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Wallner, A.; Bichler, Max; Buczak, K.; Dillmann, I.; Käppeler, F.; Karakas, Amanda I.; Lederer, C.; Lugaro, M.; Mair, Klaus; Mengoni, A.; Schätzel, G.; Steier, Peter; Trautvetter, H. P.

doi:10.1103/physrevc.93.045803

Cited by 28 publications

(18 citation statements)

References 53 publications

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“…Activation by high-intensity neutron irradiations combined with accelerator mass spectrometry (AMS) [31][32][33][34] offers an extremely powerful tool to measure cross sections through ultra-low isotope-ratio detection, irrespective of half-lives, and decay schemes of the reaction products. The analysis of activated samples via the AMS method was successfully introduced for the study of the neutron-capture cross section of 62 Ni [35] and extended to a number of other neutron induced reactions [33,[36][37][38][39][40][41][42].…”

Section: Measurementsmentioning

confidence: 99%

Stellar and thermal neutron capture cross section of Be9

et al. 2019

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The neutron capture cross section of 9 Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasistellar neutron spectrum of kT = 25 keV and for a spectrum at E n = 473 ± 53 keV. Despite the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4 ± 0.6 and 8.4 ± 1.0 μb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian-averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of σ th = 8.31 ± 0.52 mb.

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Section: Measurementsmentioning

confidence: 99%

Stellar and thermal neutron capture cross section of Be9

et al. 2019

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“…As noted above, we do not include rotation in our models. Rotational mixing could strongly affect the s-process by mixing 14 N, a neutron poison via the 14 N(n,p) 14 C reaction (Wallner et al 2016), into the 13 C pocket (Herwig et al 2003;Siess et al 2004;Piersanti et al 2013). Investigations are currently under way to establish the strength of this rotational effect and the link with the astereoseismology observational constraints that the cores of giant stars and white dwarfs have lower rotation periods than expected by stellar models (Cantiello et al 2014).…”

Section: The Inclusion Of 13 C Pocketsmentioning

confidence: 99%

Heavy-element yields and abundances of asymptotic giant branch models with a Small Magellanic Cloud metallicity

Karakas

Lugaro

Carlos

et al. 2018

Monthly Notices of the Royal Astronomical Society

101

106

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We present new theoretical stellar yields and surface abundances for asymptotic giant branch (AGB) models with a metallicity appropriate for stars in the Small Magellanic Cloud (SMC, Z = 0.0028, [Fe/H] ≈ −0.7). New evolutionary sequences and postprocessing nucleosynthesis results are presented for initial masses between 1M and 7M , where the 7M is a super-AGB star with an O-Ne core. Models above 1.15M become carbon rich during the AGB, and hot bottom burning begins in models M ≥ 3.75M . We present stellar surface abundances as a function of thermal pulse number for elements between C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., 12 C/ 13 C), which can be compared to observations. The integrated stellar yields are presented for each model in the grid for hydrogen, helium and all stable elements from C to Bi. We present evolutionary sequences of intermediate-mass models between 4-7M and nucleosynthesis results for three masses (M = 3.75, 5, 7M ) including s-process elements for two widely used AGB mass-loss prescriptions. We discuss our new models in the context of evolved AGB stars and post-AGB stars in the Small Magellanic Clouds, barium stars in our Galaxy, the composition of Galactic globular clusters including Mg isotopes with a similar metallicity to our models, and to pre-solar grains which may have an origin in metal-poor AGB stars.

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“…Furthermore, rotational mixing can be present while the neutrons are released inside 13 C and 14 N pockets produced, e.g., by overshoot. This mixing can strongly inhibit the s process by carrying 14 N, which is a neutron poison via the 14 N(n,p) 14 C reaction (Wallner et al 2016), from the 14 N pocket (and/or the H-burning ashes, if the 14 N pocket is absent) into the 13 C pocket (Herwig et al 2003;Siess et al 2004;Piersanti et al 2013).…”

Section: Current Models For the Formation Of 13 C Pocketsmentioning

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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Accelerator mass spectrometry measurements of theC13(n,γ)C14and

Cited by 28 publications

References 53 publications

Stellar and thermal neutron capture cross section of Be9

Stellar and thermal neutron capture cross section of Be9

Heavy-element yields and abundances of asymptotic giant branch models with a Small Magellanic Cloud metallicity

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

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