Vol.33,

The alpha ternary fission half-lives of thorium isotopes have been studied using the Coulomb and proximity potential models. The role of the deformation effects and the angle of orientation were included during the evaluation of the total potential. Fragment combinations were identified using cold valley plots of the driving potential. The half-lives and yields were evaluated using the penetration probability. The dependence of the logarithmic half-lives on different angles of orientation was studied. The evaluated alpha ternary fission yield was compared with that of the available experiments with and without deformations. The half-lives obtained in the present work were compared with those of the available data. Possible alpha ternary fission fragments were identified in the isotopes of thorium. The alpha ternary fission half-lives were compared to the binary fission half-lives. The binary fission half-lives are dominant in the ^209-225Th nuclei, and the ternary fission half-lives are dominant in the isotopes of the ^226-238Th nuclei.

463

With global warming, the demand for diversified energy sources has increased significantly. Transportable micro reactors are important potential supplements to the global power market and are a promising development direction. This paper describes a 5 MW integrated long-life S-CO₂ cooled vehicular micro reactor (VMR) design based on tristructural isotropic (TRISO) fuel particles that aims to provide electricity for industrial power facilities, remote mines, and remote mountainous areas that are not connected to central power grids. First, to facilitate transportation, flexible deployment, and simplified operation and maintenance requirements, the VMR core and auxiliary system were designed to be reasonably small and as simple as possible. Second, the TRISO fuel particles used in the proposed VMR offer excellent properties, such as high inherent security and nonproliferation, which are vital for reactors in remote areas. In addition, a long core lifetime was achieved using the compact core design and enhanced fuel loading capacity, which is challenging when using TRISO as fuel. Finally, to make the VMR economically competitive in terms of improved neutron performance and fuel efficiency compared to similar designs, large-size TRISO particles and tube-in-duct fuel assembly were utilized and different core configurations were schemed and simulated to obtain the design that best satisfied the proposed criteria. The lifetime and burnup in the final optimized VMR were satisfactory at 21 years and 43.9 MWd/kgU, respectively, with an adequate shutdown margin and excellent safety parameters to ensure safe operation.

472

In the field of neutronics analysis, it is imperative to develop computer-aided modeling technology for Monte Carlo (MC) codes to address the increasing complexity of reactor core components by converting 3D CAD model (boundary representation, BREP) to MC model (constructive solid geometry, CSG). Separation-based conversion from BREP to CSG is widely used in computer-aided modeling MC codes because of its high efficiency, reliability, and easy implementation. However, the current separation-based BREP-CSG conversion is poor for processing complex CAD models, and it is necessary to divide a complex model into several simple models before applying the separation-based conversion algorithm, which is time-consuming and tedious. To avoid manual segmentation, this study proposed a MeshCNN-based 3D-shape segmentation algorithm to automatically separate a complex model. The proposed 3D-shape segmentation algorithm was combined with separation-based BREP-CSG conversion algorithms to directly convert complex models. The proposed algorithm was integrated into the computer-aided modeling software cosVMPT and validated using the Chinese fusion engineering testing reactor model. The results demonstrate that the MeshCNN-based BREP-CSG conversion algorithm has a better performance and higher efficiency, particularly in terms of CPU time, and the conversion result is more intuitive and consistent with the intention of the modeler.

511

Microfission chambers loaded with highly enriched fissile materials are widely used for measuring power in reactors. The neutron sensitivity of the microfission chamber is a key parameter that determines the accuracy of the power measurement. To evaluate the performance of the FC4A microfission chamber, in this work, we introduced an accurate and validated model of the microfission chamber, a performed Monte Carlo simulation of the neutron sensitivity of the microfission chamber with GEANT4 code, and conducted an irradiation experiment on the neutron irradiation effect platform #3 of the Xi'an Pulsed Reactor. We compared the simulated sensitivity with the experimental results, which showed that the sensitivity obtained from the simulation was in good agreement with the experimental results. In addition, we studied the impact of the design parameters of the fission chamber on the calculated neutron sensitivity of the microfission chamber.

439

The response functions of a 4π summing BGO detector were established using extensive experimental measurements and GEANT4 simulation. The partial and total efficiencies for all components of the γ-ray interaction with the BGO detector were also measured. These response functions and efficiencies will be used in the β-Oslo method experiments to study the neutron capture cross-sections of radioactive heavy ions. The application of the response functions of the BGO detector under simulated continuum γ-rays and source measurement γ-rays proves that the method and response functions are reliable.

354

Open plasma stealth technology excited by radionuclides is known to have several problems: 1) Owing to disturbance from airflow, the plasma distribution is unstable. 2) The plasma is highly dependent on the atmosphere; therefore, it is difficult to modulate in target stealth. 3) Concerns regarding radiation harassment prevents the application of this method. To avoid these problems, an enclosed plasma stealth method is introduced. Via simulation on an infinite conducting plate, this method was found to effectively solve the above concerns, which may offer a new approach for the practical application of plasma stealth technology excited by radionuclides, especially for small-satellite stealth because of its light weight and self-provided plasma.

391

To satisfy the accurate positioning requirement of the calibration source in the Jiangmen Underground Neutrino Observatory (JUNO), a Tonpilz-type hydrophone with low radioactivity and high electroacoustics is developed. The radioactivity of the proposed hydrophone is strictly controlled by selecting pure raw materials, especially active piezoelectric ceramics. The electroacoustic performance of the hydrophone is improved by making structural optimization. High sensitivity and aimed directivity are achieved using 33-mode piezoelectric ceramic rings arranged in series and improvement of the radiating head of the Tonpilz hydrophone, respectively. All electroacoustic performances are studied through finite element analyses. The simulations indicate that the electroacoustic performances of the hydrophones in linear alkylbenzene-based liquid scintillator can be approximately predicted according to the results in water because their differences caused by two types of acoustic media, water and liquid scintillator, are known. The tests show that the hydrophone prototype can achieve a maximum sensitivity of -209.3 dB and a beamwidth of 132.2°at a frequency of 143 kHz. In addition, eight hydrophones only contributed to a background radioactivity level of 26 ± 4 mHz in the neutrino analysis.

433

Neural network methods have recently emerged as a hot topic in computed tomography (CT) imaging owing to their powerful fitting ability; however, their potential applications still need to be carefully studied because their results are often difficult to interpret and are ambiguous in generalizability. Thus, quality assessments of the results obtained from a neural network are necessary to evaluate the neural network. Assessing the image quality of neural networks using traditional objective measurements is not appropriate because neural networks are nonstationary and nonlinear. In contrast, subjective assessments are trustworthy, although they are time- and energy-consuming for radiologists. Model observers that mimic subjective assessment require the mean and covariance of images, which are calculated from numerous image samples; however, this has not yet been applied to the evaluation of neural networks. In this study, we propose an analytical method for noise propagation from a single projection to efficiently evaluate convolutional neural networks (CNNs) in the CT imaging field. We propagate noise through nonlinear layers in a CNN using the Taylor expansion. Nesting of the linear and nonlinear layer noise propagation constitutes the covariance estimation of the CNN. A commonly used U-net structure is adopted for validation. The results reveal that the covariance estimation obtained from the proposed analytical method agrees well with that obtained from the image samples for different phantoms, noise levels, and activation functions, demonstrating that propagating noise from only a single projection is feasible for CNN methods in CT reconstruction. In addition, we use covariance estimation to provide three measurements for the qualitative and quantitative performance evaluation of U-net. The results indicate that the network cannot be applied to projections with high noise levels and possesses limitations in terms of efficiency for processing low-noise projections. U-net is more effective in improving the image quality of smooth regions compared with that of the edge. LeakyReLU outperforms Swish in terms of noise reduction.

411

The lattice of the Shanghai Synchrotron Radiation Facility (SSRF) storage ring was upgraded in the Phase-II beamline project, and thus far, 18 insertion devices (IDs) have been installed. The IDs cause closed-orbit distortions, tune drift, and coupling distortions in the SSRF storage ring, all of which are significant issues that require solutions. In this study, an ID orbit feedforward compensation system based on a response matrix using corrector coils was developed, and it was applied to all commissioned IDs in the SSRF storage ring. After correction, the maximum ID-induced horizontal and vertical orbit distortions were less than 5.0 μm and 3.5 μm, respectively. Some interesting phenomena observed during the measurement process were explained. Additionally, optical and coupling feedforward systems were developed using quadrupole and skew quadrupole magnets installed on the front and back of elliptically polarizing undulators (EPUs). Moreover, over nearly four months of operation, the developed strategy delivered a satisfactory performance in the SSRF storage ring.

394

A dilation X-ray detector (DIXD) based on time dilation and microchannel plate (MCP) gated technology has been reported. The DIXD passes a driving pulse along the transmission photocathode (PC) to obtain a dilated electron signal and finally achieves a high time resolution of 12 ps. Furthermore, the waveform of the PC driving pulse can be obtained using the DIXD, and a DIXD oscillographic function can be obtained. An experiment is presented to demonstrate the DIXD oscilloscope. The waveform of the PC driving pulse from points t₁ to t₁₂ is achieved by the DIXD. The waveform agrees well with that measured by a high-speed oscilloscope with a difference of less than 6%. The maximum theoretical bandwidth of the DIXD oscilloscope is theoretically studied. The bandwidth is limited by the potential difference between the PC and mesh. When the potential difference is 3.4 kV, the theoretical limiting bandwidth is 1000 GHz. The bandwidth increases with an increase in the potential difference.

372

In this study, the anti-noise performance of a pulse-coupled neural network (PCNN) was investigated in the neutron and gamma-ray (n-γ) discrimination field. The experiments were conducted in two groups. In the first group, radiation pulse signals were pre-processed using a Fourier filter to reduce the original noise in the signals, whereas in the second group, the original noise was left untouched to simulate an extremely high-noise scenario. For each part, artificial Gaussian noise with different intensity levels was added to the signals prior to the discrimination process. In the aforementioned conditions, the performance of the PCNN was evaluated and compared with five other commonly used methods of n-γ discrimination: (1) zero crossing, (2) charge comparison, (3) vector projection, (4) falling-edge percentage slope, and (5) frequency gradient analysis. The experimental results showed that the PCNN method significantly outperforms other methods with outstanding FoM-value at all noise levels. Furthermore, the fluctuations in FoM-value of PCNN were significantly better than those obtained via other methods at most noise levels and only slightly worse than those obtained via the charge comparison and zero-crossing methods under extreme noise conditions. Additionally, the changing patterns and fluctuations of the FoM-value were evaluated under different noise conditions. Hence, based on the results, the parameter selection strategy of the PCNN was presented. In conclusion, the PCNN method is suitable for use in high-noise application scenarios for n-γ discrimination because of its stability and remarkable discrimination performance. It does not rely on strict parameter settings and can realize satisfactory performance over a wide parameter range.

529

The ring imaging Cherenkov (RICH) detector for particle identification (PID) is being evaluated for the future super tau-charm facility (STCF) complex. In this work, the prototype readout electronics for the RICH PID detector is designed. The prototype RICH PID detector is based on a thick gas electron multiplier combined with a micromegas detector for Cherenkov light detection. Considering that there will be a large number (~690,000) of detector channels in the future RICH detector, the readout electronics faces many challenges to precisely measuring time and charge information, such as reducing the noise, increasing density, and improving precision. The requirements of the readout electronics are explored, the down-selection of the ASICs is made and thus a prototype readout electronics is designed and implemented. Tests are also conducted to evaluate the performance of the prototype readout electronics, and the results indicate that the time resolution is better than ~1 ns (RMS) when the input charge is greater than ~12 fC based on the APV25 chip, while the time resolution is better than ~1 ns (RMS) at an input charge of over ~48 fC based on the AGET and STCF ASIC chips, and the equivalent noise charge is better than ~0.5 fC (RMS) @ 20 pF based on the three ASICs. The test results indicate that the prototype readout electronics design meets the requirement of the future RICH PID detector and thus provides a reference for future engineering.

480

Among the various scanning techniques, spot and raster scanning are the most frequently adopted. Raster scanning turns off the beam only when each isoenergy slice irradiation is completed. This feature intrinsically solves the leakage dose and frequent beam-switching problems encountered during spot scanning. However, to shorten the delivery time of raster scanning, a sophisticated dose control strategy is required to guarantee dose distribution. In this study, a real-time compensation method with raster scanning for synchrotron systems was designed. It is characterized by a small spot-spacing planning strategy and real-time subtraction of the transient number of particles delivered between two planning-spot positions from the planned number of particles of the subsequent raster point. The efficacy of the compensation method was demonstrated by performing accurate raster scanning simulations with an in-house simulation code and accurate final dose evaluations with a commercial treatment planning system. Given the similar dose evaluation criteria under a practical high scanning speed, compared with the spot scanning method, the total delivery time of the compensated raster scanning method was significantly shortened by 53.3% in the case of irradiating a cubical target and by 28.8% in a pelvic case. Therefore, it can be concluded that real-time compensated raster scanning with a fast scanning configuration can significantly shorten the delivery time compared to that of spot scanning. It is important to reduce the pressure on patients caused by prolonged immobilization and to improve patient throughput capacity at particle therapy centers.

348

A novel Fe-10Cr ferritic/martensitic steel called SIMP was chosen to investigate synergistic effects of H and He on the mechanical properties of structural materials for innovative nuclear energy systems. Sequential and separate irradiation experiments on SIMP steel specimens at room temperature using H and He ions with various energy levels were conducted to produce an ion deposition plateau at 300–650 nm. The indentation stress–strain responses were examined using spherical nanoindentation tests after the irradiation experiments. It was found that the sequential irradiation by He and H produced a higher indentation yield stress than separate irradiation, indicating that the hardening was enhanced by the synergy of the H and He irradiation. The micro-mechanism responsible for enhancing the hardening of the SIMP steel through the H and He synergy was investigated using Doppler broadening spectroscopy detection and transmission electron spectroscopy observations.

658