We have studied natural parity states in 26 Mg via the 22 Ne( 6 Li, d) 26 Mg reaction. Our method significantly improves the energy resolution of previous experiments and, as a result, we report the observation of a natural parity state in 26 Mg. Possible spin-parity assignments are suggested on the basis of published γ -ray decay experiments. The stellar rate of the 22 Ne(α, γ ) 26 Mg reaction is reduced and may give rise to an increase in the production of s-process neutrons via the 22 Ne(α, n) 25 Mg reaction.

No abstract

For stars with 0.8 M⊙ ≤ M ≤ 8.0 M⊙, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18 O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as cool bottom processing (CBP), was proposed for low-mass AGB stars. The 18 O depletion observed within certain stellar environments and within presolar grain samples may result from the 18 O + p processes during CBP. We report here on a study of the 18 O(p,γ) 19 F reaction at low energies. Based on our new results, we found that the resonance at E lab R = 95 keV has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18 O(p,γ) 19 F is presented.