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。     

反应堆宇宙线缪子成像蒙特卡罗模拟研究

宇宙线缪子成像可对第二代反应堆压水堆(PWR)堆芯进行成像,即使在严重核事故下,常规方法无法监测时,仍可探知堆芯状态,了解堆芯情况。论文基于PWR主要结构参数建立详细的模拟模型,通过Geant4程序进行模拟,对反应堆堆芯进行图像重建,并对图像进行降噪处理。研究结果表明,宇宙线缪子可对堆芯高Z材料成像,核燃料轮廓清晰可见,利用大角度宇宙线缪子对PWR堆芯进行成像、对堆芯状态进行监控的方法可行。若要实现这种方法,使用多个8 m×8 m的大面积位置灵敏探测器,在3个月内可以实现。     

多气隙阻性板室探测器位置分辨性能的模拟研究

多气隙阻性板室(MRPC)具有效率高、时间分辨优异、性价比高以及便于大面积制造的优点,成为缪子成像技术径迹探测器的良好选择。提高MRPC的位置分辨能力,是近年来的研究重点。本文使用ANSYS Maxwell计算了MRPC的三维静电权场,在此基础上研究了在相同MRPC结构下,读出板背面接地、读出条间距以及宽度占比对MRPC位置分辨能力的影响,同时给出了改善MRPC位置分辨性能的设计建议是读出条间距1 mm、宽度占比50%～60%。     

多气隙阻性板室探测器位置分辨性能的模拟研究

多气隙阻性板室（MRPC）具有效率高、时间分辨优异、性价比高以及便于大面积制造的优点，成为缪子成像技术径迹探测器的良好选择。提高MRPC的位置分辨能力，是近年来的研究重点。本文使用ANSYS Maxwell计算了MRPC的三维静电权场，在此基础上研究了在相同MRPC结构下，读出板背面接地、读出条间距以及宽度占比对MRPC位置分辨能力的影响，同时给出了改善MRPC位置分辨性能的设计建议是读出条间距1 mm、宽度占比50%~60%。     

缪子成像系统中二维位置分辨探测器研制

介绍了一种应用于缪子成像系统的新型二维高位置分辨探测器,MRPC探测器的有效面积为1 072 mm×1 072 mm,先后对探测器在宇宙线和X射线下测试其性能,结果表明探测效率高于98%,位置分辨好于272μm。     

康普顿相机的GEANT4模拟与反投影图像重建

模拟构建了双层康普顿相机,利用康普顿散射原理,获取γ光子在两层探测器发生散射前后沉积的能量和位置信息,通过一定算法进行图像重建,获得放射源位置信息。该相机具有灵敏度高、体积小、应用范围广等优点。通过蒙特卡罗方法模拟了具有双层条状结构位置灵敏探测器(散射探测器、吸收探测器)组成的康普顿相机,其两层探测器分别由Si和Ge材料构成。利用反投影图像重建算法实现了放射源图像重建,当单点源与探测器距离为40 mm时,成像的效率为0.38%,位置分辨率达到8.0 mm,角分辨率达到3°。对于不同位置和不同个数点源的情况下,检验了反投影重建算法在康普顿相机放射源空间重建中的效果。     

缪子对小尺寸中低原子序数物质三维成像技术的模拟研究

缪子成像是一种利用天然本底辐射中极具穿透力的缪子射线通过散射或透射技术对高原子序数Z或隐藏物体进行无损成像的技术。当前的研究对象是大尺寸的高Z物质,而针对小尺寸的中低Z物质的成像技术在国内鲜见报道。本文提出了一种针对小尺寸中低Z物质的三维成像技术,利用Geant4软件模拟了缪致次级粒子的产生过程,模拟结果表明次级粒子主要为电子和γ光子,通过缪致次级粒子与入射缪子符合探测技术筛选入射缪子径迹,利用有限角度成像算法对待测物体进行了三维图像重建,结果表明,该技术适合于小尺寸的中低Z物质成像,尤其对小尺寸中Z物质的重建效果明显,重建图像可区分08 cm的凹槽。     

多气隙电阻板室探测X射线研究

介绍了多气隙电阻板室(MRPC)的结构和原理,用蒙特卡罗方法计算了MRPC对X射线的灵敏度,并进行了脉冲X光机实验.实验表明,MRPC有望作为大面积的阵列探测器用于X射线成像技术研究.     

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.     

Characteristics of pulsed photo-stimulated luminescence and thermoluminescence for the identification of gamma irradiated poultry eggs

Pulsed photo-stimulated luminescence (PPSL) is a simple screening method that can be employed qualitatively at the spot for the detection of eggs treated with ionizing radiation.Due to the variations in the results during storage,the eggs of ostrich,duck,hen,and quail were irradiated to doses of 0,1,2,and 3 kGy.Most of the samples were incorrectly identified during storage after four months of irradiation.Thermoluminescence (TL) technique was also tried by using egg shells in order to confirm the irradiation treatment in eggs.TL glow curves were recorded between the temperatures 50℃to 400℃at the rate of 5°/s for all the control and irradiated samples.On the basis of integrated areas of first glow curves (TL1),the glow curve ratios (TL1/TL2) and the shapes of maxima of TL1, the irradiation treatment of all the eggs was confirmed.Furthermore,the presence of calcite and aragonite minerals that cause the TL signal in the egg shells were studied using X-ray diffraction spectrometry.     

数字射线扫描成像系统MTF的测试分析

为有效实现数字射线扫描成像检测系统性能的定量分析评价,据此进行检测工艺参数的优化,对数字射线扫描成像检测系统调制传递函数(Modulation transfer function,MTF)进行了测试分析。采用刀口工具、双线型像质计、分辨率测试卡,对系统在不同焦点大小、放大倍数、运动方向的检测情况,分别进行了MTF的测试并进行了比较。结果表明,双线型像质计与分辨率测试卡的测试结果基本一致,但双线型像质计更便于对比度的定量计算;双线型像质计的对比度传递函数近似符合二次曲线,经转换得到的调制传递函数值高于刀口法的测试值,刀口法计算数值偏低的原因在于运动不平稳所带来的不利影响。分析表明,数字射线扫描成像系统性能受到多个因素的共同影响,MTF测试结果可较全面地对影响因素进行定量评价,可用于确定最佳的检测参数或找出等价的参数组合。     

基于物理体模CT图像的1岁儿童体素体模构建

本文介绍了基于1岁儿童物理体模（Model 704-D）的CT图像和中国成年男性参考人体素体模(CRAM)的1岁儿童体素体模（CPP01）的构建,包括通过对物理体模扫描得到OCP01体模（基于儿童物理体模的CT图像建立的一粗略的体素体模）,进而构建和优化CPP01。该体素体模的各器官组织的质量与GBZ/T 200.2-2007所给数据的相对偏差约在5%以内,且其外部轮廓和主要器官的位置与Model 704-D相匹配。     

Activity level of gross α and gross β in airborne aerosol samples around the Qinshan NPP

The monitoring results of gross α and gross β activity from 2001 to 2005 for environmental airborne aerosol samples around the Qinshan NPP base are presented in this paper. A total of 170 aerosol samples were collected from monitoring sites of Caichenmen village, Qinlian village, Xiajiawan village and Yangliucun village around the Qinshan NPP base. The measured specific activity of gross α and gross β are in the range of 0.02 ～ 0.38 mBq/m3 and 0.10 ～ 1.81 mBq/m3, respectively, with an average of 0.11 mBq/m3 and 0.45mBq/m3, respectively. They are lower than the average of 0.15 mBq/m3 and 0.52mBq/m3, of reference site at Hangzhou City. It is indicated that the specific activity of gross α and gross β for environmental aerosol samples around the Qinshan NPP base had not been increased in normal operating conditions of the NPP.     

Simulation of the mixing process in FCIs with hydrodynamic fragmentation model

Fuel Coolant Interactions (FCIs) are important issues in nuclear reactor severe accident analysis. In FCIs, fragmentation model of molten droplets is a key factor to estimate degree of possible damage. In this paper, the mixing process in FCIs is studied by the simulation of MIXA experiment with hydrodynamic fragmentation model. The result shows that hydrodynamic fragmentation model underestimates the fragmentation rate of high temperature molten droplets under the condition of low Weber numbers. It is concluded that models based on thermal fragmentation mechanism should be adopted to analyze the FCI process and its consequence.     

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

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NUCLEAR SCIENCE AND TECHNIQUES Volume 25,2014

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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.     

Probing stray surface electric patch fields using Rydberg atoms

The stray electric “patch” fields present at a Au(1 1 1) surface are investigated by studying the ionization of Rydberg atoms incident at near-grazing angles. Measurements of the threshold conditions required to observe the resulting ions are used to estimate how large such stray fields can be. The data show that the stray fields can be sizeable, as large as ∼10³ V cm⁻¹ 100 nm from the surface and ∼20 V cm⁻¹ 500 nm from the surface, and illustrate the potential of Rydberg atoms for detecting and characterizing surface electric fields.