用正电子湮没技术研究H/He中性束辐照钨钾合金中缺陷的演化

钾掺杂钨合金是一种典型的弥散强化钨基材料,钾掺入在提高钨材料抗冲击能力的同时,也引入大量缺陷,这些缺陷会对合金在服役过程中氢原子和氦原子的存在形态以及演变产生影响.本文使用正电子湮没谱学方法从微观角度研究辐照后钨钾合金中的缺陷信息,通过对氢氦相关缺陷的正电子湮没参数进行模拟,发现氢原子对正电子寿命的影响比氦原子小,弥散...     

正电子湮没技术在金属和合金研究中的应用进展

评述了正电子没技术（ＰＡＴ）在金属和合金研究中如下几个领域的应用进展：（１）金属间化合物空位形成的焓的测定;（２）淬火、辐照、形变及充氢等引起的缺陷及回复过程;（３）金属和合金的相变;（４）非晶、准晶及纳米晶的研究;（５）ＰＡＴ作为材料无损检测新技术的研究。     

掺杂Na+的KC1色心激光晶体的正电子湮没研究

本文用正电子湮没方法研究了在掺Na⁺条件下,单纯、附色和γ射线辐照的KC1单晶的湮没寿命以及Doppler展宽S参数与掺Na⁺量的关系.结果表明掺Na⁺量为800ppm的KC1单晶空位浓度最小,为4.24×10¹⁷/cm³,它接近于纯KC1晶体的空位浓度.在附色的KC1晶体中存在明显的F心.S参数主要是受卤族阴离子外层电子的影响.此外还掺Na⁺的KC1单晶正电子湮机制进行了讨论.     

Co掺杂纳米ZnO微结构的正电子湮没研究

利用正电子湮没技术研究了10 at.% Co掺杂的Co₃O₄/ZnO纳米复合物中退火对缺陷的影响. 利用X射线衍射(XRD)测量了Co₃O₄/ZnO纳米复合物的结构和晶粒尺寸. 随着退火温度升高,Co₃O₄相逐步消失,ZnO晶粒尺寸也有显著增加. 经过1000 ℃以上退火后,Co₃O₄相完全消失,并出现了CoO的岩盐结构. 正电子湮没寿命测量显示出Co₃O₄ /ZnO纳米复合物中存在大量的Zn空位和空位团. 这些空位缺陷可能存在于纳米复合物的界面区域. 当退火温度达到700 ℃后Zn空位开始恢复,空位团也开始收缩. 900 ℃以上退火后,所有空位缺陷基本消失,正电子寿命接近ZnO完整晶格中的体态寿命值. 符合多普勒展宽谱测量也显示Co₃O₄ /ZnO纳米复合物经过900 ℃以上退火后电子动量分布与单晶ZnO基本一致,表明界面缺陷经过退火后得到消除. 关键词： ZnO 界面缺陷 正电子湮没     

锡,铅掺杂下的Bi—2212超导相的正电子湮没研究

以正电子寿命谱和多普勒展宽谱为主要实验手段，并结合Ｘ射线物相分析和电阻测量，系统地研究了在不同的锡掺杂量下，Ｂｉ－２２１２超导相电子态及结构细节的变化在低掺杂时，Ｓｎ＾４＋优先占据Ｂｉ位，导致了载充子浓度的提高和耦合的加强，有利于超导转变温度的提高。     

用正电子湮没技术研究USY沸石的“二次孔”结构

测量了NaY及USY沸石的正电子寿命谱．得到NaY沸石有四个寿命分量：两个短寿命分量和两个长寿命分量．两个长寿命分量中，τ₃，τ₄分别是o-Ps在β笼和超笼中的湮没．USY沸石有五个寿命分量：两个短寿命分量和三个长寿命分量，三个长寿命分量中，τ₃为o-Ps在笼中的湮没，τ₄，τ₅分别为o-Ps在“二次微孔”和“二次中孔”中的湮没．与NaY沸石相比，在真空中，USY的τ₄增加到 关键词：     

正电子湮没谱和光致发光谱研究掺锌GaSb质子辐照缺陷

用正电子湮没谱和光致发光谱研究了质子辐照后掺锌GaSb中的缺陷.通过分析正电子的缺陷寿命τ₂及强度I₂的变化发现,在高能质子的辐照下产生了双空位缺陷V_GaV_Sb,可能同时产生了小的空位团.正电子平均寿命τ_av和S参数随着质子辐照剂量的变化也证明了这一结论.通过分析不同质子辐照剂量下掺锌GaS     

聚四氟乙烯中正电子湮没寿命谱中等寿命成份湮没过程性质研究

用时间选择谱仪-磁猝灭测量方法并经适当数据处理,研究了聚四氟乙烯高聚物中正电子湮没寿命谱中等成份(～1ns)的湮没过程性质.确定其为自旋三重态正电子素即o-Ps的猝灭.     

正电子湮没技术

 正电子湮没技术（ＰＡＴ）是一项较新的核技术．它是利用正电子与物质的相互作用来获得凝聚态物质的微观结构、电子动量分布及缺陷状态等信息的实验技术．正电子是电子的反粒子,这种粒子首先是狄拉克在１９３０年建立相对论量子力学时预言其存在的．两年以后安德逊（Ａｎｄｅｒｓｏｎ在宇宙射线中发现了它．它是人们发现的第一种反粒子．正电子与电子一样,同属于轻子．正电子和电子作为基本粒子的属性列于表１．从表中可以看出正电子与电子具有相同的静止质量和自旋,所带的电荷和电子的电量相等,不过是正的,因而也具有正的磁矩．但是,正电子和电子之间也有重要的区别．     

形变充氢多晶纯钴中缺陷的正电子湮没研究

用正电子寿命和多普勒线形参数测量技术,研究了形变和形变充氢多晶钴试样的缺陷性质及其回复行为。观察到形变样品阴极充氢后,氢致缺陷为一定量的位错和空位以及少量的空位团。没有观察到微空洞和微裂纹的产生。单空位的回复温度范围为73—260℃,位错和空位团的退火发生在350—670℃温度范围。测得空位的迁移激活能为E_v^m=1.09±0.07eV。 关键词：     

Characterisation of atomic-scale defects in ODS ferritic alloys by positron annihilation

The vacancy-type defects and their local chemical environment in different ODS alloys produced in the USA (14YWT), China (K5) and Russia (ODS EP-450) are studied. The Angular Correlation of Annihilation Radiation (ACAR), which is one of the positron annihilation spectroscopy method, was used. It was shown that in all alloys, except 14YWT, the dominant type of positron traps are vacancy-like defects, localised in matrix or associated with dislocations and/or interfaces of the incoherent particles. In the case of 14YWT alloy, which contains Y–Ti–O nanoclusters of a high density, the positrons confine and annihilate at O-vacancy pairs or complexes within nanoclusters. It is testified by enhanced electron density in annihilation sites and neighbourhood of Ti and Y atoms. These results, obtained by the ACAR method, indicate that the vacancies play an essential role in the formation of nanoclusters in ODS 14YWT alloy as it was theoretical predicted by first-principle calculations.     

Positron annihilation study of the annealing behaviour of alpha induced defects in tungsten

Abstract

Positron lifetime and Doppler broadening measurements have been performed on alpha-irradiated tungsten to study the evolution of defects during isochronal annealing from 100°C to 1050°C. Vacancy-impurity complexes dissociate at the earlier stages and release the vacancies. Monovacancies start migrating at 400°C. The vacancy clusters coarsen to form microvoids in the region from 350°C to 650°C and remain stable upto 750°C. Some of the clusters collapse into vacancy loops. Dislocation/vacancy loops and microvoids start annealing around 750°C. The role of impurities and grain boundaries on the annealing behaviour of the defects is also discussed.     

用正电子研究NaCl在NaY沸石上的固溶过程

用正电子湮没谱学研究NaCl与NaY沸石机械混合后, NaCl在NaY中的固溶扩散过程.分别测量不同质量比的NaCl/NaY［(1—20)%］经500℃烘烤1h，NaCl/NaY(15%)经不同温度烘烤1h,以及NaCl/NaY(15%)经500℃烘烤不同时间后的正电子寿命谱.所有寿命谱都出现了5个寿命分量, 其中第3，4，5寿命分别与β笼、超笼及沸石微粒界面空洞的大小和数量相关.实验表明正电子湮没谱学能敏感地表征NaCl在NaY中的固溶扩散过程. 关键词： 正电子湮没谱学 氯化钠 沸石     

慢正电子束流技术在金属/合金微观缺陷研究中的应用

正电子湮没谱学技术是研究材料微观结构非常有效的一种核谱学分析方法, 主要用于获取材料内部微观结构的分布信息, 特别是微观缺陷结构及其特性等传统表征方法难以获取的微观结构信息. 近年来, 在慢正电子束流技术快速发展的基础上, 正电子湮没谱学技术在薄膜材料表面和界面微观结构的研究中得到了广泛应用. 特别是该技术对空位型缺陷的高灵敏表征能力, 使其在金属/合金材料表面微观缺陷的形成机理、缺陷结构特性及其演化行为等研究方面具有独特的优势. 针对材料内部微观缺陷的形成、演化机理以及缺陷特性的研究, 如缺陷的微观结构、化学环境、电子密度和动量分布等, 正电子湮没谱学测量方法和表征分析技术已经发展成熟. 而能量连续可调的低能正电子束流, 进一步实现了薄膜材料表面微观结构深度分布信息的实验表征. 本文综述了慢正电子束流技术应用研究的最新进展, 主要围绕北京慢正电子束流装置在金属/合金材料微观缺陷的研究中对微观缺陷特性的表征和表面微观缺陷演化行为的应用研究成果展开论述.     

Defect structure studies using positron annihilation spectroscopy

The positron annihilation method is a new addition to the range of sensitive complementary nuclear techniques available for materials’ research. The preferential sensitivity of positrons towards micro-defect domains which are not assessable by other techniques makes it an attractive tool for many materials science problems. The present paper is intended as a brief introduction on the principle of measurements and its potential is exemplified with the help of results on some metallic and ceramic systems.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800(a fast photomultiplier)to form the small size γ-ray detectors,a compact lifetime spectrometer has been built for the positron annihilation experiments.The system time resolution FWHM=193 ps and the coincidence counting rate -8 cps/μCi were achieved.A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested,which is in agreement with the typical values published in the previous lectures.     

Investigation of radiation defects in Fe-Cr alloy

Abstract

The kinetics of radiation defect accumulation and subsequent recovery during/after electron irradiation below 273 K, at 323 K and 373 K were investigated for the Fe-15.7 at.% Cr using positron annihilation measurements at room temperature. Formation of vacancy clusters was observed at all of the irradiation temperatures. The formation of clusters and kinetics of their accumulation point to mobility of vacancies at least at room temperature. The cluster rearrangement and variations in the cluster configuration take place during annealing.     

A compact positron annihilation lifetime spectrometer

Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size γ-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate ～8 cps/μCi were achieved. A lifetime value of 219±1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.     

Effect of vacancy charge state on positron annihilation in silicon

The charge-state-dependent lattice relaxation of mono-vacancy in silicon is studied using the first-principles pseu- dopotential plane-wave method. We observe that the structural relaxation for the first-neighbor atoms of the mono-vacancy is strongly dependent on its charge state. The difference in total electron density between with and without charge states in mono-vacancy and its relevant change due to the localized positron are also examined by means of first-principles simu- lation, demonstrating the strong interplay between positron and electron. Our calculations reveal that the positron lifetime decreases with absolute charge value increasing.