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： 地球科学 >> 海洋科学 提交时间： 2023-05-31
摘要： 涡致混合扩散是物理海洋研究中的热点和难点问题。本文基于有效扩散理论，研究示踪物等值线在海表地转湍流的多尺度搅拌作用下，发生拉伸、扭曲、变形、折叠等改变其几何拓扑结构的现象，并探讨了等值线分形长度的变化与混合效率的关系。研究结果表明，在地转流场的搅拌下，示踪物的等值线会被迅速拉长，并产生丰富的精细结构。这种分形式的增长可达原长度的10-20倍，是混合效率提高的主要原因；而涡丝和锋面伴随的梯度增强虽然也有贡献，但为次要因素。另一方面，在示踪物模拟过程中，小尺度扩散会通过不可逆混合对示踪物进行均匀化，从而抹平等值线的精细结构，抑制等值线的增长，限制混合效率的提高。基于数盒子算法计算了等值线的分形维度，其数值在1.4到1.6之间，介于一维和二维之间。但由于地转湍流数据分辨率的限制，无法考虑更小尺度（次中尺度过程）的搅拌作用，可能低估了等值线的分形长度和混合效率。本研究将海洋混合与等值线几何特征联系了起来，初步得到了分形长度和混合效率两者的经验关系式，未来可以利用图像识别等成熟遥感技术将海洋示踪物等值线的几何特征直接转换为混合效率，为诊断分析海洋混合及其参数化提供了一种新的思路。
分类： 核科学技术 >> 核科学技术其他学科 提交时间： 2023-05-31
摘要： Laminar -scanning (TGS), an advanced -ray nondestructive analysis technique, is capable of locating and analyzing the nuclides in radioactive nuclear waste, and the scanning of TGS falls into two parts (e.g., transmission measurement and emission measurement). To be specific, transmission measurement lays the basis for the accurate measurement of non-uniform radionuclide content in TGS scanning. The scan data were obtained using the Monte Carlo tool Geant4 simulation, and a total of 25 voxels were divided into 5 in length and 5 in width in a square barrel. In this study, the encoding cropping algorithm based on the draped foot vector judgment was adopted to rapidly calculate the voxel trace matrix within the square bucket of nuclear waste, and the transmission images were reconstructed using the Ordered Subsets Expectation-Maximization(OSEM). The results indicated that the cropping speed of the improved coding algorithm was significantly increased compared with the original algorithm, and the relative mean deviation (RMD) and root mean square error(RMSE) between the reconstructed attenuation coefficient and the reference standard value tended to decrease with the increase of the cropped line segments in the voxel, and the Pearson correlation coefficient(PCC) tended to converge to be 1.0. The image quality evaluation parameters of high media density materials were better than those of low media density materials in the above three indexes. The reconstruction effect was relatively poor under the more complex filling material. When there were more than 10 cropped line segments in the voxel, the reconstruction data generally tended to be stable. The graphical trimming algorithm is capable of rapidly calculating the trace matrix of the scanned voxels, it shows the advantages of speed and efficiency, and it can serve as a novel method to solve the trace matrix of TGS nuclear waste transmission scans.
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) reactionsdue to the uncertainties of the entrance- and exit-channel optical model potentials are examined with the30Si(3He,d)31P, 13B(d,3He)12Be, and 34S(3He,d)35Cl reactions at incident energies of 25 MeV, 46 MeV, and25 MeV, respectively within the framework of distorted wave Born approximation. Differential cross sectionsat the first peaks in the angular distributions of these reactions are found to be uncertain within around 5% dueto the uncertainties of the optical model potentials from an result of 20000 times of calculations with the opticalpotential parameters randomly sampled. This amount of uncertainties is found to be nearly independent of theangular momentum transfer and the target masses within the studied range of incident energies. Uncertaintiesof the single proton spectroscopic factors obtained by matching the theoretical and experimental cross sectionsat 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 0.1620.232. 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/(haa) and 5.16 t/(haa), 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 t of neutron stars based upon the neutron-star radius and the neutron-skin thickness data within a thermodynamicalmethod. The uniform and Gaussian distributions for the t prior are adopted in the Bayesianapproach. It has a larger probability to have values higher than 0.1 fm3 for t as the uniform priorand the neutron-star radius data are used. We found that this is controlled by the curvature Ksym ofthe nuclear symmetry energy. This phenomenon will not happen if Ksym is not extremely negative,i.e., Ksym > -200 MeV. The obtained t 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 t 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 densityand pressure is quantitatively investigated. The most probable value of 0.08 fm^3 for t is obtainedfrom the L-Ksym relation raised by Holt et al. and the larger values are preferred by the other tworelations.
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： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-05-31
摘要： The nuclear fuel assembly is the core component of a nuclear reactor. In a pressurized water reactor fuel assembly, the top-connection structure connects the top nozzle to the guide thimble. Its performance reliability is essential for the stability of the nuclear fuel assembly. In this study, an assembly-oriented reliability analysis method for top-connection structures is presented by establishing an assembly-oriented top-connection structure parameter modeling method and a nonlinear contact gap and penetration correction method. A reliability model of the top-connection assembly structure, including multiple stochastic design variables, was constructed, and the overall reliability of the top-connection assembly structure was obtained via a Kriging model and Monte Carlo simulation. The acquired experimental data were consistent with real-world failure conditions, which verified the practicability and feasibility of the reliability analysis method proposed in this study.
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： 图书馆学、情报学 >> 图书馆学 提交时间： 2023-05-31
摘要： 目的/意义 美国是最早开展信息组织教育的国家之一，信息组织类课程设置和教育较为完善和先进，对其开展研究可为我国高校信息组织类课程设置和教育提供参考和借鉴。 过程/方法 本文选取美国LIS专业排名靠前的15所高校作为调查对象，围绕课程设置、课程内容、教学模式和考核方式，对其开设的信息组织类课程进行网络调查和研究。 结果/结论 发现美国高校图书情报专业教育课程设置具有重视信息组织类课程、信息组织选修课多、具有跨学科特性、课程设置符合时代需求且注重实践、教学多元化及考核多维度的特点，并在此基础上提出了美国高校信息组织类课程设置和教育对我国高校信息组织类课程设置及教育的启示，以期为新文科背景下我国图书情报专业发展提供参考和借鉴。
分类： 图书馆学、情报学 >> 情报学 提交时间： 2023-05-31
摘要： 目的/意义 以美国情报界最新年度全球威胁评估报告为分析基础，明确其战略情报工作方向，把握美国情报全球安全威胁认知，进而为我国国家安全工作提供参考与借鉴。 方法/过程 采用文本分析、总结归纳等研究方法对报告内容进行剖析解读，得出美国情报界对国际竞争非传统安全跨国问题及地区冲突等关键问题尤为重视。 结果/结论 综合上述分析，参考美国全球安全战略的最新动向，最终建议我国国家安全工作要以总体国家安全观为指引，以前瞻性的视角防范化解国内外存在的潜在风险，坚决维护国家安全。
分类： 化学 >> 核化学 提交时间： 2023-05-31
摘要： The rapid development of advanced techniques for selective and efficient U(VI) extraction from aqueous solutions is essential for addressing U(VI) environmental pollution and energy issues. Here, we share recent progress in U(VI) extraction from aqueous solutions, especially the most frequently applied techniques such as adsorption, catalysis (photocatalysis, piezocatalysis, and electrocatalysis), chemical deposition, and reduction by zero-valent metal particles. We attempt toelucidate the strategies and various mechanisms that contribute to the enhancement of selective U(VI) extraction. At the end of our review, we highlight the outlook, challenges, and prospects for the development of this field.
分类： 物理学 >> 核物理学 提交时间： 2023-05-31
摘要： lead-shielded HPGe detector and offline gray 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 CSdata were thoroughly analyzed using the covariance analysis method. The results were subsequentlycompared 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： 核科学技术 >> 辐射物理与技术 提交时间： 2023-05-31
摘要： Carbon-ion radiotherapy (CIRT) offers unique physical and biological advantages over photon radiotherapy. However, somematerials and devices in the CIRT treatment room become radioactive under bombardment by therapeutic carbon-ion beamsdue to nuclear reactions, thereby leading to possible radiation hazards to medical staff and additional and unwanted dosesto patients. This study assessed the level of induced radioactivity in the treatment room of the Heavy-Ion Medical Machine(HIMM) in Wuwei. Monte Carlo simulations using PHITS were performed for a conservative case under the conditions ofmaximum beam energy and intensity provided by the HIMM facility. The geometry and configuration of Treatment Room2 of the HIMM facility in Wuwei were adopted. We evaluated the activation of air, the phantom, and the components ofthe beamline, such as the primary collimator (PC), ridge filter (RF), and multileaf collimator (MLC). For air activation,we calculated the medical staff immersion external exposure and inhalation internal exposure caused by the correspondingradionuclides. For phantom activation, we estimated the additional dose to the patients family members owing to secondaryphotons after treatment. In addition, the exemption or non-exemption of the component material activation was assessed.The results showed that external radiation caused by air activation was the main source of the annual effective dose atapproximately 0.5mSv/y. The induced radioactivity exposure to family members of a patient after CIRT was approximately40Sv, sufficiently lower than the public dose limit of 1mSv/a. The induced radioactivity of the PC, RF, and MLC was allabove the exempt levels after the devices were retired, whereas the induced radioactivity of the RS and compensator couldreach the exempt levels after one patient session. Our study indicated that medical staff engaged in CIRT should stay awayfrom the high-dose-rate area of induced radioactivity along the beam direction, shorten the residence time in the treatmentroom as much as possible, and store the activated components in isolation after the equipment is out of use. Thus, this studyprovides guidance for accurately assessing the level of induced radioactivity in the treatment room for CIRT.
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, sd 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 0.620.7 and 0.320.7, 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： 医学、药学 >> 临床医学 提交时间： 2023-05-31 合作期刊: 《中国全科医学》
摘要： 背景 浙江省嵊州市自 2022 年 8 月起开展医疗保险门诊支付方式改革，通过实施总额预算、更新人头费测算标准、改进激励约束机制等政策逐步开展按人头付费改革，激励基层医疗卫生机构提供适宜的基本医疗服务，降低基层医疗费用支出，促进医疗保险基金的可持续发展。目的 分析浙江省嵊州市基本医疗保险门诊按人头付费政策对基层医疗卫生机构费用的影响机制，为完善相关支付制度提供参考。方法 于 2022 年 47 月，以capitationmedical costs等为英文检索词，以按人头付费医疗费用等为中文检索词，检索 2000-01-01至 2022-07-31 PubMed、Web of Science、中国知网、万方数据知识服务平台等数据库中与按人头付费相关的文献，同时梳理嵊州市实行按人头付费相关的政策文件、政府报告及新闻报道等；于 2022 年 912 月，对嵊州市按人头付费政策制定与实施者代表进行个人访谈（n=13）。采用系统动力学方法对浙江省嵊州市门诊总额预算下按人头付费改革政策对费用的影响机制进行定性分析。结果 将嵊州市本轮医疗保险支付方式改革的政策绘制成因果关系图，得到 5条反馈回路。结果显示：按人头总额预算政策的实行能激励基层医疗卫生机构为居民提供规范的医疗服务，促进提高基层签约率，从而控制医疗费用支出；科学的人头费用标准能够激励基层医疗卫生机构自主控制医疗费用；提高医疗保险报销比例，可以切实减轻患者就医负担；完善绩效考核制度，有利于持续提升基层医疗卫生机构服务能力；加强信息共享机制的建设，实现数据共享互通，能整体性地提高居民的健康水平。结论 实施按人头付费改革配合多项政策措施，能够提高基层签约率和就诊率，拓宽医疗保险基金来源，保证医疗保险基金的可持续性，提高基层医疗卫生机构的医疗水平和服务能力，改善居民健康状况，最终有利于改善慢性病的防治效果。
分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2023-05-31
摘要： 本文提出了一种超钚同位素辐照生产过程的快速诊断方法，实现了Pu-238、Cm-242、Cm-244和Cf-252的产量提升。
分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2023-05-30
摘要： 为了减少中子全截面谱仪（NTOX）在U-235共振能区的实验不确定度并改善探测效率，一个含锂闪烁探测器被考虑在中国散裂中子源 (CSNS) 的 Back-n 束线上发展为全截面谱仪。在考虑Back-n的强-flash和中子环境后设计了基于Cs2LiLaBr6 (CLLB)的快响应中子全截面谱仪-FAST.使用 Geant4模拟了CLLB在不同的 6Li/7Li 丰度比下的响应和不同厚度 CLLB 闪烁体对中子和 射线的响应比。 分别考虑不同的闪烁参数、物理设计和光读出模式，模拟了CLLB的中子-鉴别性能。 提出了CLLB的初步设计结果：厚度为 4-9 mm、边长>50 mm 的 CLLB（Li-6富集度>90%） 闪烁体，以覆盖能谱仪位置的 50mm 中子束，侧读出到SiPM甄别以避免强束流照射的辐照损伤。 研究中的中子-甄别性能模拟技术可以为Back-n束流线上其他中子诱发反应截面的测量提供技术支持。
点击量
通过
点击量
下载量
评论
待评议
