Impact of the Latest ²² Ne+ <i>α</i> Reaction Rates on Nucleosynthesis in Massive Stars and Galactic Chemical Evolution

Abstract In massive stars (initial mass of ≳9 M ⊙ ), the weak s - (slow neutron capture) process produces elements between Fe and Zr, enriching the Galaxy with these elements through core-collapse supernova explosions. The weak s -process nucleosynthesis is driven by neutrons produced in the 22 Ne( α , n ) 25 Mg reaction during convective He core and C shell burning. The yields of heavy elements thus depend on the 22 Ne( α , n ) 25 Mg and the competitive 22 Ne( α , γ ) 26 Mg reaction rates, which are dominated by several narrow-resonance reactions. While the accuracy of these rates has been under debate for decades, recent experimental efforts, including ours, drastically reduced these uncertainties. In this work, we use a set of 280 massive star nucleosynthesis models calculated using different 22 Ne( α , n ) 25 Mg and 22 Ne( α , γ ) 26 Mg rates and a galactic chemical evolution (GCE) study to probe their impact on the weak s -process elemental abundances in the Galaxy. The GCE was computed with the OMEGA+ code, using the new sets of stellar yields with different 22 Ne+ α rates. From GCE, we find that these rates are causing up to 0.45 dex of variations in the [Cu/Fe], [Ga/Fe], and [Ge/Fe] ratios predicted at solar metallicity. The greatest impact on the stellar nucleosynthesis and GCE results derives from uncertainties in the ( α , n ) strength ( ωγ ( α , n ) ) of the E x = 11.32 MeV resonance. We show that variations observed in the GCE calculations for weak s -process elements become negligibly smaller than dispersions found in observations once the ωγ ( α , n ) is accurately determined within the uncertainty of 10%–20% (typically reported experimental errors for the resonance) in future nuclear physics experiments.