D-D中子辐照单晶TiO2的损伤特性

利用兰州大学强流中子发生器出射的单能D-D中子对单晶TiO2(金红石相)进行辐照,分别测量了样品的正电子寿命谱及XRD谱。中子辐照会在样品内部产生大量的空位缺陷,由于晶格中Ti原子的位移阈能约为O原子的2倍,因此中子辐照在样品内部产生的空位缺陷以氧空位(VO)为主。结果表明,单晶内部捕获正电子的陷阱Ti空位(VTi)在中子辐照后电子密度增大,可能与Ti空位周围O空位的引入有关,O空位的出现减弱了Ti空位处的库仑排斥作用,使空位体积减少。后续测试的XRD也得到相同的结果,样品由于中子辐照而在c轴方向的晶面间距发生变化,并导致单晶TiO2的结晶度变差。     

两类钒基合金的辐照硬化研究

钒合金(V-Cr-Ti系列)是重要的聚变堆结构候选材料,但是相比于铁素体/马氏体钢等其他候选材料,有关钒合金(V-Cr-Ti)的辐照损伤研究较为缺乏。利用载能离子束模拟聚变堆中子辐照条件,对V-4Cr-4Ti和V-5Cr-5Ti两种样品进行了载能He离子和重离子辐照实验。实验采用离子束梯度减能方法在样品中产生辐照损伤的坪区,利用纳米压痕技术测试材料的辐照硬化效应。结果表明,样品纳米硬度的深度递减现象可以用Nix-Gao模型很好描述,高能重离子辐照的样品中软基体效应可以有效避免;在He离子辐照情形,He浓度(以原子百万分率计(Atomic parts per million,APPM))/位移损伤(以每原子平均离位数计(Displacement per atom,DPA))大于4 200/0.2时,两种钒合金样品出现硬化饱和现象;相近位移损伤水平下,He与空位的结合导致缺陷集团的加速长大,致使材料的辐照硬化远大于重离子辐照情形。     

高能铁离子辐照单晶氧化铝产生的色心研究

室温下利用紫外-可见吸收光谱和荧光光谱技术对1.157GeV的56Fe离子注入辐照的单晶三氧化二铝(α-Al2O3)进行了测量分析,研究了辐照产生的阴离子空位的形成和演化规律.测量结果显示,高能Fe离子辐照产生了多种阴离子空位型缺陷,其中包括F、F 、F2 、F22 和F2心.随入射离子剂量的增加,各类缺陷的数量逐渐增大,并在高剂量时趋于饱和,但各类缺陷间的相对数量存在一定的比例,不随剂量的增加而有明显变化.用单离子饱和损伤模型对实验结果进行了拟合,获得各类色心的产生截面在40-90 nm2之间.与TRIM程序计算结果比较后发现,室温下辐照时阴离子单空位的产生速率约是由核能损过程在低温下产生缺陷速率的一半.     

CMOS器件p、γ、β辐照损伤等效剂量分析计算

建立了CMOS电子元器件中质子、电子和光子辐照损伤 (电子 空穴对和离位原子浓度 )计算模型。利用微机化的电子 光子簇射过程模拟程序EGS4和TRIM程序分别计算了电子 ( β)、光子 (γ)和质子 ( p)辐照在CMOS器件各层中产生的电子 空穴对和离位原子浓度。计算结果表明 ,在CMOS器件桥结绝缘层中 ,电子产生的电子 空穴对和离位原子浓度最高 ,光子次之 ,质子最低 ,这表明电子辐照损伤最高 ,光子次之 ,质子最小。     

慢正电子束研究质子辐照CLAM钢产生的缺陷及其退火行为

为了研究中国低活化马氏体CLAM钢的辐照损伤机理,本文利用慢正电子技术研究了质子辐照CLAM钢时所产生的缺陷及其退火回复行为,发现辐照在材料中产生空位团数密度随质子注量增加而增多,而其尺度增大并不明显.辐照仅产生原子尺度的空位和空位团,400℃退火可以使缺陷很好地消除.此外分析了硅对CLAM钢辐照性能的影响,实验上没有观察到硅的添加抑制了质子辐照缺陷的产生.     

中子辐照GaAs的变温正电子寿命研究

用正电子湮没寿命谱研究中子辐照前后半绝缘ＧａＡｓ在等时退火过程中的缺陷行为．发现辐照后的样品大约从７０℃起空位－填隙子对和空位－反格点缺陷开始复合．５００℃前空位和空位团可消除．７４０℃后可能会重新产生缺陷。ＶＡｓ是一种浅势阱，对正电子的束缚能大约为０．０３１－０．０３２ｅＶ。     

BCC铁中的级联碰撞模拟研究

正材料在受到辐照时,入射粒子与材料晶格原子相互作用,经历碰撞、缺陷形成及退火等过程,最终导致材料内部微观结构的演化。在入射粒子与晶格原子碰撞之后,首先产生初级离位原子(PKA);之后,PKA在晶格之间引发一系列碰撞级联,随着时间推移,有很大一部分在级联碰撞过程中产生的离位原子逐渐湮灭;几ps之后,材料内部组织渐趋稳定,并有间隙原子、空位等缺陷残留。由于整个级联碰撞过程时间非常短,难以通过实验观察其演变过程,一般采用计算机模拟的     

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。     

Co掺杂ZnO的快中子辐射损伤研究

用中子发生器上D-D反应的2.5MeV中子辐照Co掺杂ZnO和对照样品纯ZnO单晶。室温下测量了样品的X射线衍射谱、光致发光谱和透射光谱。结果表明,快中子辐照后的纯ZnO单晶中引入了氧空位(VO)和氧错位(OZn)缺陷,且有少量的锌填隙(Zni)和氧填隙(Oi)缺陷。Co掺杂ZnO中存在的Co以及钴氧化物纳米团簇由于快中子轰击而分解消失。快中子与替代Zn2+的Co2+的碰撞导致大量的Co2+离开ZnO晶格点位,导致Co掺杂ZnO中引入钴填隙杂质和锌空位(VZn)缺陷。中子辐照后的所有样品依然呈纤锌矿结构并沿c轴高度择优取向。表明纯ZnO和掺Co氧化锌半导体材料具有良好的抗辐照性能,在空间器件方面具有应用潜力,且有助于在ZnO点缺陷方面的研究。     

中子辐照注量对单晶硅中缺陷退火行为的影响

用正电子湮没寿命和多普勒加宽测量研究了不同注量中子辐照的氩气氛区熔单晶硅中缺陷的退火行为，发现不同中子注量辐照时，辐照致空位型缺陷的退火行为十分类似，并均在５５０℃时退火消除；但辐照致双空位浓度、二次双空位和四空位型缺陷的产生、浓度和消除温度很不相同。简单陷阱模型不适用于５００℃以下退火的离中子注量辐照的单晶硅，但能部分适用于中等注量辐照的单晶硅。     

Molecular-dynamics simulation of threshold displacement energies in lithium aluminate

Threshold displacement energies in LiAlO₂ were evaluated using molecular dynamics technique. A pairwise potential model was adopted for simplicity, with reliance on high ionicity of LiAlO₂. In all the three elements, the threshold displacement energy varied considerably depending on the displacement direction of the primary knock-on atom. The average displacement energies of Li, O and Al over 342 displacement directions were evaluated to be 22, 37 and 84 eV, respectively. The order of these values are consistent with the number of generated defects in displacement cascade simulation with initial PKA energy of 1-5 keV, where the number of generated defects was the largest in Li and the smallest in Al in proportion to the number of atoms included in the system, regardless of the initial PKA energy.     

Defect production considerations for gamma ray irradiation of reactor pressure vessel steels

Motivated by the recent interest in gamma ray embrittlement of nuclear reactor pressure vessels (RPVs), calculations were performed to evaluate aspects of defect production by gammas in iron and steel. In addition to determining displacement damage cross-sections, the atomic recoil energy dependence of gamma-induced defect production was described by integral recoil damage spectra, W(T), and their associated median recoil damage energies, T_1/2. These latter characterizations, should be particularly useful in evaluating the contribution of gamma ray generated defects to microstructural changes causing radiation embrittlement. The results for monoenergetic gammas, as well as for gamma rays with a spectrum of energies characteristic of a RPV, reveal T_1/2 values of <100 eV, about three orders of magnitude smaller than for fast-neutrons, the radiation of primary concern in previous embrittlement studies. The relative contributions of various gamma interactions to defect production, as well as the role of light alloy element-induced secondary displacement mechanisms, are also considered.     

内嵌金属的多壁碳纳米管辐射损伤研究

辐射损伤性能是制约核电池效能和使用寿命的重要因素。美国研究者Popa-Simil提出基于碳纳米管、金属复合结构材料的概念核电池,可实现核能到电能的高效转换,其设计中利用了碳纳米管的抗辐射损伤特性。本文通过建立包覆金属铜的多壁碳纳米管模型,采用分子动力学方法,对内嵌金属的多壁碳纳米管体系进行了辐射损伤的模拟研究。从配位缺陷数、溅射原子数、完美结构缺陷(Perfect structure defect,PST)原子数以及总的辐射损伤量等方面,与无内嵌金属的碳纳米管体系进行了分析对比。发现在有金属铜内嵌的情况下,溅射原子产额与无金属内嵌情况差别不大,但配位数缺陷和PST缺陷减小。表明内嵌金属起到支撑的效果,降低多壁碳纳米管在辐照下的形变,增强了其自修复能力,从而使得辐照耐受性能有所增强。     

Molecular-dynamics simulation of threshold displacement energies in zircon

Molecular-dynamics simulations were used to examine the displacement threshold energy (E_d) surface for Zr, Si and O in zircon using two different interatomic potentials. For each sublattice, the simulation was repeated from different initial conditions to estimate the uncertainty in the calculated value of E_d. The displacement threshold energies vary considerably with crystallographic direction and sublattice. Based on the present simulations and previous experimental studies, this work recommends E_d values of 75, 75 and 60 eV for Zr, Si and O, respectively, to be used in Monte Carlo simulations of irradiation damage profile in zircon.     

Dynamic studies of defect mobility using high voltage electron microscopy

The large variety of observed defect-structure development by electron irradiation in fcc and bcc metals is classified from the view point of point-defect mobilities. Vacancy mobility is obtained from the defect structure change caused by the annihilation of vacancies accumulated by irradiation, and their motion activation energy is obtained from the interstitial cluster growth at high temperatures. Mobility of interstitial atoms and their interaction with impurities are obtained from the variation of interstitial cluster formation. Various observed effects of electron radiation induced motion of point defects are explained by the displacement of atoms by the transfer of energy comparable with the migration activation energy of each point defect. The observed superficial temperature dependence of the induced diffusion of vacancies in fcc metals is attributed to divacancies created by the induced diffusion. An efficient method to obtain the self-diffusion energies is proposed with results for some metals.     

Re-evaluation of neutron displacement cross sections for silicon carbide by a Monte Carlo approach

Neutron displacement cross sections for SiC are re-evaluated by a Monte Carlo approach, with damage energies of primary recoils calculated by the stopping and range of ions in matter (SRIM) code. The validity of the Monte Carlo model is examined by the case of iron, and the results show good agreement with the reference values. Neutron displacement cross sections for SiC at energies up to 100 MeV are calculated, and averaged over the neutron spectra of a fusion DEMO reactor, the high flux test module of the International Fusion Materials Irradiation Facility, and typical fission test reactors. Gas production is also calculated for those neutron irradiation facilities. Finally, the suitability of the displacement cross sections is discussed. The results on comparison among neutron irradiation of different facilities by the current displacement cross sections are similar to those by results of the previous work. Moreover, since neutron displacement cross sections in this study are calculated with damage energies of primary recoils calculated by SRIM, neutron damage evaluated by our displacement cross sections is suitable for correlation with damage by heavy ions calculated by SRIM.     

Molecular dynamics simulation of displacement cascades in Ni-Mo alloy

Molecular dynamics method is used to investigate the displacement cascades in Ni-Mo binary alloy. Effects of the irradiation temperature, energy of the primary knock-on atoms and concentration of solute Mo atoms are taken into consideration on radiation damage to the Ni-Mo alloy. It is found that Mo atoms reduce production of the Frenkel pairs at 100 K, while they enhance defect production at 300 K and 600 K. Size of the largest defect clusters decreases with increasing concentrations of Mo atoms(C_(Mo)) at 100 K, but it increases with CMo at 300 K and 600 K. Most of the point defects get clustered in cascades leaving only a few vacancies and interstitials isolated.     

碳化硅结势垒肖特基二极管的质子辐射效应

碳化硅结势垒肖特基二极管(SiC JBS)是新一代航天器电推进系统的关键部件,但高能粒子辐射严重威胁其可靠性与稳定性。为揭示其辐射损伤机理,为其抗辐射加固设计与考核评估储备数据,本研究基于加速器开展了先进商用SiC JBS 10~20 MeV中能质子地面辐照实验,并提取器件辐照前后的正向伏安特性、反向伏安特性、电容电压等电学参数及缺陷特性。系统分析器件关键特性随辐照条件的改变规律。结果显示,质子辐照引起了器件肖特基势垒升高、载流子浓度降低,且10 MeV较低能质子导致的位移损伤退化更严重。分析认为,PN结界面缺陷导致高性能商用SiC JBS反向电学性能对中能质子的辐照更加敏感,正向特性相对稳定,辐照生碳缺陷造成载流子去除效应是引起SiC JBS性能退化的主要机制。     

Combined computational and experimental study of Ar beam induced defect formation in graphite

Irradiation of graphite, commonly used in nuclear power plants, is known to produce structural damage. Here, experimental and computational methods are used to study defect formation in graphite during Ar irradiation at incident energies of 50 eV. The experimental samples are analyzed with scanning tunneling microscopy to quantify the size distribution of the defects that form. The computational approach is classical molecular dynamic simulations that illustrate the mechanisms by which the defects are produced. The results indicate that defects in graphite grow in concentrated areas and are nucleated by the presence of existing defects.     

Production of defects in hexagonal boron nitride monolayer under ion irradiation

Atomistic computer simulations based on analytical potentials are employed to investigate the response of a hexagonal boron nitride monolayer to irradiation with noble gas ions having energies from 35 eV up to 10 MeV. Probabilities for creating different types of defects are calculated as functions of ion energy and incidence angle, along with sputtering yields of boron and nitrogen atoms. The presented results can be used for the optimization of ion processing of single-layer and bulk hexagonal boron nitride samples and for predicting the evolution of the material in radiation hostile environments.