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： 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： 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： 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： 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： 物理学 >> 核物理学 提交时间： 2023-05-31
Xu,Miaofu
Zhang,Xiangzhen
Ye,Rui
Wang,Jincan
Bian,Xiaojuan
Gao,Yao
Li,Minxian
Chen,Fusan
Yang,Xiaochen
Ge,Rui
摘要：A 3W1 superconducting wiggler (SCW) with the pole gap of 68 mm was successfully tested and installed in a BEPC II storage ring in November, 2019. The goal of zero liquid helium consumption was achieved, and the cryogenic system exhibited a 12% residual cooling capacity (approximately 0.69 W @4.2K). The 3W1-SCW was set to operate at 2.49 T and has been operating for more than seven months. Three instances of magnet quenching occurred during the normal operation. The evaporated helium gas can be recycled to the helium gas recycling system when the pressure in the helium tank is higher than the parameter value（the setpoint of the presssur value is 1.2 bara）. The cryogenic system can be recovered within 4 h if sufficient liquid helium is available to inject into the cryostat.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：Theoretical uncertainties of single proton transfer cross sections of the (3He,d) and (d,3He) reactions
due to the uncertainties of the entrance- and exit-channel optical model potentials are examined with the
30Si(3He,d)31P, 13B(d,3He)12Be, and 34S(3He,d)35Cl reactions at incident energies of 25 MeV, 46 MeV, and
25 MeV, respectively within the framework of distorted wave Born approximation. Differential cross sections
at the first peaks in the angular distributions of these reactions are found to be uncertain within around 5% due
to the uncertainties of the optical model potentials from an result of 20000 times of calculations with the optical
potential parameters randomly sampled. This amount of uncertainties is found to be nearly independent of the
angular momentum transfer and the target masses within the studied range of incident energies. Uncertainties
of the single proton spectroscopic factors obtained by matching the theoretical and experimental cross sections
at different scattering angles are also discussed.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
Guan Yongjing
Chen Wu
Wang Shenzhen
Hua Yuxin
Jing Qiaoyan
Liu Zhiyong
Huang Chunping
Wang Deyu
Wang Huijuan
He Xianwen
Mario De Cesare
Cui Liangjia
He Hua
Fan Kaidi
Guo Zichen
摘要：The spatial distributions of 239+240Pu and 137Cs in soils from Longji Rice Terraces were investigated to evaluate soil erosion. The activity concentrations of 239+240Pu and 137Cs in the surface soils of the paddy fields were in the range of 0.089-0.734 and 1.80-7.88 mBq/g, respectively. The activities of 239+240Pu and 137Cs showed very similar distribution trends, first increasing and then decreasing with increasing elevation. The 240Pu/239Pu atom ratios in the surface soils ranged from 0.162–0.232. The activities of 239+240Pu and 137Cs in the soil cores tended to be uniformly distributed within the plowed layer and declined exponentially below this depth. The mean soil erosion rates of Longji Rice Terraces estimated by 239+240Pu and 137Cs tracer methods were 5.44 t/(ha·a) and 5.16 t/(ha·a), respectively, which demonstrated that plutonium can replace 137Cs as an ideal tracer for soil erosion research in the future. Landform features are the main factors affecting the distribution of plutonium and 137Cs as well as soil erosion in the Longji Rice Terraces.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：In this work we perform a Bayesian inference of the crust-core transition density ρt of neutron stars based upon the neutron-star radius and the neutron-skin thickness data within a thermodynamical method. The uniform and Gaussian distributions for the ρt prior are adopted in the Bayesian approach. It has a larger probability to have values higher than 0.1 fm 3 for ρt as the uniform prior and the neutron-star radius data are used. We found that this is controlled by the curvature Ksym of the nuclear symmetry energy. This phenomenon will not happen if Ksym is not extremely negative, i.e., Ksym > -200 MeV. The obtained ρt is 0.075+0.005-0.01fm^3 at 68% confifidence level when both the neutron-star radius and the neutron-skin thickness data are taken into account. The strongly anti-correlations between ρt and the slope L, curvature of the nuclear symmetry energy are observed. The dependence of the three L-Ksym correlations predicted in the literature on the crust-core density and pressure is quantitatively investigated. The most probable value of 0.08 fm^3 for ρt is obtained from the L-Ksym relation raised by Holt et al. and the larger values are preferred by the other two relations.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：A simulation code, GOAT, is developed to simulate single-bunch intensity-dependent effects and their interplay in the proton ring (pRing) of the Electron-Ion Collider in China (EicC) project. GOAT is a scalable and portable macroparticle tracking code written in Python and coded by object-oriented programming technology. It allows for transverse and longitudinal tracking, including impedance, space charge effect, electron cloud effect, and beam-beam interaction. In this paper, physical models and numerical approaches for the four types of high-intensity effects, together with the benchmark results obtained through other simulation codes or theories, are presented and discussed. In addition, a numerical application of the cross-talk simulation between the beam-beam interaction and transverse impedance is shown, and a dipole instability is observed below the respective instability threshold. Different mitigation measures implemented in the code are used to suppress the instability. The flexibility, completeness, and advancement demonstrate that GOAT is a powerful tool for beam dynamics studies in the EicC project or other high-intensity accelerators.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：Bonner多球谱仪(BBS)求解中子能谱是一个复杂的多维模型，需要使用复杂的优化算法求解第一类Fredholm积分方程。针对极大似然期望最大化(MLEM)算法容易陷入局部最优，粒子群优化(PSO)算法易得到粒子飞行方向和步长不合理，导致迭代无效，影响效率和精度的问题，提出了一种改进的PSO-MLEM算法用于中子能谱展开。利用动态加速因子平衡全局和局部搜索能力，提高算法的收敛速度和精度。首先，采用蒙特卡罗方法对BBS进行模拟，得到BBS的响应函数和计数率。模拟计数率时，采用了国际原子能机构403号技术报告中的4个参考光谱作为蒙特卡罗方法的输入参数。采用PSO-MLEM算法对中子能谱展开，通过展开能谱与参考能谱的差异进行验证。最后，利用BBS对252Cf中子源进行测量，并采用PSO-MLEM算法展开实验中子谱。与最大熵反卷积(MAXED)、PSO和MLEM算法相比，PSO-MLEM算法参数更少，并自动调整动态加速因子以解决局部最优问题。PSO-MLEM算法的收敛速度分别是MLEM和PSO算法的1.4倍和3.1倍。与PSO、MLEM和MAXED算法相比，PSO-MLEM算法的相关系数分别提高了33.1%、33.5%和1.9%，相对平均误差分别降低了98.2%、97.8%和67.4%。
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：lead-shielded HPGe detector and offline g–ray spectra of the residual product were used to measure the cross-section (CS) and ratios of isomeric CS (sm/sg) in 134Xe(n,2n)133m,gXe reactions at different energies including 13.5, 13.8, 14.1, 14.4, and 14.8 MeV, relative to 93Nb(n,2n)92mNb reaction CS. The target was high-purity natural Xe gas under high pressure. T(d,n)4He reaction was used to produce neutrons. The TALYS code (1.95 version) for nuclear reactions was used for calculations along with the default parameters and various nuclear level density models. The uncertainties present in the measured CS data were thoroughly analyzed using the covariance analysis method. The results were subsequently compared to the theoretical values, evaluation data, and previous experimental findings. Thus, the CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5,13.8 and 14.1 MeV neutron energies are reported for the first time. This work advances our knowledge of pre-equilibrium emission in the (n,2n) reaction channel by resolving inconsistencies in Xe data.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要：The properties of exotic nuclei are the focus of the present research. Two-neutron halo structures of neutron-rich 17,19B were experimentally confirmed. We studied the formation mechanism of halo phenomena in 17, 19B using the complex momentum representation method applied to deformation and continuum coupling. By examining the evolution of the weakly bound and resonant levels near the Fermi surface, s–d orbital reversals and certain prolate deformations were observed. In addition, by analyzing the evolution of the occupation probabilities and density distributions occupied by valence neutrons, we found that the ground state of 15B did not exhibit a halo, and the ground states of 17B and 19B exhibited halos at 0.6≤β2≤0.7 and 0.3≤β2≤0.7, respectively. The low-l components in the valence levels that are weakly bound or embedded in the continuous spectrum lead to halo formation.
分类： 物理学 >> 核物理学 提交时间： 2023-05-23
摘要：In this study, we theoretically investigate the feasibility of using laser-wakefield accelerated (LWFA) electrons for the photonuclear measurement of nuclear isomers according to the characteristics of the electrons obtained from LWFA experiments conducted at the Compact Laser Plasma Accelerator (CLAPA) laboratory. The experiments at the CLAPA show that a stable electron beam with an energy of 78–135 MeV and a charge of 300-600 pC can be obtained. The bremsstrahlung spectra were simulated using Geant4, which suggests that a bremsstrahlung source with a peak intensity of 1019 photons/s can be generated. Theoretical calculations of isomer production cross-sections from the photonuclear reactions on six target nuclei, 197Au, 180Hf, 159Tb, 115In, 103Rh, and 90Zr were performed and compared with the available experimental data in EXFOR, which suggest that further experiments are required for a series of photonuclear reaction channels. Flux-averaged cross-sections and isomer ratios (IR) resulting from such bremsstrahlung sources are theoretically deduced. The results suggest that IR measurements can be used to constrain nuclear components, such as γ strength function and optical model potential. In addition, the detection of the decay characteristics was evaluated with Geant4 simulations. The use of the LWFA electron beam and its bremsstrahlung for photonuclear studies involving nuclear isomers is anticipated.
分类： 物理学 >> 核物理学 提交时间： 2023-05-19
摘要：How nuclides decay in the superheavy region is key information for investigating new elements beyond oganesson and the island of stability. The Random Forest algorithm is applied to study the competition between different decay modes in the superheavy region, including α decay, β− decay, β+ decay, electron capture and spontaneous fission. The observed half-lives and dominant decay mode are well reproduced. The dominant decay mode of 96.9 % nuclei beyond 212Po is correctly described. α decay is predicted to be the dominant decay mode for isotopes in new elements Z = 119 − 122, except for spontaneous fission in some even-even ones because of the increased Coulomb repulsion and odd-even effect. The predicted half-lives show the existence of a long-lived spontaneous fission island at the southwest of 298Fl caused by the competition of nuclear deformation and Coulomb repulsion. More understanding of spontaneous fission, especially beyond 286Fl, is crucial to search for new elements and the island of stability.
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