Revisiting the neutron poison ¹⁶O in s-process nucleosynthesis

Elements heavier than iron are principally produced in two processes involving neutron capture, viz. the rapid(r)-process and the slow(s)-process. The s-process takes place in AGB stars where neutrons are produced in nuclear reactions, ¹³C(α, n)¹⁶O and ²²Ne(α, n)²⁵Mg. The neutrons produced may be absorbed by elements such as ¹⁴N, ¹⁶O, ²⁵Mg, thus hindering nucleosynthesis. Among these so-called neutron poisons, ¹⁶O plays an important role being one of the major constituents of the s-process sites. Neutron capture by ¹⁶O leads to the production of ¹⁷O. This nucleus may interact with a ⁴He nucleus through two reactions, ¹⁷O(α, n)²⁰Ne and ¹⁷O(α, n)²¹Ne. The first one releases the neutrons, thus partially nullifying the poisoning effect of ¹⁶O. Preliminary results for rates of these reactions based on recent data, obtained in the R-matrix approach, will be presented. (author)