Measurement of the reaction 17O(α,n)20Ne and its impact on the s process in massive stars

Best, A.; Beard, M.; Görres, J.; 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.

Abstract

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 into the stellar environment. This ratio is of particular relevance to constrain the s process yields of fast rotating massive stars at low metallicity. Purpose: Recent results on the (α,γ) channel have made it necessary to measure the (α,n) reaction more precisely and investigate the effect of the new data on s process nucleosynthesis in massive stars. Method: The 17O(α,n (0+1) ) reaction has been measured with a moderating neutron detector. In addition, the (α,n 1 ) channel has been measured independently by observation of the characteristic 1633 keV γ transition in 20Ne. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. (α,n) and (α,γ) resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature. Result: The reaction channels 17O ( α , n 0 ) 20Ne and 17O ( α , n 1 γ ) 20Ne were measured in the energy range E α =800 keV to 2300 keV. A new 17O(α,n) reaction rate was deduced for the temperature range 0.1 GK to 10 GK. At typical He burning temperatures, the combination of the new (α,n) rate with a previously measured (α,γ) rate gives approximately the same ratio as current compilations. The influence on the nucleosynthesis of the s process in massive stars at low metallicity is discussed. Conclusions: It was found that in He burning conditions the (α,γ) channel is strong enough to compete with the neutron channel. This leads to a less efficient neutron recycling compared to a previous suggestion of a very weak (α,γ) channel. S process calculations using our rates confirm that massive rotating stars do play a significant role in the production of elements up to Sr, but they strongly reduce the s process contribution to heavier elements. © 2013 American Physical Society.

Citation

Best, A., Beard, M., Görres, J., 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. (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

• Journal Article Type: Article
• Acceptance Date: Nov 1, 2012
• Online Publication Date: Apr 22, 2013
• Publication Date: Apr 22, 2013
• Deposit Date: Oct 23, 2018
• Publicly Available Date: Nov 7, 2018
• Journal: Physical Review C - Nuclear Physics
• Print ISSN: 0556-2813
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 87
• Issue: 4
• Article Number: 045805
• DOI: https://doi.org/10.1103/physrevc.87.045805
• Public URL: https://hull-repository.worktribe.com/output/561811
• Publisher URL: https://journals.aps.org/prc/abstract/10.1103/PhysRevC.87.045805
• Contract Date: Oct 23, 2018