分类: 核科学技术 >> 核探测技术与核电子学 提交时间: 2024-05-27
摘要: Shielding material is critical for downhole pulsed neutron tool design as it directly influences the accuracy of formation measurements. A well-designed shield configuration ensures that the response of the tool is maximally representative of formation without being impacted by tool and borehole environment. This manuscript investigates the effects of boron-containing materials on neutron and gamma detectors based on a newly designed logging-while-drilling tool, which is currently undergoing manufacturing process. As boron content increases, its ability to absorb thermal neutrons significantly enhances. Through simulation, it is proven that boron carbide (B4C) can be used as an effective boron shielding material for thermal neutrons and therefore employed in this work. To shield against thermal neutrons migrating from mud pipes, the optimal shielding thicknesses for near and far neutron detectors are determined to be 5mm and 4mm. For an example, at a porosity of 25 p.u., the near neutron sensitivity shows a 5.6% increase in response. Furthermore, in order to shield capture gamma generated by thermal neutrons once they enter tool from the mud pipe and formation, the internal and external shields for the gamma detector is evaluated. Results show internal shield needs 75% boron content while the external shield is of 14.2mm thickness and 25% boron content to minimize tool effect.
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-05-28
摘要: 未知放射源搜寻定位是核安检、核应急领域的重要研究课题。为提高寻源效率、适应多源环境探测,提出了一种融合到达角的粒子滤波寻源方法。首先,构建了自主定位与到达角感知相结合的放射源搜寻硬件平台,给探测器引入了位置和角度信息;其次,在粒子滤波基础上考虑到达角信息,动态收缩放射源搜寻区域,进而提高搜寻效率;最后,在自主寻源路径规划中采用到达角引导的机器人姿态调整,增强机器人寻源的灵活度。仿真实验证明此方法可正确有效工作,利用放射源开展的测试进一步验证了该方法对于多源搜寻的实用性。
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2017-08-23
摘要: 钨基材料以其高熔点、高导热率、良好的抗中子辐照和抗溅射腐蚀等优异性能,被视为未来核聚变装置中最有前景的面向等离子材料。在聚变服役环境下,14MeV的高能中子以及低能氢/氦粒子流对钨基材料造成严重的辐照损伤。研究材料的辐照损伤与氢氦效应机理对揭示辐照引起材料微观结构与性能的变化以及探索开发新型抗辐照材料具有重要的意义。近年来,随着计算模拟技术的发展,多尺度模拟方法在聚变堆关键材料辐照损伤与氢氦效应机理研究方面有着广泛的应用。本文主要结合作者近几年的研究实践,介绍了纳米晶钨/铁的抗辐照损伤机理、钨中氢滞留机制、合金元素强化界面机制、嬗变元素偏聚及其对氦泡形成机制的影响。通过多尺度模拟方法来获取材料在辐照环境下的不同时间/空间层次的结构演化信息,从而揭示材料的辐照损伤与氢氦效应机理,为聚变堆面向等离子体材料的优化设计与性能调控提供理论基础。
分类: 核科学技术 >> 核聚变工程技术 提交时间: 2017-10-27
摘要: Structured Abstract: Purpose: EAST is a tokamak fusion device running in ultra-high vacuum condition. To avoid polluting the inner vessel environment, solid lubrication has been applied on the surface of bearings and gears which exposed to the vacuum. Design/methodology/approach: anti-friction MoS2 coatings penetrating with different atoms have been developed by multi-target magnetron sputtering deposition technique. This paper presents the comparative testing of tribological properties for three kinds of MoS2-based coating layers. Findings: based on the test results, MoS2-Ti-C coating films are supposed to be the final selection due to the better performance of friction coefficient and lubrication longevity. Originality/value: finally, the detailed information has been characterized for the hybrid coatings which can provide some references for applications of solid lubrications in similar condition of high vacuum and temperature.
分类: 核科学技术 >> 核聚变工程技术 提交时间: 2017-10-27
摘要: Purpose – The purpose of this paper is to develop a serial redundant manipulator system applied in nuclear fusion environment. It will allow remote inspection and maintenance of plasma facing components in the vacuum vessel of fusion device without breaking down the ultra-high vacuum condition during physical experiments. Design/methodology/approach – Firstly, considering the dynamic sealing of actuators to avoid polluting the vacuum condition inside fusion reactor, the mechanical design of robot system has been introduced. The redundant manipulator system has 11 degree of freedoms in total with an identical modular design. Besides, to improve the position accuracy, an error prediction model has been built based on the experimental study and back-propagation neural network (BPNN) algorithm. Findings – Currently, the implementation of the manipulator system has been successfully finished in both atmosphere and vacuum condition. The validation of BPNN model shown an acceptable prediction accuracy (94%~98%) compared with the real measurement. Originality/value – This is a special robot system which is practically used in a nuclear fusion device in China. Its design, mechanism and error prediction strategy have great reference values to the similar robots in vacuum and temperature applications.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-05-26
摘要: The Very Large Area gamma-ray Space Telescope (VLAST) is a mission concept proposed to detect gamma#2;ray photons through both Compton scattering and electron-positron pair production mechanisms, thus enablingthe detection of photons with energies ranging from MeV to TeV. This project aims to conduct a comprehensivesurvey of the gamma-ray sky from a low-Earth orbit using an anti-coincidence detector, a tracker detectorthat also serves as a low-energy calorimeter, and a high-energy imaging calorimeter. We developed a MonteCarlo simulation application of the detector using the GEANT4 toolkit to evaluate the instrument performance,including the effective area, angular resolution, and energy resolution, and explored specific optimizations ofthe detector configuration. Our simulation-based analysis indicates that the current design of the VLAST isphysically feasible, with an acceptance above 10 m2 sr which is four times larger than that of the Fermi-LAT,an energy resolution better than 2% at 10 GeV, and an angular resolution better than 0.2 ◦ at 10 GeV. TheVLAST project promises to make significant contributions to the field of gamma ray astronomy and enhanceour understanding of the cosmos.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-05-28
摘要: 离子束放射治疗(放疗)越来越广泛地被运用于肿瘤治疗,目前使用传统X射线计算机断层扫描(CT)来制定离子放疗治疗计划时存在相对阻止本领(RSP)具有较大误差的问题,理想的方式是直接使用高能离子束对患者成像,生成离子放疗治疗计划设计时所需的医学图像,避免RSP转换从而减小RSP的误差。本研究使用蒙特卡罗程序Geant4/Gate搭建了离子CT模拟平台,设计了理想与现实两种离子CT成像系统探测器,利用最大似然法和ASD-POCS算法实现了图像重建,研究了理想与现实两种设置、多种能量以及不同离子种类对模体内硫、磷、碳和钙四种材料插件重建RSP误差的影响。结果表明,330MeV质子在理想与现实设置两种情况下的RSP相对误差都小于1.547%,理想设置下的RSP相对误差远小于现实设置,现实设置下各材料的RSP重建误差接近理想设置下的三倍;质子的RSP相对误差随着能量的增加而减小,在230MeV时的RSP相对误差最大,在硫、磷、碳和钙四种材料中分别为2.855%、2.468%、1.653%、2.553%。在330MeV时的RSP相对误差达到最小,在硫、磷、碳和钙四种材料中分别为0.181%、0.351%、0.250%和0.245%;在能量330MeV/u下,碳离子在硫、磷、碳和钙四种材料中的RSP相对误差分别为0.060%、0.281%、0.150%、0.082%,误差均在0.281%以内,RSP相对误差小于330MeV的质子。因此,与质子CT相比,碳离子CT能为离子放疗治疗计划设计提供更为精确的RSP数据。
分类: 物理学 >> 核物理学 提交时间: 2018-07-10
摘要: 本文分析讨论了加速器的百年历史, 从思想的萌芽、理论的突破与准备、技术的准备与储存、实验的成功、加速器的未来与展望等几个方面进行了论述。
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-05-26
摘要: CF系列燃料组件是中核集团自主研发的先进三代核电反应堆核心部件,为分析CF2燃料组件在多对中值工况下,驱动线运动部件在水和空气中的摩擦力与落棒性能,采用1:1的CF2模拟燃料组件配合自主设计研发的可调节旋转式顶盖首次实现了多个错对中值的集成,能够对多个错对中值进行科学准确的调节。获取了驱动线在水和空气两种介质中全行程、多错对中值工况下的摩擦力与落棒性能数据。落棒总时间和棒到缓冲口时间均随着对中值增加而增大,但缓冲时间基本保持一致。燃料组件与控制棒在最大对中值工况下运行良好,摩擦力没有超过允许极限值,也未发生在大对中值工况下的卡棒现象。该研究结果为CF系列燃料组件的设计定型、安全评定与软件开发提供了重要的试验依据,其方法可推广至后续CF3等燃料组件的科研项目中。
分类: 物理学 >> 核物理学 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2017-08-28
摘要: In this paper, the calorimetric power measurement method for electron cyclotron resonance heating system on EAST are presented. This method requires measurement of the water flow through the cooling circuits and the input and output water temperatures in each cooling circuit. Usually, the inlet water temperature is controlled to be stable to get more accurate results. The influence of the inlet water temperature change on the measurement results is analyzed for the first time in this paper. A novel temperature calibration method is proposed also. This kind of calibration method is accurate and effective, and can be easily implemented.
分类: 物理学 >> 基本粒子与场物理学 分类: 物理学 >> 核物理学 提交时间: 2017-09-10
摘要: 超核物理是核物理的一个重要分支,其微观理论的基本出发点为超子-核子相互作用。研究超子-核子相互作用不仅有助于理解奇异性在粒子物理与核物理中的作用,还可以检验SU(3)味对称性及其破缺程度。文章首先回顾了超核物理的起源,随后简要列举了在核物理、粒子物理以及天体物理等领域中,与超核物理相关的几个前沿热点问题,并指出研究超子-核子相互作用的重要性。接下来文章着重介绍超子-核子相互作用的理论研究历史及发展现状。在现有的相关工作中,研究方法主要包括唯象模型、格点量子色动力学模拟和手征有效场论。其中手征有效场论作为低能区量子色动力学的有效理论,在研究介子、重子等微观系统中展现出了独特的优势。因此,文章特别介绍了基于手征有效场论的超子-核子相互作用最新理论研究进展。
分类: 物理学 >> 核物理学 提交时间: 2018-06-20
摘要: 本文讨论了加速结构中的解析求解问题, 主要讨论了场和等效电路两种求解方法。
分类: 物理学 >> 核物理学 提交时间: 2017-01-04
摘要: 摘要 摘要 高亮度的超短电子束团的产生是目前电子直线加速器的一个研究方向。 常规加速器与基于等离子体的加速器都能产生超短(亚皮秒)束团。本文简要描述了一台产生超短电子束团加速器装置,并进行了模拟研究。
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: In order to improve the particle identification capability of the Beijing Spectrometer III (BESIII),t is proposed to upgrade the current endcap time-of-flight (ETOF) detector with multi-gap resistive plate chamber (MRPC) technology. Aiming at extending ETOF overall time resolution better than 100ps, the whole system including MRPC detectors, new-designed Front End Electronics (FEE), CLOCK module, fast control boards and time to digital modules (TDIG), was built up and operated online 3 months under the cosmic ray. The main purposes of cosmic ray test are checking the detectors' construction quality, testing the joint operation of all instruments and guaranteeing the performance of the system. The results imply MRPC time resolution better than 100ps, efficiency is about 98%燼nd the noise rate of strip is lower than 1Hz/(scm2) at normal threshold range, the details are discussed and analyzed specifically in this paper. The test indicates that the whole ETOF system would work well and satisfy the requirements of upgrade.
分类: 物理学 >> 核物理学 提交时间: 2017-08-22
摘要: The ground state properties including radii, density distribution and one neutron separation energy for C, N, O and F isotopes up to the neutron drip line are systematically studied by the fully self-consistent microscopic Relativistic Continuum Hartree-Bogoliubov (RCHB) theory. With the proton density distribution thus obtained, the charge-changing cross sections for C, N, O and F isotopes are calculated using the Glauber model. Good agreement with the data has been achieved. The charge changing cross sections change only slightly with the neutron number except for proton-rich nuclei. Similar trends of variations of proton radii and of charge changing cross sections for each isotope chain is observed which implies that the proton density plays important role in determining the charge-changing cross sections.
分类: 物理学 >> 核物理学 提交时间: 2018-01-01
摘要: 本文研究了直线加速器中高次空间谐波对束流动力学的影响.
分类: 物理学 >> 核物理学 提交时间: 2016-09-12
摘要: In the pp→tt¯ process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb−1 of pp collision data at s√= 8 TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair (mtt¯> 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within −2 <|yt|−|yt¯|< 2 is measured to be 4.2 ± 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three tt¯ mass bins is also presented.
分类: 物理学 >> 核物理学 提交时间: 2017-08-22
摘要: The Relativistic Continuum Hartree-Bogoliubov (RCHB) theory, which properly takes into account the pairing correlation and the coupling to (discretized) continuum via Bogoliubov transformation in a micro- scopic and self-consistent way, has been reviewed together with its new interpretation of the halo phenomena observed in light nuclei as the scattering of particle pairs into the continuum, the prediction of the exotic phenomena — giant halos in nuclei near neutron drip line, the reproduction of interaction cross sections and charge-changing cross sections in light exotic nuclei in combination with the Glauber theory, better restora- tion of pseudospin symmetry in exotic nuclei, predictions of exotic phenomena in hyper nuclei, and new magic numbers in superheavy nuclei, etc. Recent investigations on new effective interactions, the density dependence of the interaction strengthes, the RMF theory on the Woods-Saxon basis, the single particle resonant states, and the resonant BCS (rBCS) method for the pairing correlation, etc. are also presented in some details.
分类: 物理学 >> 核物理学 提交时间: 2021-03-03
摘要: 本文讨论了常规电子直线加速器的设计问题, 并以一台 10 MeV 的电子直线加速器为例穿插其中讨论了常规电子直线加速器的设计。常规电子直线加速器由电子枪、聚束部分、光速部分所组成,而且在直线对撞机装置、自由电子激光装置中经常用到束团压缩部分。我们对每一部分都进行了分析与讨论,主要包括纵向、横向束流动力学方面, 总结了一系列的行之有效的设计思想与方法。
分类: 物理学 >> 核物理学 提交时间: 2017-11-27
摘要: Neutral beam injection has been recognized as one of the most effective means for plasma heating.According to the research plan of the EAST physics experiment, two sets of neutral beam injector were built and operational in 2014. The paper presents the development of beam diagnosis system for EAST neutral beam injector (NBI) and the latest experiment results obtained on the test-stand and EAST-NBI-1 and 2. The results show that the optimal divergence angle is (0.62°, 1.57°) and the full energy particle is up to 77%. They indicate that EAST NBI work properly and all targets reach or almost reach the design targets. All these lay a solid foundation for the achievement of high quality plasma heating for EAST.