Search Results (147)

In molten salt reactors (MSRs), molten salt performs dual essential roles as fuel and coolant. The continuous circulation of the fuel salt in the primary loop inevitably leads to significant neutron activation of loop components, particularly the structural alloys of the heat exchanger (HX) and the coolant salt within the HX. This activation is strongly influenced by delayed neutron fluxes generated by the migration of delayed neutron precursors (DNPs) within the flowing fuel salt. Accurate quantification of the radioactivity of primary HX components is essential for establishing reliable modular replacement strategies, optimizing shutdown maintenance schedules, and ensuring operational safety. To address this requirement, a comprehensive simulation methodology has been developed to model the DNP transport through the primary HX in a small modular molten salt reactor (SM-MSR). It aims to quantitatively evaluate activation levels of HX structural alloys and circulating coolant salt within the HX. Comparative simulations were conducted to contrast scenarios with dynamic DNP migration and static-fuel scenarios excluding it. The results indicate that consideration of DNP migration increases the neutron flux at the top region of the HX by approximately three orders of magnitude compared with the static-fuel scenario. This elevates coolant salt radioactivity by over 50%. Significant increases in irradiation damage parameters (displacements per atom and helium production) are observed in the upper sections of HX structural alloys. These findings highlight the necessity of incorporating DNP migration effects for accurate prediction of primary loop component neutron activation. This provides a reference for future shielding design optimization, irradiation damage assessments, and shutdown dose rate calculations in the SM-MSR. Full article

Atmospheric aerosols modulate Earth’s radiation balance through direct effects and through their role as cloud condensation nuclei (CCN), contributing to variability in near-surface temperature (NST). Galactic cosmic rays (GCRs) further influence aerosol–cloud interactions by enhancing particle formation and growth, but combined aerosol optical depth (AOD)–GCR effects on NST remain poorly constrained across climates. Using satellite and reanalysis data, we examine joint influences on NST anomalies at three neutron-monitoring stations, Oulu, Newark, and Hermanus, during 2000–2022. The sites share similar geomagnetic cutoffs but contrasting climates, enabling separation of ionization from geomagnetic shielding. Multiple linear regression (MLR) captures AOD effects and their modulation by GCR flux. Adding an interaction term (AOD × GCR) improves fit, raising adjusted R² from 0.22→0.31 (Oulu), 0.37→0.52 (Newark), and 0.69→0.78 (Hermanus). ECMWF reanalysis shows hydrophilic organic matter aerosol (OMA) dominates (0.19, 0.29, 0.41 µg kg⁻¹ at Oulu, Newark and Hermanus), with sulphate elevated at Oulu/Newark and coarse sea salt at Hermanus. Elevated OMA and sulphate at Oulu/Newark imply GCR-enhanced fine CCN and cooling, whereas humid, sea-salt-rich Hermanus favors ion-mediated growth of larger hygroscopic particles that increase longwave trapping and warming. Findings provide site-specific evidence that GCR ionization modulates aerosol processes and contributes to regional NST variability, informing improved parameterizations in climate models. Full article

This review systematizes data on the phase composition and key properties of compounds in the W–B system, including thermodynamic stability, crystal structure, and hardness. The current understanding of the binary W–B phase diagram and the stability of individual borides is discussed, alongside the influence of defects and non-stoichiometry on their properties. The main methods for synthesizing these materials and producing coatings based on them are summarized. Potential applications of tungsten borides are highlighted, particularly for high-temperature environments, cutting tools, and protective and functional coatings. Finally, key directions for future research are outlined, focusing on the refinement of phase equilibria, the scaling of production methods, and the development of W–B-based materials with tailored performance characteristics. Full article

Superheated liquid detectors (SLDs) exhibit strong sensitivity to fast neutrons and intrinsic insensitivity to gamma radiation, making them promising candidates for detecting shielded nuclear materials in security and non-proliferation applications. This work evaluates the feasibility of octafluoropropane-based superheated droplet detectors (SDDs) for identifying neutron-emitting materials concealed behind common attenuators. A combined acoustic and optical readout system was implemented, including a validated pulse-shape analysis method and a machine-learning-based bubble detection algorithm using YOLOv5. The optical system achieved a detection precision of approximately 80% within the defined region of interest. While the acoustic system remains the primary and more mature detection channel, the optical approach demonstrates feasibility but is not yet operationally ready for field deployment. Experiments with an AmBe neutron source and various shielding materials demonstrate that SDDs reliably detect fast neutrons under realistic inspection conditions while remaining insensitive to gamma radiation. These results support the feasibility of SLD-based systems as low-cost, passive tools for detecting shielded nuclear materials in field environments. Full article

Shutdown dose rate (SDDR) assessments have been performed for the DEMO tokamak model, including the latest design and environmental configurations. The main objective of this study was to evaluate the shutdown radiation fields and establish dose rate limits to ensure safe personnel access to the Vacuum Vessel (VV) and nearby components. The simulations were based on the DEMO baseline model, further refined with the minor updates of the lower port, equatorial port limiter, and upper port assemblies. The computational approach employed the Monte Carlo particle transport code MCNP for neutron and photon transport calculations, coupled with the activation and decay code FISPACT-II to determine time-dependent decay gamma source terms. The mesh-coupled Rigorous Two-Step (R2Smesh) methodology developed in KIT was applied to achieve spatially resolved decay of photon source distributions and to compute corresponding SDDR 3D maps within the DEMO reactor configuration. The results provide a detailed characterization of the residual radiation environment inside the VV, offering insight into the accumulated activity, shielding performance of different materials, and potential access scenarios for maintenance operations in next-generation fusion devices. Full article

Fast neutron shielding is a critical component of radiation protection design. Conventional exponential attenuation models based on the narrow-beam (beam approximation) assumption often exhibit large deviations in realistic geometries because they neglect the contribution of scattered neutrons—an effect that becomes particularly prominent for thick hydrogenous shields such as polyethylene. To improve the accuracy of rapid shielding estimates, this study systematically investigates how the “source–shield–detector” geometric configuration influences fast neutron scattering in polyethylene. To overcome the limited adaptability of traditional build-up factor corrections in complex geometries, we propose a physics-informed scattering correction (SC) model. By introducing key geometric parameters—source-to-shield distance, shield thickness, and detector distance—the model dynamically modifies the classical exponential attenuation formulation and analytically integrates the scattered-neutron contribution to the detector flux. Validation against 70 representative geometric configurations simulated with the Monte Carlo code Geant4 shows that the proposed model reduces the mean absolute percentage error (MAPE) from approximately 54% for the exponential attenuation model to approximately 20%, effectively addressing severe flux underestimation in moderately thick shielding cases (5–20 cm). The results provide a practical and reliable tool, as well as a semi-empirical theoretical basis, for fast and accurate engineering estimation of polyethylene-based fast neutron shielding. Full article

This study evaluates lead-free high-density polyethylene (HDPE) composites reinforced with high-Z oxides (Bi₂O₃, WO₃, Gd₂O₃, TeO₂, and a Bi₂O₃/WO₃ hybrid) as lightweight materials for gamma-ray and fast-neutron shielding. A hybrid computational framework combining Phy-X/PSD with Geant4 Monte Carlo simulations was used to obtain key shielding parameters, including the linear and mass attenuation coefficients (μ, μ/ρ), half-value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), effective electron density (N_eff), exposure and energy-absorption buildup factors (EBF, EABF), and fast-neutron removal cross section (Σ_R). The incorporation of heavy oxides produced a pronounced improvement in gamma-ray attenuation, particularly at low energies, where the linear attenuation coefficient increased from below 1 cm⁻¹ for neat HDPE to values exceeding 130–150 cm⁻¹ for Bi- and W-rich composites. In the intermediate Compton-scattering region (≈0.3–1 MeV), all oxide-reinforced systems maintained a clear attenuation advantage, with μ values around 0.12–0.13 cm⁻¹ compared with ≈0.07 cm⁻¹ for pure HDPE. At higher photon energies, the dense composites continued to outperform the polymer matrix, yielding μ values of approximately 0.07–0.09 cm⁻¹ versus ≈0.02 cm⁻¹ for HDPE due to enhanced pair-production interactions. The Bi₂O₃/WO₃ hybrid composite exhibited attenuation behavior comparable, and in some regions slightly exceeding, that of the single-oxide systems, indicating that mixed fillers can effectively balance density and shielding efficiency. Oxide addition significantly reduced exposure and energy-absorption buildup factors below 1 MeV, with a moderate increase at higher energies associated with secondary radiation processes. Fast-neutron removal cross sections were also modestly enhanced, with Gd₂O₃-containing composites showing the highest values due to the combined effects of hydrogen moderation and neutron capture. The close agreement between Phy-X/PSD and Geant4 results confirms the reliability of the dual-method approach. Overall, HDPE composites containing about 60 wt.% oxide filler offer a practical compromise between shielding performance, manufacturability, and environmental safety, making them promising candidates for medical, nuclear, and aerospace radiation-protection applications. Full article

The growing use of radiation technologies has increased the need for shielding materials that are lightweight, safe, and adaptable to complex geometries. While lead remains highly effective, its toxicity and weight limit its suitability, driving interest in alternative materials. The process of 3D printing enables the rapid fabrication of customized shielding geometries; however, only limited research has focused on 3D-printed polymer composites formulated specifically for mixed photon–neutron fields. In this study, we developed a series of 3D-printable ABS-based composites incorporating tungsten (W), bismuth oxide (Bi₂O₃), gadolinium oxide (Gd₂O₃), and boron nitride (BN). Composite filaments were produced using a controlled extrusion process, and all materials were 3D printed under identical conditions to enable consistent comparison across formulations. Photon attenuation at 120 kVp and neutron attenuation using a broad-spectrum Pu–Be source (activity 4.5 × 10⁷ n/s), providing a mixed neutron field with a central flux of ~7 × 10⁴ n·cm⁻²·s⁻¹ (predominantly thermal with epithermal and fast components), were evaluated for both individual composite samples and layered (sandwich) configurations. Among single-material prints, the 30 wt% Bi₂O₃ composite achieved a mass attenuation coefficient of 2.30 cm²/g, approximately 68% of that of lead. Layered structures combining high-Z and neutron-absorbing fillers further improved performance, achieving up to ~95% attenuation of diagnostic X-rays and ~40% attenuation of neutrons. The developed materials provided a promising balance between 3D-printability and dual-field shielding effectiveness, highlighting their potential as lightweight, lead-free shielding components for diverse applications. Full article

The notable interest in materials with high-performance multifunctional properties, coupled with the diverse availability of raw materials—despite geopolitical controversies—allows for the design of a wide variety of new materials. Flexible materials with inorganic fillers derived from rare earths are of particular interest, as elements such as gadolinium have multiple properties of high technological interest. In particular, gadolinium oxides and borates have not been explored as fillers in special rubbers, such as FKM fluoroelastomers, which correspond to copolymers based on hexafluoropropylene and difluorovinylidene. It is in this context that the present work consists of obtaining and characterizing FKM-based compounds containing gadolinium(III) oxide, gadolinium borate, or thermally treated gadolinium borate. The promising results allow us to identify unique qualities imparted by this type of filler in fluoroelastomers, especially regarding mechanical properties. In fact, the increase in tensile strength of the compounds reached up to 162%. Likewise, the elongation at break was almost doubled. DMA identified that the reinforcing effect of gadolinium compounds is limited; it is hypothesized that the electronic nature of gadolinium, with its available f orbitals, influences the structure of FKM and, consequently, its properties. Taken together, these results provide relevant information for the development of new materials that, due to their boron and gadolinium-based composition—both elements with high neutron capture cross sections—could be used in neutron shielding applications. Full article

Environmentally friendly materials with superior structural, physical, optical, and shielding capabilities are of great technological importance and are continually being investigated. In this work, novel multicomponent borate glasses with the composition xTiO₂-10BaO-5Al₂O₃-5WO₃-20Bi₂O₃-(60-x) B₂O₃, where 0 ≤ x ≤ 15 mol%, were produced via the melt-quenching technique. The increase in TiO₂ content results in a decrease in molar volume and a corresponding increase in density, indicating the formation of a compact, rigid, and mechanically hard glass network. Elastic constant measurements further confirmed this behavior. FTIR analysis confirms the transformation of BO₃ to BO₄ units, signifying improved network polymerization and structural stability. The prepared glasses exhibit an optical absorption edge in the visible region, demonstrating their strong ultraviolet light blocking capability. Incorporation of TiO₂ leads to an increase in refractive index, optical basicity, and polarizability, and a decrease in the optical band gap and metallization number; all of these suggest enhanced electron density and polarizability of the glass matrix. Radiation shielding properties were evaluated using Phy-X/PSD software. The outcomes illustrate that the Mass Attenuation Coefficient (MAC), Effective Atomic Number (Z_eff), Linear Attenuation Coefficient (LAC) increase, while Mean Free Path (MFP) and Half Value Layer (HVL) decrease with increasing TiO₂ at the expense of B₂O₃, confirming superior gamma-ray attenuation capability. Additionally, both TiO₂-doped and undoped samples show higher fast neutron removal cross sections (FNRCS) compared to several commercial glasses and concrete materials. Overall, the incorporation of TiO₂ significantly enhances the optical performance and radiation-shielding efficiency of the environmentally friendly glass system, making these potential candidates for advanced photonic devices and radiation-shielding applications. Full article

As a promising class of structure/function integrated materials, aluminum-based boron carbide composites exhibit exceptional mechanical properties, neutron shielding capabilities, and excellent thermophysical properties, demonstrating significant potential for applications in nuclear energy, aerospace, and national defense industries. This paper systematically reviews recent research progress on aluminum-based boron carbide composites with a focus on technical advancements and persistent challenges in fabrication, material properties, and applications. Future research directions are outlined, aiming to provide a guideline for further advancing this field. Full article

The increasing demand for sustainable and multifunctional materials in radiation shielding and optical applications has driven research toward utilizing natural and waste-derived reinforcements in polymer matrices. However, achieving effective attenuation performance across different radiation types using eco-friendly fillers remains a significant challenge. In this study, polyvinyl chloride (PVC)/Polystyrene (PSt) blend composites (1:1 weight ratio) were reinforced with powdered snail shell (SSP) as a biogenic additive, aiming to enhance their shielding and optical performance. Composites containing 5%, 10%, 20%, and 30% SSP (w/v) were fabricated and characterized. Key parameters including linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), mean free path (MFP), half-value layer (HVL), and effective atomic number (Zeff) were measured using a variable-energy X-ray source (13.37–59.54 keV) and ULEGe detector. Fast neutron shielding performance and theoretical values for build-up factor (EBF) and macroscopic neutron cross-sections were also calculated. The results showed a marked improvement in X-ray attenuation with increasing SSP content (SSP30 > SSP20 > SSP10 > SSP5), while neutron shielding declined due to the high oxygen content of SSP. Among the tested samples, the SSP30 composite exhibited the highest X-ray attenuation efficiency, whereas the SSP5 composition showed the greatest enhancement in optical reflectance and neutron absorption, indicating optimal performance in these respective tests. Additionally, 5% SSP incorporation improved optical reflectance by 12%, indicating enhanced photon backscattering at the material surface. This behavior contributes to improved gamma shielding efficiency by reducing photon penetration and enhancing surface-level attenuation. These findings highlight the potential of snail shell-based fillers as low-cost, sustainable reinforcements in multifunctional polymer composites. Full article

This study investigates the design and experimental evaluation of Fe–B–Si-based bilayer composites engineered for dual shielding against gamma rays and thermal neutrons. The materials integrate a boron-enriched amorphous Fe matrix with surface coatings of high-Z fillers—lead (Pb) and tungsten (W)—dispersed in an epoxy resin. W or Pb powders (20–40 µm) were dispersed in epoxy resin at a high filler loading (60–70 wt% metal, approximately several tens to one by weight). This ensured a dense and uniform coating structure. The metallic fillers were high-purity (≥99.9%) powders. Gamma-ray attenuation was examined using ¹³⁷Cs and ⁶⁰Co sources at photon energies of 661.7, 1173, and 1332 keV, while thermal neutron shielding was assessed with a moderated Am-Be neutron source. The effects of boron concentration (13–21 at%) in the matrix and coating thickness (80–400 μm) were systematically evaluated. Increasing boron content markedly enhanced thermal neutron attenuation, reaching up to 29%, whereas Pb- and W-filled coatings achieved more than 85% gamma-ray attenuation at 661.7 keV. All measurements were repeated three times; standard deviations were below 2% across conditions, confirming reproducibility and indirectly indicating uniform coating dispersion. At 661.7 keV, the half-value and tenth-value layers (HVL/TVL) were derived from the measured linear attenuation coefficients to benchmark performance. Notably, W coatings delivered shielding efficiency comparable to Pb while offering advantages in environmental safety, mechanical robustness, and regulatory compliance. These results highlight the potential of Fe–B–Si bilayer composites as lightweight, scalable, and lead-free shielding materials for aerospace electronics, portable radiation protection devices, and modular panels for satellites and nuclear facilities. Full article

This study investigates neutron radiation sources in medical cyclotrons used for PET isotope production, focusing on differences between ¹⁸F and ¹¹C. Neutron and gamma dose rates were measured in the bunker and operator control room during routine production with an 11 MeV Eclipse cyclotron. ¹⁸F production generated approximately 2.5 times higher neutron levels in the bunker than ¹¹C. Shielding performance also varied: the same wall reduced neutron fluxes by factors of k_F = 14,000 for ¹⁸F and k_C = 86,000 for ¹¹C, while gamma shielding was similar for both isotopes (k_γ ≈ 28,000). However, the neutron shielding factor calculated from the data for ¹⁸F should be taken as k_F ≥ 1.4 × 10⁴, because several neutron readings reached the upper limit of the detector range, which indicates a partial underestimation of the dose in the bunker. Consequently, neutron levels in the control room during ¹⁸F production were about 15-fold higher than during ¹¹C production. These differences result from distinct neutron generation mechanisms. The ¹⁸O(p,n)¹⁸F reaction produces primary neutrons with a Maxwellian spectrum (~2.5 MeV), while ¹¹C neutrons arise solely from secondary interactions in structural materials. The findings emphasize the need for composite shielding adapted to isotope-specific spectra. Annual dose estimates (260 ¹⁸F and 52 ¹¹C productions) showed neutron exposure (3.78 mSv/year, 57%) exceeded gamma exposure (2.82 mSv/year, 43%). The total dose of 6.6 mSv/year is ~33% of regulatory limits, supporting compliance but underscoring the need for dedicated neutron dosimetry. Full article