Neutron Inelastic Scattering Cross Sections Research Articles

GENESIS: Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering

Improved neutron inelastic scattering cross section data are needed to inform integral benchmark studies and advance applications in a wide variety of areas including nuclear energy, stockpile stewardship, nonproliferation, and space exploration. Neutron inelastic scattering also serves as a non-selective probe of low-lying nuclear structure. To help meet these needs, the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) was constructed at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. This array couples high-resolution γ-ray detectors and fast neutron detectors to achieve single and coincident n/γ detection over a broad energy range. The current configuration of the array includes 26 organic liquid scintillators and four high-purity germanium detectors (two single-crystal and two four-crystal CLOVER detectors with two-fold segmentation). The array was constructed with minimal supporting material and designed to cover a wide range of secondary particle angles and energies with limited inter-element scattering. Data acquisition is accomplished using Mesytec MDPP-16 multi-channel high-resolution digital pulse processing modules. The array characteristics, including γ-ray and neutron energy resolution, timing resolution, and detection efficiency were measured and used to validate a Geant4 model of the array. The primary sources of neutron background and the uncertainties in the determination of incident and secondary neutron energy were assessed. GENESIS provides a new capability to address nuclear data needs and facilitates the advancement of a wide range of nuclear applications.

Tetrahedral triple-Q magnetic ordering and large spontaneous Hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2

The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120° structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q magnetic ordering with the associated topological Hall effect (non-zero σxy(H = 0)). We also present a theoretical framework that describes the emergence of this magnetic ground state, which is further supported by the electronic structure measured by angle-resolved photoemission spectroscopy. Additionally, our measurements of the inelastic neutron scattering cross section are consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state.

From 232Th(n, n’γ) cross sections to level production and total neutron inelastic scattering cross sections

To probe the neutron inelastic scattering off 232Th, an experiment took place at the EC-JRC Geel conducted with the experimental setup GRAPhEME to detect emitted γ-rays. The prompt γ-ray spectroscopy method was used and 70 experimental 232Th(n, n’γ) cross sections were obtained from the experimental data. Combining these cross sections, nuclear-structure data available in databases and hypotheses to complete the latter, neutron inelastic level production cross sections in 232Th and the total inelastic cross section were calculated. For the first time, the total inelastic cross section of an actinide nucleus was derived on the total neutron energy range from experimental data only. Comparisons of (n, n’) cross section data with evaluated data reveal a good agreement between them all above 300 keV of neutron energy. TALYS calculations are compatible but lower than the evaluated data.

Neutron elastic and inelastic cross section measurements on silicon from 0.8–8 MeV

Neutron elastic and inelastic scattering differential cross sections were measured at angles between 30∘ and 155∘ with incident neutron energies between 0.8 and 8 MeV. The measured differential scattering cross sections are compared to existing measurements and the ENDF/B-VIII.0, the JEFF-3.3, and the JENDL-4.0 data evaluations, as well as theoretical calculations from the TALYS-1.95 nuclear reaction code. Our results are reasonably well described by values from the ENDF/B-VIII.0 and JEFF-3.3 compilations. However, below 4 MeV, our backward-angle elastic scattering results tend to be lower than database/calculated values, suggesting that less recoil damage would occur than expected. Above 6 MeV, larger backward-angle cross sections are observed suggesting the opposite. Deexcitation γ rays produced in the inelastic scattering process were also studied for neutron energies between 1.9 and 4.5 MeV. Neutron inelastic scattering cross sections deduced from 28Si(n,nγ1) γ-ray production cross sections confirm our 28Si(n,n1) results. To the extent that data from GELINA and our experimental results can be compared, we have excellent agreement between the neutron inelastic scattering cross sections.

Measurement of U238(n,n′γ ) cross section data and their impact on reaction models

A better knowledge of $(n,xn)$ reaction cross sections is important for both reaction modeling and energy applications. This article focuses on inelastic scattering of neutrons off $^{238}\mathrm{U}$ for which improvements are needed to better constrain evaluations and solve inconsistencies in nuclear power reactor calculations. A new precise measurement of $(n,xn\ensuremath{\gamma})$ reaction cross sections on $^{238}\mathrm{U}$ has been performed at the GELINA (Geel Electron LINear Accelerator) neutron facility operated by EC-JRC-Geel (Belgium) with the GRAPhEME (GeRmanium array for Actinides PrEcise MEasurements) setup. The prompt $\ensuremath{\gamma}$-ray spectroscopy method coupled to time-of-flight measurements is used to extract $(n,xn\ensuremath{\gamma})$ cross section values which can be further combined to infer the total neutron inelastic scattering cross section. Cross section data for 18 $\ensuremath{\gamma}$ transitions (five never measured before) are presented and compared to the data in the literature. Emphasis is especially given to the uncertainty determination to produce partial cross section data as accurate as possible. Due to intrinsic limitations of the experimental method, the use of additional nuclear structure information coupled with theoretical modeling is required to determine the total $(n,{n}^{\ensuremath{'}})$ cross section over the whole neutron energy range. We have investigated modeling aspects of the $^{238}\mathrm{U}(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ cross sections related to the description of compound nucleus and preequilibirum mechanisms as well as the discrete part of nuclear structure. Through comparison between experimental and calculated $(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ cross sections, we pinpoint inaccuracies in the description of specific reaction mechanisms and challenge recently implemented models. This helps improving the whole modeling of the $(n,{n}^{\ensuremath{'}})$ reaction.

Incoherent approximation for neutron up-scattering cross sections and its corrections for slow neutrons and low crystal temperatures

The incoherent approximation (IA) is often used for calculating the one-phonon inelastic neutron scattering cross section for arbitrary solids. It is valid for thermal neutrons but for slow neutrons it requires a correction, which is significant for isotopes that are strong coherent scatterers. In this article, we present the extension of the Placzek--Van Hove corrections for slow neutrons in the limit of low temperatures using the example of solid \emph{ortho}-deuterium (sD$_2$). Our approach yields realistic one-phonon up-scattering cross sections for sD$_2$ and shows the IA to be a factor of 2 to 5 too high for ultracold neutron (UCN) up-scattering in sD$_2$. Our calculations are compared with previously published Monte Carlo calculations of the one-phonon cross section based on the dynamic structure function $S(q,\omega)$ of polycrystalline \emph{ortho}-deuterium and are found to be consistent with them. Furthermore, we provide the means for easily replicable calculations of the one-phonon up-scattering cross sections of solid \emph{ortho}-deuterium for slow neutrons. These should from now on be used in calculations and simulations of UCN scattering in sD$_2$.

Magnetic monopoles and toroidal moments in LuFeO3 and related compounds

Magnetic monopoles and toroidal order are compelling features that have long been theorized but remain elusive in real materials. Multiferroic hexagonal ferrites are an interesting realization of frustrated triangular lattice, where magnetic order is coupled to ferroelectricity and trimerization. Here we propose a mechanism, through which magnetic monopolar and toroidal orders emerge from the combination of 120$^\circ$ antiferromagnetism and trimerization, present in hexagonal manganites and ferrites. The experimentally observable signatures of magnetic monopolar and toroidal orders are identified in the inelastic neutron scattering cross section, simulated from a microscopic model of LuFeO3. The non-reciprocal magnon propagation is demonstrated.

Experimental verification of neutron inelastic scattering cross section for iron

Results of experimental verification of results on neutron inelastic scattering cross section for iron obtained in measurements of spectra of neutrons undergoing inelastic scattering at incident neutron energies of 6.0, 7.0 and 8.0 MeV and their calculations within the framework of statistical theory of nuclear reactions and direct interactions are presented. Description is given of the methodology of measurements and simulation calculations. Spectra of neutrons undergoing inelastic scattering obtained for iron in the process of experiments are analyzed in comparison with calculated data. New measurements of neutron inelastic scattering spectra and their analysis within the framework of contemporary modeling understanding allowed formulating proposal on introduction of corrections in the indigenous BROND-2.2 library of recommended evaluated neutron data and insignificant corrections in the most recent version of the library BROND-3.

Экспериментальное тестирование сечения неупругого рассеяния нейтронов на железе

Экспериментальное тестирование сечения неупругого рассеяния нейтронов на железе

Study of the 15N(p,n)15O reaction as a monoenergetic neutron source for the measurement of differential scattering cross sections

The 15N(p,n) reaction is a promising candidate for the production of monoenergetic neutrons with energies of up to 5.7 MeV at the facilities where the T(p,n)3He reaction cannot be used. The characteristic properties of this reaction were studied focusing on its suitability as a source of monoenergetic neutrons for the measurement of differential scattering cross sections in the neutron energy range of 2 MeV to 5 MeV . For this purpose differential and integral cross sections were measured and the choice of optimum target conditions was investigated. The reaction has already been used successfully to measure of elastic and inelastic neutron scattering cross sections for natPb in the energy range from 2 MeV to 4 MeV and for 209Bi and 181Ta at 4 MeV .

Inspection of56Feγ-Ray angular distributions as a function of incident neutron energy using optical model approaches

Neutron inelastic scattering cross sections measured directly through (n,n) or deduced from γ-ray production cross sections following inelastic neutron scattering (n,n′ γ) are a focus of basic and applied research at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator). For nuclear data applications, angle-integrated cross sections are desired over a wide range of fast neutron energies. Several days of experimental beam time are required for a data set at each incident neutron energy, which limits the number of angular distributions that can be measured in a reasonable amount of time. Approximations can be employed to generate cross sections with a higher energy resolution, since at 125o , the a 2 P 2 term of the Legendre expansion is identically zero and the a 4 P 4 is assumed to be very small. Provided this assumption is true, a single measurement at 125o would produce the γ-ray production cross section. This project tests these assumptions and energy dependences using the codes CINDY/SCAT and TALYS/ECIS06/SCAT. It is found that care must be taken when interpreting γ-ray excitation functions as cross sections when the incident neutron energy is < 1000 keV above threshold or before the onset of feeding.

A Phonon-Based Covariance Methodology for ENDF S(α, β) and Thermal Neutron Inelastic Scattering Cross Sections

The S(α, β) double-differential thermal neutron scattering law tabulated in Evaluated Nuclear Data File (ENDF) File 7 is, by convention, produced theoretically through fundamental scattering physics models. Currently, no published ENDF evaluations contain covariance data for S(α, β) or associated scattering cross sections. Furthermore, no accepted methodology exists for quantifying or representing these covariances. Thermal scattering cross sections depend on the interatomic structure and dynamics of the material. For many solids, the influence of these properties on inelastic scattering cross sections can be adequately described through the phonon energy spectrum. The phonon spectrum can be viewed as a probability density function and is commonly the fundamental input for calculating S(α, β). Probable variation in the shape of the phonon spectrum may be established that characterizes uncertainties in the physics models and methodology employed in its production. Through Monte Carlo sampling of perturbations from the reference phonon spectrum, an S(α, β) covariance matrix may be generated. With appropriate sensitivity information, the S(α, β) covariance matrix can be propagated to generate covariance data for differential and integral cross sections. In this work, hexagonal graphite is used as an example material for demonstrating the proposed procedures for analyzing, calculating, and processing uncertainty information for theoretically generated thermal neutron inelastic scattering data.

Experimental measurements with Monte Carlo corrections and theoretical calculations of neutron inelastic scattering cross section of 115In

The neutron inelastic scattering cross section of In115 has been measured by the activation technique at neutron energies of 2.95, 3.94, and 5.24MeV with the neutron capture cross sections of Au197 as an internal standard. The effects of multiple scattering and flux attenuation were corrected using the Monte Carlo code GEANT4. Based on the experimental values, the In115 neutron inelastic scattering cross sections data were theoretically calculated between the 1 and 15MeV with the TALYS software code, the theoretical results of this study are in reasonable agreement with the available experimental results.

Experimental measurement and Monte Carlo correction of neutron inelastic scattering cross section of 115 In

Experimental measurement and Monte Carlo correction of neutron inelastic scattering cross section of 115 In

Integral cross section measurement of theU235(n,n′)U235mreaction in a pulsed reactor

The integral measurement of the neutron inelastic cross section leading to the 26-minute half-life $^{235m}\mathrm{U}$ isomer in a fission-like neutron spectrum is presented. The experiment has been performed at a pulsed reactor, where the internal conversion decay of the isomer was measured using a dedicated electron detector after activation. The sample preparation, efficiency measurement, irradiation, radiochemistry purification, and isomer decay measurement will be presented. We determined the integral cross section for the $^{235}\mathrm{U}(n,{n}^{\ensuremath{'}})^{235m}\mathrm{U}$ reaction to be $1.00\ifmmode\pm\else\textpm\fi{}0.13\phantom{\rule{0.28em}{0ex}}\mathrm{b}$. This result supports an evaluation performed with talys-1.4 code with respect to the isomer excitation as well as the total neutron inelastic scattering cross section.

Undergraduate Measurements of Neutron Cross Sections

Undergraduate students at the University of Dallas have investigated basic properties of nuclei through γ-ray and neutron spectroscopy following neutron scattering. The former has been used primarily for nuclear structure investigations, while the latter has been used to measure neutron scattering cross sections important for fission reactor applications. A series of (n,n’) and (n,n’γ) measurements have been made on 54Fe and 56Fe to determine neutron cross sections for scattering to excited levels in these nuclei. The former provides the cross sections directly and the latter are used to deduce inelastic neutron scattering cross sections by measuring the γ-ray production cross sections to states not easily resolved in neutron spectroscopy. All measurements have been completed at the University of Kentucky Accelerator Laboratory using a 7-MV Model CN Van de Graaff accelerator, along with the neutron production and neutron and γ-ray detection systems located there. Students participate in accelerator operation, experimental setup, data acquisition, and data analyses. An overview of the research program and student contributions is presented.

Fast-neutron Induced Reactions at the nELBE Time-of-flight Facility

The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf is being rebuilt and extended with a low-background experimental hall. The neutron radiator consists of a liquid lead circuit without additional neutron moderators. The useful neutron spectrum extends from some tens of keV to about 10 MeV. nELBE is intended to deliver cross section data of fast-neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. Before the extension of the facility, the photon production cross section of 56Fe was measured with an HPGe detector and the inelastic neutron scattering cross section to the first few excited states in 56Fe was determined. The neutron total cross sections of Au and Ta were determined in the energy from 200 keV to 7 MeV in a transmission experiment.

Generation of an [formula omitted] Covariance Matrix by Monte Carlo Sampling of the Phonon Frequency Spectrum

Formats and procedures are currently established for representing covariances in the ENDF library for many reaction types. However, no standard exists for thermal neutron inelastic scattering cross section covariance data. These cross sections depend on the material's dynamic structure factor, or S(α,β). The structure factor is a function of the phonon density of states (DOS). Published ENDF thermal neutron scattering libraries are commonly produced by modeling codes, such as NJOY/LEAPR, which utilize the DOS as the fundamental input and directly output the S(α,β) matrix. To calculate covariances for the computed S(α,β) data, information about uncertainties in the DOS is required. The DOS may be viewed as a probability distribution function of available atomic vibrational energy states in a solid. In this work, density functional theory and lattice dynamics in the harmonic approximation were used to simulate the structure of silicon dioxide (α-quartz) to produce the DOS. A range for the variation in the partial DOS for silicon in α-quartz was established based on limits of variation in the crystal lattice parameters. Uncertainty in an experimentally derived DOS may also be incorporated with the same methodology. A description of possible variation in the DOS allowed Monte Carlo generation of a set of perturbed DOS spectra which were sampled to produce the S(α,β) covariance matrix for scattering with silicon in α-quartz. With appropriate sensitivity matrices, it is shown that the S(α,β) covariance matrix can be propagated to generate covariance matrices for integrated cross sections, secondary energy distributions, and coupled energy-angle distributions.

Elastic and Inelastic Neutron Scattering Cross Sections for natPb, 209Bi, and natTa in the Energy Range from 2 MeV to 4 MeV

Elastic and Inelastic Neutron Scattering Cross Sections for natPb, 209Bi, and natTa in the Energy Range from 2 MeV to 4 MeV

Statics and dynamics of weakly coupled antiferromagnetic spin-12ladders in a magnetic field

We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work is motivated by recent experiments on the compound (C5H12N)2CuBr4 (BPCB). We use a combination of numerical and analytical methods, in particular the density matrix renormalization group (DMRG) technique, to explore the phase diagram and the excitation spectra of such a system. We give detailed results on the temperature dependence of the magnetization and the specific heat, and the magnetic field dependence of the nuclear magnetic resonance (NMR) relaxation rate of single ladders. For coupled ladders, treating the weak interladder coupling within a mean-field or quantum Monte Carlo approach, we compute the transition temperature of triplet condensation and its corresponding antiferromagnetic order parameter. Existing experimental measurements are discussed and compared to our theoretical results. Furthermore we compute, using time dependent DMRG, the dynamical correlations of a single spin ladder. Our results allow to directly describe the inelastic neutron scattering cross section up to high energies. We focus on the evolution of the spectra with the magnetic field and compare their behavior for different couplings. The characteristic features of the spectra are interpreted using different analytical approaches such as the mapping onto a spin chain, a Luttinger liquid (LL) or onto a t-J model. For values of parameters for which such measurements exist, we compare our results to inelastic neutron scattering experiments on the compound BPCB and find excellent agreement. We make additional predictions for the high energy part of the spectrum that are potentially testable in future experiments.