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Plastic scintillator detectors are widely used in nuclear physics experiments and applications. The interpretation of the data often relies on simulation to understand the performance of the detectors and to assist with the analysis of decay energies and widths of neutron-rich nuclei. A neutron scattering experiment was conducted at the Los Alamos Neutron Science Center (LANSCE) to study neutrons scattering from H and C nuclei in plastic scintillators for neutrons with energy 20 to 400 MeV. The detector array consisted of a single detector bar serving as target, and a 45° ramp of detectors 2 m downstream. Results for three interaction observables, including scintillation light detected, kinetic energy distribution following the first scatter, and scattering angle, were compared with predictions from two Geant4-based simulation packages, referred to here as G4-Physics and MENATE_R. Agreement between simulation and data was best for events consisting of a single hit, and poorer for events consisting of two hits. 

Abstract Neutron-induced reactions play an important role in fundamental nuclear physics, nuclear astrophysics, and applications. In the case of reactions on rare isotopes, there are limited options for direct experimental measurements. The Neutron Target Demonstrator project at Los Alamos National Laboratory seeks to test the feasibility of moderating spallation neutrons within a 1 m$$^3$$ $_{}^3$ graphite cube to create a standing neutron target for neutron-induced reaction measurements in inverse kinematics. This paper presents the results of experimental neutron flux distribution tests using neutron sources (ranging from 1 keV to 50 MeV) created by accelerators at the University of Notre Dame and Texas A&M University. Measurements were made with both the full graphite cube as well as a ”half cube” setup in which half of the graphite cube was removed. The measured distributions agree with simulated distributions in the case of the full cube moderator, although there remain discrepancies in certain cases for the half cube moderator. The results shown here will provide useful information for an upcoming experimental campaign to test the neutron target proof-of-principle. 

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.