Decay properties of ${}^{22}\mathrm{Ne}+\alpha$ resonances and their impact on $s$-process nucleosynthesis

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 ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction, is not well constrained in the important temperature regime from $\sim 0.2$--$0.4$~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 ${}^{22}\mathrm{Ne}({}^6\mathrm{Li},d){}^{26}\mathrm{Mg}$ reaction in inverse kinematics, detecting the outgoing deuterons and ${}^{25,26}\mathrm{Mg}$ recoils in coincidence. We have established a new $n/\gamma$ decay branching ratio of $1.14(26)$ for the key $E_x=11.32$ MeV resonance in ${}^{26}\mathrm{Mg}$, which results in a new $(\alpha ,n)$ strength for this resonance of $42(11)\mu$eV when combined with the well-established $(\alpha ,\gamma )$ strength of this resonance. We have also determined new upper limits on the $\alpha$ partial widths of neutron-unbound resonances at $E_x=11.112,$ $11.163$, $11.169$, and $11.171$ MeV. Monte-Carlo calculations of the stellar ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ and ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from $\sim 0.2$--$0.4$~GK.

17 pages, 4 figures, accepted for publication in Phys. Lett. B

References in corpus (2)

• Neutron spectroscopy of ${}^{26}$Mg states: constraining the stellar neutron source ${}^{22}$Ne($\alpha ,n$)${}^{25}$Mg
• Experimental evidence of a natural parity state in ${}^{26}$Mg and its impact to the production of neutrons for the s process

Cited by in corpus (14)

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• The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning
• The study of key reactions shaping the post main-sequence evolution of massive stars in underground facilities
• Study of (${}^6$Li, $d$) and (${}^6$Li, $t$) reactions on ${}^{22}$Ne and implications for $s$-process nucleosynthesis
• Underground Measurements of Nuclear Reaction Cross-Sections Relevant to AGB Stars
• Study of the ${}^{22}$Mg waiting point relevant for x-ray burst nucleosynthesis via the ${}^{22}$Mg($\alpha$,$p$)${}^{25}$Al reaction
• Network structure of thermonuclear reactions in nuclear landscape
• Enhanced production of 60Fe in massive stars
• Direct measurement of the low energy resonances in ${}^{22}\mathrm{Ne}(\alpha ,\gamma {)}^{26}\mathrm{Mg}$ reaction
• The ${}^{22}$Ne($\alpha$,n)${}^{25}$Mg reaction -- state of the art, astrophysics, and perspectives
• Strength measurement of the $E_{\alpha }^{lab}$ = 830 keV resonance in ${}^{22}\mathrm{Ne}(\alpha ,\mathrm{n}{)}^{25}\mathrm{Mg}$ reaction using a stilbene detector
• Impact of the latest 22Ne+α reaction rates on nucleosynthesis in massive stars and galactic chemical evolution
• Trans-Fe elements from Type Ia Supernovae. I. Heavy element nucleosynthesis during the formation of near-Chandrasekhar white dwarfs