Neutron Distribution Research Articles

Visualization and quantification of Li distribution in garnet solid electrolytes Li6.25La3Zr2Al0.25O12

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for all-solid-state batteries due to its structural stability and high Li+ ionic conductivity, but high-purity LLZO crystallizes in a low-conductivity tetragonal phase at room temperature (RT). Al doping stabilizes the cubic structure, yet its impact on Li+ migration is not fully understood. Using Li6.25La3Zr2Al0.25O12 (LLZAO) as a model, we conducted temperature-dependent neutron powder diffraction (NPD), neutron pair distribution function (nPDF), and density-functional theory (DFT) computations. NPD results, supported by nPDF, show Li+ ions at 24d and 96h sites, excluding 48g. Al at 24d adjusts the distribution of Li, improving ionic conductivity near RT. Maximum Entropy Method analyses indicate a temperature-driven 3D Li diffusion pathway of 24d-96h-96h-24d channels, confirmed by DFT. This work will enhance the understanding of Li diffusion and the optimization of ionic conductivity in garnet-type solid electrolytes.

Clinical evaluation of performance, stability, and longevity of an accelerator system designed for boron neutron capture therapy utilising a beryllium target.

Boron neutron capture therapy for recurrent head and neck cancer has been approved as an insurance covered treatment in Japan since June 2020. The Kansai BNCT Medical Center has installed the NeuCure® BNCT system developed by Sumitomo Heavy Industries. This system utilises a beryllium target with a 30 MeV proton beam to generate neutrons. To date, the center has treated over 300 patients and the system is also used for quality control and fundamental research experiments. Information on the stability and longevity of the system is important for facilities and hospitals considering installation of a BNCT system in the future, particularly after an exchange of a major component, such as the target. The beam output (neutron and gamma ray) was measured before and after the exchange of the target. The thermal neutron, fast neutron and gamma ray distribution inside a water phantom was evaluated and the results showed no significant change in the beam quality after the exchange of the target. Furthermore, no significant change in the neutron flux as a function of increasing number of accumulated protons on the target was observed up to a value of just under 400 mAh. The NeuCure® BNCT system has been shown to be highly stable and the frequency of target replacement was much less than lithium target-based accelerators.

Toxic, radioactive, and disordered: a total scattering study of TlTcO4.

A detailed variable temperature neutron total scattering study of the potential nuclear waste matrix TlTcO4 was conducted. The long-range average structure of TlTcO4 undergoes an orthorhombic Pnma to tetragonal I41/amd phase transition below 600 K, consistent with previous synchrotron X-ray diffraction studies. However, several anomalies were observed in the Rietveld refinements to the neutron powder diffraction data, such as large atomic displacement parameters at low temperature and a shortening of the Tc-O bond distance upon heating. Modelling the short-range local structure of both the low- and high-temperature data required a lowering of symmetry to the monoclinic P21/c model due to the stereochemical activity of the Tl+ 6s2 lone pairs. Density functional theory calculations also verified this model to have a lower ground state energy than the corresponding long-range average structure. It is concluded that at low temperatures, the Tl+ 6s2 lone pairs are 'frozen' into the structure. Upon heating, the rigid TcO4 tetrahedra begin to rotate, as governed by the Γ3+ and M4+ modes. However, there is a disconnect between the two length scales, with the 6s2 lone pair electrons remaining stereochemically active on the local scale, as observed in the neutron pair distribution function fits. The orthorhombic Pnma to tetragonal I41/amd phase transition is seemingly the result of a change in the correlation length of the Tl+ 6s2 lone pairs, leading to a larger unit cell volume due to their uncorrelated displacements.

Multi-zone cooperative reconstruction network for off-situ monitoring of the core neutron field

Neutron field monitoring based on the ex-core detection signals is an effective means to obtain the neutron distribution when the core environment is harsh. The existed off-situ reconstruction methods of neutron fields belong to global solution, which inevitably reduces the local reconstruction accuracy of neutron field. In this paper, a novel Multi-zone Cooperative Reconstruction Network (MCRNet) is proposed based on deep learning, and the assistance and synchronous gating mechanisms are designed to realize the collaborative reconstruction between different core zones. This study performed reconstruction experiments on CLEAR-I and HBR, respectively. The results show that the average relative deviation ARD is within 2 %, and the ratio of units with a RD greater than 10 % RRD≥10% is within 6.5 %. It means that for the neutron field with different scales, the MCRNet can accurately reconstruct the neutron field of some core regions under the complex core changes.

Ba3Ti0.4W1.6O8.6: An Oxygen- and B-Site-Deficient 9R Hexagonal Perovskite Exhibiting Triple Conduction.

The hexagonal perovskite derivatives Ba3M'M″O8.5 featuring a hybrid structure composed of 9R hexagonal perovskite and palmierite structure motifs exhibit significant oxide ionic conductivity due to the highly disordered oxide-ion and M-cation sublattices. Herein, we report the structure and electrical properties of the perovskite Ba3Ti0.4W1.6O8.6. Three-dimensional (3D) electron diffraction (ED), neutron powder diffraction (NPD), and neutron pair distribution functions (nPDF) revealed a 9R hexagonal perovskite structure for Ba3Ti0.4W1.6O8.6 with fully occupied central M2 sites, partially occupied outer M1 sites, and oxygen-deficient cubic c-BaO2.6 sublayers. These cation and oxygen arrangements differ significantly from those in Ba3M'M″O8.5 and enable Ba3Ti0.4W1.6O8.6 to capture atmospheric water and O2, resulting in triple conduction (oxide ion, proton, and hole) under wet air conditions. Proton and oxide ion conductions predominate at temperatures <400 and >650 °C in wet Ar and dry air, respectively. Bond-valence site energy calculations, together with structure analysis, deciphered that the two-dimensional oxide-ion diffusion pathways along the c-BaO2.6 layers are disrupted by the M1 vacancies, thereby resulting in relatively low oxide ionic conductivity. Our findings open up a new strategy of utilizing the cation's propensity of coordination geometry to design new oxygen- and B-site-deficient perovskites and thus achieve desired conductivity.

Fast neutron generation with few-cycle, relativistic laser pulses at 1 Hz repetition rate

Laser-driven deuterons generate neutrons with a mean energy of 2.5 MeV, through the 2H(d,n) fusion reaction in a deuterated polyethylene (dPE) tablet. The deuterium ions are accelerated by 12 fs, 21 mJ laser pulses interacting with a 0.2 µm thin dPE foil at a peak intensity of 1018 W/cm2. The laser was operated at 1 Hz repetition rate in bursts of 75 shots. The interaction was characterized and recorded for each laser shot. The ion spectra were measured in the forward and backward directions by Thomson ion spectrometers. Neutron events were detected by a time-of-flight (ToF) system consisting of four plastic scintillators positioned at various angles around the experimental chamber. The maximum cut-off energy of the forward accelerated protons and deuterons was close to 1.4 MeV and 1 MeV, while the mean values are 428 ± 63 keV and 433 ± 80 keV, respectively. Analysis of ToF distributions from 3128 shots resulted in an average yield of 1142 ± 59 neutrons per shot in the energy range of 1.5–4 MeV. The energy distribution of forward-directed neutrons peaks between 3 and 3.5 MeV. Angular dependence analysis showed a perpendicular minimum and a maximum along the deuteron beam, consistent with the expected distribution from the literature and our simulation results.

Advancements to generalized equivalence theory for preserving cross-sections of whole core simulations

The conventional two-step approach, without the use of an equivalence method, can introduce significant error for the simulation of non-LWRs (Light Water Reactors), especially fast reactors, due to the large leakage and high anisotropic neutron distribution. To improve upon the accuracy of the two-step approach, a 3D whole core model is simulated with a transport method to generate region-wise homogenized cross-sections (XS). These XS can then be used in a diffusion whole core solver during the second step to extend the application to cycle and transient analysis. Discontinuity factors (DFs) are then introduced to improve the accuracy during the simulation of the second step. With properly generated DFs from Generalized Equivalence Theory (GET), the region-averaged solutions from the first transport step can then be reproduced by the second step diffusion solver. The Monte Carlo method was selected to perform the whole core transport simulation to generate region-wise XS. However, simulating whole core problems with Monte Carlo may result in poor statistics near the peripheral region especially for partial current tallies. This paper introduces an advancement to GET to reproduce region-wise solutions for select regions when the reaction rates and surface currents have good statistics in these regions but poor statistics in other regions. A reference high-fidelity model was constructed using the Serpent 2 Monte Carlo code based on the EBR-II benchmark evaluation and verification was carried out using the TriPEN-4 method in PARCS. The results show that it is possible to reproduce the exact eigenvalue and power distributions of whole core problems in a feasible manner.

Polymer Boron-Containing Composite for Protecting Astronauts of Manned Orbital Stations from Secondary Neutron Radiation

This article considers the prospects of using heat-resistant polyimide boron-containing composites to protect astronauts of manned orbital stations from secondary neutron radiation. Variant calculations are performed regarding neutron and gamma-quanta flux distributions in a polyimide composite material with different boron content used to reduce capture radiation. The dependences of spatial distributions of thermal neutron flux density and the gamma-quanta dose rate in a polyimide composite layer with a boron content of 0 to 5% are obtained. An experimental assessment of the energy distribution of neutron and gamma radiation behind the protective polyimide composite is carried out. The introduction of boron atoms in an amount of 3.0 wt.% shows the absence of bursts of secondary gamma radiation energy in the composite, which is due to the high cross-section of thermal neutron absorption by boron atoms. As a result, with a material layer thickness of 3–10 cm, the gamma-quanta dose rate decreases by 2–3 times. The differential thermal analysis method showed that the upper limit of the working temperature of the polyimide composite is 500 °C. The polyimide matrix filled with boron atoms can find effective application in the development of new radiation-protective polymer materials used in manned orbital stations.

Bonner sphere measurements of high-energy neutron spectra from a 1 GeV/u 56Fe ion beam on an aluminum target and comparison to spectra obtained by Monte Carlo simulations

The goal of this work is to characterize the secondary neutron spectra produced by 1 GeV/u56Fe beam colliding with a thick cylindric aluminum target and to perform a quantitative comparison with simulated results obtained with Monte Carlo codes. The measurements were performed using extended-range Bonner sphere spectrometers at two positions (15° and 40°) with respect to the beam direction. The secondary radiation field was simulated using four Monte Carlo codes (FLUKA, MCNP6, Geant4 and PHITS) and several physical models of nuclei transport and interaction. Neutron and proton energy distributions were simulated for the experimental measurement positions. The simulated neutron spectra, together with data measured with Bonner sphere spectrometers, after carrying out the correction of the contributions induced by the secondary protons, were used as input for the MAXED spectrum unfolding code to obtain the measured neutron spectra. Unfolded neutron spectra were compared with simulated ones to carry out a quantitative analysis of the performance of the chosen Monte Carlo codes and their corresponding physical models. This comparison showed that, because of experimental uncertainties and physical models, there are no unique solutions for each measurement location, but a range of solutions where the true experimental neutron spectra probably lie. The results showed deviations between 4.23% and 8.42% for some simulated spectra. Regarding the total integral values of neutron fluence and ambient equivalent dose, the unfolded neutron spectra showed deviations lower than 2%.

Моделирование чувствительности литийсодержащих кристаллических сцинтилляторов к нейтронному излучению

This paper presents the results of Monte Carlo modelling of the sensitivity of the lithium containing detectors CLYC, NaIL, CLLB to thermal neutrons. The difference between the sensitivity and the neutron freepath depth of the CLYC scintillator enriched and unenriched with the 6Li isotope is shown. The analysis of the distribution of alpha particles and neutrons in the scintillator volume is performed, showing the inefficiency of the unenriched scintillator due to the fact that not all neutrons react with the crystal material. Mathematical modelling by the Monte Carlo method of the scintillator sensitivity and its comparison with respect to the irradiation direction has been carried out. It is shown that for the scintillator in the face and side geometry with the size more than 38 mm the difference in sensitivity at change of the neutron flux direction is connected only with the scintillator cross section and 6Li concentration with the same value of the specific sensitivity. The obtained model results were compared with available experimental data for NaIL and CLLB scintillators, which showed the reliability of the developed models and calculation methods.

Characterization of the PGNAA neutron beam of Isfahan MNSR through the calculations and different measurement methods

In this work, the significant characterization of the neutron beam used in the PGNAA facility of the Isfahan MNSR research reactor has been determined using both calculation and measurement. The important parameters of the beam include flux and energy distribution of neutrons, cadmium ratio, thermal neutron content (TNC), and neutron-to-gamma ratio (n/γ). In this regard, Monte Carlo simulation and experiments were implemented to find these characteristics. The experiments have been carried out through the relative and absolute activation methods using irradiation of indium foil and mica in combination with uranium foil. Moreover, the condition of the neutron beam has been investigated in terms of contamination with fast neutrons using the germanium triangle method. The results showed that the MNSR has acceptable characteristics for performing PGNAA analyses despite its low power.

Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD)3 layers as an intermediate particle phase. These layers ultimately stack to form gibbsite- or bayerite-like layered heterostructures. Ex-situ characterization of the recovered precipitates using 27Al magic angle spinning nuclear magnetic resonance spectroscopy, Raman, X-ray diffraction, and scanning electron microscopy, suggests the presence of additional intermediate states, an amorphous compound bearing both tetrahededrally- and penta-coordinated Al3+. These observations reveal the complex pathways to form Al(OD)3 monolayers via either transient pentacoordinate species or amorphous-to-ordered transitions. The subsequent crystallization of admixed gibbsite/bayerite is followed by an Al(OD)3 monolayer attachment process.

Dual Polyanion Mechanism for Superionic Transport in BH4‐Based Argyrodites

AbstractPolyanion rotations are often linked to cation diffusion, but the study of multiple polyanion systems is scarce due to the complexities in experimentally determining their dynamic interactions. This work focuses on BH4‐based argyrodites, synthesized to achieve a high conductivity of 11 mS cm−1. Advanced tools, including high‐resolution X‐ray diffraction, neutron pair distribution function analysis, and mutinuclear magic‐angle‐spinning nuclear magnetic resonance (NMR) spectroscopy and relaxometry, along with theoretical calculations, are employed to unravel the dynamic intricacies among the dual polyanion lattice and active charge carriers. The findings reveal that the anion sublattice of Li5.07PS4.07(BH4)1.93 affords an even temporal distribution of Li among PS43− and BH4−, suggesting minimal trapping of the charge carriers. Moreover, the NMR relaxometry unveils rapid BH4− rotation on the order of ∼GHz, affecting the slower rotation of neighboring PS43− at ∼100 MHz. The PS43− rotation synchronizes with Li+ motion and drives superionic transport. Thus, the PS43− and BH4− polyanions act as two‐staged dual motors, facilitating rapid Li+ diffusion.

Characterization of Neutron Irradiator as a Source of Reference Radiation Field for Calibrating Dosemeters and Doserate Meters at PSI Laboratory

A new neutron calibration laboratory has been installed at the Paul Scherrer Institute in Switzerland. The calibration laboratory has been equipped with a newly developed neutron irradiator with two calibration benches, remote control instruments and related ancillary equipment for calibrating dosemeters and doserate meters. The actual dimensions of the calibration laboratory are 2.0 m (H) X 6.8 m (W) X 12.6 m (L). On the steel grid at a height of 2 m from the basement floor, two calibration benches are installed. A transport channel is installed in the middle of the benches for the transfer of the radiation sources. The radiation sources are moved from the safe position of the irradiator to the reference irradiation position using an air pressure unit. The reference position is at a height of 1.2 m from the grid floor. The neutron irradiator is equipped with two Am-Be sources. Characterization of neutron radiation field has been calculated in detail by the MCNPX neutron transport code as well as energy distribution of neutrons and contribution of scattered neutrons. Experimentally, it was measured with a neutron/gamma digital spectrometric system equipped with a stilbene detector. The quality of the neutron radiation field has been characterized by ambient dose equivalent rate and the shape of the Am-Be spectra has been verified with the ISO-8529 standard.

Antineutrino Opacity in Neutron Stars in Models Constrained by Recent Terrestrial Experiments and Astrophysical Observations

Inthe present paper, we investigate neutral current (NC) antineutrino scattering with the constituents of neutron star (NS) matter at zero temperature. The modeling of standard matter in NS is constructed within the framework of both extended relativistic mean-field (E-RMF) and nonrelativistic Korea-IBS-Daegu-SKKU energy density functional (KIDS-EDF) models. In the E-RMF model, we use a new parameter, G3(M), which was constrained by the recent PREX II experiment measurement of neutron distribution in 208Pb, while the KIDS-EDF models are constrained by terrestrial experiments, gravitational-wave signals, and astrophysical observations. Using both realistic and well-constrained matter models, we then calculate the antineutrino differential cross-section (ADCS) and antineutrino mean free path (AMFP) for the interaction between antineutrinos and neutron star (NS) matter constituents using linear response theory. It is found that the AMFP for the KIDS0 and KIDSA models are smaller compared to the SLy4 model and the E-RMF model with the G3(M) parameter. The AMFP result of the Skyrme model with the SLy4 parameter set is found to have a prediction almost similar to that of the E-RMF model with the G3(M) parameter. Contributions of each nucleon to the total AMFP are also presented for the G3(M) model.

Refined determination of the weak mixing angle at low energy

The weak mixing angle is a fundamental parameter of the electroweak theory of the standard model whose measurement in the low-energy regime is still not precisely determined. Different probes are sensitive to its value, including atomic parity violation, coherent elastic neutrino-nucleus scattering, and parity-violating electron scattering on different nuclei. In this work, we attempt for the first time to combine all these various determinations by performing a global fit that also takes into account the unavoidable dependence on the experimentally poorly known neutron distribution radius of the nuclei employed, for which a new measurement using proton-cesium elastic scattering became available. By using all present direct determinations of the neutron distribution radius of cesium, we find sin2ϑW=0.2396−0.0019+0.0020, which should supersede the previous value determined from atomic parity violation on cesium. When including electroweak only, but also indirect, determinations of the neutron distribution radius of cesium, the uncertainty reduces to 0.0017, maintaining the same central value and showing excellent agreement independently of the method used. Published by the American Physical Society 2024

Understanding the influence of local structure distortions on Na-ion migration in perovskite solid electrolytes

The perovskite structured oxides of composition ABO3 are considered strong candidates for solid-state electrolytes in all-solid-state batteries due to their chemical and structural flexibility. However, further improvements must be made before they become commercially viable, and this requires a clear understanding of the structure-property relationships. In this study, the local structure of the perovskite sodium-ion solid electrolyte series Na1/2−xLa1/2−xSr2xZrO3 (NLSZ, x = 14, 16, 18, 116) was investigated via neutron total scattering. Small-box modelling against the neutron pair distribution function with the orthorhombic Pbnm structure showed local-scale features that deviate from the average structure. Big-box modelling revealed significant differences between the bonding configurations of the different A-site cations, which impacts the ionic conductivity of the material. This study demonstrates how understanding local-scale disorder is important for tuning the structure-property relationships of inorganic solid-state electrolyte materials in sustainable battery technologies.

Difference between the Distributions of Intermediate and Slow Neutrons from the Outlet Channel of a Photoneutron Source

Difference between the Distributions of Intermediate and Slow Neutrons from the Outlet Channel of a Photoneutron Source

The Energy and Angular Distributions of Neutrons from (γ, N)-Reactions on γ-Beams Produced by Backward Compton Scattering at Eγ ≲ 40 MeV

The Energy and Angular Distributions of Neutrons from (γ, N)-Reactions on γ-Beams Produced by Backward Compton Scattering at Eγ ≲ 40 MeV

Study on the contribution matrix for EAST radial neutron camera system

The EAST (Experiment Advanced Superconductor Tokamak) Radial Neutron Camera (RNC) is designed to measure the temporal and spatial distribution of fast neutrons. The system primarily consists of detector components, shielding collimators, support structure, and data acquisition system. We have studied on the neutronic transport through MCNP with EAST reference D-D neutron source (EAST #77160), and calculated the plasma neutron source chord integral along the observation sightlines and scattering neutrons from structural facilities. Contribution matrixes, incorporating both uncollided and scattered neutrons determines the response from the neutron source to every detector unit. We evaluate the RNC primarily through the variation of the RNC sightlines to improve detector performance by reducing interference particles, thereby laying the foundation for subsequent upgrades. Benefiting from these measurements, we can better study the detector signals in relation to corresponding plasma configurations in the future.