Neutron Source Research Articles

Properties analysis on interlayer within lithium target and its beam uniformity for accelerator-based Boron Neutron Capture Therapy

In order to enhance the performance and lifetime of the lithium target used in accelerator-based neutron sources for Boron Neutron Capture Therapy (BNCT) treatment, an exploration of target design was conducted based on the 2.8 MeV, 20 mA proton beam. A comparison between scanning magnets and octupole magnets was performed for beam uniform, with octupole magnets selected to effectively avoid localized high thermal densities over short durations. Exploration was conducted on the performance of tantalum and vanadium as interlayers within the lithium target, considering aspects such as cooling, hydrogen diffusion, and neutron performances. This study revealed that, as the majority of energy deposition occurs within the interlayer, the presence of an appropriately thick tantalum or vanadium interlayer has minimal impact on cooling effectiveness, ensuring temperatures remain below 144 °C. The addition of an interlayer effectively reduces the maximum hydrogen concentration in copper, thus preventing copper blistering. Within the investigated thickness range, the interlayer does not affect neutron spectrum in the forward direction of the target, mitigating concerns regarding its impact on beam shaping.

Integrated modeling of anisotropic neutron yields of classical and spherical tokamaks

Estimations of counting rates of neutron spectrometers in experiments on controlled fusion with magnetic confinement, as well as calculations of energy resolved flux densities of fusion neutrons from plasma to the walls of a reactor require spatial integration of the local, usually anisotropic function of the neutron source. The integrated modeling consists of three main stages. First, sources of fast particles in beam- or wave-heated plasma are calculated. The next stage deals with spatial, energetic, and angular velocity distributions of plasma ions. Finally, double differential rate coefficients of nuclear fusion reactions are computed. This article describes calculations of spatial distributions of nuclear fusion reaction rates in classical and spherical tokamaks and the anisotropy of the neutron yield and spectra. The results are based on analytical formulas for energetic and angular distributions of the local source of fusion products in plasma. Examples of energetic spectral densities of neutron fluxes on first walls are presented, as well as energy resolved counting rates of collimated neutron spectrometers for perpendicular and tangential lines of sight.

Measurements of Carbon Content and Retained Austenite Volume Fraction in Steels by Neutron Bragg-edge Transmission Analysis at a Compact Neutron Source, AISTANS

Measurements of Carbon Content and Retained Austenite Volume Fraction in Steels by Neutron Bragg-edge Transmission Analysis at a Compact Neutron Source, AISTANS

Dynamic fringe field effect of the rapid ramping quadrupole magnets at a Rapid Cycling Synchrotron

For a DC quadrupole magnet, the normalized magnetic field distribution along the beam trajectory is mainly determined by the mechanical structure of the magnet and remains almost independent of the exciting current. However, the magnetic field measurement results of the Rapid Cycling Synchrotron (RCS) at the China Spallation Neutron Source (CSNS) show that the normalized magnetic field distribution along the beam trajectory varies during the exciting current ramping process for rapid ramping magnets. Consequently, for rapid ramping quadrupole magnets, there are significant differences between the dynamic and static magnetic field gradient distribution. And the changes in the distribution of the magnetic field gradient can cause time dependent tune-shifts during the exciting current ramping process. For RCS, the tune is crucial, and the shifts of tune may lead to the beam approaching the resonance line, thereby causing beam loss. The impact of the fringe field effect of the rapid ramping quadrupole magnets on beam dynamics at CSNS-RCS was detailly studied. A new method for correcting the time-dependent tune shifts caused by the dynamic field distribution, based on waveform compensation at the quadrupole magnets, has also been proposed for the RCS of CSNS. Related simulation and experiment have been conducted, and the simulation results and experimental results are consistent with theoretical study results.

Properties of W–Ta Materials of the Neutron-Producing Target of the Subcritical Assembly at the National Scientific Centre ‘Kharkiv Institute of Physics and Technology’ of the National Academy of Sciences of Ukraine

The works in the field of radiation materials science of target materials of neutron sources based on the subcritical assemblies controlled by linear accelerators of electrons or protons, so-called accelerator driven systems (ADS), are reviewed. Now, electronuclear ADS systems are the prototype of safe nuclear reactors of the 5th generation. In connection with the physical start-up of the neutron source facility of the National Scientific Centre ‘Kharkiv Institute of Physics and Technology’ of the N.A.S. of Ukraine (NSC ‘KhIPT’ NASU), the target of which is fabricated from powdered tungsten covered with tantalum, the issues of preparation technology, construction, and physical and mechanical properties of W–Ta materials of targets in non-irradiated and irradiated states are considered. The nuclear-physical processes of radiation damage to the target during co-irradiation of it with both neutrons of a subcritical assembly and high-energy e- and γ-beams are analyzed. The target resources of ADS systems are estimated. As noted, the difficulty of predicting the ‘survivability’ of the W–Ta target also relates to the fact that, except for the works carried out at the NSC ‘KhIPT’ NASU in 70–90th of the last century, there are no experimental works in the world on the radiation damage of reactor materials by high-energy electrons with an energy of 100 MeV and above.

Development of a bi-solvent liquid scintillator with slow light emission

One of the most promising approaches for the next generation of neutrino experiments is the realization of large hybrid Cherenkov/scintillation detectors made possible by recent innovations in photodetection technology and liquid scintillator chemistry. The development of a potentially suitable future detector liquid with particularly slow light emission is discussed in the present publication. This cocktail is compared with respect to its fundamental characteristics (scintillation efficiency, transparency, and time profile of light emission) with liquid scintillators currently used in large-scale neutrino detectors. In addition, the optimization of the admixture of wavelength shifters for a scintillator with particularly high light emission is presented. Furthermore, the pulse-shape discrimination capabilities of the novel medium was studied using a pulsed particle accelerator driven neutron source. Beyond that, purification methods based on column chromatography and fractional vacuum distillation for the co-solvent DIN (Diisopropylnaphthalene) are discussed.

Deterministic and stochastic computational models for the analysis of Nuclear Power Plant (NPP) start-up operations

The aim of this paper is to present an overview of both the deterministic and stochastic aspects of nuclear power plant (NPP) start-up and start-up accident scenarios. The neutron kinetics and corresponding nuclear reactor control mechanisms associated with deterministic NPP start-up are explained. The stochastic behaviour of neutron kinetics is explained and the procedures required to safely start-up an NPP due to these stochastic phenomena are outlined. Specific attention is given to the stochastic behaviour of neutrons in a low neutron source regime and the corresponding mathematical methods required for modelling such phenomena during NPP start-up accidents. The Pál-Bell equations are compared against the forward generating function equations utilising the gamma approximation in their ability to model NPP start-up accidents. The Pál-Bell equations are shown to be necessary to accurately calculate the maturity time for systems with either a very low neutron source strength or a very rapid reactivity insertion profile. Both the Hurwitz calculation route and MacMillan calculation route for low neutron source systems are explained. Full deterministic and stochastic calculations are performed for multiple nuclear reactor systems to illustrate the necessary analyses required for low neutron source NPP start-up accident scenarios.

Economical Experimental Device for Evaluating Thermal Conductivity in Construction Materials under Limited Research Funding

African scientific research faces formidable challenges, particularly with limited access to state-of-the-art measurement instruments. The high cost associated with these devices presents a significant barrier for regional research laboratories, impeding their ability to conduct sophisticated experiments and gather precise data. This predicament not only hampers the individual laboratories but also has broader implications for the African scientific community and the advancement of knowledge in developing nations—the financial cost barrier considerably impacts the research quality of these laboratories. Reflection on technical and economical solutions needs to be quickly found to help these countries advance their research. In civil engineering, the thermal conductivity property is the most important measurement for characterizing heat transfer in construction materials. Existing devices (i.e., conductometers) in a laboratory are expensive (approximately EUR 30,000) and unavailable for some African laboratories. This study proposes a new and affordable device to evaluate thermal conductivity in construction materials. The method involves establishing a thermal flux between a heat source (from the Joule effect provided by steel wool where a current is circulating) and a cold source (generated by ice cubes) under steady-state conditions. The development of the cylindrical prototype is based on the comparative flux-meter method outlined in the measuring protocol of the ASTM E1225 standard document. Experiments were conducted on four distinct materials (polystyrene, wood, agglomerated wood, and rigid foam). The results indicate a correct correlation between the experimental values obtained from the newly developed prototype and the reference values found in the literature. For example, concerning the experimental polystyrene study, the detailed case analysis reveals a good correlation, with a deviation of only 4.88%. The percent error found falls within the acceptable range indicated by the standard recommendations of the ASTM E1225 standard, i.e., within 5% acceptable error.

Shielding development for the spallation neutron source VENUS instrument

VENUS is a neutron imaging instrument that will use a broad range of neutron wavelengths, from epithermal to cold energies, and will include enhanced contrast mechanisms. It will offer novel energy-selective imaging techniques directly connecting complex engineering materials and systems’ structures, properties, and functions to reveal practical and fundamental answers about their real-world performance. The instrument will be built at SNS beamline 10, facing the decoupled poisoned hydrogen moderator. The driving cost for the instrument is the beamline and instrument cave shielding. Final analyses were performed to evaluate the thickness and composition of shielding materials for the instrument cave and beamline to meet radiation safety criteria for the instrument to start up in 2024 after completing the SNS proton power upgrade.

Ultra-high charge electron acceleration for nuclear applications

Ultra-intense laser-plasma wakefield accelerator possess several superior properties compared with the traditional radio-frequency accelerators. These characteristics include femtosecond duration, micro-source size, and ultra-dense beam density, result in highly advantageous for various important applications. In this paper, we reviewed the generation of ultra-intense and high charge electron beam based on laser-plasma acceleration and its nuclear applications in Shanghai Jiao Tong University, including the production of 10 s nC charge beams, the generation of ultra-high flux neutron source on the order of 1019 n/cm2/s, and the excitation of nuclear isomers with the peak efficiency on the order of 1015 particle/s. This laser driving ultra-dense electron source, in conjunction with the plasma environment, presents immense potential in addressing critical problems in astrophysics, and facilitating various nuclear applications. Based on above progress in nuclear astrophysics, a new research plateform about laboratory astrophysics with a 2.5 PW laser will be constructed in TDLI institute.

Improving flame resistance and shielding properties for cross-linked polyethylene (XLPE) using nanoclay filler

Polymers play an essential role in both industry and medical fields due to their diverse and adaptable properties. In this work, prepared crosslinking polyethylene (XLPE) samples with hydrophilic bentonite nanoclay fillers (H2Al2O6Si) at concentrations of 0, 1, 2.5, 4, and 5 wt% enhance their flame-retardant and radiation shielding efficiency. The research investigated flame retardancy and thermal stability parameters. The XLPE/H2Al2O6Si nanocomposite polymer sheets were exposed to a collimated beam of fast neutrons using an Am/Be neutron source (5 Ci) and to gamma radiation using a 137Cs point source (5 μCi) to assess their radiation shielding properties. The study found that uniform dispersion of nanoclay particles enhanced the thermal properties of the composite, forming a char layer that acted as a barrier, slowing thermal decomposition and reducing the heat release rate. Limiting oxygen index (LOI) increased from 28% to 34%, and burning rate improved with higher nanoclay concentrations. Additionally, absorption and optical band gap calculations decreased with increasing filler concentrations. Radiation attenuation capabilities increased by approximately 40% for neutrons and 30% for gamma radiation compared to pure XLPE. The study concluded that incorporating nanoclay fillers into XLPE enhances its shielding capabilities and improves flame resistance properties, making the prepared samples suitable for various industrial applications.

2D kinetic-ion simulations of inverted corona fusion targets

Laser-driven “inverted corona” fusion targets have attracted interest as a low-convergence neutron source and platform for studying kinetic physics. The scheme consists of a hollow or gas-filled spherical shell made of deuterated plastic. The shell has one or more laser entrance holes (LEH), resembling a spherical hohlraum. The laser passes through the LEH’s and illuminates the interior surface of the shell, ablating a plasma that travels inward towards the target center. Long ion mean free paths in the converging plasma can lead to significant interpenetration, atomic mix, and other kinetic effects. In this work we report on numerical simulations of inverted corona targets using the kinetic-ion, fluid–electron hybrid particle-in-cell (PIC) approach in 2D RZ geometry. 2D simulations suggest that shape effects do not have a significant impact on plasma evolution and observed yield trends are primarily the result of 1D kinetic mix mechanisms. Simulations are also compared against available experimental data recorded at the OMEGA laser facility. In particular, synthetic x-ray emission images show good qualitative agreement with experimental results, albeit with an apparent timing discrepancy for the two-sided vacuum target. More generally, we demonstrate the potential of hybrid-PIC simulations for full-system modeling and experimental design, including collisional absorption of laser energy, plasma evolution, mix, and fusion burn.

Implementation of optically simulated luminescent dosimeter for quality control of gamma ray dose of an accelerator-based neutron source.

Neutron beams utilized for performing BNCT are composed of a mixture of neutrons and gamma rays. Although much of the dose delivered to the cancer cells comes from the high LET particles produced by the boron neutron capture reaction, the dose delivered to the healthy tissues from unwanted gamma rays cannot be ignored. With the increase in the number of accelerators for BNCT, a detector system that is capable of measuring gamma ray dose in a mixed neutron/gamma irradiation field is crucial. Currently, BeO TLDs encased in quartz glass are used to measure gamma ray dose in a BNCT irradiation field. However, this type of TLD is no longer commercially available. A replacement dosimetry system is required to perform the recommended ongoing quality assurance of gamma ray measurement for a clinical BNCT system. The purpose of this study is to evaluate the characteristics of a BeO OSLD detector system under a mixed neutron and gamma ray irradiation field and to assess the suitability of the system for routine quality assurance measurements of an accelerator-based BNCT facility. The myOSLD system by RadPro International GmbH was evaluated using the accelerator-based neutron source designed for clinical BNCT (NeuCure BNCT system). The readout constancy, linearity, dose rate effect, and fading effect of the OSLD were evaluated. Free-in-air and water phantom measurements were performed and compared with the TLD results and Monte Carlo simulation results. The PHITS Monte Carlo code was used for this study. The readout constancy was found to be stable over a month-long period and similar to the TLD results. The OSLD readout signal was found to be linear, with a high coefficient of determination (R2≥0.999) up to a proton charge of 3.6C. There was no significant signal fading or dose rate dependency. The central axis depth dose and off-axis dose profile measurements agreed with both the TLD and Monte Carlo simulation results, within one standard deviation. The myOSLD system was characterized using an accelerator system designed for clinical BNCT. The experimental measurements confirmed the OSLD achieved similar, if not superior to, the currently utilized dosimetry system for routine QA of an accelerator-based BNCT system. The OSLD system would be a suitable replacement for the current TLD system for performing routine QA of gamma ray dose measurement in a BNCT irradiation field.

Identification of Urban Ventilation Corridor System Using Meteorology and GIS Technology: A Case Study in Zhengzhou, China

Urban ventilation corridors are designed to enhance air quality, alleviate urban thermal conditions, reduce pollution and energy consumption, as well as improve human comfort within cities. They play a pivotal role in mitigating environmental impacts, particularly in densely populated urban areas. Based on satellite remote sensing data, meteorological observations, basic geographic information of Zhengzhou City and its surroundings, and urban planning data, we analyzed the urban wind environment, urban heat island, ecological cold sources, and ventilation potential. The findings reveal several key insights: (1) Dominant winds in Zhengzhou City predominantly originate from the northwest, northeast, and south, influenced by topography and the monsoon climate, with seasonal variations. These wind patterns are crucial considerations for designing primary ventilation corridors. (2) The urban heat island exhibits a polycentric spatial distribution, with intensity decreasing from the city center towards the periphery. Ecological cold sources, primarily situated in the city outskirts, act as reservoirs of fresh air that mitigate the urban heat island effect through designated corridors. (3) A preliminary corridor system, termed “eight primary and thirteen secondary corridors”, is proposed for Zhengzhou City based on an integrated assessment of ventilation potential, urban surface roughness, and sky view factor. This research contributes to advancing the understanding of urban ventilation systems and provides practical insights for policymakers, urban planners, and researchers seeking sustainable solutions to mitigate climate impacts in rapidly urbanizing environments in the region.

New technologies for beam spectrometry, quality assurance, real-time monitoring and microdosimetry in BNCT

Boron neutron capture therapy (BNCT) is a next-generation radiotherapy that combines neutron beams with boron compounds that selectively accumulate in cancer cells. Because this therapy requires neutrons for irradiation, compact accelerator-based neutron source devices that can be installed in hospitals are being developed around the world. Clinical trials of several devices have been conducted in Japan, China, and South Korea. The most advanced device was approved by the Japanese regulatory authorities in 2020. As a result, BNCT with the device is being implemented as an insured therapy for recurrent head and neck cancer at two hospitals in Japan. Thus, the development of accelerator-based neutron generators is proceeding in the field of BNCT. However, much remains to be done to establish this therapy as a common cancer treatment and to make it available worldwide. Dosimetry methods in BNCT are one of the issues. In the treatment, the dose given to a patient by neutron irradiation has to be estimated accurately. However, it is difficult to measure neutrons accurately and in real time. Currently, the neutron dose delivered to patients during treatment is not measured. Instead, the current of the charged particles that irradiate the neutron target material is measured to indirectly evaluate the neutron fluence and dose. In addition, accurate dose estimation based on reactions with neutrons and various elements in a human body uses the Monte Carlo method, which is computationally time-consuming. To address these dosimetry issues, several neutron fluence and dose measurement methods are being developed. This review briefly describes the current dosimetry methods and then presents several methods under development that allow real-time neutron measurements applicable to BNCT.

Calibration of the sensitivity of the bibenzyl-based scintillation detector to 1–5 MeV neutrons

The neutron time-of-flight (nTOF) detector, which is based on bibenzyl, an organic crystal scintillator with low afterglow, is used to diagnose the fuel areal density of target capsules by measuring the down-scattered neutron ratio. This paper presents a method for calibrating the sensitivity of bibenzyl scintillation detectors to 1–5 MeV down-scattered neutrons. The distributions of detector sensitivity are analyzed using the Monte-Carlo method. The analysis shows that most light output of neutrons below 5 MeV comes from recoil protons. Therefore, the sensitivity of the back-scattered neutron can be calculated with the 2.45 MeV neutron sensitivity and the relative responses of the 1–5 MeV protons. These responses are calibrated using a deuterium-deuterium implosion neutron source at a 100-kJ laser facility and a monoenergetic proton beam at a Van de Graaf accelerator, respectively. The total uncertainty of the calibration for 1–5 MeV neutron sensitivity ranges from 5% to 9%. This calibration method provides accurate measurements for the broad-spectrum neutron sensitivity of scintillation detectors.

Microstructural changes in the welding of titanium-stabilized steels

Abstract At the Central Institute for Engineering, electronics, and Analytics (ZEA-1 by its acronym in German) of the Jülich Research Center GmbH, a cryostat was developed for the European Spallation Neutron Source (ESS) and manufactured from a titanium-stabilized austenitic stainless steel alloy (EN 1.4571). After tungsten inert gas welding, the welds exhibited a black, patchy discoloration. After materialographic preparation, the phenomena were examined using microscopic methods to assess their impact on the strength of the weld and thus on the usability of the cryostat. Not only could the impact on the cryostat operation be assessed, but the formation mechanism could be elucidated and suitable measures could be outlined to avoid the black, patchy discoloration.

A novel 4H–SiC thermal neutron detector based on a metal-oxide-semiconductor structure

Energy resolution and leakage current are two key parameters for semiconductor neutron detectors. Metal-Oxide-Semiconductor (MOS) detectors introduce an additional oxide layer compared to Schottky Barrier Diodes (SBDs) detectors in order to reduce leakage current. However, this also leads to a degradation in energy resolution due to the introduction of an additional dead layer. Therefore, optimizing the thickness of the oxide layer is important for MOS detectors. In this study, a 4H–SiC-based MOS thermal neutron detector was designed with comprehensive consideration of the oxide layer. Subsequently, a prototype of the detector was fabricated and tested. The prototype of the MOS detector achieved an nA-level leakage current under a reverse bias of −200 V. Additionally, it demonstrated good energy resolution performance in a moderated D-T neutron source test. The MOS detector was able to clearly distinguish between the two reaction channels of 10B converter events, which is consistent with the theoretical branching ratio. This work highlights the potential application of 4H–SiC-based MOS detectors for thermal neutron detection.

Experimental assessment of ozonated ice: Preparation, stability, and preservation effects on shrimp (Metapenaeus ensis)

Ozonated ice not only retains the inherent performance and function of ozone, but also serves as a cold source for food preservation. However, its preparation is challenging due to the low solubility and instability of ozone in water. So here, the major preparation techniques and the storage stability of ozonated water and ice were studied. Besides, the impact of ozonated ice treatment on the quality of shrimp (Metapenaeus ensis) was explored. To achieve these ends, a set of ozonated ice preparation devices was established, and the optimal conditions for producing ozonated water and ice were confirmed as follows: using 0 °C deionized water as the water source, achieving an outlet flow rate of 80 L/h, cyclically mixing gas-liquid twice, adding 1.0 g/kg of polyoxypropylene oxyethylene glycol ether (POGE), and freezing at −80 °C. Regarding ozone stability, an increase in initial ozone concentration and storage temperature, along with a decrease in water purity, resulted in a shorter half-life of ozone in water. Additionally, a lower storage temperature was conducive to prolonging the half-life of ozonated ice, while the addition of POGE had little effect. In practical application, under the optimal conditions for producing ozonated water and ice without POGE, shrimp stored in ozonated ice demonstrated superior sensory scores, whiteness values, and shear force compared to those stored in normal ice. Concurrently, they displayed reduced levels of TVC, TVB-N, and pH. Furthermore, the application of ozonated ice treatment mitigated blackening and improved odor quality. Consequently, this research offers a scientific foundation for the industrial application of ozonated water and ice and serves as a reference for preventing the deterioration and quality loss of shrimp and other seafood products.

Safety considerations for cryogenic hydrogen circulation system in China spallation neutron source phase II project

Cryogenic hydrogen circulation system is a critical infrastructure of the China Spallation Neutron Source phase II project. Safety considerations related to hydrogen are paramount for the stable operation of the system. This study focuses on the cryogenic hydrogen circulation system within the context of the China Spallation Neutron Source phase II project and conducts a detailed investigation of hydrogen safety issues throughout the process. The operational modes and fault occurrence mitigation strategies of the cryogenic hydrogen circulation system are analyzed and discussed. Additionally, employing centralized layout, zoning management, and multiple barrier layers as guiding concepts for hydrogen safety design, the study addresses physical and interlocking control designs concerning hydrogen distribution, hydrogen venting, vacuum, hydrogen circulation pressure control, and hydrogen leakage. Drawing upon the successful experiences of the first-phase project, the hydrogen safety design of the cryogenic hydrogen circulation system in the China Spallation Neutron Source phase II project provides valuable insights for the development and optimization of hydrogen safety designs across various industrial domains.