X射线安检设备中双能量方式下 R值提取

X射线装置已被证实具有揭示物质的分子或原子特性的能力,这种特性对于探测违禁品是相当重要的.尽管X射线探测方法作为一种自动探测违禁品的有效手段已经开始商业化,然而大多数技术还不是很成熟.R是与有效原子序数直接相关的量,通过推证R值算法来获得被检物质属性,进而找出危险品的存在.     

高能X射线双能成像系统中多能谱探测器研究

高能X射线双能成像系统能够对被检物的材料进行识别,但是当被检物的质量厚度较小时,对其材料识别变得很困难.本文提出了利用多能谱探测器的方法,来提高对较薄材料的识别能力,并使用蒙特卡罗方法进行了一系列模拟计算,首先计算了探测器晶体厚度变化时X射线的沉积规律,然后计算了不同探测器结构和参数情况下材料识别的效果.从模拟计算的结果可知,采用适当的多能谱探测器将使得系统对质量厚度较小的物质,尤其是高Z材料的识别效果有明显改善.     

A curve-based material recognition method in MeV dual-energy X-ray imaging system

High-energy dual-energy X-ray digital radiography imaging is mainly used in the material recognition of cargo inspection. We introduce the development history and principle of the technology and describe the data process flow of our system. The system corrects original data to get a dual-energy transparence image. Material categories of all points in the image are identified by the classification curve,which is related to the X-ray energy spectrum. For the calibration of classification curve, our strategy involves a basic curve calibration and a real-time correction devoted to enhancing the classification accuracy. Image segmentation and denoising methods are applied to smooth the image. The image contains more information after colorization. Some results show that our methods achieve the desired effect.     

An experimental study of dual-energy CT imaging using synchrotron radiation

The measurement of electron density is important for medical diagnosis and charged particle radiotherapy treatment planning.Traditionally,electron density is obtained by CT imaging using the relationship between CT-number and electron densities established beforehand.However,the measurement is not accurate due to the beam hardening effect.In this paper,we propose a simple and practical electron density acquisition method based on dual-energy CT technique.For each sample,the CT imaging is conducted using two selected X-ray energy from synchrotron radiation.A post-processing dual-energy reconstruction method is used.Linear attenuation coefficients of the scanned samples are obtained by FBP reconstruction.The effective atomic number and electron density are got by solving the dual-energy simultaneous equations.Different phantoms and breast tissues were scanned in this experimental study under 10 keV and 30 keV monochromatic X-rays.The distribution of effective atomic numbers and electron densities of the scanned phantoms were obtained by Dual-energy CT image reconstruction,which agrees well with the theoretical values.Compared with conventional methods,the measurement accuracy is greatly improved, and the measurement error is reduced to about 1%.This experimental study demonstrates that DECT imaging based on synchrotron radiation source is applicable to medical diagnosis for quantitative measurement with high accuracy.     

X射线CT成像条状伪影校正

X射线CT成像过程中,由光子饥饿引起的CT图像中的条状伪影退化了CT图像的质量,增大了CT图像的数值统计误差,进而影响到材料探测结果。本文提出了一种基于自适应中值滤波的条状伪影校正方法,该方法依据投影数据的幅值自适应地设定滤波的窗口尺寸。针对多个相邻探元处于光子饥饿状态的情况,设定了阈值,判断中值滤波后的投影信号幅值是否处于阈值之下,否则继续扩大滤波窗口,直至满足阈值判断准则。本文通过实验验证了方法的有效性,该方法简单易行,适于实际工程应用。     

一种基于双能X射线与前向散射的爆炸物检测方法

本文简要介绍了爆炸物检测领域的各种现行方法,指出了它们的优缺点。与它们相比,本文探讨的新方法具有一系列独特的优点。本文作者提出了一种新颖的爆炸物检测方法,即(双能X射线) (前向散射法)。使用双能X射线法可以得到被检测物质的有效原子序数信息,利用X射线的前向散射可以得到被检测物质的密度信息,而有效原子序数和密度这两个特征量的组合就可以有效地表征爆炸物的存在。     

X射线工业CT中的数据采集

介绍了X射线工业CT中数据采集的一种方法.将X射线转换成与之成线性关系的微弱电流信号,通过检测电流信号测量出X射线的相对强度.这种采集方法可根据X射线的剂量强度,灵活的改变电流检测电路的参数,因此适用于不同能量级的X射线的采集.该X射线采集方法已经成功应用工业CT数据采集系统中.     

应用双能X线骨密度仪测定131名健康妇女骨密度变化

应用双能X线骨密度仪（DEXA）测定131名不同年龄和绝经年限妇女骨密度（BMD）变化,并观察外周血液中雌二醇（E2）、卵泡刺激素（FSH）、碱性磷酸酶（AKP）、骨钙素（BGP）、血钙、血磷等指标,探讨BMD和E2、AKP、BGP、Ca、P的相互关系。结果表明,妇女随着年龄及绝经年限增加,BMD及E2水平逐年下降,BMD和E2呈正相关;绝经后各组BGP和AKP明显高于绝经前各组,BMD和AKP、BGP呈负相关;血钙水平于绝经早期有一过性增加,以后略有下降,并保持在一相对稳定水平;血磷各组变化不大。由此可见,DEXA是一种理想的骨密度测定仪。BMD测定和E2、AKP、BGP等生化指标可以早期诊断绝经后骨质疏松症、预测骨折发生。     

工业CT系统中射线源的精确定位

为了实现工业CT系统射线源的精确定位,设计了射束中心位置测试专用装置,并开发了测试程序.利用该装置对两套工业CT系统进行了测试,修正了射线源的位置,精度达到士0.1mm.结果表明,利用该装置对射线源进行定位后,获取的图像质量有明显改善,并能够降低射线源位置调节机构的设计难度.     

Energy-dependent neutron mean-life and pulsed experiments in crystalline moderators

The decay of a thermalized neutron pulse in a small beryllium assembly is analysed in terms of energy-dependent neutron mean lifetimes. It is shown that the time evolution of the total neutron density is correctly predicted by this approach once the moderator dynamics is described in suitable detail. The correct way of interpreting die-away time measurements is finally discussed.     

缝丝法强流离子束发射度测量中系统误差的模拟研究

本文分析了缝丝法测量强流离子束发射度时系统误差的主要来源,并用模拟计算的方法研究了不同误差来源所带来的误差大小。对于rms发射度测量,因缝采样、忽略缝宽和丝直径、以及空间电荷效应所引起的系统误差均可忽视,而短缝采样和设置较大的阈值则会引起显著的系统误差。     

Restructure behavior analysis in fast breeder reactor MOX fuel by X-ray CT

Both high- and low-density MOX fuel pellets of uranium and plutonium oxides were irradiated in the experimental fast reactor JOYO. After irradiation, these fuel pellets were examined by X-ray CT and their irradiation behavior was evaluated for formation of the central void. In particular, the central void size and temperature of fuel pellets at the beginning and end of irradiation were analyzed. The central voids in the low-density fuel pellets were bigger than those of the high-density fuel pellets at the same linear heating rate (LHR), and the threshold LHR and temperature at which the central voids were formed were lower than those of the high-density fuel pellets. It was understood from these results that the irradiation behaviors of high- and low-density fuel pellets were different.     

Investigation on applicability of time-averaged X-ray CT images in two-phase flow measurement

ABSTRACT

Measuring the void fraction between fuel rods contributes to optimizing the geometrical design of fuel bundles for boiling water reactors (BWR). In this article, a method for reconstructing a three-dimensional void fraction distribution of two-phase flow by using an X-ray CT system is proposed. The performance was evaluated by both simulation and experiment. The simulation results suggested that the accuracy of the proposed method was within ±0.02, and from the experimental results, the void fraction in gas-liquid two-phase flows was successfully obtained with sufficient accuracy.     

450keV锥束CT系统的散射校正研究

在450keV锥束工业CT成像系统中,对投影数据进行适当的散射校正是一步重要的数据校正.结合国内外散射校正方法研究的现状,对一种用散射校正板来进行散射校正方法的原理和实现进行了深入的研究.实验结果表明,这种校正方法能够对450KeV锥束CT成像系统进行有效地散射校正.     

低能X射线工业CT探测器光电转换效率的研究

光电转换效率是低能工业CT探测器的重要性能参数。分析了几种常用闪烁晶体的发光效率、几何尺寸、发光波长等参数对光电转换效率的影响,并通过实验测试比较了不同厚度(闪烁体沿X射线方向的尺寸)的CsI(TI)和CdWO4闪烁体探测器的光电转换效率。证明在低能工业CT中,CsI(TI)比CdWO4更适合用作X射线探测器闪烁体材料,且闪烁体的厚度对光电转换效率的影响很大。这对优化工业CT系统探测器闪烁体的选型与尺寸设计具有一定的参考价值。     

Upgrading of X-ray CT technology for analyses of irradiated FBR MOX fuel

The X-ray CT technology previously developed by JAEA was upgraded. The shape of the X-ray source beam was changed from a circular shape to an elliptical one and the collimator slit width was decreased from 0.3 to 0.1 mm. The X-ray detector was improved by changing a CdWO₄ scintillator to a highly sensitive silicon semiconductor detector. The analysis code of X-ray CT image was revised with respect to the number of points by using two kinds of experimental results and taking into account the effects of crack existence and deviation of the central void position from the radial center of a fuel pellet. As a result, high resolution X-ray CT images could be obtained on the transverse cross section of irradiated fuel assemblies. The error of the dimensional measurement was improved from ±0.1 to ±0.03 mm by upgrading the instrument and revising the analysis code of X-ray CT image. The discriminating accuracy of density difference could be increased, and the low density region (undisturbed region) and high density region (equi-axial and columnar regions) in the X-ray CT image on the cross section of irradiated fuel could be discriminated from each other. The reliability of fuel performance analysis improves because a large number of PIE data can be collected, compared with the conventional destructive PIE.     

工业CT用X射线机射线强度分布研究

X射线机是工业CT中使用最广泛的X射线源,但因阳极效应以及自身结构的限制,其射线强度空间分布不均匀,系统的研究和测量其射线强度分布对于实际应用十分必要。利用Cs I(Tl)光电二极管探测器测量了射线强度在不同轴线上随角度的分布,给出了理论分析,并与蒙特卡罗法计算结果做了对比,提出了"展宽效应",解释了边界射线强度分布展宽的现象。比较了大、小焦点射线强度分布的情况,给出了其在阴极末端出现差异的原因。结合其在竖直方向的射线强度分布以及对称性,给出了X射线强度的二维分布。结果表明,在张角20°(10°+10°)的范围内,射线强度分布均匀(最大相对偏差4.59%),张角越大均匀性越差,在阴极端边界射线分布出现外延。