found that the major uncertainties are due to the 13 C(α,n) 16 O, the 19 F(α,p) 22 Ne, and the 14 N(p,γ) 15 O reactions. A change in the corresponding reaction rates within the present experimental uncertainties implies surface 19 F variations at the AGB tip lower than 10%, thus much smaller than observational uncertainties. For some α capture reactions, however, cross sections at astrophysically relevant energies are determined on the basis of nuclear models, in which some low-energy resonance parameters are very poorly known. Thus, larger variations in the rates of those processes cannot be excluded. That being so, we explore the effects of the variation in some α capture rates well beyond the current published uncertainties. The largest 19 F variations are obtained by varying the 15 N(α,γ) 19 F and the 19 F(α,p) 22 Ne reactions. Conclusions. The currently estimated uncertainties of the nuclear reaction rates involved in the production and destruction of fluorine produce minor 19 F variations in the ejecta of AGB stars. Analysis of some α capture processes that assume a wider uncertainty range determines 19 F abundances in better agreement with recent spectroscopic fluorine measurements at low metallicity. In the framework of this scenario, the 15 N(α,γ) 19 F and the 19 F(α,p) 22 Ne reactions show the strongest effects on fluorine nucleosynthesis. The presence of poorly known low-energy resonances make such a scenario possible, even if it is unlikely. We plan to measure these resonances directly.

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The13C(α,n)reaction and its role as a neutron source for thesprocess

Cited by 124 publications

References 36 publications

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

Effects of nuclear cross sections on¹⁹F nucleosynthesis at low metallicities

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The13C(α,n)reaction and its role as a neutron source for thesprocess

Cited by 124 publications

References 36 publications

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Toward a self-consistent and unitary reaction network for big-bang nucleosynthesis

Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements

Effects of nuclear cross sections on19F nucleosynthesis at low metallicities

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Effects of nuclear cross sections on¹⁹F nucleosynthesis at low metallicities