Search Results (785)

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV ¹³¹Xe ions at fluences ranging from 1 × 10¹¹ to 3.3 × 10¹³ ions/cm². Raman analysis reveals that all fundamental vibrational modes of the garnet structure remain observable up to the highest fluence, with the preservation of garnet crystalline topology/absence of secondary crystalline phases. However, significant line broadening (FWHM increase by 20–100%) and low-frequency shifts indicate progressive lattice disorder and phonon-defect scattering. High-frequency Ga-O stretching modes (A_1g, T_2g ~740 cm⁻¹) remain the most resistant to irradiation, while low-energy translational modes involving Gd³⁺ ions exhibit pronounced degradation and partial disappearance at high fluence. Complementary nanoindentation measurements show radiation-induced softening: hardness decreases by up to ≈60% at 3.3 × 10¹³ ions/cm², consistent with amorphization and overlapping ion tracks (~10–12 μm deep). Raman spectroscopy shows that the garnet lattice remains as the only crystalline phase up to 3.3 × 10¹³ ions/cm², while significant line broadening, mode suppression and a strong hardness decrease indicate progressive structural disorder and partial amorphization of the near-surface region. These results demonstrate that GGG maintains crystalline integrity below the track-overlap threshold (~6 keV/nm) but undergoes strong structural relaxation and mechanical weakening once this limit is exceeded. A new analytical methodology has been developed to quantify radiation-induced structural degradation. Full article

This study theoretically investigates the coupling efficiency of multi-Gaussian Shell-mode (MGSM) beams in ocean turbulence. The expression for the fiber-coupling efficiency of the MGSM beams propagating through oceanic turbulent media is derived using the cross-spectral density function. Numerical simulations are performed to examine the relationship between fiber-coupling efficiency and the beam order, and the scintillation index of the MGSM beams in ocean turbulence is also examined. In the analysis of transmission efficiency, the effects of the receiving aperture and source coherence on transmission efficiency are investigated, taking into account ocean turbulence induced by salinity and temperature fluctuations. The analysis of the fiber-coupling efficiency for MGSM beams presented in this work provides insights for optimizing the design of free-space optical communication systems. Full article

Tritium (³H) is a low-energy β emitter commonly found in environmental water samples, and its routine monitoring requires highly sensitive techniques capable of achieving low detection limits. Liquid scintillation counting (LSC) is the standard method for low-level ³H analysis; however, quenching significantly affects detection efficiency and minimum detectable activity (MDA), and systematic evaluations across different quench levels and measurement approaches remain limited. This study evaluates quench-related uncertainties in low-level ³H measurement using two ultra-low background liquid scintillation counters, Quantulus 1220 and GCT 6220. High- and low-quench conditions were created by varying sample-to-cocktail ratios, and performance was assessed through detection efficiency, minimum detectable activity (MDA), and stability. Under the relative measurement method with limited quench variation, GCT 6220 achieved higher efficiency, lower background, and lower detection limits. Under the internal standard method with broader quench spans, Quantulus 1220 produced smoother efficiency–quench curves and more stable results. Thus, GCT 6220 is advantageous for sensitivity-demanding scenarios, while Quantulus 1220 is better suited for quench-correction applications. Full article

We experimentally demonstrate an 80 Gbit/s Nyquist-dense wavelength division multiplexed (Nyquist-DWDM) transmission system operating in a simulated atmospheric turbulence channel. The system utilizes eight wavelength-tunable lasers with 100 GHz spacing, modulated by cascaded Mach–Zehnder modulators, to generate phase-locked Nyquist pulse sequences with a 10 GHz repetition rate and a temporal width of 66.7 ps. Each channel is synchronously modulated with a 10 Gbit/s pseudo-random bit sequence (PRBS) and transmitted through controlled weak turbulence conditions generated by a temperature-gradient convection chamber. Experimental measurements reveal that, as the turbulence intensity increases from $C_n^2=1.01\times {10}^{-16}$ to $5.71\times {10}^{-16} {\mathrm{m}}^{-2/3}$, the signal-to-noise ratio (SNR) of the edge channel (C29) and central channel (C33) decreases by approximately 6.5 dB while maintaining stable Nyquist waveform profiles and inter-channel orthogonality. At a forward-error-correction (FEC) threshold of $3.8\times {10}^{-3}$, the minimum receiver sensitivity is −17.66 dBm, corresponding to power penalties below 5 dB relative to the back-to-back condition. The consistent SNR difference (<2 dB) between adjacent channels confirms uniform power distribution and low inter-channel crosstalk under turbulence. These findings verify that Nyquist pulse shaping substantially mitigates phase distortion and scintillation effects, demonstrating the feasibility of high-capacity DWDM free-space optical (FSO) systems with enhanced spectral efficiency and turbulence resilience. The proposed configuration provides a scalable foundation for future multi-wavelength FSO links and hybrid fiber-wireless optical networks. Full article

In this study, a two-dimensional gamma-ray source localization system using a mesh array of plastic scintillating fibers and an artificial neural network is presented. The system covers a 200 cm by 100 cm area using SCSF-78 multi-cladded fibers. A novel U-shaped fiber topology connects both fiber ends to one side, requiring only two data-acquisition systems. Silicon photomultiplier arrays measure fast time-of-flight under optimized operating conditions to maximize signal yield. An independent artificial neural network model map measured time-of-flight values to spatial coordinates, compensating for systematic non idealities. Performance was validated using a Cesium-137 source at 20 random test positions. The artificial neural network method achieved a mean full-scale error of 4.6%. This demonstrated a 79.34% accuracy improvement over direct theoretical calculation, which had a mean full-scale error of 22.5%. The system showed consistent performance, achieving a two-dimensional standard deviation of 0.492 cm during repeatability assessment. This methodology provides a practical, efficient approach to two-dimensional radiation source localization suitable for real time monitoring and contamination mapping. Full article

To achieve a substantial enhancement in thermodynamic efficiency, Generation IV nuclear reactors are designed to operate at significantly elevated temperatures compared to conventional reactors. Moreover, they typically employ a fast neutron spectrum, characterized by higher neutron energy and flux. This combination results in a considerably more intense radiation environment within the core relative to traditional thermal neutron reactors. Therefore, the measurement of neutron flux in the core of Generation IV nuclear reactors faces the challenge of a high-temperature and high-radiation environment. Conventional neutron flux monitoring equipment—including fission chambers, gas ionization chambers, scintillator detectors, and silicon or germanium semiconductor detectors—faces considerable challenges in Generation IV reactor conditions. Under high temperatures and intense radiation, these sensors often experience severe performance degradation, significant signal distortion, or complete obliteration of the output signal by noise. This inherent limitation renders them unsuitable for the aforementioned applications. Consequently, significant global research efforts are focused on developing neutron detectors capable of withstanding high-temperature and high-irradiation environments. The objective is to enable accurate neutron flux measurements both inside and outside the reactor core, which are essential for obtaining key operational parameters. In summary, the four different types of neutron detectors have different performance characteristics and are suitable for different operating environments. This review focuses on 4H-SiC, diamond detectors, high-temperature fission chambers, and self-powered neutron detectors. It surveys recent research progress in high-temperature neutron flux monitoring, analyzing key technological aspects such as their high-temperature and radiation resistance, compact size, and high sensitivity. The article also examines their application areas, current development status, and offers perspectives on future research directions. Full article

Free-space optical (FSO) communication provides high-capacity and secure links but is strongly impaired by atmospheric turbulence, which induces multi-scale irradiance fluctuations. Traditional approaches such as adaptive optics, multi-aperture and multiple-input multiple-output FSO schemes offer limited robustness under rapidly varying turbulence, while statistical fading models such as log-normal and Gamma–Gamma cannot represent multi-scale temporal correlations. This work proposes a hybrid deep learning framework that explicitly separates high-frequency scintillation and low-frequency power drift through a conditional variational autoencoder and a bidirectional long short-term memory dual-branch architecture with an adaptive gating mechanism. Trained on OptiSystem-generated datasets, the model accurately reconstructs irradiance distributions and temporal dynamics. For model-assisted signal compensation, it achieves an average 79% bit-error-rate (BER) reduction across all simulated scenarios compared with conventional thresholding and Gamma–Gamma maximum a posteriori detection. Transfer learning further enables efficient adaptation to new turbulence conditions with minimal retraining. Experimental validation shows that the compensated BER approaches near-zero, yielding significant improvement over traditional detection. These results demonstrate an effective and adaptive solution for turbulence-impaired FSO links. Full article

In this paper, hybrid space–time–polarization schemes for processing high-frequency (HF) radio signals transmitted through the ionospheric layers are proposed. Ionospheric radio wave propagation is characterized by several impairments, including attenuation, scintillation, dispersion, and Faraday rotation. The use of hybrid schemes combining spatial digital processing and a single-input multiple-output (SIMO) scheme based on the spatial and polarization principles is proposed. The simulation is based on a preliminary estimate of signal attenuation and spatial coordinates based on ray tracing at a distance of 1000 km between the transmitter and the receiving digital antenna array. Additionally, the bit error rates and data capacity are obtained for various configurations of hybrid spatial and polarizing types of the proposed architectures. In addition, an algorithm for modeling a broadband HF signal in the ionosphere based on the inverse discrete Fourier transform (IDFT) and the Watterson narrowband model is proposed. Schemes for processing the wideband orthogonal frequency division multiplexing (OFDM) signals after passing through the ionosphere layers are represented as well. Results indicate that the optimal configuration employs hybrid processing utilizing ordinary (O) and extraordinary (X) wave polarization, combined with spatial digital processing in a SIMO architecture. Full article

Radioactively contaminated sandy soil is commonly encountered during nuclear facility decommissioning and nuclear accident response, and its rapid sorting and volume reduction are crucial for achieving waste minimization and lowering remediation costs. This study designed and developed a radiation measurement system based on a large-volume plastic scintillator and a NaI array detector, focusing on the design, implementation, and performance validation of its radiation detection and signal processing subsystems. The system employed differential measurement to obtain the net radioactive count rate of sandy soil, while enhancing energy spectrum stability through programmable gain control and temperature stabilization. Experimental results demonstrated that both plastic scintillator arrays effectively achieved dynamic background subtraction within a 1.8 s measurement cycle, with net count rate errors controlled below 10%. The NaI detector array achieved an energy resolution better than 8% at 662 keV, with the peak channel drift within ±1 channel. Rapid activity measurements for radioactive sources such as ²⁴¹Am and ¹³⁷Cs exhibited errors below 10%, meeting the key technical requirements for sandy soil separation and volume reduction. These findings provided data support and methodological reference for subsequent system integration and engineering application of sorting and volume reduction equipment. Full article

A novel series of Gd₂O₃-doped Pb₃O₄–Sb₂O₃–B₂O₃–Bi₂O₃ glasses was synthesized via the conventional melt-quenching technique to explore their structural, thermal, and optical properties for potential photonic and medical phototherapy applications. X-ray diffraction and SEM analyses confirmed the amorphous and homogeneous nature of the samples, while their FTIR spectra revealed characteristic Pb–O, Sb–O, Bi–O, and B–O vibrational bands indicative of a stable glass network. Differential scanning calorimetry (DSC) demonstrated good thermal stability, suitable for high-temperature optical applications. Optical absorption and emission studies indicated the presence of prominent Gd³⁺ ion transitions, with a strong and sharp ultraviolet emission at 311 nm (⁶P_7/2→⁸S_7/2) when excited at 274 nm. The emission intensity and lifetime increased with Gd₂O₃ concentrations of up to 1.0 mol%, beyond which concentration quenching was observed. The optimized composition exhibited a reduced optical band gap and enhanced NB-UVB emission efficiency, suggesting efficient energy transfer with minimal non-radiative losses. These results establish the designed glass system as a promising multifunctional material for NB-UVB-based phototherapy, UV-laser generation, scintillation, and other next-generation photonic devices. Full article

NUSES is a pathfinder satellite that will be deployed in a low Earth orbit, designed with new technologies for space-based detectors. Ziré is one of the payloads of NUSES and aims to measure the spectra of electrons, protons, and light nuclei in a kinetic energy range spanning from a few MeVs to several hundred MeVs, as well as photons in the energy range from 0.1 MeV to 30 MeV. Ziré consists of a Fiber TracKer (FTK), a Plastic Scintillator Tower (PST), a calorimeter (CALOg), an AntiCoincidence System (ACS) and a Low Energy Module (LEM). The FTK is based on thin scintillating fibers read out by Silicon Photomultiplier (SiPM) arrays. We assembled a prototype of Ziré (Zirettino) equipped with a single FTK layer, a reduced number of PST layers and a partially instrumented CALOg. A preliminary version of the Ziré custom Front-End Board (FEB) featuring the on-the-shelf ASIC CITIROC by OMEGA/Weeroc was used for the readout. We carried out several beam test campaigns at CERN’s PS facility and a dynamic qualification test. The performance of FTK will be presented and discussed. Full article

The aim of this study was to find out whether, just like in March 2015, daily regular GPS positioning disturbances caused by ionospheric scintillations occurred in other months of the solar activity cycle 24. The GPS positioning 90-s kinematic solutions of selected 46 months covering 11 years were used to search for regular daily scintillation events. The hypothesis on predictable regular daily ionospheric scintillation was tested. Scintillation waves were discovered as a result of space weather impact with the sidereal day regularity. It leads to the conclusion that the radiation originates from the interplanetary medium. The enhancement of radiation waves by solar activity is similar to Pc1 waves. The regular daily ionospheric scintillation waves are recorded at any time of the day. In the years with low solar activity in 2010 and 2012, regular scintillation waves were not found. It cannot be claimed that the comparison of daily regular ionospheric scintillation cases over time with the mentioned Pc1 wave cases indicates any interrelation. Full article

The X and Gamma Imager and Spectrometer (XGIS) on board THESEUS is a finely pixelized and modular instrument designed for broadband high-energy transient detection. XGIS consists of two cameras, each composed of 10 supermodules, with each supermodule further divided into 10 modules and each module made with 64 independent readout pixels based on Silicon Drift Detectors coupled with 5 × 5 × 30 mm³ CsI scintillator bars. An algorithm to quickly read out the signals from the 64 pixels and send them in chronological order through the module and supermodule logic up to the camera logic is under development. Furthermore, a challenge for space-based high-energy instruments is distinguishing X-/gamma-ray photons while effectively rejecting background photons and particles, including electrons, protons, and heavier cosmic rays. Unlike traditional systems that rely on anticoincidence systems, XGIS aims to achieve background rejection through an innovative readout logic that analyzes the spatial and temporal properties of energy deposits in the detector. By leveraging the finely pixelized structure, the readout system can differentiate single-photon events from charged-particle tracks based on energy deposition patterns and event topology. Full article

Background: The asymmetric distribution of optical photons near the edges of Positron Emission Tomography (PET) sensor modules introduces errors in the coordinate reconstruction of scintillation events when center-of-gravity (CoG) algorithms are utilized. This issue, sometimes referred to as the “edge effect”, results in overlap of crystal pixel signatures in flood maps and potential image artifacts in reconstructed PET images. Methods: Partly segmented 5 mm thick borosilicate light guides with slits cut parallel to the edges are filled with barium sulfate to restrict the spread of optical photons near the edges of the light guide. Data acquisitions are performed using single PET sensor modules in coincidence, both with single and multiplexed channel readout. CoG and truncated center-of-gravity (TCoG) methods are used for coordinate reconstruction. Results: A 22 × 22 array of crystal signatures are distinguishable on crystal flood maps produced using sensor modules with solid light guides and 24 × 24 arrays can be identified when using a partly segmented light guide. The pixel resolution around the edges and corners of the flood map is further improved when TCoG is used for coordinate reconstruction. Summary: We show that the introduction of a partly segmented light guide greatly improves coordinate reconstruction accuracy at the edges of a sensor module. In addition, it is demonstrated that the partly segmented light guides can be used in parallel with other proposed methods designed to fix the “edge effect”, including TCoG, to further coordinate reconstruction improve accuracy and crystal flood map quality. Full article

Acoustic waves, as mechanical waves, can perturb atmospheric pressure during propagation, altering the refractive index and turbulence distribution. This study explores a method to mitigate the impact of atmospheric turbulence on optical wave transmission using a linear array acoustic source. We investigated the transmission characteristics of vortex beam superposition states under acoustic perturbation, examining the effects of different wave frequencies and propagation distances on the acoustic field distribution, scintillation index, and atmospheric refractive index structure constant. The results show that acoustic field distributions vary with frequency, and a stable acoustic field is achievable with proper configuration. The scintillation index and refractive index structure constant are influenced by both the acoustic wave propagation distance and sound pressure level. Furthermore, a higher sound pressure level of the source enhances the impact of the linear array acoustic waves on both the scintillation index and the atmospheric refractive index structure constant. This research presents a novel approach to improving optical wave transmission by mitigating atmospheric turbulence. Full article