Abstract
The astrophysical s-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding s-process nucleosynthesis is the neutron flux generated by the Ne22(α,n)25Mg reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing Ne22(α,γ)26Mg reaction, is not well constrained in the important temperature regime from ∼0.2–0.4 GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the Ne22(Li6,d)26Mg reaction in inverse kinematics, detecting the outgoing deuterons and Mg25,26 recoils in coincidence. We have established a new n/γ decay branching ratio of 1.14(26) for the key Ex=11.32 MeV resonance in Mg26, which results in a new (α,n) strength for this resonance of 42(11)μeV when combined with the well-established (α,γ) strength of this resonance. We have also determined new upper limits on the α partial widths of neutron-unbound resonances at Ex=11.112, 11.163, 11.169, and 11.171 MeV. Monte-Carlo calculations of the stellar Ne22(α,n)25Mg and Ne22(α,γ)26Mg rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from ∼0.2–0.4 GK.
Highlights
Understanding the production of nuclides heavier than iron is a crucial part of our global quest to understand the origin of the elements
The s-process occurs in relatively moderate stellar environments—the He-shell burning phase of intermediate-mass asymptotic giant branch (AGB) stars and the He-core and C-shell burning phases of massive (M > 8M ) stars—and involves a series of neutron capture reactions on stable or near-stable nuclei [1]
Neutron capture rates on stable isotopes are typically known to an accuracy of 20% or better, and the s-process offers a prime opportunity to compare predicted nucleosynthesis yields with astronomical observations and meteorite and stardust analyses [1,2,3,4]
Summary
Understanding the production of nuclides heavier than iron is a crucial part of our global quest to understand the origin of the elements. A better understanding of s-process nucleosynthesis is helpful in working towards a complete understanding of the r-process in the era of multi-messenger astronomy At stellar temperatures, both 22Ne(α, n)25Mg and 22Ne(α, γ)26Mg proceed through resonant capture to natural-parity states in the compound nucleus, 26Mg. For a given resonance, the key properties determining its contribution to the stellar rate are the α + 22Ne resonance energy and the resonance strengths, ωγ(α,n) and ωγ(α,γ).. Taken in conjunction with the resonance parameters (J, Γn, Γγ) established by Massimi et al, this results in new upper limits on both the (α, n) and (α, γ) strengths for the four natural-parity states in this region identified in Refs. Taken in conjunction with the resonance parameters (J, Γn, Γγ) established by Massimi et al, this results in new upper limits on both the (α, n) and (α, γ) strengths for the four natural-parity states in this region identified in Refs. [20, 21]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
