高能闪光照相中陡坡准直体成像性能实验研究

在针对FTO样品的高能闪光照相实验中,比较了一般准直体与陡坡准直体对FTO样品的成像性能。结果表明,陡坡准直体对降低散射及缩小照射量量程非常有效,可得到层次分明的底片图像;采用一般准直体则无法得到有意义的样品图像。对实验进行了蒙卡模拟,模拟结果与实验结果一致。     

数字化网络化多通道闪光X射线成像系统

介绍了研制的数字化网络化多通道闪光X射线成像系统，它能以正交方式同步获取多瞬时纳秒X射线透视图像。所获取的图像立即数字化和通过网络传送，完全没有胶片系统的冲洗、等待和交流的麻烦，是研究和检测弹道、射流、穿甲、爆炸、喷射和高速运动机械的重要技术。描述了系统的组成和实际测量的绺弹道图像，介绍了自动进行目标分裂、弹道轮廓计算和三维空腔图像重建的效果。     

Study on premixing phase of steam explosion at JAERI

Melt jet breakup and fragmentation has been studied in ALPHA program at JAERI. In the first two experiments of the MJB series, a jet of molten lead–bismuth eutectic alloy was released into a deep pool of saturated water. The steam generation rate was measured and correlated with the jet behavior observed by a high-speed camera. The jet breakup length and debris size distribution were also evaluated. In parallel with the experimental study, JASMINE code has been developed for the simulation of a steam explosion process. The models of melt jet breakup and the particle breakup in the code were assessed by analyzing FARO-L14 and ALPHA MJB experiments.     

扫描式数字X射线胸部摄影系统的研制

扫描式数字X射线摄影系统属DR范畴,除具有DR的一般优点外,还具有散射射线影响小(零本底)、低剂量和低成本三大优点.探讨了以固体线阵探测器为基础的扫描式数字X射线胸部摄影系统的构建,包括系统整体设计方案、关键技术问题的阐述以及系统性能分析,并提出了进一步提高系统性能的可行方法.     

Spectral reconstruction of the flash X-ray generated by Dragon-I LIA based on transmission measurements

The Dragon-I linear induction accelerator(LIA)at China Academy of Engineering Physics generates 20 Me V flash X-rays mainly for radiography applications in fluid dynamics.Its spectral information is quite important for diagnostic X-ray imaging applications,but because of its short pulse and great radiation intensity,direct measurement is impossible.In this work,we propose a new method based on transmission measurements to obtain the flash X-ray spectrum.Pure iron cylinders were used as attenuation material,and alanine dosimeters were attached on their rear bottom to record the dose after different degrees of attenuation.Iterative least square method was used to unfold the spectrum,while Geant4 Monte Carlo code was used to simulate the X-ray spectrum.The unfolded spectrum and the simulated spectrum have a high degree of consistency,with the reduced chi-square value of 0.044.This shows that the method is reliable in estimating megavoltage highintensity X-ray spectrum.     

A compact micro-beam system using a tapered glass capillary for proton-induced X-ray radiography

A compact micro-beam system, containing a tapered glass capillary tube with a tip diameter on the order of 10 μm, was constructed to examine the applicability of capillary-generated micro-beams to high-contrast radiography based on proton-induced quasi-monochromatic X-rays. The transport efficiency of swift protons (2-3 MeV) through the capillary was examined as a function of the capillary tilt angle and the capillary tip diameter. We obtained transport efficiencies of approximately three times larger than would be expected from the geometrical shape of the capillary. This enhancement indicates that a focusing effect occurred in the capillary. A metallic thin foil was irradiated with the micro-beam and quasi-monochromatic X-rays were produced. By calculating the X-ray yields induced by proton bombardment in the foil and comparing them with the X-ray counts observed at the detector, the throughput efficiency of the X-ray imaging system was evaluated. We demonstrated magnification radiography of a small object to show that a spatial resolution on the order of 10 μm was achievable in our system.     

Phase separation of metal-added corium and its effect on a steam explosion

To simulate a relocation of molten core material and its interaction phenomenon with water during a severe accident in a nuclear reactor, a typical corium of UO₂/ZrO₂/Zr/Stainless steel mixed at a 62 wt%, 15 wt%, 12 wt% and 11 wt%, respectively, was melted and then cooled down to become a solidified ingot. It was shown that the molten corium was separated into two layers, of which the upper layer was oxide mixtures and the lower layer was metal alloys. The upper layer was UO₂ and ZrO₂ and the lower layer mostly consisted of metal mixtures such as uranium, zirconium and stainless steel. Iron content varied with the positions and about a half of it existed as an alloy such as Fe₂U. Uranium metal was produced by reduction of UO₂ by zirconium metal. The average densities of the upper oxide layer and the lower metal layer were 8.802 and 9.411 g/cm³, respectively. In another test, metal-added molten corium was poured into water and it showed that a steam explosion could occur by applying an external trigger.     

Effect of melt water interaction configuration on the process of steam explosion

Steam explosion experiments are performed at various modes of melt water interaction configuration using prototypic corium melt. The tests are performed to simulate both melt water interaction in a partially flooded cavity and melt water interaction in a cavity with submerged reactor. The tests are performed using zirconia and corium melts. The behavior of melt jet fragmentation during the flight in the air and fragmentation and mixing of melt jet in water is investigated by a high-speed video visualization and by comparison of debris size distribution and morphology of debris. Strength of steam explosion is estimated by measuring dynamic pressure and dynamic force.     

Identification of origin of single aerosol particles using polycapillary X-ray lens

A micro X-ray fluorescence (Micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) and a laboratory X-ray source was designed to carry out the XRF analysis of single aerosol particles. The minimum detection limit (MDL) of this Micro-XRF spectrometer was 9 ppm for the Fe-Kα. The percentage of the particles of vehicle exhaust among aerosol particles was studied in Beijing, Chinese capital, during the test of odd-even driving restrictions for Beijing 2008 Olympics Games. This Micro-XRF spectrometer had potential applications in the analysis of single aerosol particles.     

The effect of corium composition and interaction vessel geometry on the prototypic steam explosion

This paper discusses the results of steam explosion experiments using molten material consisting of UO₂ and ZrO₂ mixture, which is called corium, to simulate a prototypic steam explosion in a nuclear reactor during a postulated severe accident. About 5–10 kg of molten material with enough superheat was poured into a pool of water in a test section at room temperature to simulate ex-vessel steam explosion in the reactor situation. Most of the experiments were externally triggered. The purpose of the experiments was to investigate the effect of material composition and average void fraction on the strength of a prototypic steam explosion, which were highlighted as major unresolved issues.The experiments were performed using two kinds of mixtures, one, corium A, at 70:30 weight percent composition of UO₂ and ZrO₂, close to eutectic composition, and the other, corium B, at 80:20 weight percent. Also, two kinds of cylindrical test sections having a different diameter were used. It turned out that corium A was likely to produce an energetic steam explosion, while corium B seldom led to an energetic steam explosion. The existence of mush phase for the non-eutectic mixture is suggested to be the reason for the difference. Comparative cross sectional views of the corium particles by scanning electron microscope supported the proposed argument. The tests performed with a narrow test section seldom led to an energetic steam explosion for both materials. An increase in average void is suggested to be the reason for the non-explosive behavior, which is consistent with the physical models employed in the current steam explosion computer codes.     

单颗粒大气气溶胶的同步辐射微束X射线研究

在北京同步辐射装置4W1B光束线的荧光站,用束斑大小为20 μm×10 μm的X射线微束分析了污染排放源PM10单颗粒和环境空气监测样品PM10单颗粒,得到了单颗粒的X射线荧光谱。实验结果表明,来自不同污染排放源的颗粒物,它们的能谱具有明显的特征,根据颗粒物的能谱可以识别颗粒物的来源。     

Nondestructive measurement of the coating thickness for simulated TRISO-coated fuel particles by using phase contrast X-ray radiography

The TRISO-coated fuel particle for a HTGR (high temperature gas-cooled reactor) is composed of a nuclear fuel kernel and outer coating layers. The coating layers consist of a buffer PyC (pyrolytic carbon) layer, an inner PyC (I-PyC) layer, a SiC layer, and an outer PyC (O-PyC) layer. X-ray radiography is one of the nondestructive alternatives to measure a coating thickness without generating a radioactive waste. Phase contrast X-ray radiography technology is more powerful for acquiring a radiograph with clear boundaries, when compared with a conventional X-ray radiography. The contrast can be enhanced for weakly absorbing materials in a phase contrast X-ray radiograph by detecting an intensity variation due to the variation of a phase of the X-rays in the boundary between two objects. Phase contrast X-ray radiograph was acquired from a simulated TRISO-coated fuel particle with a micro-focus X-ray imaging system. The coating thickness was nondestructively measured from the phase contrast X-ray image for the fuel particle.     

X-ray lasing experiments on matched-line photon pumping in plasma ions

Enhancement of gain in the X-ray spectral region at increased population densities may be possible by photon pumping of specific levels through the absorption of intense line emission at the same energy from other ions. Experiments on a Na⁹⁺ pumping Ne⁸⁺ test case are described. The neon ions are shown to be produced from cryogenically frozen layers; and 25 MW of pump line emission at 11 Å has been measured in early experiments. Plans are described for a combined gain experiment.     

反散射数字辐射成像系统

反散射成像法是数字辐射成像的主要方法之一，介绍了获得反散射数字图像的实验装置，并着重分析了针对此装置获得的反散性图像的处理方法。     

A microfocus X-ray tube based on a microstructured X-ray target

We present a novel concept to develop a microfocus X-ray tube based on a microstructured X-ray target that is irradiated with a nonfocused electron beam. X-ray emissions from the microstructured targets with various morphologies were studied using Monte-Carlo simulation code MCNP5. The calculations revealed that the microstructured targets are quite capable of minimizing the effective X-ray spot size compared with those of conventional transmission-type X-ray targets. Based on the simulation results of X-ray brightness, optimum geometric parameters were derived for the microstructured targets with different morphologies. Moreover, the stability of the microstructured target against heat loads delivered by an electron beam was also investigated under both the continuous and pulsed operation modes. From the analysis, the limitations of the maximum allowable electron beam currents for the stable operation of the X-ray targets are presented. The combination of the microstructured targets and nonfocused electron beam allows the miniaturization of a microfocus X-ray tube by eliminating the needs for massive and complex focusing devices.     

基于支持向量机的核爆地震自动识别

针对核爆地震识别问题的特点,提出利用支持向量机(SVM)方法进行核爆地震的自动识别。该方法借助算法的内在能力来实现特征的选择变换,不必像传统方法那样将很大的精力用于特征空间的降维处理。同时,由于该方法建立在结构风险最小化准则上,而不是仅仅使经验风险最小,所以,它具有好的推广能力。实际数据处理结果表明,该方法在小样本情况下性能优于神经网络,可以很好地克服过学习问题。     

同步辐射软X射线对单细胞的辐射损伤

应用国家同步辐射实验室软X射线显微术光束线的光学系统,搭建了适合软X射线单细胞辐照损伤效应研究的实验装置,选择氧元素K吸收边能量对Hela细胞进行单细胞辐照,运用单细胞凝胶电泳技术进行辐照损伤评价.实验结果表明,辐射损伤效应与辐射剂量有依赖性关系.     

9Be(d,n)加速器中子源中子照相的研究

加速器中子源比反应堆中子源更具灵活性,北京大学正在发展基于RFQ加速器的小型中子照相装置.为了更好地设计和优化此装置,实现高品质的中子照相,我们在北京大学4.5 MV静电加速器上建立了中子照相实验平台,包括科学级制冷、高灵敏度、低噪声的CCD数字成像系统,模拟基于厚铍靶9Be(d,n)反应RFQ中子源的条件,并利用此系统开展中子成像技术的研究.实验在像平面热中子注量率为5×103 cm-2·s-1或快中子注量率为3.7×104 cm-2·s-1的情况下获得了一定质量的热中子及快中子照片.当利用RFQ直线加速器强中子源时将可获得更高质量的图片,从而可以满足大多数的应用需要.     

Application of different delayed neutron data sets to the analysis of rod drop experiments on VVER cores

Rod-drop experiments performed on VVER-440 reactors are analysed using different delayed neutron data sets. It is found that for these experiments the 8 group data sets of Spriggs et al [6] give results in agreement with the original 6 group sets of Keepin on which they are based. The results obtained using Brady and England data [3] are markedly different. Sensitivity studies are made to analyse these differences.