Thermonuclear ¹⁷O( n,3)¹⁸O Reaction Rate and Its Astrophysical Implications

A new thermonuclear 17O(n, 3)18O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have first calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 ∼2 GK, by up to a factor of ∼80. The astrophysical impacts of our rate have been examined in both s-process and r-process models. In our main s-process model, which simulates flash-driven convective mixing in metal-deficient asymptotic giant branch stars, both 18O and 19F abundances in interpulse phases are enhanced dramatically by factors of ∼20-40 due to the new larger 17O(n, 3)18O rate. It shows, however, that this reaction hardly affects the weak s-process in massive stars since the 17O abundance never becomes significantly large in the massive stars. For the r-process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting loophole effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model; however, these significant differences are almost completely eliminated if the fission recycling is considered.