基于X射线背散射分能域探测的物质识别方法

本文提出了一种新的物质分类识别方法,为探测金属刀具、爆炸装置和毒品等违禁品提供新思路。该方法采用分能域的X射线背散射探测成像方法,通过分析被测物质在高低两种能量下的背散射信号来获得被测物质的等效原子序数信息;经过蒙特卡罗仿真与实验验证确定了物质分类识别曲线,并仿照双能透视物质分类着色方法对背散射扫描图像中不同等效原子区间的物质进行着色。研究发现该方法受光子计数量影响较大,通过提升探测器信噪比可以增强背散射扫描系统的物质识别能力。     

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。     

一种测量高强度直流X光机辐射能谱的方法

介绍了一种康普顿散射法测量高强度直流X射线能谱的方法,分析了X光机辐射谱与散射谱强度的关系表达式。在测量系统中使用能量分辨能力较好的高纯锗探测器,通过测量X光机照射低原子序数材料的散射能谱,再根据不同能量X射线在该散射立体角上的散射截面回推,从而获得X光机的辐射能谱。最后,给出了X光机的工作电压分别为15、80和100 kV时,散射法测量得到的钨靶X射线辐射谱。     

严重事故堆芯μ子成像监测重建方法研究

严重事故发生时,堆芯变化对于跟踪事故进程、确定应急方案十分重要。宇宙射线μ子成像监测技术具有高穿透力、对高原子序数物质敏感等特点,已被证明适用于核材料的监测。图像重建算法是实现这一技术的关键难点之一,由于待测目标物体为高原子序数物质,通常会在其周围伴随着灰度值相近的点状噪声。本文为提高重建质量,便于严重事故期间应急人员实时监测堆芯变化,提出了在径迹重建算法的基础上使用巴特沃斯滤波技术消除点状干扰的重建方法,初步模拟实验结果表明,该方法可有效降低噪声,从而验证了该方法的有效性。     

基于神经网络的核材料类型识别

针对核查前提．用人工神经网络技术对核材料类型识别进行了研究。实验结果表明,基于神经网络的分类器经过训练,能够有效识别不同类型的核材料,证明该方法用于现场核查中具有一定的可行性和实践意义。     

宇宙射线μ子探测高Z材料的仿真研究

利用Geant4建立宇宙射线μ子探测高Z材料的仿真系统,采用最大似然算法,研究用于μ子探测的位置灵敏探测器漂移管的位置分辨率及系统成像时间对成像结果的影响。当漂移管的位置分辨率优于200μm、成像时间在1～2min内可对相对独立的高Z物质快速识别,本研究也为漂移管的设计加工提供了理论依据。     

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.     

X—X方法

提出了采用可控Ｘ射线激发源激发样品、测定散射Ｘ射线的全谱、根据不同物质的谱线形态差异来确定所测定物质的组分（有效原子序数）、用于完成现场快速及在线测量的Ｘ－Ｘ方法。该方法实用、经济、安全、对环境无污染，有广阔的应用前景。     

X─X方法

提出了采用可控Ｘ射线激发源激发样品、测定散射Ｘ射线的全谱、根据不同物质的谱线形态差异来确定所测定物质的组分（有效原子序数）、用于完成现场快速及在线测量的Ｘ－Ｘ方崐法。该方法实用、经济、安全、对环境无污染，有广阔的应用前景。     

235U富集度的检测

采用γ能谱法和PC/FRAM软件分析检测铀样品中²³⁵U的富集度。实验结果表明,随机抽样的2个铀样品中,²³⁵U富集度测定值与标称值间相对偏差均在3%以内。该方法可用于铀样品中²³⁵U富集度的测量,并为今后核材料的测量提供一定的参考。     

Similarity in Pressure Dependence among Separation Factors of Thermal Diffusion Column in Total-Reflux Operation

Research on laser Compton scattering gamma-ray-based nuclear transmutation has been carried out to identify a method of reducing the hazards of long-lifetime radioactivity of nuclear waste. To study the photonuclear reaction experimentally, a laser Compton scattering gamma-ray facility was built on a storage ring at NewSUBARU and ~17MeV gamma-ray photons were produced. An investigation on the reaction rate of radioactive iodine waste was carried out. Based on the characteristics of laser Compton scattering gamma rays, a cylindrical target was adopted for the irradiation experiment. The radioactivity of the irradiated target was measured and the transmutation reaction rate was deduced. Experimental results were close to simulation findings.     

Energy distributions of multiple backscattered photons in materials

Backscattering of gamma photons from a material is of fundamental importance in radiation shielding,industrial and medical applications, radiation dosimetry,and non-destructive testing. In Compton scattering, incident photons undergo multiple scatterings within the material(target) before exiting. Gamma photons continue to soften in energy as the number of scatterings increases in a thick target; in other words, the energy of gamma photons decreases as the scatterings increase in case of a thick target and results in the generation of singly and multiply scattered events. In this work, the energy distribution of backscattered gamma photons with backscattering intensity and energy probabilities were calculated by using the Monte Carlo method for metallic, biological, and shielding materials with various thicknesses of slab geometry. The materials under study were targeted with gamma photons of 0.279, 0.662, 1.250, and 2.100 Me V energies. In addition, the energy distributions of multiply scattered gamma photons were studied for materials with infinite geometry.The results are presented and discussed in detail by comparing with other Monte Carlo calculations.     

宇宙射线缪子核材料快速检测算法研究

根据宇宙射线缪子库伦散射角进行核材料快速检测具有重要意义。本文利用Geant4获取的U、Pb、Fe的缪子库伦散射角数据集，分析缪子散射探测数据的分布特征。使用支持向量机测试了缪子散射探测数据的概率分布函数参数和峭度对不同材料分类的性能，提出基于分布特征的宇宙射线缪子核材料快速检测算法。结果表明，该算法仅用数量为10 000的缪子散射探测数据，能实现对相同厚度的U、Pb、Fe的分类，分类准确率达到989%以上。     

基于武器级铀的核弹头内部炸药探测的模拟研究

在军备控制核查技术领域,核弹头内部炸药的探测是一项重要的研究。本文利用GEANT4软件研究了基于武器级铀的核弹头(即铀弹头)内部炸药的被动探测法(利用铀弹头内部裂变中子作为中子源)的可行性,计算得到了从铀弹头中出射的γ射线能谱,能谱的形状与预期相符,但由于铀弹头内部裂变中子与炸药中~(14) N反应产生的特征γ光子的事例率太低,该方法可能不适用于铀弹头的现场测量。因此又利用GEANT4软件研究了铀弹头内部炸药的主动探测法(利用铀弹头外部的中子源对铀弹头进行辐照)的可行性。研究结果表明,主动探测法可在1h内实现对铀弹头内部炸药中~(14) N的探测和确认,进而能为判定铀弹头内部是否含有炸药提供重要依据。     

Measurements and Calculations of Angular Flux Spectra Emitted from Lithium and Graphite Slabs with D-T Neutron Source

Angular dependent flux spectra from slab assemblies (lithium and graphite) were measured to test nuclear data and calculational methods for D-T fusion reactor neutronics. The collimated 14 MeV neutron source could be applied by the use of an associated particle method and the neutron spectra from 14 to 2 MeV were observed with TOF technique. The measured spectral pattern was dependent on the anisotropy of secondary neutrons emitted from both the elastic and the non-elastic scattering for 14 MeV neutrons. As for the numerical calculations, one-dimensional discrete ordinates transport codes (ANISN and NITRAN) were used. The multigroup cross sections processed with SPTG4Z from ENDF/B-IV were used as common nuclear data base. The problems of calculational methods and nuclear data were discussed in comparison with the experimental data and it was clarified that sufficient nuclear data of angular dependent cross sections for the non-elastic scattering have not been available in ENDF/B-IV and that the anisotropy of the scattering could not be calculated with ANISN which utilized the scattering kernel generated by incorrect treatment of scattering kinematics in the processing code. However, good agreement between the measurements and calculations was obtained by the use of NITRAN system with the appropriate processing codes of inelastic scattering anisotropies. It was shown that the NITRAN system was useful for anisotropic neutron transport calculations.     

Line-Scanning Proportional Counter Camera

A new method was developed for imaging spatial distributions of photons, charged particles, or neutrons over large areas by a line-scanning camera. This camera uses a linear position-sensitive proportional counter (PSPC) based on resistance-capacitance (RC) position encoding. 1-6 Applications of this camera include low-dose, medium-resolution radiography of large objects (>2 by 2 m); and, in nuclear medicine, low-dose, whole-body radionuclide imaging and radiography with low energy photons (<150keV). A prototypic camera was built and tested to scan an area of 60 by 100 cm. The spatial resolution is 1 by 1 mm fwhm for radiography with 60-keV photons and 3 by 3 mm fwhm for radionuclide imaging with 50-keV photons (limited by collimator resolution). Compared to point-by-point scanning, the line-scanning method reduces the mechanical complexity of the camera and eliminates problems encountered in construction of large-area, high pressure PSPCs. This method is superior to the area PSPC for imaging objects >60 by 60cm.     

基于天然μ子散射特征评估铀板内水平狭缝宽度的方法

针对经典μ子成像方法用于特殊对象结构探测的技术难点,提出了一种通过直接比较对象发生结构变化前后μ子散射特征的差异来进行形变类型和尺度判定的新思路,称为正向参比法。相比于经典的逆向反演法,该方法在原理上对于初始结构已知的特殊核对象的结构变化探测更有优势。从初步模拟结果来看,在合理的天然μ子通量下,该方法可实现铀板内亚毫米尺度水平狭缝的存在及其尺度的准确判定。     

高能评价核数据处理方法

为满足加速器驱动次临界系统ADS等高能核装置的蒙特卡罗输运计算需求,通过对相关核数据处理模块的改进,建立了一套基于我国自主的群常数制作软件Ruler与国际公认的核数据处理系统NJOY耦合的中高能评价核数据处理方法及程序系统。通过该方法基于日本高能评价核数据库JENDL-HE-2007制作了ACE格式连续点截面库,并通过一系列绘图及简单问题的蒙特卡罗输运计算,验证了该库是完整的、合理的,可用于蒙特卡罗输运计算,证明了Ruler与NJOY功能模块耦合的方法可用于高能评价核数据的处理。     

High energy X-ray computed tomography for industrial applications

A high energy X-ray computed tomography (CT) system with an electron linear accelerator was developed to image cross-sections of large-scale and high-density materials. An electron linear accelerator is used as the X-ray source. The maximum X-ray energy is 12 MeV, and the average energy is around 4 MeV. The intensity of the X-ray fan beam passing through the test object is measured by a 15-channel detector array. CWO (CdWO₄) scintillators and photodiodes are used as the X-ray detectors. The crosstalk noise due to scattering of X-ray photons by adjacent detectors is reduced to less than 1.6% by installing tungsten shields between the scintillators. Extra channels are used to compensate for base line shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-rays transmitted in a 420-mm thick iron block. A spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter