17O(α,γ)21Ne and17O(α, n)20Ne for the weak s process

Go?rres, J.; Gu?ray, R. T.; O?zkan, N.; Best, A.; Görres, J.; Beard, M.; Couder, M.; deBoer, R.; Falahat, S.; Güray, R. T.; Kontos, A.; Kratz, K.-L.; LeBlanc, P. J.; Li, Q.; O'Brien, S.; Özkan, N.; Pignatari, M.; Sonnabend, K.; Talwar, R.; Tan, W.; Uberseder, E.; Wiescher, M.

doi:10.1063/1.4768509

Investigation of neutron-induced reactions at n_TOF: An overview of the 2009-2012 experimental program (2014)
Journal Article
Guerrero, C., Altstadt, S., Andrzejewski, J., Audouin, L., Barbagallo, M., Bécares, V., …Tarrío, D. (2014). Investigation of neutron-induced reactions at n_TOF: An overview of the 2009-2012 experimental program. Nuclear data sheets, 119, 5-9. https://doi.org/10.1016/j.nds.2014.08.004

The neutron time-of-flight facility n TOF is operating at CERN (Switzerland) since 2001, having started in 2009 a new campaign with an upgraded spallation target. The ambitious program carried out includes a large number of experiments in nuclear tec... Read More about Investigation of neutron-induced reactions at n_TOF: An overview of the 2009-2012 experimental program.

Barium isotopic composition of mainstream silicon carbides from Murchison : constraints for s-process nucleosynthesis in asymptotic giant branch stars (2014)
Journal Article
Savina, M. R., Pellin, M. J., Willingham, D. G., Pignatari, M., Bisterzo, S., Cristallo, S., …Willingham, D. (2014). Barium isotopic composition of mainstream silicon carbides from Murchison : constraints for s-process nucleosynthesis in asymptotic giant branch stars. The Astrophysical journal, 786(1), 66. https://doi.org/10.1088/0004-637x/786/1/66

We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ(138... Read More about Barium isotopic composition of mainstream silicon carbides from Murchison : constraints for s-process nucleosynthesis in asymptotic giant branch stars.

Current quests in nucleosynthesis: Present and future neutron-induced reaction measurements (2014)
Journal Article
Praena, J., Pignatari, M., Mastinu, P., Martín-Hernández, G., Prete, G., Quesada, J., & Sabaté-Gilarte, M. (2014). Current quests in nucleosynthesis: Present and future neutron-induced reaction measurements. EPJ Web of Conferences, 66, 07022. https://doi.org/10.1051/epjconf/20146607022

We present some open questions in nucleosynthesis focused on the measurement of relevant neutron capture cross-sections and on new experimental methods. We review the recent 63 Ni(n,γ) experiment carried out at the n-TOF facility at CERN and its astr... Read More about Current quests in nucleosynthesis: Present and future neutron-induced reaction measurements.

Ni62(n,γ) and Ni63(n,γ) cross sections measured at the n_TOF facility at CERN (2014)
Journal Article
Lederer, C., Massimi, C., Berthoumieux, E., Colonna, N., Dressler, R., Guerrero, C., …Tassan-Got, L. (2014). Ni62(n,γ) and Ni63(n,γ) cross sections measured at the n_TOF facility at CERN. Physical Review C - Nuclear Physics, 89(2), Article 025810. https://doi.org/10.1103/physrevc.89.025810

The cross section of the Ni62(n,γ) reaction was measured with the time-of-flight technique at the neutron time-of-flight facility n-TOF at CERN. Capture kernels of 42 resonances were analyzed up to 200 keV neutron energy and Maxwellian averaged cross... Read More about Ni62(n,γ) and Ni63(n,γ) cross sections measured at the n_TOF facility at CERN.

Chemical abundances in bright giants of the globular cluster M62 (NGC 6266) (2014)
Journal Article
Yong, D., Alves Brito, A., Da Costa, G. S., Alonso-García, J., Karakas, A. I., Pignatari, M., …Norris, J. E. (2014). Chemical abundances in bright giants of the globular cluster M62 (NGC 6266). Monthly notices of the Royal Astronomical Society, 439(3), 2638-2650. https://doi.org/10.1093/mnras/stu118

With the exception of Terzan 5, all the Galactic globular clusters that possess significant metallicity spreads, such as ω Cen and M22, are preferentially the more luminous clusters with extended horizontal branches. Here we present radial velocities... Read More about Chemical abundances in bright giants of the globular cluster M62 (NGC 6266).

Experimental neutron capture data of 58 Ni from the CERN n-TOF facility (2014)
Journal Article
Žugec, P., Barbagallo, M., Colonna, N., Bosnar, D., Altstadt, S., Andrzejewski, J., …Wright, T. J. (2014). Experimental neutron capture data of 58 Ni from the CERN n-TOF facility. Physical Review C - Nuclear Physics, 89(1), 014605-1-014605-9. https://doi.org/10.1103/physrevc.89.014605

The ⁵⁸Ni(n,γ) cross section has been measured at the neutron time of flight facility n_TOF at CERN, in the energy range from 27 meV up to 400 keV. In total, 51 resonances have been analyzed up to 122 keV. Maxwellian averaged cross sections (MACS) hav... Read More about Experimental neutron capture data of 58 Ni from the CERN n-TOF facility.

Impact of the uncertainty in α-captures on 22Ne on the weak s-process in massive stars (2014)
Journal Article
Nishimura, N., Hirschi, R., Pignatari, M., Herwig, F., Beard, M., Imbriani, G., …Wiescher, M. (2014). Impact of the uncertainty in α-captures on 22Ne on the weak s-process in massive stars. AIP conference proceedings, 1594(1), 146-151. https://doi.org/10.1063/1.4874059

Massive stars at solar metallicity contribute to the production of heavy elements with atomic masses between A = 60 and A = 90 via the so-called weak s-process (which takes place during core He and shell C burning phases). Furthermore, recent studies... Read More about Impact of the uncertainty in α-captures on 22Ne on the weak s-process in massive stars.

Angular distribution in the neutron-induced fission of actinides (2013)
Journal Article
Leong, L., Tassan-Got, L., Tarrio, D., Audouin, L., Paradela, C., Duran, I., …González, R. (2013). Angular distribution in the neutron-induced fission of actinides. EPJ Web of Conferences, 62, 08003. https://doi.org/10.1051/epjconf/20136208003

Above 1 MeV of incident neutron energy the fission fragment angular distribution (FFAD) has generally a strong anisotropic behavior due to the combination of the incident orbital momentum and the intrinsic spin of the fissioning nucleus. This effect... Read More about Angular distribution in the neutron-induced fission of actinides.

Measurement of the MACS of Ta 181 (n, γ) at kT=30 keV as a test of a method for Maxwellian neutron spectra generation (2013)
Journal Article
Praena, J., Mastinu, P., Pignatari, M., Quesada, J., García-López, J., Lozano, M., …Martín-Hernández, G. (2013). Measurement of the MACS of Ta 181 (n, γ) at kT=30 keV as a test of a method for Maxwellian neutron spectra generation. Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment, 727, 1-6. https://doi.org/10.1016/j.nima.2013.05.151

Measurement of the Maxwellian-Averaged Cross-Section (MACS) of the Ta(n,γ)181 reaction at kT=30 keV by the activation technique using an innovative method for the generation of Maxwellian neutron spectra is presented. The method is based on the shapi... Read More about Measurement of the MACS of Ta 181 (n, γ) at kT=30 keV as a test of a method for Maxwellian neutron spectra generation.

Relics of ancient post-AGB stars in a primitive meteorite (2013)
Journal Article
Jadhav, M., Pignatari, M., Herwig, F., Zinner, E., Gallino, R., & Huss, G. R. (2013). Relics of ancient post-AGB stars in a primitive meteorite. Astrophysical journal. Letters, 777(2), L27. https://doi.org/10.1088/2041-8205/777/2/l27

Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme... Read More about Relics of ancient post-AGB stars in a primitive meteorite.

Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains? (2013)
Journal Article
Fujiya, W., Hoppe, P., Zinner, E., Pignatari, M., & Herwig, F. (2013). Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains?. Astrophysical journal. Letters, 776(2), L29. https://doi.org/10.1088/2041-8205/776/2/l29

We report C, Si, and S isotope measurements on 34 presolar silicon carbide grains of Type AB, characterized by 12 C/ 13 C < 10. Nitrogen, Mg-Al-, and Ca-Ti-isotopic compositions were measured on a subset of these grains. Three grains show large 3... Read More about Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains?.

Reproducing the observed abundances in RCB and HdC stars with post-double-degenerate merger models - Constraints on merger and post-merger simulations and physics processes (2013)
Journal Article
Menon, A., Herwig, F., Denissenkov, P. A., Clayton, G. C., Staff, J., Pignatari, M., & Paxton, B. (2013). Reproducing the observed abundances in RCB and HdC stars with post-double-degenerate merger models - Constraints on merger and post-merger simulations and physics processes. The Astrophysical journal, 772(1), 59. https://doi.org/10.1088/0004-637x/772/1/59

The R Coronae Borealis (RCB) stars are hydrogen-deficient, variable stars that are most likely the result of He-CO WD mergers. They display extremely low oxygen isotopic ratios, 16 O/ 18 O ≃ 1-10, 12 C/ 13 C ≥ 100, and enhancements up to 2.6 dex in... Read More about Reproducing the observed abundances in RCB and HdC stars with post-double-degenerate merger models - Constraints on merger and post-merger simulations and physics processes.

Silicon carbide grains of type C provide evidence for the production of the unstable isotope ³²Si in supernovae (2013)
Journal Article
Pignatari, M., Zinner, E., G. Bertolli, M., Trappitsch, R., Hoppe, P., Rauscher, T., …Thielemann, F. (2013). Silicon carbide grains of type C provide evidence for the production of the unstable isotope ³²Si in supernovae. Astrophysical journal. Letters, 771(1), Article L7. https://doi.org/10.1088/2041-8205/771/1/L7

Carbon-rich grains are observed to condense in the ejecta of recent core-collapse supernovae (SNe) within a year after the explosion. Silicon carbide grains of type X are C-rich grains with isotopic signatures of explosive SN nucleosynthesis have bee... Read More about Silicon carbide grains of type C provide evidence for the production of the unstable isotope ³²Si in supernovae.

On the internal pollution mechanisms in the globular cluster NGC 6121(M4): Heavy-element abundances and AGB models (2013)
Journal Article
D’Orazi, V., Campbell, S. W., Lugaro, M., Lattanzio, J. C., Pignatari, M., & Carretta, E. (2013). On the internal pollution mechanisms in the globular cluster NGC 6121(M4): Heavy-element abundances and AGB models. Monthly notices of the Royal Astronomical Society, 433(1), 366-381. https://doi.org/10.1093/mnras/stt728

Globular clusters display significant variations in their light-element content, pointing to the existence of a second stellar generation formed from the ejecta of an earlier generation. The nature of these internal polluters is still a matter of deb... Read More about On the internal pollution mechanisms in the globular cluster NGC 6121(M4): Heavy-element abundances and AGB models.

Measurement of the reaction 17O(α,n)20Ne and its impact on the s process in massive stars (2013)
Journal Article
Best, A., Beard, M., Görres, J., Couder, M., Deboer, R., Falahat, S., …Wiescher, M. (2013). Measurement of the reaction 17O(α,n)20Ne and its impact on the s process in massive stars. Physical Review C - Nuclear Physics, 87(4), Article 045805. https://doi.org/10.1103/physrevc.87.045805

Background: The ratio between the rates of the reactions 17O ( α , n ) 20Ne and 17O ( α , γ ) 21Ne determines whether 16O is an efficient neutron poison for the s process in massive stars, or if most of the neutrons captured by 16O(n,γ) are recycled... Read More about Measurement of the reaction 17O(α,n)20Ne and its impact on the s process in massive stars.

Abundances of neutron-capture elements in stars of the Galactic disk substructures (2013)
Journal Article
Mishenina, T. V., Pignatari, M., Korotin, S. A., Soubiran, C., Charbonnel, C., Thielemann, F., …Basak, N. Y. (2013). Abundances of neutron-capture elements in stars of the Galactic disk substructures. Astronomy and Astrophysics, 552, A128. https://doi.org/10.1051/0004-6361/201220687

Aims. The aim of this work is to present and discuss the observations of the iron peak (Fe, Ni) and neutron-capture element (Y, Zr, Ba, La, Ce, Nd, Sm, and Eu) abundances for 276 FGK dwarfs, located in the Galactic disk with metallicity-1 < [Fe/H]... Read More about Abundances of neutron-capture elements in stars of the Galactic disk substructures.

Production of carbon-rich presolar grains from massive stars (2013)
Journal Article
Pignatari, M., Wiescher, M., Timmes, F., De Boer, R. J., Thielemann, F. K., Fryer, C., …Hirschi, R. (2013). Production of carbon-rich presolar grains from massive stars. Astrophysical journal. Letters, 767(2), Article L22. https://doi.org/10.1088/2041-8205/767/2/L22

About a year after core-collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events,... Read More about Production of carbon-rich presolar grains from massive stars.

Neutron capture cross section of unstable Ni63: Implications for stellar nucleosynthesis (2013)
Journal Article
Wallner, A., Vlastou, R., Vlachoudis, V., Vermeulen, M. J., Versaci, R., Ventura, A., …Variale, V. (2013). Neutron capture cross section of unstable Ni63: Implications for stellar nucleosynthesis. Physical review letters, 110(2), Article 022501. https://doi.org/10.1103/physrevlett.110.022501

The Ni63(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n-TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged c... Read More about Neutron capture cross section of unstable Ni63: Implications for stellar nucleosynthesis.

The 12C +12C reaction and the impact on nucleosynthesis in massive stars (2012)
Journal Article
Pignatari, M., Hirschi, R., Wiescher, M., Gallino, R., Bennett, M., Beard, M., …X. Timmes, F. (2013). The 12C +12C reaction and the impact on nucleosynthesis in massive stars. The Astrophysical journal, 762(1), Article 31. https://doi.org/10.1088/0004-637X/762/1/31

Despite much effort in the past decades, the C-burning reaction rate is uncertain by several orders of magnitude, and the relative strength between the different channels 12 C( 12 C, α) 20 Ne, 12 C( 12 C, p) 23 Na, and 12 C( 12 C, n) 23 Mg is poorly... Read More about The 12C +12C reaction and the impact on nucleosynthesis in massive stars.

17O(α,γ)21Ne and17O(α, n)20Ne for the weak s process (2012)
Journal Article
Best, A., Görres, J., Beard, M., Couder, M., deBoer, R., Falahat, S., …Wiescher, M. (2012). 17O(α,γ)21Ne and17O(α, n)20Ne for the weak s process. AIP conference proceedings, 1498, 309-313. https://doi.org/10.1063/1.4768509

The ratio of the reaction rates of the competing channels 17 O(αγ) 21 Ne and 17 O(α,n) 20 Ne determines the efficiency of 16 O as a neutron poison in the s process in low metallicity rotating stars. It has a large impact on the element production, ei... Read More about 17O(α,γ)21Ne and17O(α, n)20Ne for the weak s process.

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