Search for: All records

Abstract Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as⁶⁰Fe (iron) and²⁶Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed⁶⁰Fe/²⁶Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing⁶⁰Fe, and one reaction in particular, the neutron-capture on⁵⁹Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of⁶⁰Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted⁶⁰Fe/²⁶Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models. 

The recent discovery and spectroscopic measurements of ${}^{27}\mathrm{O}$and ${}^{28}\mathrm{O}$suggests the disappearance of the $N=20$shell structure in these neutron-rich oxygen isotopes. We measured one- and two-proton removal cross sections from ${}^{27}\mathrm{F}$and ${}^{29}\mathrm{Ne}$, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations. The invariant mass technique was used to reconstruct the two-body ( ${}^{24}\mathrm{O}+n$) and three-body ( ${}^{24}\mathrm{O}+2n$) decay energies from knockout reactions of ${}^{27}\mathrm{F}$(106.2 MeV/u) and ${}^{29}\mathrm{Ne}$(112.8 MeV/u) beams impinging on a ${}^9\mathrm{Be}$target. The one-proton removal from ${}^{27}\mathrm{F}$strongly populated the ground state of ${}^{26}\mathrm{O}$and the extracted cross section of $3.4_{-1.5}^{+0.3}$mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from ${}^{29}\mathrm{Ne}$an upper limit of 0.08 mb was extracted for populating states in ${}^{27}\mathrm{O}$decaying though the ground state of ${}^{26}\mathrm{O}$. The measured upper limit for the population of the ground state of ${}^{26}\mathrm{O}$in the two-proton removal reaction from ${}^{29}\mathrm{Ne}$indicates a significant difference in the underlying nuclear structure of ${}^{27}\mathrm{F}$and ${}^{29}\mathrm{Ne}$. Published by the American Physical Society2024