Direct Experiments of Neutron Capture on Stable and Unstable Isotopes for Stellar Nucleosynthesis Studies

TL;DR

This paper reviews recent advances in direct neutron-capture experiments crucial for understanding stellar nucleosynthesis, highlighting progress, challenges, and future prospects in measuring reactions on stable and unstable isotopes.

Contribution

It provides a comprehensive overview of recent experimental techniques and results in neutron-capture measurements, emphasizing improvements and future directions for nuclear astrophysics.

Findings

Significant progress in measuring stable isotope neutron captures.

First-time measurements of radioactive branching-point nuclei.

Identification of current limitations and strategies for future experiments.

Abstract

Neutron-capture reactions provide essential nuclear-physics input for modeling the synthesis of heavy elements in stars. The growing precision of stellar spectroscopy and isotopic measurements in presolar SiC grains now demands cross sections with improved accuracy over the full energy range, and access to unstable nuclei relevant to slow (s-) process branchings and the intermediate (i-) process. This article reviews recent progress in direct neutron-capture measurements, focusing on time-of-flight (TOF) experiments at CERN n_TOF and complementary activation techniques. Substantial advances have been achieved for stable s-only and bottleneck isotopes, significantly improving constraints on s-process models. In parallel, the combination of high instantaneous neutron fluxes and advanced detector systems has facilitated first-time measurements of several radioactive branching-point nuclei. Feasibility studies, however, reveal current limitations related to sample availability, background conditions, and restricted energy coverage. In this context, the complementarity between TOF and activation emerges as a central strategy. Future developments, including high-flux facilities and novel inverse-kinematics experiments in ion storage rings, are expected to extend the boundaries of neutron-capture measurements, overcoming current limitation