LBO晶体的生长缺陷研究

采用化学腐蚀光学显微法和同步辐射截面形貌术研究了三硼酸锂（LBO）晶体的生长缺陷,实验结果表明,LBO晶体中的主要缺陷是位错、包裹物和扇形界。讨论了这些缺陷形成的原因和降低缺陷的措施。     

微重力生长HgCdTe材料的微观缺陷

采用正电子湮没寿命谱方法,对空间微重力及重力条件下生长的碲镉汞材料中的微观缺陷进行了研究。结果表明,在空间微重力条件下生长的ＭＣＴ晶体中,其空位型缺陷浓度低于地球上有重力条件下生长的晶体,并且缺陷浓度沿轴向的分布比较均匀。     

MeV金离子辐照聚苯乙烯微球的各向异性形变

在低温条件下用Au离子辐照法实现了聚苯乙烯(PS)微球的各向异性形变.PS微球在离子辐照下呈现出不同于SiO2微球的形变特点.照后PS微球整体收缩,在平行于离子入射方向上收缩尤甚,使照后PS微球呈长轴垂直与离子入射方向的椭球.采用加掩膜辐照法,在同一晶体上特定区域实现微球的形变.此工作为重离子辐照在光子晶体中引入可控缺陷奠定了基础.     

LiNdP4O12晶体的生长缺陷

LiNdP4O12(LNP）晶体是一种新型的激光材料。本报道了用同步辐射X射线白光形貌术和光学显微法研究由助熔剂籽晶旋转法生长的LNP晶体的生长缺陷,观察到了圆形生长台阶及精细的系列台阶结构,对晶体中的包裹物和位错缺陷等进行了详细的观察描述,还发现了一种比较奇特的腐蚀沟槽,分析了这种腐蚀沟槽的形成机理及各种缺陷的成因和克服办法。     

热压纳米晶铜的硬度性能

采用自悬浮定向流法制备纳米铜粉末,利用不同的工艺参数在真空热压炉中压制成直径一定厚度不同的纳米晶体铜圆柱体。通过XRD、SEM、分析天平、硬度仪等分析测试手段,研究了块体硬度与晶粒大小、密度、晶体结构的关系。结果表明：较薄块体硬度随晶粒长大而降低,两者关系基本符合Hall-Petch经验公式;较厚块体各区域密度差异不明显,受表面缺陷状态及晶粒大小影响,其各处硬度差异较大（1.4～2.2GPa）。     

金红石辐照损伤的分子动力学模拟

为了研究辐照条件下金红石的耐辐照损伤能力，采用GULP软件包拟合出了与实验值吻合的势函数，并采用LAMMPS软件包计算出了金红石的离位阈能和高能粒子反冲条件下的位移级联。通过统计球坐标系下266个出射方向的离位能，利用缺陷形成概率的定义得出Ti和O原子的离位阈能分别为(78.3±1.0) eV和(42.6±2.0) eV。采用VORONOI缺陷统计方法，计算了300 K、10 keV出射能量条件下缺陷数量随辐照时间演化信息，结果表明：Ti原子作为初始出射原子产生的缺陷数量整体高于O原子产生缺陷的数量，在最大无序阶段产生的空位、填隙和不同类型反位缺陷通过空位-填隙复合作用和kick-out机制逐渐减少，有效地降低了晶体的无序度，提高了基材耐辐照损伤性能。     

电子辐照高纯铁电阻率回复的团簇动力学模拟

电阻率回复实验是研究材料辐照损伤机理的有效手段,可表征材料中辐照缺陷数量的变化。本文基于平均场速率理论开发了模拟辐照缺陷演化的团簇动力学程序,模拟了高纯铁经3MeV电子辐照至2.0×10-6 dpa后等时时效过程的缺陷演化过程,并与电阻率回复实验结果进行了对比。模拟结果表明,辐照缺陷数量随温度升高的演化过程与电阻率的变化趋势吻合得很好,电阻率回复的峰值分别对应于间隙原子、间隙原子团簇、空位团簇等缺陷的数量变化。该方法对于研究材料辐照损伤机理具有重要意义。     

用于正电子发射断层成像的闪烁晶体

正电子发射断层成像要求闪烁晶体材料具有高光输出、短衰减时间和强阻止本领,且价格低廉。本文综述了闪烁晶体材料最新的发展状况和其特征对正电子发射断层成像系统的性能影响。     

熔盐/辐照环境中细结构等静压石墨的结构和化学稳定性研究

熔盐堆以石墨作为反射体和慢化体,熔盐与石墨直接接触,石墨在熔盐中的腐蚀反应和辐照损伤是值得研究的问题。本文采用自主研发的细结构石墨,阻隔熔盐浸渗,采用30 MeV He+模拟中子辐照,研究不同温度及熔盐环境下石墨微观形貌、微结构和化学结构的变化。研究结果表明,高温环境下,由于高温的退火效应,石墨缺陷密度的增加及形貌的变化都远小于室温环境。辐照后的石墨与熔盐接触,其缺陷密度略微降低。这种微结构的改善与高温熔盐环境中的退火效应及熔盐固化引起内部微裂纹的闭合有关。辐照后的熔盐浸泡可在石墨C—C键结构中引入C—F键,且C—F键的形成与缺陷密度及缺陷类型密切相关。稳定的空位簇及间隙原子的迁移均会影响层间化合物的形成,从而产生限制C—F键形成的环境,进而降低由层间化合物的形成对石墨表面结构的破坏。     

闪烁晶体各向异性效应的研究动态

闪烁晶体是核辐射探测器中的重要材料,具有密度大、光输出高、均匀性好以及衰减快等优点,广泛应用在医疗卫生、安全检查、高能物理、油矿勘探等领域。同一闪烁晶体经常表现出较大的性能差异,人们通常将其归因于晶体制备工艺的差异,而容易忽略晶体各向异性对晶体性能的影响。随着PbWO4、Lu2Si2O7:Ce、LaBr3:Ce和LaCl3:Ce等非立方相晶体的出现,闪烁晶体的各向异性效应越来越受到重视。论文综述了闪烁晶体的各向异性研究,分析了闪烁晶体的各向异性效应对晶体应用的影响。     

The Effects of Dislocations and Crystal Defects on the Energy Resolution and Response Uniformity of Mercuric Iodide Detectors

The energy resolution and response uniformity of HgI2 detectors to nuclear radiation depends strongly on dislocation density and distribution in the HgI2 crystal bulk. Several large planar detectors fabricated from the interiors of large single crystals verified this dependence. Scanning with collimated low-energy (6 keV) and medium-energy (60 keV) gamma-rays confirmed the association of poor resolution and counting efficiency with regions of high dislocation density and crystal imperfection.     

The Effect of Dislocation on the Energy Resolution of High-Purity Germanium Detectors

The energy resolution of high-purity Ge detectors depends on the dislocation density and distribution in the single crystal. This correlation could be shown in a number of planar detectors with different dislocation densities. Scanning with collimated electrons and gamma-rays revealed the strong dependence of local detector performance on dislocation density.     

小角X射线散射方法测定结晶聚合物的平均过渡层厚度

一般用一维电子密度相关函数来计算结晶聚合物的过渡层厚度。由于结晶聚合物中的过渡层是弥散的，修正的Porod定律是解决这种问题的有效方法之一。本文将用相关函数法和Po-rod定律法求出的结晶聚合物的过渡层厚度进行了比较，它们的计算结果是一致的。     

冲击波加载下单晶铜动态破坏微观过程的分子动力学研究

采用嵌入原子势模型和分子动力学方法,模拟研究了冲击波加载下单晶铜动态破坏的微观过程和空洞成核及生长过程。根据原子中心对称参数变化给出了单晶铜动态破坏的微观过程,通过不同碰撞速度的模拟,讨论了冲击波加载下破碎区内物质形态分布的变化,给出了材料破坏深度的变化规律。研究发现纳米空洞在完整单晶铜中随机成核,空洞成核后,空洞表面的应力集中和原子活化易形成位错源,各种不同类型的位错的生长使空洞逐渐长大,空洞长大到一定尺寸后,邻近空洞相互作用贯通形成更大尺寸的空洞,这种空洞贯通效应造成了材料内部的宏观层裂及失效。     

Measurement of plastic strain of polycrystalline material by electron backscatter diffraction

It is important to know the degree of plastic strain in order to evaluate the susceptibility and crack growth rate of stress corrosion cracking (SCC) in stainless steel and nickel based alloy, because SCC is enhanced by the cold work and causes many problems in nuclear power plant components. In this study, electron backscatter diffraction in conjunction with scanning electron microscopy is applied to measure the plastic strain imposed to stainless steel by tensile load. A new parameter, which quantifies the spread of the crystal orientation within individual grains arising due to dislocation accumulation during plastic deformation, is correlated with imposed plastic strain. The new parameter is called ‘crystal deformation’ and is determined from the spread in misorientation from the central grain orientation. It is confirmed that this parameter has a good correlation with plastic strain and is not affected by the data density of the crystal orientation map. The dislocation density distribution is also evaluated from the misorientation from the central orientation. Relatively high dislocation density was observed near grain boundaries and grain boundary triple points, which was consistent with the observed deterioration of EBSD pattern quality in those locations.     

High-resolution x-ray monochromatic imaging for laser plasma diagnostics based on toroidal crystal

Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information.Large-field high-resolution monochromatic imaging of a He-like iron(Fe XXV) Kαcharacteristic line(6.701 keV) for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager.A high-index crystal orientation Ge(531) wafer with a Bragg angle of 75.37° and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism unde...     

MgO晶体中F型色心的电子结构和光学吸收谱研究

运用嵌入原子簇的电荷自洽离散变分方法（SCC－DVM－Xα方法）对MgO晶体中F型色心的电子结构进行了计算,并利用能量最小原理优化了色心格点周围的Mg,O离子结构,得到了MgO晶体中F,F^ 和F^2 心的能带,态密度,并讨论了色心的光学跃迁模式。计算结果表明,F,F^ 和F^2 心在MgO晶体的禁色中引入了色心能级,F和F^ 心的光学跃迁能分别是4．67eV和4．66eV,电子从色心激光发态跃迁到导带底需要吸收大的光电子跃迁能量。计算结果与实验结果符合较好,说明计算结果是合理的。     

CunAum(n+m=4)类晶结构团簇电子结构性质的第一性原理计算

用基于第一性原理的密度泛函理论计算分析了CunAum(n m=4)类晶结构团簇的电子结构性质。计算得到的晶格参数与实验值吻合较好。体系能带结构和态密度分析表明,对能级的贡献主要来自d轨道的电子,且在费米能级附近出现较强的峰,此处的光吸收作用显著增强。电荷密度分布说明,体系的键结构致密度较大,其中存在共价键和金属键,金属键主要由d轨道电子的共有化运动而形成。     

Real-time measurement of implanted deuterons by using the nuclear reaction H(d,p)H

We propose a method for real-time measurement of the density of implanted deuterons in solid materials during deuterium implantation. In this method, the density of implanted deuterons is measured by detecting the emitted protons from the deuteron fusion reaction between the incident deuterons and the implanted deuterons. A negative deuterium beam with an energy of 90 keV is used both for the implanted atoms and a probe beam to measure the implanted deuterons. The density of the implanted deuterium atoms was observed to be drastically different between the single crystal and poly-crystal in Ta.     

Microstructural analysis on helium retention of ion-irradiated and annealed tungsten foils

The helium retention characteristics and helium bubble distribution in tungsten were studied using ³He(d,p)⁴He nuclear reaction analysis (NRA) and transmission electron microscopy (TEM) on two forms of tungsten: single crystal and polycrystalline, implanted to 1 × 10^19 3He/m² at 850 °C and annealed at 2000 °C. The NRA results revealed that as-implanted single crystal and polycrystalline tungsten exhibited similar helium retention characteristics. Stepwise annealing reduced the helium retention in both single crystal and polycrystalline tungsten when the number of implantation steps and annealing time were increased. The TEM results indicated that microstructure played a large role in helium trapping; the existence of grain boundaries led to significant cavity formation and greater cavity growth. Single crystal tungsten had less trapping sites for helium, allowing long range He diffusion during annealing. The decrease of He retention in polycrystalline tungsten during stepwise annealing was probably due to significant recrystallization, resulting in decrease of grain boundary density.