Constraining Nucleosynthesis in Neutrino-driven Winds: Observations, Simulations, and Nuclear Physics

Abstract

A promising astrophysical site to produce the lighter heavy elements of the first r-process peak (Z = 38 − 47) is the moderately neutron-rich (0.4 < Y e < 0.5) neutrino-driven ejecta of explosive environments, such as core-collapse supernovae and neutron star mergers, where the weak r-process operates. This nucleosynthesis exhibits uncertainties from the absence of experimental data from (α, xn) reactions on neutron-rich nuclei, which are currently based on statistical model estimates. In this work, we report on a new study of the nuclear reaction impact using a Monte Carlo approach and improved (α, xn) rates based on the Atomki-V2 α optical model potential. We compare our results with observations from an up-to-date list of metal-poor stars with [Fe/H] < −1.5 to find conditions of the neutrino-driven wind where the lighter heavy elements can be synthesized. We identified a list of (α, xn) reaction rates that affect key elemental ratios in different astrophysical conditions. Our study aims to motivate more nuclear physics experiments on (α, xn) reactions using the current and new generation of radioactive beam facilities and also more observational studies of metal-poor stars.

Cross section measurement of the 144Sm(alpha,n)147Gd reaction for studying the alpha-nucleus optical potential at astrophysical energies

“…On the other hand, the uncertainty of the recommended rate is now much smaller when compared to earlier estimates of a factor of 10 or more. The achieved accuracy of the 144 Sm(α,γ) 148 Gd rate in combination with the overall improvement for α-induced reaction rates [26] should now permit stronger constraints for astrophysical conclusions for the γ-process, similar to what has already been achieved very recently for the weak r-process [58].…”

Measurement of the 86Kr(α,n)89Sr cross section at energies relevant for the weak r-process

“…In order to reduce the uncertainty in nucleosynthesis predictions for the weak r-process, a measurement of the reaction 86 Kr(𝛼,n) 89 Sr was conducted at the TRIUMF ISAC-II facility using the EMMA recoil mass spectrometer [5] and the TIGRESS gamma-ray spectrometer [6]. This reaction was chosen as it has been identified as affecting final elemental abundances under many astrophysical conditions [7,8]. The reaction was studied in inverse kinematics at two beam energies, 2.6 AMeV and 3.1 AMeV: the former being a measurement within the range of interest for the weak r-process and the latter allowing for a comparison with a previous study that, while failing to produce a cross section, succeeded in measuring the gamma-ray spectrum for the reaction [9].…”

Constraining nucleosythesis in neutrino-driven winds using the impact of (α, xn) reaction rates

“…This reaction has been shown to affect many elemental ratios under many astrophysical conditions in the impact study of Ref. [6].…”

“…We recently performed an impact study of the (α, xn) reaction rates to the weak r-process [6], employing the Atomki-V2 αOMP [7]. We explored the phase space of the astrophysical conditions, based on Ref.…”

“…Based on the analysis above, we have identified 35 (α, xn) reactions which affect the production of the lighter heavy elements in the weak r-process (see Ref. [6] for the complete list). In the following, we discuss experimental plans to measure these important reactions at radioactive ion beam facilities.…”