Measurement of the reaction ONe and its impact on the process in massive stars
Physical Review C—Nuclear Physics, 2013•APS
Background: The ratio between the rates of the reactions 17 O (α, n) 20 Ne and 17 O (α, γ)
21 Ne determines whether 16 O is an efficient neutron poison for the s process in massive
stars, or if most of the neutrons captured by 16 O (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 …
21 Ne determines whether 16 O is an efficient neutron poison for the s process in massive
stars, or if most of the neutrons captured by 16 O (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 …
Background: The ratio between the rates of the reactions ONe and ONe determines whether O is an efficient neutron poison for the process in massive stars, or if most of the neutrons captured by O are recycled into the stellar environment. This ratio is of particular relevance to constrain the process yields of fast rotating massive stars at low metallicity.
Purpose: Recent results on the channel have made it necessary to measure the reaction more precisely and investigate the effect of the new data on process nucleosynthesis in massive stars.
Method: The O reaction has been measured with a moderating neutron detector. In addition, the channel has been measured independently by observation of the characteristic 1633 keV transition in Ne. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. and resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature.
Result: The reaction channels ONe and ONe were measured in the energy range keV to 2300 keV. A new O reaction rate was deduced for the temperature range 0.1 GK to 10 GK. At typical He burning temperatures, the combination of the new rate with a previously measured rate gives approximately the same ratio as current compilations. The influence on the nucleosynthesis of the process in massive stars at low metallicity is discussed.
Conclusions: It was found that in He burning conditions the 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 channel. 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 process contribution to heavier elements.
American Physical Society