Neutron capture cross sections for s-process studies

Zongyu, Bao; Käppeler, F.

doi:10.1016/0092-640x(87)90011-8

Cited by 137 publications

(80 citation statements)

References 26 publications

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“…Winters & Macklin 1982 and references therein), a fundamental role in precise measurements of the key cross-sections was played by the Karlsruhe group of Franz Käppeler and coworkers (see e.g. Käppeler et al 1989, Bao & Käppeler 1987, Beer et al 1992. They sustained the stellar s-process studies with a continuous flow of high-precision cross-section data, without which the recent improvements in the field would have been impossible.…”

mentioning

confidence: 99%

Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation

Busso

Gallino

Wasserburg

1999

Annu. Rev. Astron. Astrophys.

1,150

1,182

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We present a review of nucleosynthesis in AGB stars outlining the development of theoretical models and their relationship to observations. We focus on the new high resolution codes with improved opacities, which recently succeeded in accounting for the third dredge-up. This opens the possibility of understanding low luminosity C stars (enriched in s-elements) as the normal outcome of AGB evolution, characterized by production of 12 C and neutron-rich nuclei in the He intershell and by mass loss from strong stellar winds. Neutron captures in AGB stars are driven by two reactions: 13 C(α,n) 16 O, which provides the bulk of the neutron flux at low neutron densities (N n ≤ 10 7 n/cm 3 ), and 22 Ne(α,n) 25 Mg, which is mildly activated at higher temperatures and mainly affects the production of s-nuclei depending on reaction branchings. The first reaction is now known to occur in the radiative interpulse phase, immediately below the region previously homogenized by third dredge-up. The second reaction occurs during the convective thermal pulses. The resulting nucleosynthesis phenomena are rather complex and rule out any analytical approximation (exponential distribution of neutron fluences). Nucleosynthesis in AGB stars, modeled at different metallicities, account for several observational constraints, coming from a wide spectrum of sources: evolved red giants rich in s-elements, unevolved stars at different metallicities, presolar grains recovered from meteorites, and the abundances of s-process isotopes in the solar system. In particular, a good reproduction of the solar system main component is obtained as a result of Galactic chemical evolution that mixes the outputs of AGB stars of different stellar generations, born with different metallicities and producing different patterns of s-process nuclei. The main solar s-process pattern is thus not considered to be the result of a standard archetypal sprocess occurring in all stars. Concerning the 13 C neutron source, its synthesis requires penetration of small amounts of protons below the convective envelope, where they are captured by the abundant 12 C forming a 13 C-rich pocket. This penetration cannot be modeled in current evolutionary codes, but is treated as a free parameter. Future hydrodynamical studies of time dependent mixing will be required to attack this problem. Evidence of other insufficiencies in the current mixing algorithms is common throughout the evolution of low and intermediate mass stars, as is shown by the inadequacy of stellar models in reproducing the observations of CNO isotopes in red giants and in circumstellar dust grains. These observations require some circulation of matter between the bottom of convective envelopes and regions close to the H-burning shell (cool bottom processing). AGB stars are also discussed in the light of their possible contribution to the inventory of short-lived radioactivities that were found to be alive in the early solar system. We show that the pollution of the protosolar nebula by a close-by AGB st...

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mentioning

confidence: 99%

Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation

Busso

Gallino

Wasserburg

1999

Annu. Rev. Astron. Astrophys.

1,150

1,182

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“…The idea of an experimental and theoretical stellar neutron cross section database for s-process studies was picked up 16 years later by Bao and Käppeler (1987). This compilation included cross sections for (n, γ) reactions between 12 C and 209 Bi, some (n, p) and (n, α) reactions (from 33 Se to 59 Ni) and also (n, γ) and (n, f ) reactions for long-lived actinides.…”

Section: Status Of Experimental (N γ) Cross Sectionsmentioning

confidence: 99%

Nuclear Physics of thesProcess

Dillmann¹,

Pardo²,

Käppeler³

et al. 2008

Publ. – Astron. Soc. Aust

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Abstract:Starting from a sketch of the s-process concept formulated 50 years ago, the nuclear physics data for s-process calculations are briefly reviewed with emphasis on the status of neutron capture cross sections and beta decay rates. Accurate and comprehensive experimental data are mandatory as direct input for s-process calculations as well as for improving the complementary information from nuclear theory. The current challenges of the field are discussed in the light of new or optimized methods and state-of-theart facilities, indicating the potential for accurate measurements and the possibility to study cross sections of radioactive isotopes. These opportunities will be considerably enriched by the enormous improvements provided by new facilities. The s Process in RetrospectLooking back on the founding papers of Nuclear Astrophysics published 50 years ago by Burbidge et al. (1957, hereafter referred to as B 2 FH) and by Cameron (1957) it is inspiring to see that already the entire s-process panorama was sketched in its essential parts. The visionary view of these papers is the more admirable as the basics were still pretty incomplete. This is certainly also true for the s process. In spite of the fact that neither the neutron source reactions nor the neutron capture cross sections in the astrophysically relevant energy range were known apart from some rudimentary information, all essential features had been inferred from these meager information. The product of the stellar (n, γ) cross sections and of the resulting s abundances, σ N s , which represents the reaction flow, was found to be a smooth function of mass number A. From the composite slope of this function two different s processes were postulated. The steep decline between A ≈ 63 and 100 was interpreted as the result of an s-process site with not enough neutrons available per 56 Fe seed to build the nuclei to their saturation abundances. In the mass region beyond A ≈ 100, the much smaller slope was suggesting that steady flow was achieved and that all of these nuclei reached their saturation abundances. It was concluded that 'the two different processes might have occurred in two different red-giant stars ' (Burbidge et al. 1957), completely consistent with what is now called the weak s process during core He burning 1,2 and shell C burning (Raiteri et al. 1991(Raiteri et al. , 1993Limongi et al. 2000) in massive stars 1 http://www.ucolick.org/∼alex 2 http://www.mporzio.astro.it/∼limongi on the one hand and the main s component contributed by thermally pulsing low mass asymptotic giant branch (AGB) stars (Straniero et al. 1995;Gallino et al. 1998;Arlandini et al. 1999) on the other hand. Eventually, the identification of the s-process sites has been shown to be an important ingredient for quantitative studies of galactic chemical evolution (Travaglio et al. 1999(Travaglio et al. , 2001(Travaglio et al. , 2004.The main difficulty that prevented further conclusions was due to the lack of reliable neutron capture cross sections. In total, the cros...

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“…This paper reviewed the role of neutron capture reactions in the nucleosynthesis of heavy elements and presented a table of recommended (experimental or semiempirical) Maxwellian averaged cross sections at kT = 30 keV (MACS30) for nuclei between carbon and plutonium. The idea of an experimental and theoretical stellar neutron cross section database was picked up by Bao and Käppeler [6] in 1987 for s-process studies. This compilation included cross sections for (n, γ) reactions between 12 C and 209 Bi, some (n, p) and (n, α) reactions for isotopes between 33 S and 59 Ni, and also (n,γ) and (n,f) reactions for long-lived actinides.…”

Section: The Kadonis S-process Databasementioning

confidence: 99%

“…KADoNiS has been updated four times until now [11], with the present KADoNiS v1.0 being the most extensive update so far. The previously missing datasets for stable 6 Li, 10,11 B, and 17 O were included, and recommendations are given based on experimental data. The values from most recent evaluated libraries ENDF/B-VII.1 [12] and JENDL-4.0 [13] were included, and were used in many cases instead of older time-of-flight measurements.…”

Section: The Kadonis S-process Databasementioning

confidence: 99%

The new KADoNiS v1.0 and its influence on the s-process

Dillmann¹

2015

Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII)

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Neutron capture cross sections for s-process studies

Cited by 137 publications

References 26 publications

Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation

Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation

Nuclear Physics of thesProcess

The new KADoNiS v1.0 and its influence on the s-process

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