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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.


A. Best

M. Beard

J. Görres

M. Couder

R. Deboer

S. Falahat

R. T. Güray

A. Kontos

K.-L. Kratz

P. J. Leblanc

Q. Li

S. O'Brien

N. Özkan

K. Sonnabend

R. Talwar

W. Tan

E. Uberseder

M. Wiescher


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.

Journal Article Type Article
Publication Date Apr 22, 2013
Journal Physical Review C - Nuclear Physics
Print ISSN 0556-2813
Electronic ISSN 1089-490X
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 87
Issue 4
Article Number 045805
APA6 Citation 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),
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