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arXiv · 2009.13169

Low Energy measurement of the $^{96}\mathrm{Zr}(α,n)^{99}\mathrm{Mo}$ reaction cross section and its impact on weak r-process nucleosynthesis

G. G. Kiss·T. N. Szegedi·P. Mohr·M. Jacobi·Gy. Gyürky·R. Huszánk·A. Arcones
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Abstract

Lighter heavy elements beyond iron and up to around silver can form in neutrino-driven ejecta in core-collapse supernovae and neutron star mergers. Slightly neutron-rich conditions favour a weak r-process that follows a path close to stability. Therefore, the beta decays are slow compared to the expansion time scales, and ($α$,n) reactions become critical to move matter towards heavier nuclei. The rates of these reactions are calculated with the statistical model and their main uncertainty, at energies relevant for the weak r-process, is the $α$+nucleus optical potential. There are several sets of parameters to calculate the $α$+nucleus optical potential leading to large deviations for the reaction rates, exceeding even one order of magnitude. Recently the $^{96}$Zr($α$,n)$^{99}$Mo reaction has been identified as a key reaction that impacts the production of elements from Ru to Cd. Here, we present the first cross section measurement of this reaction at energies (6.22 MeV $\leq$ E$_\mathrm{c.m.}$ $\leq$ 12.47 MeV) relevant for the weak r-process. The new data provide a stringent test of various model predictions which is necessary to improve the precision of the weak r-process network calculations. The strongly reduced reaction rate uncertainty leads to very well-constrained nucleosynthesis yields for $Z = 44 - 48$ isotopes under different neutrino-driven wind conditions.

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G. G. Kiss, T. N. Szegedi, P. Mohr, M. Jacobi, Gy. Gyürky, R. Huszánk, A. Arcones. 2021-03-02. Low Energy measurement of the $^{96}\mathrm{Zr}(α,n)^{99}\mathrm{Mo}$ reaction cross section and its impact on weak r-process nucleosynthesis. https://doi.org/10.3847/1538-4357%2Fabd2bc

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