Traditionally, neutron-γ discrimination in organic scintillators relies on techniques such as time-of-flight (ToF) selection and pulse-shape discrimination (PSD). However, particle identification through graphical cuts remains challenging in the low-charge regime due to poor signal-to-noise ratios (SNR). In this work, we propose SINAPSE, a lightweight deep learning framework for accurate and explainable neutron-γ discrimination in the low-charge regime. The framework employs a dual-branch architecture that combines a 1-dimensional convolutional autoencoder for waveform denoising with a classifier for particle identification. Random augmentations are applied to high-SNR waveforms to simulate low-charge conditions, enabling robust extrapolation into regimes where conventional PSD labels are unreliable. We show that SINAPSE achieves superior denoising performance compared to conventional digital signal processing techniques, and outputs well-calibrated probabilities, consistent with traditional graphical cuts. Finally, we apply SHAP (SHapley Additive exPlanations) values to show that model decisions are driven by physically meaningful pulse-shape features, confirming consistency with established PSD principles.

Lead-208 is the heaviest known doubly magic nucleus and its structure is therefore of special interest. Despite this magicity, which acts to provide a strong restorative force toward sphericity, it is known to exhibit both strong octupole correlations and some of the strongest quadrupole collectivity observed in doubly magic systems. In this Letter, we employ state-of-the-art experimental equipment to conclusively demonstrate, through four Coulomb-excitation measurements, the presence of a large, negative, spectroscopic quadrupole moment for both the vibrational octupole 31− and quadrupole 21+ state, indicative of a preference for prolate deformation of the states. The observed quadrupole moment is discussed in the context of the expected splitting of the 3−⊗3− two-phonon states, due to the coupling of the quadrupole and octupole motion. These results are compared with theoretical values from three different methods, which are unable to reproduce both the sign and magnitude of this deformation. Thus, in spite of its well-studied nature, Pb208 remains a puzzle for our understanding of nuclear structure. Published by the American Physical Society 2025

Prompt fission neutron spectra (PFNS) are crucial to any neutronic simulation of critical nuclear systems. An experimental setup dedicated to the measurements of PFNS of very high accuracy was developed at the Los Alamos Neutron Science Center (LANSCE) some ten years ago. It allows for the measurement of PFNS for neutron induced fission at the Weapon Neutron Research (WNR) neutron source of the LANSCE. A measurement of the PFNS from the 235U(n,f) reaction was realized recently and is currently analyzed. Preliminary results are presented here and are compared to present nuclear data evaluations.

The presence of 240Pu in nuclear fuels for reactors has resulted in high uncertainties in the results of reactor and nuclear transmutation calculations because of deficiencies in 240Pu-related nuclear data. Specifically for the prompt fission neutron spectrum (PFNS) of 240Pu, there is only one neutron-induced, (𝑛,𝑓), measurement at 0.85 MeV incident neutron energy and only one complete spontaneous fission, (sf), measurement. This limited availability of data does not sufficiently guide nuclear data evaluations of these quantities. Here, we report on a measurement of both the 240Pu(sf) and the 240Pu(𝑛,𝑓) PFNS, both over the emitted neutron energy range of 0.79–10.0 MeV, and from incident neutron energies of 1.0–20.0 MeV for the (𝑛,𝑓) reaction. Measurements were made with a hemispherical array of liquid scintillators at the high-energy Los Alamos Neutron Science Center white neutron source at the Weapons Neutron Research facility as part of the joint LANL-LLNL Chi-Nu experimental campaign to measure actinide fission neutron spectra. These measurements are the first of their kind, and provide clear experimental evidence for second-chance fission, third-chance fission, and pre-equilibrium neutron emission processes in neutron-induced fission of 240Pu, and are the first ever measurements above 1 MeV incident neutron energy.3 MoreReceived 16 February 2024Accepted 29 April 2024DOI:https://doi.org/10.1103/PhysRevC.109.064611©2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFissionNeutron physicsNuclear reactorsNucleon induced nuclear reactionsPhysical SystemsTransmutation & power generation with acceleratorsPropertiesA ≥ 220Nuclear Physics

The prompt fission neutron spectrum (PFNS) from neutron-induced fission is a fundamental quantity for the behavior of nuclear reactors, and has been measured many times on a wide variety of nuclei and covering different ranges of incident and emitted neutron energies. However, results from past measurements are frequently called into question in modern nuclear data evaluations because of a lack of thorough experimental documentation and incomplete uncertainty analyses. The Chi-Nu experiment at Los Alamos National Laboratory was designed to produce high-precision measurements of the PFNS of major actinides over a wide range of incident and emitted neutron energies, and with the documentation and covariance analysis required to ensure that the results of this experiment maintain their impact long into the future, thereby avoiding this pitfall of past measurements. In this work we describe the Chi-Nu experiment along with summaries of the treatment of and methods developed to address two important components of the analysis of Chi-Nu data: random-coincidence backgrounds and MCNP simulations. Furthermore, we describe the first results for correlations not just between all data points collected on a single target nucleus, but also between all data points from separate Chi-Nu measurements on 235U and 239Pu. These correlations are important for accurately calculating ratios of the PFNS from one actinide to another, which are rare and can be informative for nuclear data evaluation efforts.

The characteristics of 126,128 Xe were investigated in Coulomb excitation measurements performed at the National Superconducting Cyclotron Laboratory (NSCL) Re-accelerator facility, ReA3, Michigan State University (MSU). The Xe nuclei were accelerated to sub-barrier energies and were impinged on 196 Pt and 208 Pb targets in separate experimental runs. The scattered nuclei and the de-excitation γ-rays were detected using the JANUS setup. Electromagnetic matrix elements were extracted from the experimental data with the help of the GOSIA/GOSIA2 codes. The results were compared to schematic Davydov-Filippov γ-rigid rotor theoretical calculations and large-scale calculations within a newly-established microscopic shell model (called PMMU model). The experimental results agree well with the theoretical predictions, except for the quadrupole moments of the second 2 + states in both nuclei, therefore challenging the interpretation of the γ-bands structure.

The covariance committee of CSEWG (Cross Section Evaluation Working Group) established templates of expected measurement uncertainties for neutron-induced total, (n, γ ), neutron-induced charged-particle, and (n,xn) reaction cross sections as well as prompt fission neutron spectra, average prompt and total fission neutron multiplicities, and fission yields. Templates provide a list of what uncertainty sources are expected for each measurement type and observable, and suggest typical ranges of these uncertainties and correlations based on a survey of experimental data, associated literature, and feedback from experimenters. Information needed to faithfully include the experimental data in the nuclear-data evaluation process is also provided. These templates could assist (a) experimenters and EXFOR compilers in delivering more complete uncertainties and measurement information relevant for evaluations of new experimental data, and (b) evaluators in achieving a more comprehensive uncertainty quantification for evaluation purposes. This effort might ultimately lead to more realistic evaluated covariances for nuclear-data applications. In this topical issue, we cover the templates coming out of this CSEWG effort–typically, one observable per paper. This paper here prefaces this topical issue by introducing the concept and mathematical framework of templates, discussing potential use cases, and giving an example of how they can be applied (estimating missing experimental uncertainties of 235 U(n,f) average prompt fission neutron multiplicities), and their impact on nuclear-data evaluations.

Neutron scattering cross sections and angular distributions are leading terms in descriptions of neutron transport through any system. Despite the fundamental importance of nuclear data on these quantities, significant gaps in understanding and lack of experimental data persist in heavier elements and down to lighter structural materials, such as iron and aluminum. Recent measurements on carbon have also shown definitive proof that the neutron angular distribution can change with respect to the emission angle of γ -rays from inelastic scattering, thereby complicating γ -tagged measurements of inelastic neutron scattering. In this work, we describe the emerging program at Los Alamos National Laboratory for measurements of neutron scattering cross sections and neutron, γ -ray, and correlated n-γ angular distributions utilizing liquid scintillator detectors and the Correlated Gamma-Neutron Array for Scattering (CoGNAC) of CLYC scintillators. Currently, these detectors are operated simultaneously with the in-progress array of CLYC detectors in an inverted position, and data analysis techniques are being developed to span scattering measurements from light nuclei up through actinides. Preliminary results for measurements on 12 C, 27 Al, and 56 Fe are presented here with a description of the analysis methods applied and anticipated capabilities of the full-scale detection system.

The $Q=4.4398$ MeV $^{12}\mathrm{C}(n,n\text{'}\ensuremath{\gamma})$ cross section was measured using a white incident neutron source through the detection of $\ensuremath{\gamma}$ rays only and $n\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences using a segmented liquid scintillator detector array. While the $n\text{\ensuremath{-}}\ensuremath{\gamma}$ technique utilized here is more generally applicable to a wide variety of neutron scattering measurements, the $\ensuremath{\gamma}$-only technique was successfully applied to this reaction to exploit the precise time resolution and high efficiency of this detection system to yield results with unprecedented statistical precision and total uncertainties $<2%$ from reaction threshold up to 16 MeV incident neutron energy, clearly resolving many features in this reaction that were previously not well known. The $\ensuremath{\gamma}$-only and $n\text{\ensuremath{-}}\ensuremath{\gamma}$ results are consistent with each other for the majority of the incident energy range covered in this paper, thereby lending validation to the $n\text{\ensuremath{-}}\ensuremath{\gamma}$ technique for future measurements, though significant disagreements are observed between both results and with the ENDF/B-VIII.0 nuclear data evaluation. These differences are particularly noticeable in the recently evaluated energy range below 6.5 MeV, and also near 14 MeV where a ``sawtooth''-like feature is observed similar to that in other $^{12}\mathrm{C}+\phantom{\rule{0.16em}{0ex}}n$ reaction channels. Both $\ensuremath{\gamma}$-only and $n\text{\ensuremath{-}}\ensuremath{\gamma}$ results are presented here with thorough covariance derivations.

Auditory cortical plasticity deficits in schizophrenia are evidenced with electroencephalographic (EEG)-derived biomarkers, including the 40-Hz auditory steady-state response (ASSR). Aiming to understand the underlying oscillatory mechanisms contributing to the 40-Hz ASSR, we examined its response to transcranial alternating current stimulation (tACS) applied bilaterally to the temporal lobe of 23 healthy participants. Although not responding to gamma tACS, the 40-Hz ASSR was modulated by theta tACS (vs sham tACS), with reductions in gamma power and phase locking being accompanied by increases in theta-gamma phase–amplitude cross-frequency coupling. Results reveal that oscillatory changes induced by frequency-tuned tACS may be one approach for targeting and modulating auditory plasticity in normal and diseased brains.

We study $\ensuremath{\gamma}$-ray emission following $^{239}\mathrm{Pu}(n,f)$ over an incident neutron energy range of $2<{E}_{i}<40$ MeV. We present the first experimental evidence for positive correlations between the total angular momentum generated in fission and the excitation energy of the compound nucleus prior to fission. The $\ensuremath{\gamma}$-ray multiplicity increases linearly with incident energy below the second-chance fission threshold with a slope of $0.085\ifmmode\pm\else\textpm\fi{}0.010\phantom{\rule{4pt}{0ex}}{\mathrm{MeV}}^{\ensuremath{-}1}$. This linear trend appears to hold for the average excitation energy of the compound nucleus between $9<\ensuremath{\langle}{E}_{x}\ensuremath{\rangle}<19$ MeV. Most of the multiplicity increase comes from an enhancement around a $\ensuremath{\gamma}$-ray energy of 0.7 MeV, which we interpret as stretched quadrupole $\ensuremath{\gamma}$ rays that indicate an increase in total fission-fragment angular momentum with excitation energy.

With the recent emergence of fast nuclear reactors, there has been a corresponding increasing interest in $^{238}\mathrm{U}$-related nuclear data. However, while existing literature data span much of the energy ranges of interest for the prompt fission neutron spectrum (PFNS) for neutron-induced fission of $^{238}\mathrm{U}$, most literature data sets are highly correlated, and thus new, independent measurements of this quantity are needed. In this work, we report the results of a new measurement of the $^{238}\mathrm{U}$ PFNS at the Los Alamos Neutron Science Center for incident neutron energies from 1.5--20.0 MeV, and outgoing neutron energies of 0.01--10.0 MeV. With some notable exceptions, the present results generally agree with existing literature data, especially with regard to features relating to multichance fission and pre-equilibrium features in the PFNS, thus adding confidence to existing nuclear data evaluations and filling in gaps of knowledge at previously unmeasured incident neutron energies. This result is the third in a series of PFNS measurements by the Chi-Nu collaboration now spanning all three major actinides, $^{239}\mathrm{Pu}$, $^{235}\mathrm{U}$, and $^{238}\mathrm{U}$. Thus, for the first time, we report reliable experimental PFNS ratios and average PFNS energy comparisons for measurements of all three of these isotopes including accurate correlations between the different, but correlated experiments.