宇宙线缪子散射成像模拟与算法研究

本文验证了基于Micromegas探测器的宇宙线缪子散射成像系统进行快速核材料检测的可行性,并对实验室宇宙线缪子成像系统原型进行参数估算。基于Geant4程序开发了用于模拟宇宙线缪子物理过程、传输径迹及Micromegas探测器响应的模拟程序。在模拟数据的基础上,实现并改进了两种主要的宇宙线缪子散射成像算法。根据模拟和成像结果,1 m×1 m成像系统可在10 min内检测到被重元素屏蔽的核材料。10 cm×10 cm成像系统的缪子事例触发率为0.16 s~(-1),要获得较为清晰的成像结果,要求探测器位置分辨率达到300μm,探测器增益为1 000时实际测量事例至少需要20 h。     

宇宙射线μ子成像重建算法研究

图像重建算法是成像技术中的重要组成部分。介绍了基于多次库仑散射的宇宙射线μ子成像基本原理,系统研究了现有μ子的成像算法,通过对模拟实验成像结果的对比,分析了各种算法的特点,总结了各种算法在成像精度和运算速度上的优点与不足,并在此基础上,对μ子成像算法未来的发展趋势进行了探讨。     

灰色关联聚类在宇宙射线μ子成像中的应用

该工作为宇宙线μ子探测裂变核材料研究中的一部分.宇宙射线μ子成像目标存在粒子数偏少的客观条件,符合灰色系统理论的“小样本”、“贫信息”的特点,首次探索应用灰色关联聚类分析提高宇宙射线μ子成像中对物质区分效率的方法.     

大面积MRPC宇宙线缪子成像原型装置的研制

大面积位置灵敏探测器阵列是宇宙线缪子散射成像系统的关键部分。研发了适用于研制的73.6 cm×73.6 cm大面积二维读出位置灵敏MRPC探测器上的双精细复用读出电子学,构建了一个包括上下2组、每组各3块大面积MRPC的宇宙线缪子散射成像原型实验装置。该装置通过上下两块塑料闪烁体进行触发,实验数据经过处理后能重建缪子径迹,采用PoCA图像重建算法,获得了散射成像实验图像,结果与蒙特卡罗理论模拟结果相一致,为进一步研究宇宙线缪子成像物理机制、成像算法等提供了良好的实验平台。     

宇宙射线μ子成像蒙特卡罗模拟研究

正当前,核恐怖及核材料走私己成为国际安全面临的重大挑战。宇宙线μ子具有极强的穿透能力,能用于对被屏蔽核材料的检测。μ子穿越物质时在低Z物质和高Z物质中的散射角有明显的差异,为了验证成像方法的可行性对μ子成像进行了蒙特卡罗模拟。蒙特卡罗模拟采用的是Geant4     

宇宙线缪子散射成像模拟与算法研究

本文验证了基于Micromegas探测器的宇宙线缪子散射成像系统进行快速核材料检测的可行性，并对实验室宇宙线缪子成像系统原型进行参数估算。基于Geant4程序开发了用于模拟宇宙线缪子物理过程、传输径迹及Micromegas探测器响应的模拟程序。在模拟数据的基础上，实现并改进了两种主要的宇宙线缪子散射成像算法。根据模拟和成像结果，1 m×1 m成像系统可在10 min内检测到被重元素屏蔽的核材料。10 cm×10 cm成像系统的缪子事例触发率为0.16 s^-1，要获得较为清晰的成像结果，要求探测器位置分辨率达到300 μm，探测器增益为1 000时实际测量事例至少需要20 h。     

复用读出MRPC探测器性能标定与实验研究

多气隙阻性板室(MRPC)以其探测面积大、时间和位置分辨优异、成本低廉、探测效率高等优点,成为宇宙线散射成像径迹探测器的优良选择。为评估复用读出的MRPC探测器用于宇宙线散射成像实验的性能,搭建了一套测试标定实验平台,对12块MRPC探测器进行了完整的标定测试。经过实验研究,选定了8 400 V的适宜工作高压,并分别根据“与”逻辑和“或”逻辑,评估了复用读出前后MRPC的探测效率。     

宇宙射线μ子探测裂变核材料的模拟研究

平均能量为3~4 GeV的宇宙射线μ子在海平面的通量约为1/(cm2.min),这些μ子有很强的穿透力,能够穿透目前常用的防护层。μ子与物质作用主要发生小角度库伦散射,散射角与物质的原子序数有关。利用μ子穿过不同物质时所产生的散射角不同来辐射成像,研究μ子的累计通量条件下,辨别低、中、高Z三类物质的可行性。     

基于卷积神经网络的μ子散射成像材料识别方法研究

本文采用卷积神经网络的机器学习方法进行了μ子成像的材料识别，通过迭代训练数据获得最优模型并测试样品在不同测量时间下的识别准确度。在中国原子能科学研究院的μ子散射成像装置上开展了不同材料的测试实验，根据实验测量数据进行径迹重建并计算μ子的入射和散射角，构建基于卷积神经网络结构的材料识别模型进行特征提取，实现对材料的分类识别，并进一步引入残差和特征矩阵提高了材料的识别准确度。实验结果表明，对于10 cm×10 cm×10 cm的钨块，材料识别准确度在测量5 min时达到99.1%,在测量10 min时达到100.0%。这种基于卷积神经网络的方法为μ子散射成像材料识别提供了一种新途径。     

μ子成像检测技术在福岛第一核电厂应用现状与发展趋势

μ子成像检测技术是对大型构筑物进行内部调查的有效探测手段之一。通过对福岛第一核电厂反应堆堆芯μ子成像技术应用实例,说明了在核能领域μ子成像检测技术应用的现状。综述了μ子成像检测系统的探测装置、信号采集与处理系统、数据传输系统的主要性能特点,并对其发展趋势进行了展望。     

Identification of radiation treatment of wheat （Triticum aestivum. L）and rice （Oryza sativa. L） samples using thermoluminescence of contaminating minerals

Food irradiation is gaining popularity worldwide and this technology is important to improve quality and reduce the post harvest losses of food. Because of the rapid commercialization of irradiated foods throughout the world, compliance of different regulations relating to use of technology in different countries and demand of consumers for clear labelling of irradiated foods, there is need for the development of analytical methods to detect radiation treatment of food. Among several methods studied so far, thermoluminescence （TL） is an important method that can be used to find out the irradiation history of food that contain even a very minute amount of dust particles. In this study, the irradiated and unirradiated wheat and rice samples were analyzed using the TL method. The samples were purchased from the local market of Peshawar and irradiated to radiation doses of 0.5 and 1.0 kGy using Co-60 gamma irradiator at the Nuclear Institute for Food and Agriculture （NIFA）, Peshawar. The mineral contaminants were isolated by jet water, ultrasonic treatment, and density gradient. TL glow curves of the isolated minerals from irradiated and unirradiated samples were recorded between the temperature ranges of 50-500℃ using a TL reader. Generally, the glow curves for irradiated samples showed much higher TL intensities （TL1） than the unirradiated samples. The results were normalized by rerradiation of mineral samples to gamma-ray dose of 1.0 kGy followed by determination of the second glow curves （TL2）. The ratio of the area of first glow curve to that of second glow curve （TL1/TL2） was calculated for selected temperature intervals and compared with the recommended values for unirradiated and irradiated samples. Finally, the shapes of the glow curves for irradiated and unirradiated samples were also analyzed. On the basis of these results （comparison of TL-intensities, TL1/TL2 ratios and shapes of the glow curves）, all the irradiated and unirradiated samples of wheat and rice were unequivocally identified.     

The preclinical pharmacological study of dopamine transporter imaging agent 18F-FP-β-CIT

The paper is to study pharmacologic characteristics of 18F-FP-β-CIT (18F-N-(3-fluoropropyl)-2β- carbomethoxy-3β- (4-iodophenyl)nortropane) as an imaging agent for dopamine transporter. The radiochemical purity of 18F-FP-β-CIT in aqueous solution was over 95% after standing at room temperature for 4h. Biodistribution displayed rapid uptake in rat brain (1.375 %ID/organ at 5min and 0.100 %ID/organ at 180 min) and the striatal uptake was 1.444,0.731, 0.397, 0.230 and 0.146 %ID/g at 5, 30, 60, 120 and 180 min, respectively. The values of striatum/cerebellum,striatum/frontal cortex and striatum / hippocampus in rat's brain at 30 min were 3.38, 2.17 and 2.40 respectively. The uptake in striatum can be blocked by β-CFT, suggesting that 18F-FP-β-CIT binds to DAT peculiarly. The compound was rapidly cleared from monkey's blood. The striatal uptake was bilaterally decreased in the left-sided lesioned PD rats, compared with normal control. Brain PET imaging studies in normal monkey showed that 18F-FP-β-CIT was concentrated in striatum. The test of undue toxicity showed that the dose received by mice was 1250 times as by human, which indicates that 18F-FP-β-CIT is very safe. So 18F-FP-β-CIT is a promising PET imaging agent for DAT with safety and validity.     

PLASMA SCIENCE AND TECHNOLOGY AUTHOR INDEX TO VOLUME 16(2014)

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Radioactivity levels in soil of salt field area,Kelambakkam,Tamilnadu,India

Soil samples in and around salt field area have been analyzed for natural radioactivity concentration using gamma ray spectrometer.The activity concentration for ~(232)Th,~(238)U and ~(40)K are ranged from 27.88 to 45.27 Bq/kg, from BDL to 13.30 Bq/kg,and from 135.54 to 381.28 Bq/kg,respectively.The measured activity concentrations for these radionuclides were compared with world average activity of soil.The average activity concentration of ~(232)Th in the present study is 1.19 times higher than world median value while the activity of ~(238)U and ~(40)K is found to be lower. The absorbed dose rates due to these radionuclides were calculated.The average absorbed gamma dose rate due to the presence of ~(232)Th,~(238)U and ~(40)K in soil samples is 36.99 nGy·h~(-1).These results indicate no radiological anomaly. The data presented in this study will serve as a base line survey for primordial radionuclides concentration in the study area.     

Non-FDG PET imaging of brain tumors

Due to relatively high uptake of glucose in the brain cortex, the use of FDG PET imaging is greatly limited in brain tumor imaging, especially for low-grade gliomas and some metastatic tumours. More and more tracers with higher specificity were developed lately for brain tumor imaging. There are 3 main types of non-FDG PET tracers： amino acid tracers, choline tracers and nucleic acid tracers. These tracers are now widely applied in many aspects of brain tumor imaging. This article summarized the general use of non-FDG PET in different aspects of brain tumor imaging.     

基于NPL-NMC系统的γ测量子系统的建模与优化

在军控核查中,核部件的质量、丰度、年龄属性需采用无损方法进行核查,NPL-NMC系统是一套利用中子多重性测量核部件质量属性的装置,为建立完善的属性测量系统,还需在NPL-NMC系统的基础上建立γ测量子系统。本文通过设计γ测量子系统在NPL-NMC系统上的布局及对中子屏蔽的优化,使系统能对铀部件的丰度、年龄属性进行测量。模拟计算结果表明,该γ测量子系统能很好地满足军控核查对铀部件丰度、年龄属性测量的要求。     

Improvement of carbon fiber surface properties using electron beam irradiation

Carbon fiber-reinforced advance composites have been used for structural applications,mainly on account of their mechanical properties.The main factor for a good mechanical performance of carbon fiber-reinforced com- posite is the interfacial interaction between its components,which are carbon fiber and polymeric matrix.The aim of this study is to improve the surface properties of the carbon fiber using ionizing radiation from an electron beam to obtain better adhesion properties in the resultant composite.EB radiation was applied on the carbon fiber itself before preparing test specimens for the mechanical tests.Experimental results showed that EB irradiation improved the ten- sile strength of carbon fiber samples.The maximum value in tensile strength was reached using doses of about 250 kGy.After breakage,the morphology aspect of the tensile specimens prepared with irradiated and non-irradiated car- bon fibers were evaluated.SEM micrographs showed modifications on the carbon fiber surface.     

Measurement system for SSRF pulsed magnets

This paper describes the magnetic field measurement system for pulsed magnets in SSRF.The system consists of magnetic probes,analog active integrator,oscilloscope,stepper motor and a controller.An application pro- gram based on LabVIEW has been developed as main control unit.After the magnetic field mapping of a septum magnet prototype,it is verified that the test results accord with the results of theoretical calculation and computer simulation.     

旁路阀调节对高温气冷堆闭式布雷顿循环瞬态特性影响研究

闭式布雷顿循环是第4代高温堆核能系统的关键技术之一,其典型的动态过程是旁路阀调节。为分析这一过程,建立了循环中关键部件的动态模型,其中压气机在径向平衡模型基础上耦合了对附面层发展的预测,兼顾了计算效率与准确性;换热部件模型基于双曲型守恒律方程,对工质的热物性和参数的快速变化有较好的适应性。在此基础上根据回路的质量守恒和压力平衡原则将各部件的模型耦合,建立了系统的动态模型。由于旁路阀调节是氦气透平发电系统主要的功率快速调节手段,瞬态效应较为显著,以模块式高温气冷堆（HTR-10GT）旁路阀开启后的过渡过程作为算例,分析了主要循环参数的响应特性,并通过分析,给出了降低输出功率的机制。计算结果表明：系统的容积惯性对旁路阀调节的响应速度影响较大,而阀门的开度则决定了系统在末态的输出功率;回热器的温度冲击现象可能发生在调节过程中,但可通过两旁路阀联动的方式缓解;反应堆出口温度变化幅度很小,因此反应堆模型的准确程度对结果基本无影响。     

CEFR 100%额定功率运行汽轮机发电能力分析

中国实验快堆(CEFR)首次100%额定功率发电运行中,实际电功率较设计值相差较多。为判断影响机组实际发电能力的主要原因,以现场采集的运行数据和汽轮机厂商提供的设计资料为基础,进行了相应的计算分析。对汽轮机内效率进行修正,绘制汽轮机近似热力过程曲线,并通过实测的各段抽汽压力,在热力过程曲线上获得抽汽焓值;利用换热器的能量守恒和流量守恒的基本方程进行除氧器和各加热器的热平衡计算,获得各段抽汽的流量;利用汽轮机的功率计算方程,得到汽轮机发电功率的计算值。通过计算值与实际值的比较分析,得出主蒸汽参数不达标是影响CEFR汽轮机发电能力的主要因素。