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Constraining r-process nucleosynthesis via enhanced accuracy neutron-capture experiments

C. Domingo-Pardo, C. Lederer-Woods, A. Mengoni

Abstract

The isotopic abundances of r-process elements in the solar system are traditionally derived as residuals from the subtraction of s-process contributions from total solar abundances. However, the uncertainties in s-process nucleosynthesis -- particularly those arising from Maxwellian Averaged Cross Sections (MACS) -- propagate directly into the r-process residuals, affecting their reliability. Building upon the seminal work of Goriely (1999), who introduced a multi-event s-process model to quantify these uncertainties, we revisit the problem using a simplified yet effective approach. By assuming that the relative uncertainty in s-process isotopic abundances scales linearly with the MACS uncertainties from data libraries (KADoNiS), we identify a subset of isotopes for which the r-process residuals remain significantly uncertain. Using updated solar abundances (Lodders 2025) and s-process contributions from Bisterzo et al. (2014), we present a short list of isotopes that are prime candidates for improved (n,g) measurements at CERN n_TOF in the near future. Our analysis provides a practical framework for prioritizing future experimental efforts that will profit from upgrades and enhancements of the n_TOF facility. It also highlights the need to revisit key neutron-capture cross sections to refine our understanding of the r-process isotopic abundance pattern, commonly used as a benchmark in stellar models of explosive nucleosynthesis.

Constraining r-process nucleosynthesis via enhanced accuracy neutron-capture experiments

Abstract

The isotopic abundances of r-process elements in the solar system are traditionally derived as residuals from the subtraction of s-process contributions from total solar abundances. However, the uncertainties in s-process nucleosynthesis -- particularly those arising from Maxwellian Averaged Cross Sections (MACS) -- propagate directly into the r-process residuals, affecting their reliability. Building upon the seminal work of Goriely (1999), who introduced a multi-event s-process model to quantify these uncertainties, we revisit the problem using a simplified yet effective approach. By assuming that the relative uncertainty in s-process isotopic abundances scales linearly with the MACS uncertainties from data libraries (KADoNiS), we identify a subset of isotopes for which the r-process residuals remain significantly uncertain. Using updated solar abundances (Lodders 2025) and s-process contributions from Bisterzo et al. (2014), we present a short list of isotopes that are prime candidates for improved (n,g) measurements at CERN n_TOF in the near future. Our analysis provides a practical framework for prioritizing future experimental efforts that will profit from upgrades and enhancements of the n_TOF facility. It also highlights the need to revisit key neutron-capture cross sections to refine our understanding of the r-process isotopic abundance pattern, commonly used as a benchmark in stellar models of explosive nucleosynthesis.

Paper Structure

This paper contains 4 sections, 3 equations, 1 figure, 4 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Case Studies of Key Isotopes
  4. Summary and conclusions

Figures (1)

  • Figure 1: Isotopic abundances in the solar system (normalized to Si $= 10^6$) showing the decomposition into s-process and r-process components. Upper panel: Total solar system abundances from Lodders2025 (open circles), s-process contributions from Bisterzo14 (blue filled circles), and derived r-process residuals $N_{\rm r} = N_{\odot} - N_{\rm s}$ (red filled circles). Lower panel: Relative s-process contributions (percentage of total solar abundance). Error bars on r-process residuals reflect the propagated uncertainties from MACS values as described in Section \ref{['sec:methodology']}.