Identification of \(\gamma\)-decaying resonant states in 26Mg and their importance for the astrophysical s process

The 22Ne(\( \alpha\), n) reaction is expected to provide the dominant neutron source for the weak s processin massive stars and intermediate-mass (IM) Asymptotic Giant Branch(AGB) stars. However, the production of neutrons in such environments is hindered by the competing 22Ne(\(\alpha\),\(\gamma\))26Mg reaction. Here, the 11B(16O,p) fusion-evaporation reaction was used to identify \(\gamma\)-decay transitions from 22Ne + \(\alpha\) resonant states in 26Mg. Spin-parity restrictions have been placed on a number of \( \alpha\)-unbound excited states in 26 Mg and their role in the 22Ne(\(\alpha\),\(\gamma\))26Mg reaction has been investigated. In particular, a suspected natural-parity resonance at Ec.m. = 557(3) keV, that lies above the neutron threshold in 26Mg, and is known to exhibit a strong \( \alpha\)-cluster character, was observed to \( \gamma\) decay. Furthermore, a known resonance at \( E_{c.m.} = 466(4)\) keV has been definitively assigned 2+ spin and parity. Consequently, uncertainties in the 22Ne(\( \alpha\),\( \gamma\)) stellar reaction rate have been reduced by a factor of ∼ 20 for temperatures ∼ 0.2 GK.