分类： 物理学 >> 核物理学 提交时间： 2023-06-07
摘要：An ZrV2 alloy is typically susceptible to poisoning by impurity gases, which causes a considerable reduction in the hydrogen-storage properties of the alloy. In this study, the adsorption characteristics of oxygen on ZrV2 surfaces doped with Hf, Ti, and Pd are investigated, and the influence of oxygen on the hydrogen storage performance of the alloy was discussed. Subsequently, the adsorption energy, bond-length change, density of states, and differential charge density of the alloy before and after doping are analyzed using the first-principles method. The theoretical results show that Ti doping has a limited effect on the adsorption of oxygen atoms on the ZrV2 surface, whereas Hf doping decreases the adsorption energy of oxygen on the ZrV2 surface. Oxygen atoms are more difficult to adsorb at most adsorption sites on Pd-containing surfaces, which indicates that Pd has the best anti-poisoning properties, followed by Hf. The analysis of the differential charge density and partial density of states shows that the electron interaction between the oxygen atom and surface atom of the alloys is weakened, and the total energy is reduced after Hf and Pd doping. Based on theoretical calculations, the hydrogen-absorption kinetics of ZrV2, Zr0.9Hf0.1V2, and Zr(V0.9Pd0.1)2 alloys are studied in a hydrogen–oxygen mixture of 0.5 vol% O2 at 25℃. The experimental results show that the hydrogen-storage capacities of ZrV2, Zr0.9Hf0.1V2, and Zr(V0.9Pd0.1)2 decrease to 19%, 69%, and 80% of their original values, respectively. The order of alloy resistance to 0.5 vol% O2 poisoning is Zr(V0.9Pd0.1)2>Zr0.9Hf0.1V2>ZrV2. Pd retains its original hydrogen absorption performance to a greater extent than undoped surfaces, and it has the strongest resistance to poisoning, which is consistent with previous theoretical calculations.
分类： 物理学 >> 核物理学 提交时间： 2023-06-07
Zhang, Lianxin
Chen, Size
Zhang, Zaodi
Li, Taosheng
Peng, Chuan
Ren, Lei
Zhang, Rui
Xiao. Dan
Zhang. Yong
摘要：Owing to the immobility of traditional reactors and spallation neutron sources, the demand for compact thermal neutron radiography (CTNR) based on accelerator neutron sources has rapidly increased in industrial applications. Recently, thermal neutron radiography experiments based on a D-T neutron generator performed by Hefei Institutes of Physical Science indicated a significant resolution deviation between the experimental results and the values calculated using the traditional resolution model. The experimental result was up to 23% lower than the calculated result, which hinders the achievement of the design goal of a compact neutron radiography system. A GEANT4 Monte Carlo code was developed to simulate the CTNR process, aiming to identify the key factors leading to resolution deviation. The effects of a low collimation ratio and high-energy neutrons were analyzed based on the neutron beam environment of the CTNR system. The results showed that the deviation was primarily caused by geometric distortion at low collimation ratios and radiation noise induced by high 1 energy neutrons. Additionally, the theoretical model was modified by considering the imaging position and radiation noise factors. The modified theoretical model was in good agreement with the experimental results, and the maximum deviation was reduced to 4.22%. This can be useful for the high-precision design of CTNR systems.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-07
Dai, Zeyi
Nie, Yuancun
He, Jianhua
Hui, zi
Liu, Lanxin
Liu, Zishuo
Zhong,Jianhua
Guan, Jiabao
Wang, Jike
Chen, Yuan
Zou, Ye
Li, Haohu
摘要：Abstract
High-brightness electron beams are required to drive LINAC-based free-electron lasers (FELs) and storage-ring-based synchrotron radiation light sources. The bunch charge and RMS bunch length at the exit of the LINAC play a crucial role in the peak current; the minimum transverse emittance is mainly determined by the injector of the LINAC. Thus, a photoinjector with a high bunch charge and low emittance that can simultaneously provide high-quality beams for 4th generation synchrotron radiation sources and FELs is desirable. The design of a 1.6-cell S-band 2998-MHz RF gun and beam dynamics optimization of a relevant beamline are presented in this paper. Beam dynamics simulations were performed by combining ASTRA and the multi-objective genetic algorithm NSGA II. The effects of the laser pulse shape, half-cell length of the RF gun, and RF parameters on the output beam quality were analyzed and compared. The normalized transverse emittance was optimized to be as low as 0.65 and 0.92 mm·mrad when the bunch charge was as high as 1 and 2 nC, respectively. Finally, the beam stability properties of the photoinjector, considering misalignment and RF jitter, were simulated and analyzed.
分类： 物理学 >> 核物理学 提交时间： 2023-06-07
摘要：To provide a reliable and comprehensive data reference for core geometry design of graphite-moderated and low-enriched uranium fueled molten salt reactor, the influences of geometric parameters on temperature coefficient of reactivity (TCR) at an assembly level are characterized. The four-factor formula is introduced to explain how different reactivity coefficients behave in terms of fuel salt volume fraction and assembly size. The results show that fuel salt temperature coefficient (FSTC) is always negative due to a more negative fuel salt density coefficient in the over-moderated region or a more negative Doppler coefficient in the under-moderated region. Depending on the fuel salt channel spacing, the graphite moderator temperature coefficient (MTC) can be negative or positive. Further, an assembly with a smaller fuel salt channel spacing are more likely to exhibit a negative MTC. As fuel salt volume fraction increases, the negative FSTC weakens first and then increases, owing to the fuel salt density effect gradually weakening from negative feedback to positive feedback and then decreasing. Meanwhile, MTC weakens as the thermal utilization coefficient caused by the graphite temperature effect deteriorates. Thus, the negative TCR weakens first and then strengthens mainly because of the change in fuel salt density coefficient. As assembly size increases, the magnitude of FSTC decreases monotonously due to a monotonously weakened fuel salt Doppler coefficient, whereas MTC changes from gradual weakened negative feedback to gradual enhanced positive feedback. And then, the negative TCR weakens. Therefore, to achieve a proper negative TCR, particularly a negative MTC, an assembly with a smaller fuel salt channel spacing in the under-moderated region is strongly recommended.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-06
摘要：In this study, a phenomenological model of the radio frequency (RF) behavior of a superconducting cavity fundamental power coupler is proposed by analyzing the simulation results of a transient beam loading process in an extremely over-coupled superconducting cavity. Using this phenomenological model, the calculation of the transient reflected power from a superconducting cavity under beam loading can be mathematically simplified to algebraic operations without solving the differential equation governing the transient beam loading process, while maintaining the calculation accuracy. Moreover, this phenomenological model can facilitate an intuitive understanding of the significant surge in the time evolution of reflected power from a superconducting cavity in certain beam-loading processes. The validity of this phenomenological model was carefully examined in various beam loading processes and cavity conditions, and the method based on this phenomenological model was utilized in the transient RF analysis of the superconducting cavity system of the CAFe Linac, achieving satisfactory results.
分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2023-06-06
摘要：The lightweight shielding design of small reactors is a research hotspot. Based on a small helium-xenon-cooled solid reactor, the effects of thickness and number of shielding layers on the radiation dose are first studied. It is found that when photons are shielded first and the number of shielding layers is odd, the radiation dose can be significantly reduced. To reduce the weight of the shielding body, the relative thickness of the shielding layers is optimized by the genetic algorithm. The optimized scheme can reduce the radiation dose by up to 57% and helps reduce the weight by 11.84%. To determine the total thickness of shielding layers and avoid the local optimal solution, a formula that gives the relationship between the total thickness and the radiation dose is established through large-scale calculations, which has an error of 0.8%~7.45% compared with the Monte Carlo method. A semi-empirical and semi-quantitative lightweight shielding design algorithm is proposed to integrate the above works, and a code SDIC1.0 is developed to achieve the optimized lightweight shielding design for small reactors. It has been verified that the error between SDIC1.0 and Monte Carlo code RMC is about 10%, and the time has increased by 6.3 times.
分类： 物理学 >> 核物理学 提交时间： 2023-06-06
摘要： β衰变半衰期和β延迟中子发射（βn）在核物理和核能等基础科学和工业应用的发展中具有重要意义，其中β−衰变起着重要作用。许多理论模型已经被提出来描述β-衰变的半衰期，而对βn的系统研究仍然很少。本文旨在通过解析公式研究了β−-衰减半衰期和βn概率，并与实验数据进行了比较。通过考虑衰减能量、凹凸度和壳效应等主要因素，提出了β−-衰减性质的解析公式。采用自助法同时评价计算的总不确定性，由统计量和系统不确定性组成。评估了中子富区的β−-衰变半衰期、βn概率和相应的不确定性。实验中的半衰期被很好地再现了。更多的预测也提出了理论的不确定性，这有助于更好地理解实验结果和理论结果之间的差异
分类： 物理学 >> 核物理学 提交时间： 2023-06-06
摘要：Accurate 3-Dimensional (3-D) reconstruction technology for non-destructive testing based on digital radiography (DR) is of great importance for alleviating the drawbacks of the existing computed tomography (CT)-based method. The commonly used Monte Carlo simulation method ensures well-performing imaging results for DR. However, for 3-D reconstruction, it is limited by its high time consumption. To solve this problem, this study proposes a parallel computing method to accelerate Monte Carlo simulation for projection images with a parallel interface and a specific DR application. The images are utilized for 3-D reconstruction of the test model. We verify the accuracy of parallel computing for DR and evaluate the performance of two parallel computing modes—multithreaded applications (G4-MT) and message-passing interfaces (G4-MPI)—by assessing parallel speedup and efficiency. This study explores the scalability of the hybrid G4-MPI and G4-MT modes. The results show that the two parallel computing modes can significantly reduce the Monte Carlo simulation time because the parallel speedup increment of Monte Carlo simulations can be considered linear growth, and the parallel efficiency is maintained at a high level. The hybrid mode has strong scalability, as the overall run time of the 180 simulations using 320 threads is 15.35 h with 10 billion particles emitted, and the parallel speedup can be up to 151.36. The 3-D reconstruction of the model is achieved based on the filtered back projection (FBP) algorithm using 180 projection images obtained with the hybrid G4-MPI and G4-MT. The quality of the reconstructed sliced images is satisfactory because the images can reflect the internal structure of the test model. This method is applied to a complex model, and the quality of the reconstructed images is evaluated.
分类： 核科学技术 >> 辐射防护技术 提交时间： 2023-06-06
摘要：The uncertainty of nuclide libraries in the analysis of the gamma spectra of low- and intermediate-level radioactive waste (LILW) using existing methods produces unstable results. To address this problem, a novel spectral analysis method is proposed in this study. In this method, overlapping peaks are located using a continuous wavelet transform. An improved quadratic convolution method is proposed to calculate the widths of the peaks and establish a fourth-order filter model to estimate the Compton edge baseline with the overlapping peaks. Combined with the adaptive sensitive nonlinear iterative peak, this method can effectively subtracts the background. Finally, a function describing the peak shape as a filter is used to deconvolve the energy spectrum to achieve accurate qualitative and quantitative analyses of the nuclide without the aid of a nuclide library. Gamma spectrum acquisition experiments for standard point sources of Cs-137 and Eu-152, a segmented gamma scanning experiment for a 200 L standard drum, and a Monte Carlo simulation experiment for triple overlapping peaks using the closest energy of three typical LILW nuclides (Sb-125, Sb-124, and Cs-134) are conducted. The results of the experiments indicate that (1) the novel method and gamma vision (GV) with an accurate nuclide library have the same spectral analysis capability, and the peak area calculation error is less than 4%; (2) compared with the GV, the analysis results of the novel method are more stable; (3) the novel method can be applied to the activity measurement of LILW, and the error of the activity reconstruction at the equivalent radius is 2.4%; and (4) The proposed novel method can quantitatively analyze all nuclides in LILW without a nuclide library. This novel method can improve the accuracy and precision of LILW measurements, provide key technical support for the reasonable disposal of LILW, and ensure the safety of humans and the environment.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-02
Mou, Hongjin
Mao, Guangbo
Zhang, Jinquan
Zhao, Can
Guo, Jinlong
Liu, Wenjintg
Wu, Ruqun
Shen, Cheng
Zhang, Lei
Li, Junshuai
Du, Guanghua
摘要：High-energy proton microbeam facilities are powerful tools in space science, biology, and cancer therapy studies. The primary limitations of the 50 MeV proton microbeam system are the poor beam quality provided by the cyclotron and the problem of intense scattering in the slit position. Here, we present an optical design for a cyclotron-based 50 MeV high-energy proton microbeam system with a micron-sized resolution. The microbeam system, which has an Oxford triplet lens configuration, has relatively small spherical aberrations and is insensitive to changes in the beam divergence angle and momentum spread. In addition, the energy filtration included in the system can reduce the beam momentum spread from 1% to 0.02%. The effects of lens parasitic aberrations and the lens fringe field on the beam spot resolution are also discussed. In addition, owing to the severe scattering of 50 MeV protons in slit materials, a slit system model based on the Geant4 toolkit enables the quantitative analysis of scattered protons and secondary particles. For the slit system settings under a 10-micron final beam spot, very few scattered protons can enter the quadrupole lens system and affect the focusing performance of the microbeam system, but the secondary radiation of neutrons and gamma rays generated at the collimation system should be considered for the 50 MeV proton microbeam. These data demonstrate that a 50 MeV proton microbeam system with a micron-sized beam spot based on a cyclotron is feasible.
分类： 物理学 >> 核物理学 提交时间： 2023-06-02
摘要：In this study, the rapidity distribution, collective flows, and nuclear stopping power in 197Au+197 Au collisions at intermediate energies were investigated using the ultrarelativistic quantum molecular dynamics (UrQMD) model with GEMINI++ code. The UrQMD model was adopted to simulate the dynamic evolution of heavy-ion collisions, whereas the GEMINI++ code was used to simulate the decay of primary fragments produced by UrQMD. The calculated results were compared with the INDRA and FOPI experimental data. It was found that the rapidity distribution, collective flows, and nuclear stopping power were affected to a certain extent by the decay of primary fragments, especially at lower beam energies. Furthermore, the experimental data of the collective flows and nuclear stopping power at the investigated beam energies were better reproduced when the sequential decay effect was included.
分类： 物理学 >> 核物理学 提交时间： 2023-06-02
摘要：银纳米团簇(AgNCs)是一种与分子性质相似的新型纳米材料，它具有独特的应用前景。通过将AgNCs与不同的基体材料结合制备AgNC复合材料，可以极大的扩展AgNCs的应用范围。利用辐照技术，我们开发了一种简单的两步法制备银纳米团簇复合材料的合成方法。首先，将聚丙烯酸(PAA)链接枝到PE薄膜表面得到固体模板(PE-g-PAA)。随后，在模板材料表面原位还原银离子，得到AgNC复合材料(AgNCs@PE-g-PAA)。通过调整反应条件，可以很容易地控制AgNCs在复合膜上的负载程度。负载的AgNCs被锚定在PAA的羧基上并包裹在接枝链中。AgNCs的粒径仅为4.38±0.85 nm，粒径分布非常均匀。AgNCs@PE-g-PAA表现出AgNCs的荧光特性。AgNCs@PE-g-PAA的荧光很容易被Cr3+离子猝灭。该复合材料可作为荧光试纸，实现对Cr3+的目视检测。
分类： 物理学 >> 核物理学 提交时间： 2023-06-01 合作期刊: 《Nuclear Science and Techniques》
E. Aboud
S. Ahn
G. V. Rogachev
V.E. Johnson
J. Bishop
G. Christian
E. Koshchiy
C.E. Parker
D.P. Scriven
摘要：Nuclear nonproliferation is of critical importance for global security. Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect. Active interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal neutrons. Also, most conventional portal monitoring systems rely on 3 He, which has a finite and continually decreasing supply. By designing a highly segmented array of organic scintillators, we posit that we can accurately and quickly identify fissile materials, including weapons-grade plutonium and highly enriched uranium, being smuggled. We propose a new design for a fast-neutron detector that overcomes the limitations of the current generation of portal monitors. MCNP6 simulations have been performed in conjunction with the UMPBT statistical model to determine the sensitivity limitations of the proposed detector. Results suggest that the proposed detector may be 10 times more efficient than current-generation thermal neutron detectors and may be able to positively identify a 81 mg 235 U source in as little as 192 seconds utilizing active interrogation techniques.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2023-06-01
Li, Haoqing
Sheng, Liang
Zhang, Changqing
Du, Yingchao
Zhou, Zheng
Weng, Xiufeng
Xiao, Jiahao
Yin, Hongqiao
Sun, Bin
Wei, Kun
Li, Yang
Duan, Baojun
Liu, Yongtang
Zhang, Yanhong
Zhang, Mei
Song, Yan
Zhang, Xiaodong
Liu, Jun
Fu, Zhuming
Xu, Qing
摘要：Image distortion caused by angular misalignment of quadrupole magnets in high energy electron radiography is studied systematically. We propose that the distortion originates from the coupling of the motions of electron in transverse directions based on theoretical analysis via transfer matrix method. The relative angular rotation between the second and third magnetic quadrupoles is identified to be the main contributor to image distortion, which is verified by both beam dynamics simulation and experimental outcomes. In addition, different strategies to mitigate this image distortion are explored, including magnets online tuning, using higher beam energy and larger magnification factor. This study provides some criteria for designing experiments, and paves the way to achieve higher image precision.
分类： 物理学 >> 核物理学 提交时间： 2023-06-01
摘要：Compton camera-based prompt gamma (PG) imaging has been proposed for range verification during proton
therapy. However, a deviation between the PG and dose distributions, as well as the difference between the
reconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring during
clinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Compton
camera, thereby further improving the prediction accuracy of in-vivo range verification and providing a novel
method for beam monitoring during proton therapy. In this paper, we present an approach based on a subsetdriven origin ensemble with resolution recovery (SD-OE-RR) and a double evolutionary algorithm (DEA) to reconstruct the dose depth profile (DDP) from the gamma events obtained by a Cadmium-Zinc-Telluride
(CZT) Compton camera with limited position and energy resolution. Simulations of proton pencil beams with
clinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom were
used to evaluate the feasibility of the proposed method. The results show that for the monoenergetic proton
pencil beam irradiating homogeneous-material box phantom, the accuracy of the reconstructed DDP was within
0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in the
therapy simulation of thoracic tumors, the range deviation of the reconstructed spread-out Bragg peak was
within 0.8 mm, and the relative dose deviation in the peak area was less than 7% compared to the exact values.
The results demonstrate the potential and feasibility of the proposed method in future Compton-based accurate
dose reconstruction and range verification during proton therapy.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-01
摘要：研制用于精确控制电子能量的失谐系统是一个电子靶用于离子储存环的重要挑战。为此，本文为HIAF-SRing的电子靶研制了一种高精度、高电压、失谐系统，使其能在实验中产生精确的电子离子相对能量调制。该系统由辅助电源和高压失谐电源组成。辅助电源级采用工作在软开关状态的LCC谐振变换器和LC滤波器输出正弦波形为高压失谐电源供电。失谐电源由高压脉冲放大器(HVPA)与高压直流(HVDC)模块串联组成。本文介绍了失谐系统的设计与开发，并详细介绍了实验装置，测试结果表明，失谐系统符合双电子复合(DR)实验的技术要求。最后，利用失谐量测量了Fe15+ DR谱，实验数据显示了良好的实验分辨率，验证了该方法的可靠性和可行性。
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2023-06-01
分类： 核科学技术 >> 核仪器、仪表 提交时间： 2023-06-01
Shi-Xing Liu
Wei Zhang
Zi-Han Zhang
Shuang Lin
Hong-Rui Cao
Cheng-Xin Song
Jin-Long Zhao
Guo-Qiang Zhong
摘要：核安全防护通常需要同时探测中子和伽马射线，探测器的实时中子/伽马脉冲分辨是其关键性能参数。近年来，采用Cs2LiLaBr6 (CLLB)晶体的双读出探测器引起了广泛关注，论文研究电荷比较法、幅度比较法、时间比较法和脉冲梯度法的甄别性能，以及Sallen-Key滤波器的甄别效果。实验结果表明，通过合适的滤波，四种方法的品质因数(FOM)都有所提高。其中，电荷比较法抗噪声性能最佳，最适合CLLB探测器实时甄别中子/伽马脉冲。其甄别性能取决于参数、 和。在对应脉冲峰值10%的时刻，，仅需延迟640-740 ns，此刻对应3.1-3.3 MeV的电荷比较方法最优FOM大于1.46。所提出的最大分辨差模型( MDDM)计算值与最优FOM的差异小于3.9%，表明该模型可以很好地指导电荷比较法的参数选择。
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2023-06-01
摘要：In recent years, graphics processing units (GPUs) have been applied to accelerate Monte Carlo (MC) simulations for proton dose calculation in radiotherapy. Nonetheless, current GPU platforms, such as CUDA and OpenCL, suffer from cross-platform limitation or relatively high programming barrier. However, the Taichi toolkit, which was developed to overcome these difficulties, has been successfully applied to high-performance numerical computations. Based on the class II condensed history simulation scheme with various proton-nucleus interactions, we developed a proton MC transport GPU-accelerated engine using the Taichi toolkit. Dose distributions in homogeneous and heterogeneous materials were calculated for 110, 160, and 200 MeV protons and were compared with those obtained by full MC simulations using Topas. The gamma passing rates were greater than 0.99 and 0.95 with criteria of 2 mm, 2% and 1 mm, 1%, respectively, in all the tested conditions. Moreover, the calculation speed was at least 5800 times faster than that of Topas, and the number of lines of code was approximately 10 times lesser than those of CUDA or OpenCL. Our study provides a highly accurate, efficient, and easy-to-use proton dose calculation engine for algorithm developers, students, and medical physicists.
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