Jipeng Zhang

Accurate radionuclide identification is critical for nuclear safety and environmental radiation monitoring. To integrate the guiding effect of peak morphology features and the nonlinear fitting capability of data-driven models, this paper proposes a Physics-Enhanced Module (PEM). This module adopts the Laplacian of Gaussian (LoG) operator to decompose input gamma spectra and generate auxiliary features representing peak responses, which are concatenated with the original spectrum as an additional channel to inject peak position information into neural networks. Small-sample comparative experiments are conducted on a multi-label nuclide identification dataset covering 16 radionuclides, where PEM-ResNet and PEM-DenseNet are compared against vanilla ResNet and DenseNet baseline models. Experimental results demonstrate that all physics-enhanced networks outperform their corresponding baselines across all evaluation metrics. Consistent performance improvements observed on two mainstream convolutional architectures verify that the PEM effectively mitigates performance degradation induced by limited training samples. Further analysis reveals that the PEM provides the model with clearly identifiable peak response features for discrimination tasks. The integrated framework synergizes the fitting strengths of data-driven learning and the regularization merits of the fixed preprocessing module, thereby substantially improving the reliability and robustness of nuclide identification for nuclear energy applications.

Thermoelectric materials, as key materials for realizing efficient conversion of thermal and electrical energy, are crucial for renewable energy utilization and efficient energy management. However, materials with high negative thermoelectric coefficients are relatively rare. Herein, inspired by the structure and function of plant stem which is capable of blocking heavy metal ions, chitosan/CuCl₂ hydrogel (ChCu) with a huge negative thermoelectric coefficient is reported. The ChCu displayed lamellar porous structure, which is constructed synergistically by freeze‐casting technique and complexation between Cu²⁺ and chitosan. In a ChCu hydrogel subjected to a temperature gradient, most of the Cu²⁺ is immobilized within the chitosan matrix by complexation, while the thermal migration of the unbound Cu²⁺ is further intercepted by the special layered porous structure. On the contrary, Cl⁻ migrates unhindered to the cold end and accumulates, which realizes selective migration and distribution of ion/counterion. As a result, ChCu exhibits a thermoelectric coefficient as high as ‐23.8 mV K⁻¹, and can respond rapidly with a thermal voltage of 4.0 mV under a small temperature difference (ΔT = 0.3 K). This work reveals the significant influence of the polymer aggregate structure on the thermal diffusion of ions, providing an innovative strategy in designating thermoelectric materials with high‐performance, high‐efficiency and environmentally friendly.

(1) Background: The imaging energy range of a typical Compton camera is limited due to the fact that scattered gamma photons are seldom fully absorbed when the incident energies are above 3 MeV. Further improving the upper energy limit of gamma-ray imaging has important application significance in the active interrogation of special nuclear materials and chemical warfare agents, as well as range verification of proton therapy. (2) Methods: To realize gamma-ray imaging in a wide energy range of 0.3~7 MeV, a principle prototype, named a portable three-layer Compton camera, is developed using the scintillation detector that consists of an silicon photomultiplier array coupled with a Gd₃Al₂Ga₃O₁₂:Ce pixelated scintillator array. Implemented in a list-mode maximum likelihood expectation maximization algorithm, a far-field energy-domain imaging method based on the two interaction events is applied to estimate the initial energy and spatial distribution of gamma-ray sources. The simulation model of the detectors is established based on the Monte Carlo simulation toolkit Geant4. The reconstructed images of a ¹³³Ba, a ¹³⁷Cs and a ⁶⁰Co point-like sources have been successfully obtained with our prototype in laboratory tests and compared with simulation studies. (3) Results: The proportion of effective imaging events accounts for about 2%, which allows our prototype to realize the reconstruction of the distribution of a 0.05 μSv/h ¹³⁷Cs source in 10 s. The angular resolution for resolving two ¹³⁷Cs point-like sources is 15°. Additional simulated imaging of the 6.13 MeV gamma-rays from 14.1 MeV neutron scattering with water preliminarily demonstrates the imaging capability for high incident energy. (4) Conclusions: We conclude that the prototype has a good imaging performance in a wide energy range (0.3~7 MeV), which shows potential in several MeV gamma-ray imaging applications.

(1) Background: The imaging energy range of a typical Compton camera is limited due to the fact that scattered gamma photons are seldom fully absorbed when the incident energies are above 3 MeV. Further improving the upper energy limit of gamma-ray imaging has important application significance in active interrogation of special nuclear materials and chemical warfare agents, as well as range verification of proton therapy; (2) Methods: To realize gamma-ray imag-ing in a wide energy range of 0.3~7 MeV, a principle prototype, named a portable three-layer Compton camera, was developed using the scintillation detector that consist of an silicon photo-multiplier array coupled with a Gd3Al2Ga3O12:Ce pixelated scintillator array. Implemented in a list-mode maximum likelihood expectation maximization algorithm, a far-field energy-domain imaging method based on two-interaction and three-interaction events was applied to estimate the initial energy and spatial distribution of gamma-ray sources. The simulation model of detec-tors was established based on Monte Carlo simulation toolkit Geant4. The reconstructed images of a 133Ba, a 137Cs and a 60Co point-like sources were successfully obtained with our prototype in laboratory tests and compared with simulation studies; (3) Results: The proportion of effective imaging events accounted for about 2%, which made our prototype realize reconstructing the distribution of a 0.05 μSv/h 137Cs source in 10 seconds. The angular resolution for resolving two 137Cs point-like sources was 15°. Additional simulated imaging of the 6.13 MeV gamma-rays from 14.1 MeV neutron scattering with water preliminarily demonstrated the imaging capability for high incident energy; (4) Conclusions: We concluded that the prototype had good imaging per-formance in a wide energy range (0.3~7 MeV), which showed potential in several MeV gam-ma-ray imaging applications.

康普顿成像是直观感知核辐射的探测技术之一, 但因受限于探测器体积和成像事例的类型, 能量范围通常为0.3~3 MeV, 难以在对天然核素γ成像的基础上同时兼顾能量分布在3~7 MeV的瞬发γ成像应用. 覆盖0.3~7 MeV范围的宽能域γ成像是扩展核辐射探测与成像应用领域的重要发展方向之一, 基于两次散射的三层探测器结构是一种极具潜力的实现方案, 其中探测器的设计与构建是该方案的基础与关键核心. 考虑系统成本和扩展灵活性等因素, 本文选用硅光电倍增管(SiPM)阵列和钆镓铝石榴石(GAGG:Ce)阵列作为探测器材料. 根据三层探测器的成像事例要求, 分析每层探测器内的作用事例类型特征; 并基于Geant4蒙特卡罗模拟平台构建包含材料光学参数的仿真模型, 通过设置物理过程与两种信息提取方式, 对比研究了不同几何参数情形下的探测器位置散点图和探测器内作用事例类型统计结果. 根据仿真设计, 制备了由像素数为15×15, 像素大小为3.2×3.2 mm², 厚度分别为3 mm和10 mm的GAGG阵列和1.25 mm厚度光导组成的两种规格SiPM探测器模块, 并基于电子学读出系统评估了探测器模块的性能. 结果表明, 3 mm厚度的散射探测器与10 mm厚度的吸收探测器均可清晰分辨15×15像素上的作用位置, 平均峰谷比分别为9.77和11.85; 全部像素的662 keV平均能量分辨率分别可达7.21%和8.35%, 具有较好的位置与能量分辨能力. 本文所建立的仿真模型, 分析结果以及所研制的探测器模块, 为三层探测器系统构建提供了重要依据, 并为实现宽能域γ成像奠定了科学技术基础.

In this study, we propose a hybrid coded-aperture and Compton camera based on cerium-doped Gd₃Al₂Ga₃O₁₂ (GAGG:Ce) scintillator arrays coupled with Multi-Pixel Photon Counter (MPPC) arrays. The sensitive detector of the gamma camera consists of a single GAGG:Ce crystal coupled with a single-chip MPPC unit module. An impedance bridge circuit and a 64-channel data acquisition system were employed to record the code-aperture events and Compton coincidence events. After the calibration of position and energy, the total energy resolution for 662 keV gamma-rays from ¹³⁷Cs was 6.6%. The hybrid camera had the characteristics of mechanical collimation and electronic collimation at the same time. In the code aperture mode, the reconstructed images were obtained by direct deconvolution and maximum likelihood expectation maximization (MLEM) methods. In the Compton imaging mode, the energy-dependent method was applied to order the sequence of Compton scatter events. The simple back-projection algorithm and list-mode MLEM algorithm were adopted for image reconstruction. Practical performances demonstrated that the angular resolutions in two modes were measured as 5.2° and 11.4°, respectively. In addition, the hybrid camera had a desirable imaging capability in a wide energy range (32 keV–2.6 MeV) and a wide field of view (∼210° in the horizontal direction). As for the sensitivity, the camera had a commercially available sensitivity level of localizing a ¹³⁷Cs point source, producing ∼0.026 µSv/h in 5 min. Furthermore, the function of distinction for different radiation sources was preliminarily realized.

This work presents a novel stereo coded aperture gamma camera based on four detection modules placed within four quadrants. Each module includes 48 × 48 strips of Bi₄Ge₃O₁₂ scintillators, 24 × 24 pieces of silicon photomultipliers (SiPMs), and a set of data acquisition circuits. All signals from the SiPMs are individually extracted and finally simplified into 144 outputs to calculate the positions and energies of gamma-rays. Two masks of modified uniformly redundant arrays are fixed in the front of the top-right and bottom-left modules and two anti-masks are fixed in the top-left and bottom-right modules to achieve simultaneous imaging without dual measure. Once the projections of radioactive sources are determined, their source-to-detector distances can be estimated by our new multocular ranging algorithm. A series of lab and field experiments, including flood histogram and energy spectrum testing, field-of-view and angular resolution testing, real-time imaging, long-distance imaging, and ranging ability testing, with different radioactive sources, such as ¹³⁷Cs, ²²Na, ²⁴¹Am, ⁶⁰Co, ¹³³Ba, and ⁷⁵Se, have been completed to evaluate the comprehensive ability of the stereo gamma camera. The results show that the stereo gamma camera has a strong ability for the three-dimensional localization of radioactive sources over long distances with a high image sensitivity. So far, the stereo gamma camera has been successfully used in practical nuclear security and safety tasks although the angular resolution and the ranging algorithm robustness should be more optimized in the future.

Y2SiO5: Ce (YSO) scintillation with characteristics of high light yield, fast decay time and high Compton scattering fraction shows good application potential for Compton imaging. In this study, we propose a three-dimensional (3-D) scintillator detector, which is segmented by the YSO monolithic rods and pixelated by sub-surface laser engraving (SSLE) in the depth direction. Two arrays of silicon photomultipliers are optically coupled to the YSO array at each end, in which the pixels are designed for a one-to-one match. By identifying the location number of array pixels and measuring depth-of-interaction (DOI) of pixelated scintillator rods, the interaction coordinates of gamma photon can be obtained accurately. After energy consistent calibration, the energy resolutions of the pixels in 3-D detector were evaluated. The imaging test results indicate that the detector has a capability to locate a 0.1 µSv/h Cs-137 gamma-ray source within 90 seconds in 4π field-of-view (FOV). The efficiency of the imaging events is 2.2 %. By using the maximum likelihood expectation maximization (MLEM) algorithm with 10 iterations, the full width at half maximum (FWHM) of the reconstructed hotspot decreases to less than 9.0 °. This configuration mainly simplifies the calculation of interaction coordinates compared to the center of gravity method. Moreover, the higher segment precision for DOI estimation are realized thanks to the SSLE technique. The 3-D scintillator detector achieves 4π Compton imaging with high detection efficiency and high localization accuracy.