Nuclear Science and Techniques最新文献

Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance. In this study, a large field-of-view time-encoded imager was developed for gamma-ray and neutron source hotspot imaging based on a depth-of-interaction (DOI) detector. The imager primarily consists of a DOI detector system and a rotary dual-layer cylindrical coded mask. An EJ276 plastic scintillator coupled with two SiPMs was designed as the DOI detector to increase the field of view and improve the imager performance. The difference in signal time at both ends and the log of the signal amplitude ratio were used to calculate the interaction position resolution. The position resolution of the DOI detector was calibrated using a collimated Cs-137 source, and the full width at half maximum of the reconstruction position of the Gaussian fitting curve was approximately 4.4 cm. The DOI detector can be arbitrarily divided into several units to independently reconstruct the source distribution images. The unit length was optimized via Am-Be source-location experiments. A multidetector filtering method is proposed for image denoising. This method can effectively reduce image noise caused by poor DOI detector position resolution. The vertical field of view of the imager was (− 55°, 55°) when the detector was placed in the center of the coded mask. A DT neutron source at 20 m standoff could be located within 2400 s with an angular resolution of 3.5°.

A molten salt reactor (MSR) has outstanding features considering the application of thorium fuel, inherent safety, sustainability, and resistance to proliferation. However, fissile material ({^{233}hbox {U}}) is significantly rare at the current stage, thus it is difficult for MSR to achieve a pure thorium-uranium fuel cycle. Therefore, using plutonium or enriched uranium as the initial fuel for MSR is more practical. In this study, we aim to verify the feasibility of a small modular MSR that utilizes plutonium as the starting fuel (SM-MSR-Pu), and highlight its advantages and disadvantages. First, the structural design and fuel management scheme of the SM-MSR-Pu were presented. Second, the neutronic characteristics, such as the graphite-irradiation lifetime, burn-up performance, and coefficient of temperature reactivity were calculated to analyze the physical characteristics of the SM-MSR-Pu. The results indicate that plutonium is a feasible and advantageous starting fuel for a SM-MSR; however, there are certain shortcomings that need to be solved. In a 250 MWth SM-MSR-Pu, approximately 288.64 kg ({^{233}hbox {U}}) of plutonium with a purity of greater than 90% is produced while 978.00 kg is burned every ten years. The temperature reactivity coefficient decreases from (-4.0) to (-6.5) pcm K(^{-1}) over the 50-year operating time, which ensures a long-term safe operation. However, the amount of plutonium and accumulation of minor actinides (MAs) would increase as the burn-up time increases, and the annual production and purity of ({^{233}hbox {U}}) will decrease. To achieve an optimal burn-up performance, setting the entire operation time to 30 years is advisable. Regardless, more than 3600 kg of plutonium eventually accumulate in the core. Further research is required to effectively utilize this accumulated plutonium.

Because of their economy and applicability, high-power thyristor devices are widely used in the power supply systems for large fusion devices. When high-dose neutrons produced by deuterium–tritium (D–T) fusion reactions are irradiated on a thyristor device for a long time, the electrical characteristics of the device change, which may eventually cause irreversible damage. In this study, with the thyristor switch of the commutation circuit in the quench protection system (QPS) of a fusion device as the study object, the relationship between the internal physical structure and external electrical parameters of the irradiated thyristor is established. Subsequently, a series of targeted thyristor physical simulations and neutron irradiation experiments are conducted to verify the accuracy of the theoretical analysis. In addition, the effect of irradiated thyristor electrical characteristic changes on the entire QPS is studied by accurate simulation, providing valuable guidelines for the maintenance and renovation of the QPS.

The High-energy Fragment Separator (HFRS), which is currently under construction, is a leading international radioactive beam device. Multiple sets of position-sensitive twin time projection chamber (TPC) detectors are distributed on HFRS for particle identification and beam monitoring. The twin TPCs’ readout electronics system operates in a trigger-less mode due to its high counting rate, leading to a challenge of handling large amounts of data. To address this problem, we introduced an event-building algorithm. This algorithm employs a hierarchical processing strategy to compress data during transmission and aggregation. In addition, it reconstructs twin TPCs’ events online and stores only the reconstructed particle information, which significantly reduces the burden on data transmission and storage resources. Simulation studies demonstrated that the algorithm accurately matches twin TPCs’ events and reduces more than 98% of the data volume at a counting rate of 500 kHz/channel.

A dedicated weak current measurement system was designed to measure the weak currents generated by the neutron ionization chamber. This system incorporates a second-order low-pass filter circuit and the Kalman filtering algorithm to effectively filter out noise and minimize interference in the measurement results. Testing conducted under normal temperature conditions has demonstrated the system’s high precision performance. However, it was observed that temperature variations can affect the measurement performance. Data were collected across temperatures ranging from (-20) to (70;{^circ }{text{C}}), and a temperature correction model was established through linear regression fitting to address this issue. The feasibility of the temperature correction model was confirmed at temperatures of (-5) and ({40};{^circ }{text{C}}), where relative errors remained below 0.1(%) after applying the temperature correction. The research indicates that the designed measurement system exhibits excellent temperature adaptability and high precision, making it particularly suitable for measuring weak currents.

Dispersion fuels, knowned for their excellent safety performance, are widely used in advanced reactors, such as high-temperature gas-cooled reactors. Compared with deterministic methods, the Monte Carlo method has more advantages in the geometric modeling of stochastic media. The explicit modeling method has high computational accuracy and high computational cost. The chord length sampling (CLS) method can improve computational efficiency by sampling the chord length during neutron transport using the matrix chord length's probability density function. This study shows that the excluded-volume effect in realistic stochastic media can introduce certain deviations into the CLS. A chord length correction approach is proposed to obtain the chord length correction factor by developing the Particle code based on equivalent transmission probability. Through numerical analysis against reference solutions from explicit modeling in the RMC code, it was demonstrated that CLS with the proposed correction method provides good accuracy for addressing the excluded-volume effect in realistic infinite stochastic media.

The heterogeneous variational nodal method (HVNM) has emerged as a potential approach for solving high-fidelity neutron transport problems. However, achieving accurate results with HVNM in large-scale problems using high-fidelity models has been challenging due to the prohibitive computational costs. This paper presents an efficient parallel algorithm tailored for HVNM based on the Message Passing Interface standard. The algorithm evenly distributes the response matrix sets among processors during the matrix formation process, thus enabling independent construction without communication. Once the formation tasks are completed, a collective operation merges and shares the matrix sets among the processors. For the solution process, the problem domain is decomposed into subdomains assigned to specific processors, and the red-black Gauss-Seidel iteration is employed within each subdomain to solve the response matrix equation. Point-to-point communication is conducted between adjacent subdomains to exchange data along the boundaries. The accuracy and efficiency of the parallel algorithm are verified using the KAIST and JRR-3 test cases. Numerical results obtained with multiple processors agree well with those obtained from Monte Carlo calculations. The parallelization of HVNM results in eigenvalue errors of 31 pcm/(-)90 pcm and fission rate RMS errors of 1.22%/0.66%, respectively, for the 3D KAIST problem and the 3D JRR-3 problem. In addition, the parallel algorithm significantly reduces computation time, with an efficiency of 68.51% using 36 processors in the KAIST problem and 77.14% using 144 processors in the JRR-3 problem.

A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy (BNCT) is being developed based on the two-dimensional Micromegas detector. To address the issue of long processing times in traditional offline position reconstruction methods, this paper proposes a field programmable gate array based online position reconstruction method utilizing the micro-time projection chamber principle. This method encapsulates key technical aspects: a self-adaptive serial link technique built upon the dynamical adjustment of the delay chain length, fast sorting, a coordinate-matching technique based on the mapping between signal timestamps and random access memory (RAM) addresses, and a precise start point-merging technique utilizing a circular combined RAM. The performance test of the self-adaptive serial link shows that the bit error rate of the link is better than 10⁻¹² at a confidence level of 99%, ensuring reliable data transmission. The experiment utilizing the readout electronics and Micromegas detector shows a spatial resolution of approximately 1.4 mm, surpassing the current method’s resolution level of 5 mm. The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beams online, thus validating the feasibility of the position reconstruction method. The online position reconstruction method avoids traditional methods, such as bubble sorting and traversal searching, simplifies the design of the logic firmware, and reduces the time complexity from O(n²) to O(n). This study contributes to the advancement in measuring neutron beam flux for BNCT.

The most critical part of a neutron computed tomography (NCT) system is the image processing algorithm, which directly affects the quality and speed of the reconstructed images. Various types of noise in the system can degrade the quality of the reconstructed images. Therefore, to improve the quality of the reconstructed images of NCT systems, efficient image processing algorithms must be used. The anisotropic diffusion filtering (ADF) algorithm can not only effectively suppress the noise in the projection data, but also preserve the image edge structure information by reducing the diffusion at the image edges. Therefore, we propose the application of the ADF algorithm for NCT image reconstruction. To compare the performance of different algorithms in NCT systems, we reconstructed images using the ordered subset simultaneous algebraic reconstruction technique (OS-SART) algorithm with different regular terms as image processing algorithms. In the iterative reconstruction, we selected two image processing algorithms, the Total Variation and split Bregman solved total variation algorithms, for comparison with the performance of the ADF algorithm. Additionally, the filtered back-projection algorithm was used for comparison with an iterative algorithm. By reconstructing the projection data of the numerical and clock models, we compared and analyzed the effects of each algorithm applied in the NCT system. Based on the reconstruction results, OS-SART-ADF outperformed the other algorithms in terms of denoising, preserving the edge structure, and suppressing artifacts. For example, when the 3D Shepp–Logan was reconstructed at 25 views, the root mean square error of OS-SART-ADF was the smallest among the four iterative algorithms, at only 0.0292. The universal quality index, mean structural similarity, and correlation coefficient of the reconstructed image were the largest among all algorithms, with values of 0.9877, 0.9878, and 0.9887, respectively.

Topmetal-M2 is a large-area pixel sensor chip fabricated using the GSMC (130,textrm{nm}) CMOS process in 2021. The pixel array of Topmetal-M2 consists of pixels of 400 rows (times) 512 columns with a pixel pitch of (45,mathrm {mu m} times 45,mathrm {mu m}). The array is divided into 16 subarrays, with pixels of 400 rows (times) 32 columns per subarray. Each pixel incorporates two charge sensors: a diode sensor and a Topmetal sensor. The in-pixel circuit primarily consists of a charge-sensitive amplifier for energy measurements, a discriminator with a peak-holding circuit, and a time-to-amplitude converter for time-of-arrival measurements. The pixel of Topmetal-M2 has a charge input range of (sim 0{-}3,mathrm {k,e^-}), a voltage output range of (sim 0{-}180,textrm{mV}), and a charge-voltage conversion gain of (sim 59.56,mathrm {mu V/e^-}). The average equivalent noise charge of Topmetal-M2, which includes the readout electronic system noise, is (sim 43.45,mathrm {e^-}). In the scanning mode, the time resolution of Topmetal-M2 is (1,textrm{LSB} = 1.25,mathrm {mu s}), and the precision is (sim 7.41,mathrm {mu s}). At an operating voltage of (1.5,textrm{V}), Topmetal-M2 has a power consumption of (sim 49,mathrm {mW/cm^2}). In this article, we provide a comprehensive overview of the chip architecture, pixel working principles, and functional behavior of Topmetal-M2. Furthermore, we present the results of preliminary tests conducted on Topmetal-M2, namely, alpha-particle and soft X-ray tests.