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Comment on “Requirements and sensitivity analysis for temporally- and spatially-resolved thermometry using neutron resonance spectroscopy” [Rev. Sci. Instrum. 90, 094901 (2019)]
Comments are made on the original article written by Juan C. Fernandez, Cris W. Barnes, Michael J. Mocko, and Lukas Zavorka in an earlier issue of Reviw of Scientific Instruments.
EFFECT OF PORTABLE NEUTRON GENERATOR OPERATION SETTINGS ON NEUTRON RESONANCE TRANSMISSION SPECTRA
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Demonstration of non-destructive and isotope-sensitive material analysis using a short-pulsed laser-driven epi-thermal neutron source
Neutrons are a valuable tool for non-destructive material investigation as their interaction cross sections with matter are isotope sensitive and can be used complementary to x-rays. So far, most neutron applications have been limited to large-scale facilities such as nuclear research reactors, spallation sources, and accelerator-driven neutron sources. Here we show the design and optimization of a laser-driven neutron source in the epi-thermal and thermal energy range, which is used for non-invasive material analysis. Neutron resonance spectroscopy, neutron radiography, and neutron resonance imaging with moderated neutrons are demonstrated for investigating samples in terms of isotope composition and thickness. The experimental results encourage applications in non-destructive and isotope-sensitive material analysis and pave the way for compact laser-driven neutron sources with high application potential.
Anisotropic effect of a magnetic field on the neutron spin resonance in FeSe
We use inelastic neutron scattering to study the effect of a magnetic field on the neutron spin resonance (E r = 3.6 meV) of superconducting FeSe (T c = 9 K). While a field aligned along the in-plane direction broadens and suppresses the resonance, a c-axis aligned field does so much more efficiently, consistent with the anisotropic field-induced suppression of the superfluid density from the heat capacity measurements. These results suggest that the resonance in FeSe is associated with the superconducting electrons arising from orbital selective quasiparticle excitations between the hole and electron Fermi surfaces.
A new 181 Ta neutron resolved resonance region evaluation
A new 181 Ta neutron resolved resonance region evaluation has been performed from the thermal energy range up to approximately 2.5 keV. The R-matrix SAMMY code was used with the Reich–Moore approximation to evaluate resonance parameters from several experimental data sets. A Monte Carlo approach was used for resonance spin assignments and generating 59 small fictitious resonance levels which were shown to improve the cumulative level, Porter-Thomas, and Wigner distributions as compared to theoretical predictions. Covariance information was also generated for the entire resolved resonance region. Finally, the positive impact of the new evaluation was validated through benchmark calculations which were sensitive to the 181 Ta cross section and showed improvement in the reactivity bias for several benchmark cases.
Assessment of the quality of nuclear data for stable oxygen isotopes for Intentional Forensics applications
The Intentional Forensics (IF) project seeks to design a suite of tagging materials that can be used to unobtrusively “barcode” nuclear fuel. The idea being that, if the fuel leaves institutional controls and is later recovered, the “barcode” can be used to determine the provenance of the fuel. The IF project is investigating several schemes for this “barcode” and taggants with tailored isotopic compositions are once leading concept. Recently 18 O was suggested as a potential taggant [IF2023]. This report assesses the quality of 16,17,18 O evaluations in the ENDF/B-VIII.0 library [ENDF8.0]. In a neutron-rich environment such as a nuclear reactor, we are interested in two main processes – neutron scattering and neutron absorption (or capture). For the typical neutron energies encountered in a reactor, absorption is determined exclusively by the neutron radiative capture cross section (in which a neutron is absorbed, and the residual nucleus emits one or more gamma rays). The capture cross sections are described by and can be completely determined from R-matrix parameters in the ENDF evaluations. Therefore, it is sufficient to consider the quality of the neutron resonance part of these evaluations. Neutron scattering is determined mainly by the elastic scattering cross section which is very similar for all oxygen isotopes and is essentially constant until around 100 keV. The cross section varies from 3-4 barns, depending on the isotope, and 16 O has the largest elastic cross section of all isotopes. Therefore, we expect that significant amounts of 17 O and 18 O could diminish the moderating role of oxygen in fuel. We note that, in traditional power reactor, the hydrogen in the coolant water provides the vast majority of the moderation in the reactor, so the impact of 17 O and 18 O in any taggant would be minimal. At higher energies, neutron resonances start to play a role and the R-matrix parameters determine the cross sections. Fig. 1 shows the mass region near stable oxygen isotopes. As nuclei capture neutrons, they transmute into a different isotope, one unit to the right. In particular, 16 O transmutes to 17 O, 17 O transmutes to 18 O and 18 O transmutes to 19 O. 19 O, being unstable, beta decays in 27 s to 19 F. So, even if the 18 O neutron capture data is good, the fact that it transmutes into 19 F may be problematic and needs investigation. Fig. 2 from [NuDat] shows the thermal neutron capture cross sections for all nuclei in the ENDF/B-VII.1 library [ENDF7.1]. Clearly oxygen thermal capture values are quite small compared to other nuclei. Note, there is no 18 O evaluation in the ENDF/B-VII.1 library. In any event, given that neutron capture events lower the reactor reactivity and potentially induce chemical changes in the fuel, we will focus our attention on the capture part of the neutron resonances.
NEREIDS
NEREIDS (NEutron REsonance Imaging Diagnostic Suite) is a research-grade toolkit for neutron resonance imaging, providing a Rust physics core, Python bindings, and NeXus/HDF5-compliant data I/O, with a path to fast, standalone GUI workflows for VENUS/MARS.
New NDA Methods for Thorium Fuel Cycle Safeguards (Final Report)
This project developed portable Neutron Resonance Transmission Analysis (pNRTA) as a new non-destructive assay (NDA) method for thorium fuel cycles safeguards and other applications where multiple isotopes must be measured when present together. pNRTA leverages epithermal neutron resonances to assay multiple safeguards-relevant isotopes (e.g., 233 U and 235 U) when they are present together in a sample. Existing techniques are challenged by this task, driving the need for new active interrogation methods. With selected detectors, pNRTA works in high gamma-ray backgrounds from fission and activation products and 232 U progeny expected in thorium fuel cycle samples. This project leveraged a pNRTA system developed at Pacific Northwest National Laboratory (PNNL) and collaboration with the Massachusetts Institute of Technology (MIT). The system uses a commercially available deuterium-tritium (DT) neutron generator at short standoff (2 m). Key achievements in this project included: first-of-a-kind pNRTA quantitative measurements of 233 U oxide samples, an assessment of neutron detector technologies suitable for pNRTA in high gamma-ray background environments, experimentally demonstrating quantitative assay of samples containing 233 U and 235 U, and modeling studies showing the applicability of pNRTA to a wide range of material forms. Further, a custom algorithm was developed at MIT, which provided mean bias of 9% and relative standard deviation of 36% in assaying 233 U, 235 U, 238 U, and 232 Th content in eight measured samples. These outcomes form a solid technical basis for pNRTA as a new promising capability for international safeguards verification that is portable, non-destructive, quantitative, and isotopic specific.
Westcott g factors extended to arbitrary neutron energy spectra
Westcott 𝑔 factors are used in Neutron Activation Analysis (NAA) and Prompt Gamma-ray Activation Analysis (PGAA) to evaluate the impact of non-1∕𝑣 behavior in the neutron-capture cross sections of certain nuclei on activation product yields. This non-1∕𝑣 behavior arises from the presence of neutron resonances in the neutron- capture cross sections that overlap with the source neutron spectrum at low (< 5 eV) energies. Historically, Westcott 𝑔 factors that have been cataloged for NAA and PGAA applications are the result of calculations that assume a Maxwellian neutron flux distribution with a given temperature. In this work, we use this approach with updated neutron-capture cross sections from the Evaluated Nuclear Data File, version VIII.1 (ENDF/B-VIII.1) to tabulate Westcott 𝑔 factor values for a broad range of Maxwellian distribution temperatures, comparing the results against currently-available 𝑔 factors from International Atomic Energy Agency tables and other sources. Here, it was discovered during this analysis that the use of guided thermal and cold-neutron beams at certain facilities necessitates an approach for evaluating Westcott 𝑔 factors based on arbitrary non-Maxwellian spectra. In this paper, we present an approach for calculating 𝑔 factors with user-specified neutron spectra, and we demonstrate these methods to obtain Westcott 𝑔-factors for guided- and cold-neutron beams at the Budapest Research Reactor and the Forschungsreaktor München II reactor. As part of this work, open-source software has been developed that can be used to perform these calculations for applications in PGAA and NAA experiments.
239 Pu R -matrix Analysis and Neutron Multiplicities in the Neutron Energy Region up to a few keVs [Abstract]
The evaluation of 239 Pu neutron resonance parameters coupled to neutron multiplicities $\overline{v}_p$ is of particular importance to investigate the ($\mathcal{n, γf}$) reaction in which a $\mathcal{γ}$-ray emission occurs before the scission of the compound nuclear. This reaction has offered one explanation for the fluctuations in the measured values of $\overline{v}_p$ In this regard, the competition between ($\mathcal{n, γf}$) reaction and the direct fission process can be also included in the R matrix analysis of fission and capture measured data. The goal of this work is the coupled evaluation of the $\mathcal{n}$+ 239 Pu resonance parameters and related neutron multiplicities by ensuring the adoption of thermal neutron constants recently evaluated at the International Atomic Nuclear Energy as well as the recommended (thermal-neutron) induced prompt neutron fission spectrum (PFNS). Moreover, this new set of physical evaluated quantities should also guarantee the agreement for high-leakage solution benchmarks while keeping the good performance of large thermal solution assemblies.
Annual Report on NCSP Technical Support task in BNL during FY25
This work reports on the investigations done during FY 25 in collaboration with one 2025 Summer undergraduate intern through the DOE SULI program. These efforts were partially funded by the Nuclear Criticality Safety Program through the Technical Support Succession Plan task. This project, developed by Matthew Molnar, aimed to apply the BNL’s machine-learning code to correct spin mis-assignments in neutron resonances, the Bayesian Resonance Reclassifier (BRR), to the odd-even nucleus 143 Nd. For this, the handling of spingroup classification had to be further investigated and improved.
Verification of Arms Control Treaties with Resonance Phenomena
Nuclear disarmament treaties remain insufficient to neutralize the existential threat of the nuclear weapons. Technologies are necessary for verifying the authenticity of the nuclear warheads undergoing dismantlement before counting them toward a treaty partner’s obligation. Here we present a review of concepts involving isotope-specific resonance processes, Nuclear Resonance Fluorescence (NRF) [1] and Neutron Resonance Transmission Analysis (NRTA) [2, 3], used to authenticate a warhead’s fissile components by comparing them to a previously authenticated template. All information is encrypted in the physical domain by the addition of an encrypting filter to the target, leading to measurements with an outcome similar to an equation with two unknowns. Using Monte Carlo simulations and experiments we show that the measurements readily detect hoaxing attempt, while no vital isotopic or geometric information about the weapon is released. These nuclear techniques can be used to dramatically increase the reach and trustworthiness of future nuclear disarmament treaties.
140,142 Ce Neutron Cross Section Resolved Resonance Region Evaluation
A resolved resonance region evaluation of 140,142 Ce was conducted by Oak Ridge National Laboratory. Requested by the US Nuclear Criticality Safety Program, this evaluation is based on recent high-resolution transmission and capture high-resolution measurements of nat Ce and 142 Ce conducted at JRC-Geel at the Geel Linear Accelerator facility. It is also based on recently measured thermal constants available from the EX FOR database. Starting from the resonance parameters from the ENDF/B-VIII.0 library and following a preliminary R-matrix analysis, an updated set of resonance parameters and corresponding covariance in formation was derived by the fit of these experimental datasets using the Reich–Moore approximation of the R-matrix theory, as implemented in the SAMMY code system. The resolved resonance region upper energy limit for 140 Ce was kept at 200 keV, whereas the 142 Ce resonance region was extended from 13 to 26 keV. This new evaluation was found to be in good agreement not only with several integral quantities of interest to the reactor physics community, but also with the stellar Maxwellian-averaged cross section.
New capability for indirect neutron capture measurements: The DICER instrument at LANSCE
The Device for Indirect Capture on Radionuclides (DICER) implements a new indirect technique for (n,γ) studies in which the neutron capture rate is determined from analysis of resonance neutron transmission data. The DICER instrument and associated radionuclide production at the Isotope Production Facility (IPF), both at the Los Alamos Neutron Science Center (LANSCE), as well radioactive sample fabrication, have been under development in the last few years. First measurements on a radioactive sample ( 88 Zr, t ½ =83.4 days), which was recently reported to have an extremely large thermal neutron capture cross section and resonance integral, are planned for the winter of 2021. A performance overview, brief details on the 88Zr fabrication and proof of good operation results will be presented.
New NDA Methods for Thorium Fuel Cycle Safeguards (Mid-Project Report)
This project is developing new Non-Destructive Assay (NDA) safeguards techniques for emergent thorium fuel cycles based on Neutron Resonance Transmission Analysis (NRTA), which can assay 233 U and 235 U when they are present together in a sample with potentially high gamma-ray backgrounds from fission products and 232 U. Existing passive techniques face large challenges for this task so new active interrogation methods are needed. This effort is also exploring how gamma-ray signatures can complement NRTA for enhanced assayed performance. This project leverages an NRTA system being developed at PNNL in collaboration with MIT, which uses a commercially available deuterium-tritium neutron generator at short standoff (~2 m). We aim to assess the feasibility and performance of these new NDA techniques for the range of relevant samples in thorium fuel cycles. Key advancements described in this mid-project report include NRTA system design for thorium safeguards measurements, characterization of 233 U oxide powder at PNNL, a survey of detector technologies suitable for NRTA in high gamma background environments, successful preliminary demonstration of a quantitative isotopic estimation algorithm, and first NRTA measurements of a thorium sample.
Benchmarking fast-neutron response of 7 Li-enriched C 7 LYC scintillators: Simulations and experiment
New insights into the fast neutron response of 7 Li-enriched C 7 LYC scintillators have been obtained through detailed Geant4 simulations of 35 Cl(n,p) and 35 Cl(n, α) reactions that are primarily responsible for the fast neutron response of C 7 LYC. The light output of a 1” x1” C 7 LYC detector was simulated using the Birks equation for light quenching in scintillators. The simulations were benchmarked against neutron scattering data from a 12 C target obtained with a white neutron beam at the Los Alamos LANSCE facility and fourteen 1”x1” C 7 LYC detectors. Incident neutron energies extracted from time-of-flight measurements, and appropriate recoil corrections for the different detector angles were used to map the response of C 7 LYC to mono-energetic neutrons. Resonances in the 35 Cl(n,p) reaction cross-section below 3 MeV incident neutron energy were directly observed in C 7 LYC. The experimental data and simulations are compared with ENDF databases, as well as recent direct cross-section measurements of neutrons scattered from a 35 Cl target. In conclusion, the results suggest a scrutiny of the 35 Cl(n,p) and 35 Cl(n, α) cross sections at low energy in the ENDF library.
147 Sm Neutron Capture Cross Section and Resonances
Measurement of ( n,γ ) cross sections measurements are of high importance to many fields such as radiochemical diagnostics, technical nuclear forensics, nuclear physics and astrophysics, nuclear criticality safety, advanced reactors, and isotope production. For these applications an accurate characterization of the resonances in the resolved resonance region is important. In the energy range of the resonance region neutron capture, and scattering are possible so the total resonance width Γ is the sum of the gamma and neutron widths Γ = Γ γ +Γ n .