Improved light charged particle identification method using grid ionization chamber at CSNS Back-n White Neutron Source.

Comparative analysis of spectrometry results obtained for plutonium and americium-based neutron sources.

Study on migration characteristics of multi-component gases driven by the cold source of passive containment cooling system in a large enclosed space

The Practicalities of Studying Phosgene at a Neutron Source: Safety, Collaboration, and Lessons Learned

Abstract This study investigates the mechanisms by which stratospheric intrusion contributed to a heavy snowfall event in China's Middle‐Lower Yangtze River (MLYR) region during 19–24 February 2024, which prompted a second‐highest‐level emergency response. Using station and ERA5 reanalysis data, we found that accompanying a Ural blocking‐transverse trough system and an intensified East Asian subpolar jet, a stratospheric intrusion of unprecedented depth (air with 1.5/1.0 ‐PVU potential vorticity (PV) penetrating to ∼600/700 hPa) occurred on 20 February, coinciding with the peak daily snow accumulation. Using HYSPLIT trajectories and piecewise PV inversion, we found that descending stratospheric air was not a direct cold air source in the lower troposphere. Instead, the key mechanism of stratospheric impact on snowfall is the dynamical forcing from upper‐level PV anomalies. From 18 February, a high‐PV band near the transverse trough guided the southeastward convergence of three lower‐level cold air streams from high latitudes, promoting frontogenesis and cold conditions. On 20 February, intrusion‐induced PV anomalies intensified the polar jet (accounting for ∼45% of intensification) and induced a Northeast China Cold Vortex anomaly. They drove a secondary circulation with subsidence over Northeast China at the northern side of the jet entrance, ascent over the MLYR, and northerlies in between. Concurrently, lower‐boundary PV anomalies strengthened a Mongolian High‐like anticyclone. The upper‐level PV‐induced vortex transported cold air from high latitudes, while the lower‐boundary PV‐induced anticyclone advected it further southward, forming a “cold air relay mechanism.” The mid‐tropospheric latent heating intensified moisture transport, creating a deep baroclinic zone when clashing with cold air.

Abstract The tritium breeding capacity of fusion blankets is a critical factor in achieving tritium self-sufficiency in fusion reactors. Current designs for tritium production in blankets are based on neutronics simulations, whose accuracy requires experimental validation. This study focuses on the experimental validation of the neutronic design reliability of the supercritical CO 2 -cooled lithium-lead (COOL) blanket developed for the China fusion engineering test reactor (CFETR). For this purpose, an experimental mock-up was designed and fabricated to replicate the key neutronics characteristics of COOL blanket. The mock-up was irradiated using D–T neutron generator and validated using multiple techniques: tritium production rate (TPR) online monitoring with a miniature back-to-back lithium glass scintillator detector, TPR integral measurement using Li 2 CO 3 pellets analyzed by liquid scintillation counting (LSC), and neutron flux measurement with activation foils (Au, Zr). To enhance accuracy, corrections were applied for lithium-lead (PbLi) segregation based on element analysis and for neutron source intensity based on in-situ depth profiling of tritium in the tritide target. The results show excellent agreement between experiments and simulations, with calculation-to-experimental (C/E) value ranging from 0.96 to 1.11 for TPR measured by lithium-glass scintillator detectors, 0.90–1.09 for TPR by Li 2 CO 3 pellets, and 0.84–1.13 for reaction rates measured by activation foils.

Abstract Neutron imaging is a powerful non-destructive testing technique, yet its spatial resolution remains considerably inferior to that of X-ray imaging. Bridging this resolution gap to the micron-level represents a major challenge in the field. This study reports on the development and performance of a micron-resolution neutron imaging detector at the China Spallation Neutron Source (CSNS). The detector employed a custom-fabricated, ultra-thin (5 μm) scintillator based on isotopically enriched gadolinium oxysulfide ( 157 Gd 2 O 2 S:Tb), coupled with a high-magnification optical lens and a scientific CCD camera. At the Energy-Resolved Neutron Imaging Instrument (ERNI), the detector achieved a spatial resolution of 6.6 μm. The detector represents a significant leap in imaging capability at CSNS, enabling advanced non-destructive investigations at the microscale.

Abstract Accurate neutron capture cross section data are essential for validating nuclear models, understanding the origin of heavy elements, and improving reactor safety assessments. Measuring weakly absorbing nuclides at the milli-barn scale is challenging due to low-intensity signals, high-level environmental background, and sensitivity to target impurities. To investigate the capability of milli-barn scale neutron capture cross section measurement using the C6D6 detectors on the Back-n white neutron facility of the China Spallation Neutron Source (CSNS), an experiment on 209Bi(n,γ) was performed. The data were processed using the time-of-flight (TOF) method and the pulse height weighting technique (PHWT). Due to the very small capture cross section of 209Bi and the complex background, the experimental consequence showed strong statistical fluctuations, making it difficult to identify resonance structures. To address this, the average capture cross section was determined by optimizing the energy binning. The reasons for the obscured resonance structures resulted by the background were analyzed, and possible solutions were proposed. This study provides useful experience for measuring low cross section nuclides using the C6D6 detectors.

We investigate the influence of plasma scale length on electron beam stability in direct laser acceleration (DLA) using a series of experiments on multiple laser systems with peak power spanning from 20 to 140 TW. An ultrashort, relativistic-intensity laser pulse interacts with a pre-expanded near-critical-density plasma formed by a nanosecond pre-pulse. We show that plasma expansion times of tens of nanoseconds, corresponding to long, shallow density gradients, result in electron beam pointing stability below 1° (RMS). Two-dimensional particle-in-cell simulations reveal that extended scale lengths suppress laser-driven filamentation and promote sustained self-focusing, leading to a stable acceleration channel. These results establish long-scale-length plasma targets as a robust route to improving beam stability in DLA, specifically when applied as laser-driven electron and neutron sources. Using this electron source, we demonstrated photoneutron generation with up to 9.1×107 neutrons per shot.

Abstract Light water ice is an important material for cold neutron moderator applications or future criticality safety evaluations in low temperature systems. Depending on temperature and pressure conditions, crystalline and amorphous phases may coexist in the same light water ice. The purpose of this study is to elucidate the differences between crystalline and amorphous phases in light water ice in terms of thermal neutron scattering. To achieve this purpose, molecular dynamics simulations are performed to evaluated velocity auto correlation function of light water ice for the crystalline and amorphous models with SCIGRESS, and from the simulation results, thermal neutron scattering cross section data are evaluated with an analysis code called KUNSCA. The total cross section in the crystalline model shows good agreement with experimental values of light water ice at 115 K, and this suggest that the analysis in the present study is generally valid. The thermal neutron scattering cross sections in the amorphous model shows different behavior from that in the crystalline model. In the crystalline model, the inelastic scattering is dominant and higher in the cold neutron energy region (< 5 meV) than that in the amorphous model. This suggests that it may be preferable to minimize the formation of amorphous ice when using light water ice as a cold neutron source.

The planned upgrade of the neutron guide system at the Budapest Research Reactor (BRR) provides an opportunity to enhance the performance of its cold neutron source. In this work, two replacement concepts for the existing liquid hydrogen disk moderator are investigated: (i) a box-shaped para-hydrogen (pH2) moderator and (ii) assemblies of low-dimensional (flat) pH2 moderators. Both designs are optimized using the curve of full and optimal sample illumination method and through Monte Carlo simulations tailored to the BRR geometry and the thermal neutron distribution. The box pH2 moderator is found to increase the cold neutron brightness by up to 2.2 times in the 3-7 Å wavelength range. Flat moderator assemblies, as either staircases or chessboards, provide an additional gain of about 20% at 2 Å, although their advantage diminishes at longer wavelengths due to the non-uniform thermal illumination of the reactor channel and the wavelength dependence of the optimal moderator length. These results demonstrate that pH2 moderators, particularly in low-dimensional geometries, can substantially enhance the performance of the upgraded BRR cold neutron source, with the achievable gains largely limited by the thermal neutron distribution within the existing moderator channel.

Laser-driven neutron sources (LDNSs) offer unique advantages for fundamental physics and applications: ultrashort pulses providing superior energy resolution, high instantaneous flux, and a reduced footprint. While single-event neutron spectroscopy has been demonstrated with epithermal neutrons, its application for fast neutrons is more challenging and remains unproven. This demands stable multi-shot operation and detectors resilient to this particularly extreme environment. Here, a proof-of-concept experiment at the DRACO PW laser is presented. This setup stably produced ~108 fast neutrons per shot sustained over more than 200 shots at a shot-per-minute rate. Neutron time-of-flight measurements with a diamond detector at only 150 cm from the source resolved individual neutron-induced reactions at a rate consistent with simulations informed by real-time diagnostics of accompanying gammas, ions, and electrons. Combined with the recent advances in the field, this work establishes LDNSs as a promising, scalable platform for future fast neutron-induced reaction studies, particularly those involving short-lived isotopes.

In nuclear physics, magnesium is commonly employed as a monitor foil, primarily utilizing the 24Mg(n,p)24Na reaction. The resulting 24Na nuclide exhibits a moderate half-life and emits easily detectable gamma rays. Furthermore, magnesium holds significant industrial value and enables energy recycling. The “magnesium economy” represents a green circular economy that integrates new energy sources and advanced materials. Therefore, high-precision cross-section values for magnesium are of great importance for industrial applications. This paper presents cross-section values obtained using the activation method and relative measurement technique. The experiment was conducted at the CIAE 600 kV Cockcroft-Walton accelerator using a D-T neutron source. The cross-section for the 24Mg(n,p)24Na reaction was measured at 14.8 MeV via the activation method. Samples were irradiated at a 25∘ angle relative to the target head. After a cooling period, the samples were placed in a high-purity germanium detector for measurement. Theoretical calculations were employed, and corrections were applied using the Monte Carlo method to derive the final cross-section value. To enhance the precision of the magnesium cross-section measurement and minimize uncertainties, we adopted a method in which the product nuclei of the sample under study and the monitor foil were identical. This approach directly eliminated uncertainties introduced by factors such as half-life, decay branching ratio, gamma-ray detection efficiency, and beam fluctuations. This design significantly improves measurement accuracy. Compared with other data in the database, the experimental accuracy achieved in this work is substantially enhanced, providing vital support for nuclear data evaluation.

Neutron Resonance Transmission Imaging (NRTI) is an energy-dependent method based on event-mode acquisition of time-of-flight radiographs over a white neutron beam. NRTI enables the identification and mapping of elements and isotopes within the bulk of a sample with enhanced contrast, providing complementary capabilities of conventional imaging methods. Its growing adoption within the user community of the ISIS Neutron and Muon Source underscores the need for a standardised and reproducible data reduction framework to ensure consistent results. A dedicated effort towards its end-user optimisation is underway at the INES beamline of the ISIS facility. This work focuses on NRTI data treatment, detailing the normalisation pipeline and post-processing steps for qualitative isotopes and elements mapping. The methodology is demonstrated through a practical example, highlighting the steps required to achieve transmission data suitable for post-processing analysis.

IK-Frag: Frag data generator for the PHITS simulation with the inverse kinematic reaction producing a focused neutron beam

Advanced acoustically tensioned metastable fluid detectors for 10-15× over He-3 detector efficiency, real-time monitoring of moving SNMS, and spectroscopic identification of fission vs. alpha-n neutron sources

In situ fabrication and characterization of Al–Si/Al2O3 composites via powder metallurgy for Neutron shielding applications

Design analysis of neutron source based on low energy cyclotron used for small-scale accelerator-driven system.

Fluorescent Nuclear Track Detectors (FNTDs) provide high spatial resolution, wide linear energy transfer coverage, and reusability, making them well-suited for high-energy neutron dosimetry. When neutrons traverse a polyethylene converter, recoil protons are generated, and their tracks are stored inside the FNTDs and visualised through optical readout. Traditional analysis of FNTD images relies on deterministic algorithms or machine learning methods with explicit feature definition, limiting their general extension. In contrast, deep learning networks can extract image features enabling generalisation across different neutron energy spectra and dose values. In this study, a deep learning network was trained on images of FNTDs irradiated at six mono-energetic neutron energies and tested on images of FNTDs exposed to a broad-spectrum 241 Am-Be neutron source. Using raw images of irradiated FNTDs as input, the network predicted the proton tracks which were later counted. For the 241 Am-Be test dataset, a dose–response curve of identified tracks over ambient dose equivalent was fitted, and the sensitivity in terms of H ∗ ( 10 ) was extracted from the slope. When the fit was applied on the whole H ∗ ( 10 ) range, from 0 mSv up to 100 mSv, the predicted sensitivity for 241 Am-Be was S p r e d = ( 2280 ± 20 ) tracks mSv − 1 cm − 2 . The relative deviation of this predicted sensitivity from the reference sensitivity was 5.8%. When the fit considered only the H ∗ ( 10 ) range of the training dataset, namely from 5 mSv to 15 mSv, the predicted sensitivity for 241 Am-Be was S p r e d = ( 2500 ± 60 ) tracks mSv − 1 cm − 2 . This led to a relative deviation from the reference sensitivity of only 1.2%. Despite being trained solely on mono-energetic data, the model successfully generalised to the 241 Am-Be energy spectrum. • Fluorescent Nuclear Track Detector (FNTD) images segmented with deep learning. • The self-configuring nnU-Net framework was used for FNTDs. • FNTDs irradiated with mono-energetic neutrons were used as the training dataset. • Successful track identification of recoil protons. • FNTDs irradiated with broad spectrum 241 Am-Be properly predicted.

Experimental and numerical investigations of water–ice phase change under non-uniform cold source configurations