Background The competing ^ { 22 } Ne ( \alpha, \gamma ) ^ { 26 } Mg and ^ { 22 } Ne ( \alpha,n ) ^ { 25 } Mg reactions control the production of neutrons for the weak s -process in massive and AGB stars .
In both systems , the ratio between the corresponding reaction rates strongly impacts the total neutron budget and strongly influences the final nucleosynthesis .

Purpose The ^ { 22 } Ne ( \alpha, \gamma ) ^ { 26 } Mg and ^ { 22 } Ne ( \alpha,n ) ^ { 25 } Mg reaction rates must be re-evaluated by using newly available information on ^ { 26 } Mg given by various recent experimental studies .
Evaluations of the reaction rates following the collection of new nuclear data presently show differences of up to a factor of 500 resulting in considerable uncertainty in the resulting nucleosynthesis .

Methods The new nuclear data are evaluated and , where possible , correspondence between states observed in different experiments are made .
With updated spin and parity assignments , the levels which can contribute to the reaction rates are identified .
The reaction rates are computed using a Monte-Carlo method which has been used for previous evaluations of the reaction rates in order to focus solely on the changes due to modified nuclear data .

Results The evaluated ^ { 22 } Ne ( \alpha, \gamma ) ^ { 26 } Mg reaction rate remains substantially similar to that of Longland et al . but , including recent results from Texas A & M , the ^ { 22 } Ne ( \alpha,n ) ^ { 25 } Mg reaction rate is lower at a range of astrophysically important temperatures .
Stellar models computed with NEWTON and MESA predict decreased production of the weak branch s -process due to the decreased efficiency of ^ { 22 } Ne as a neutron source .
Using the new reaction rates in the MESA model results in ^ { 96 } Zr/ ^ { 94 } Zr and ^ { 135 } Ba/ ^ { 136 } Ba ratios in much better agreement with the measured ratios from presolar SiC grains .

Conclusion The ^ { 22 } Ne + \alpha reaction rates ^ { 22 } Ne ( \alpha, \gamma ) ^ { 26 } Mg and ^ { 22 } Ne ( \alpha . n ) ^ { 25 } Mg have been recalculated based on more recent nuclear data .
The ^ { 22 } Ne ( \alpha, \gamma ) ^ { 26 } Mg reaction rate remains substantially unchanged since the previous evaluation but the ^ { 22 } Ne ( \alpha . n ) ^ { 25 } Mg reaction rate is substantially decreased due to updated nuclear data .
This results in significant changes to the nucleosynthesis in the weak branch of the s -process .