Nuclei in the Cosmos (NIC XVII)

New determination of 17O+α reaction rates and impact on the s-process in metal-poor rotating massive stars

18 Sept 2023, 10:00

15m

Oral The s-process The s-process

Speaker

Faïrouz HAMMACHE (IJCLab-Orsay)

Description

The efficiency of the weak s-process in low metallicity rotating massive stars depends strongly on the ratio of the reaction rates of the two competing ${}^{17}$O($\alpha$,n)${}^{20}$Ne and ${}^{17}$O($\alpha$,$\gamma$)${}^{21}$Ne reactions, which impacts the poisoning effect of ${}^{16}$O that consumes the neutrons released by the ${}^{22}$Ne($\alpha$,n)${}^{25}$Mg reaction [1] .
However, the reaction rates of these two competing reactions are poorly known in the astrophysical energy range of interest due to the lack of spectroscopic information (partial widths, spin-parities) on the relevant states in the compound nucleus ${}^{21}$Ne. Therefore, the $\alpha$-widths of these states were determined experimentaly for the first time by measuring their $\alpha$-spectroscopic factors using the $\alpha$-transfer reaction ${}^{17}$O(${}^7$Li,t)${}^{21}$Ne. The latter was performed at MLL-Munich using the high-energy resolution magnetic spectrometer Q3D [2].
The measured differential cross sections of the different populated states as well as their analysis using the DWBA formalism will be presented, along with the obtained $\alpha$-spectroscopic factors and $\alpha$-widths of the relevant states in ${}^{21}$Ne. The new ${}^{17}$O($\alpha$,n)${}^{20}$Ne and ${}^{17}$O($\alpha ,\gamma$)${}^{21}$Ne reaction rates calculated using the obtained $\alpha$-widths will be presented and compared with previous evaluations. The new rates favour neutron recycling through the ${}^{17}$O($\alpha$,n)${}^{20}$Ne reaction and suggest an enhancement by more than 1.5 dex of the weak s-elements between zirconium and neodymium in metal-poor rotating massive stars.

[1] A. Choplin, R. Hirschi et al. Astron. Astrophys. 618, A133 (2018)
[2] F. Hammache, P. Adsley, L. Lamia et al., submitted

Presentation materials

3. Hammache-NICXVII.pdf