Nuclear Level Density and $\gamma$-ray Strength Function of $^{67}\mathrm{Ni}$ and the impact on the i-process

TL;DR

This study measures the nuclear level density and gamma-ray strength function of $^{67}$Ni using inverse-Oslo analysis, and assesses their impact on the $^{66}$Ni(n,γ) reaction rate relevant to the i-process nucleosynthesis.

Contribution

It provides new experimental data on $^{67}$Ni's NLD and $ extgamma$SF, and evaluates their influence on astrophysical reaction rates in the context of the i-process.

Findings

$^{66}$Ni(n,γ) acts as a bottleneck in one-zone models.

Impact of this reaction is reduced in multi-zone low-metallicity AGB star models.

Measured NLD and $ extgamma$SF constrain reaction rate calculations.

Abstract

Proton-$\gamma$ coincidences from $(\mathrm{d},\mathrm{p})$ reactions between a $^{66}\mathrm{Ni}$ beam and a deuterated polyethylene target have been analyzed with the inverse-Oslo method to find the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{67}\mathrm{Ni}$. The $^{66}\mathrm{Ni}(n,\gamma)$ capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and $\gamma$SF as constraints. The results confirm that the $^{66}\mathrm{Ni}(n,\gamma)$ reaction acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, the impact of this reaction is strongly dampened in multi-zone models of low-metallicity AGB stars experiencing i-process nucleosynthesis.