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The 𝛾-ray strength functions (GSFs) and nuclear level densities (NLDs) below the neutron threshold have been extracted for 111–113,116–122,124Sn from particle-𝛾 coincidence data with the Oslo method. The evolution of bulk properties of the low-lying electric dipole response has been investigated on the basis of the Oslo GSF data and results of a recent systematic study of electric- and magnetic dipole strengths in even-even Sn isotopes with relativistic Coulomb excitation. The obtained GSFs reveal a resonance-like peak on top of the tail of the isovector giant dipole resonance centered at ≈8 MeV and exhausting ≈2% of the classical Thomas-Reiche-Kuhn (TRK) sum. For mass numbers ≥118 the data suggest also a second peak centered at ≈6.5 MeV. It corresponds to 0.1%–0.5% of the TRK sum rule and shows an approximate linear increase with the mass number. In contrast with predictions of the relativistic quasiparticle random-phase and time-blocking approximation calculations, no monotonic increase in the total low-lying 𝐸⁢1 strength was observed in the experimental data from 111Sn to 124Sn, demonstrating rather similar strength distributions in these nuclei. The Oslo GSFs and NLDs were further used as inputs to constrain the cross sections and Maxwellian-averaged cross sections of (𝑛,𝛾) reactions in the Sn isotopic chain using talys. The obtained results agree well with other available experimental data and the recommended values from the JINA REACLIB, BRUSLIB, and KADoNiS libraries. Despite relatively small exhausted fractions of the TRK sum rule, the low-lying electric dipole strength makes a noticeable impact on the radiative neutron-capture cross sections in stable Sn isotopes. Moreover, the experimental Oslo inputs for the 121,123Sn ⁢(𝑛,𝛾)⁢ 122,124Sn reactions were found to affect the production of Sb in the astrophysical 𝑖 process, providing new constraints on the uncertainties of the resulting chemical abundances from multizone low-metallicity asymptotic giant branch stellar models. 

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. 

Abstract Neutron-capture cross sections of neutron-rich nuclei are calculated using a Hauser–Feshbach model when direct experimental cross sections cannot be obtained. A number of codes to perform these calculations exist, and each makes different assumptions about the underlying nuclear physics. We investigated the systematic uncertainty associated with the choice of Hauser-Feshbach code used to calculate the neutron-capture cross section of a short-lived nucleus. The neutron-capture cross section for$$^{73}\hbox {Zn}$$ ${}^{73}\text{Zn}$ (n,$$\gamma $$ $\gamma$ )$$^{74}\hbox {Zn}$$ ${}^{74}\text{Zn}$ was calculated using three Hauser-Feshbach statistical model codes: TALYS, CoH, and EMPIRE. The calculation was first performed without any changes to the default settings in each code. Then an experimentally obtained nuclear level density (NLD) and$$\gamma $$ $\gamma$ -ray strength function ($$\gamma \hbox {SF}$$ $\gamma \text{SF}$ ) were included. Finally, the nuclear structure information was made consistent across the codes. The neutron-capture cross sections obtained from the three codes are in good agreement after including the experimentally obtained NLD and$$\gamma \hbox {SF}$$ $\gamma \text{SF}$ , accounting for differences in the underlying nuclear reaction models, and enforcing consistent approximations for unknown nuclear data. It is possible to use consistent inputs and nuclear physics to reduce the differences in the calculated neutron-capture cross section from different Hauser-Feshbach codes. However, ensuring the treatment of the input of experimental data and other nuclear physics are similar across multiple codes requires a careful investigation. For this reason, more complete documentation of the inputs and physics chosen is important.