高温超导中多个正电子捕获位及其对正电子湮没参数的影响

从正电子陷阱物理图象出发，引入正电子在陷阱中湮没的竞争机制，提出了一个新的陷阱湮没模型，并采用此模型分析了高温超导材料中正电子在陷阱中湮没的特征。     

Application of positron annihilation line-shape analysis to fatigue damage for nuclear plant materials

Positron annihilation line-shape analysis is sufficiently sensitive to detect microstructural defects such as vacancies and dislocations. We are developing a portable positron annihilation system and applying this technique to fatigue damage in type 316 stainless steel and SA508 low alloy steel. The positron annihilation technique was found to be sensitive in the early fatigue life, i.e. up to 10% of the fatigue life, but showed little sensitivity in later stages of the fatigue life in type 316 stainless steel and SA508 low alloy steel. Type 316 stainless steel a higher positron annihilation sensitivity than that of SA508. It was considered that the amount of dislocation density change in the stainless steel was greater than that in the low alloy steel, because the initial microstructure contained a low dislocation density because of the solution heat treatment for the type 316 stainless steel.     

利用杠杆原理制备用于扫描隧道显微镜的钨针尖

利用杠杆平衡原理,设计了一套扫描隧道显微镜(STM)钨针尖的制备装置.它可以使针尖瞬间脱离液面,避免针尖继续腐蚀而影响针尖质量.同时它以简单的力学结构替代了传统复杂的控制电路.扫描电子显微镜使用结果表明,利用此法制备的钨针尖最小半径为50 nm.利用所制备的针尖对高序石墨进行STM扫描,效果良好,可用于原子级图像的扫描.     

Nuclear microprobe applications in materials science

Since its inception the nuclear microprobe has been used extensively in materials science studies. The ability of the technique to measure elements and isotopes by nuclear reaction analysis (NRA), particle induced X-ray emission (PIXE), Rutherford backscattering (RBS) and elastic recoil analysis (ERA) has proved particularly advantageous. There has been a notable increase in the exploitation of the technique to measure composition multidimensionally. Applications have involved the measurement of changes in the composition of materials during manufacture, fabrication and service, as these can strongly influence their properties. Examples have been drawn from plasma fusion research, the aero-industry, catalysis, power production, wear and the nuclear power industry.     

Characterization of defect accumulation in neutron-irradiated Mo by positron annihilation spectroscopy

Positron annihilation lifetime spectroscopy measurements were performed on neutron-irradiated low carbon arc cast Mo. Irradiation took place in the high flux isotope reactor, Oak Ridge National Laboratory, at a temperature of 80 ± 10 °C. Neutron fluences ranged from 2 × 10²¹ to 8 × 10²⁴ n/m² (E > 0.1 MeV), corresponding to displacement damage levels in the range from 7.2 × 10⁻⁵ to 2.8 × 10⁻¹ displacements per atom (dpa). A high density of submicroscopic cavities was observed in the neutron-irradiated Mo and their size distributions were estimated. Cavities were detected even at a very low-dose of ∼10⁻⁴ dpa. The average size of the cavities did not change significantly with dose, in contrast to neutron-irradiated bcc Fe where cavity sizes increased with increasing dose. It is suggested that the in-cascade vacancy clustering may be significant in neutron-irradiated Mo, as predicted by molecular dynamics simulations.     

正电子湮没寿命谱多指数函数拟合程序分析

本文分析美国乔治亚大学徐孝华教授提供的正电子湮没寿命谱多指数函数拟合程序NFIXED,详细地介绍了其使用方法。在使用中略加改进,对α-Fe样品的正电子湮役寿命谱进行多次计算,将获得的寿命值与通用的寿命值相比较,相差均<10ps。显然,这个程序的计算效果是好的。     

Time-of-flight spectrometry for materials analysis

A time-of-flight spectrometer for investigation of solids has been built. This type of spectrometer can be used for forward- and backward-scattering experiments. The scattered or recoiled ions are discriminated by a pair of C-foils. The emitted secondary electrons are detected by channel plates and are used as start and stop signals. Depth profiles up to 500 nm were measured with a depth resolution of 3 nm. The best mass resolution achieved under optimal conditions is 1 u. For example, the two Ga isotopes from GaAs samples have been separated. He, N, Ne and Ar ions with energies up to 10 MeV have been used as projectiles.     

Graphic-object information system “research base for reactor materials science”

Conclusions An information base for specialists in atomic science and technology is important, since the accumulated experience of development, tests, and investigations is so great and so diverse that it can be used only after a new information technology that makes it possible to assess, in a systematized and generalized form, modern possibilities and to take into account the results of previous investigations and to choose directions for new developments is introduced. The graphic-object system presented in this paper concentrates in a systematized and generalized form the accumulated potential, enables objective comparison of the characteristics of the constituent parts of the methodological and experimental basis, and can be helpful to specialists of different types. Such a system will also be an advertisement for the progress which we have made in our country in nuclear science and technology. Main Scientific Center of the Scientific-Research Institute of Nuclear Reactors. Ministry of Atomic Energy of Russia. All-Union Scientific-Research Institute of Nuclear Power Plants. Translated from Atomnaya énergiya, Vol. 76, No. 5, pp. 383–389, May, 1994.     

A geometric procedure for improved Rutherford backscattering channeling analysis of materials

Solving geometric and sample alignment issues is a major part of multi-axial Rutherford backscattering channeling (RBS-C) analysis of materials, especially involving complicated samples. However, a geometric standard does not exist for RBS-C, which complicates experimental procedures and makes experimental methods and data presentation inconsistent among different experiments. Our approach to solving RBS-C geometric issues, discussed here, is to introduce a geometric adjustment and sample manipulation procedure which defines the orientation and rotation of the sample with respect to a fixed coordinate system. This method makes rotational, alignment and sample manipulation operations involved in RBS-C more flexible and simpler. As a test case, we present multi-axial RBS-C maps of Si obtained via this methodology. Distortions arising in such RBS-C maps due to geometric effects, how they can affect alignment procedure and data extraction, and how our approach treats these issues are discussed.     

时间微分扰动角关联技术在材料科学中的应用

介绍了时间微分扰动角关联方法的基本原理及其在材料微观性质研究中的应用。     

Charging/discharge events in coated spacecraft polymers during electron beam irradiation in a scanning electron microscope

Spacecraft, such as those operating in geosynchronous orbit (GEO), can be subjected to intense irradiation by charged particles, for example high-energy (e.g. 20 keV) electrons. The surfaces of dielectric materials (for example, polymers used as “thermal blankets”) can therefore become potential sites for damaging electrostatic discharge (ESD) pulse events. We simulate these conditions by examining small specimens of three relevant polymers (polyimide, polyester and fluoropolymer), both bare and coated, in a scanning electron microscope (SEM). The coatings examined include commercial indium-tin oxide (ITO), and thin films of SiO₂ and a-Si:H deposited by plasma-enhanced chemical vapor deposition (PECVD). All coatings are found to greatly modify the observed ESD behavior, compared with that of the bare polymer counterparts. These observations are explained in terms of the model for ESD pulses proposed by Frederickson.     

A multi-parameter system for acquisition, monitoring, and analysis of scanning ion microprobe data

The multi-parameter data-acquisition system for the Eindhoven scanning ion microprobe set-up is described. The front-end part of the system is based on an M68030 in VME and handles real-time data acquisition, experiment control and data transport. It is linked to a DEC ALPHA-AXP workstation for data storage, on-line data monitoring and data analysis and off-line data analysis. The system can be used to apply simultaneously the micro-PIXE, NBS and NFS techniques to determine elemental concentration distributions on biomedical samples, but can also be used for coincident ion scattering experiments and time or dose dependent studies of e.g. ion-beam induced radiation damage.     

A variable-energy positron beam for low to medium energy research

A positron beam facility is described which provides a monoenergetic beam (± 1 eV) which is variable in energy from a few eV up to a maximum of ∼ 80 keV. The positron moderation process, beam transport, and design of the target chamber are discussed in detail. Some of the research being done with the facility is summarized, including scattering and energy-loss measurements, near-surface defect profiling studies, and low energy positron channeling studies. An ultrahigh-vacuum 2-axis goniometer is described, which is used in the channeling work.     

慢正电子寿命谱仪电子学系统原型机研制

我们采用低能脉冲调制正电子束技术设计了一套慢正电子寿命谱仪装置.此装置要求其脉冲调制系统能够给出一路边沿<2 ns、宽度≈7 ns、幅度>5 V的50 MHz脉冲信号和两路频率分别为50 MHz、200 MHz的正弦信号,同时要求其时间测量系统能达20 ns的量程和74 ps的测量精度.本文介绍了脉冲调制和时间测量系统原型机设计及各项主要指标的测试.结果表明,电子学系统原型机已达到谱仪系统设计指标要求.     

Effect of surface mechanical finishes on charging ability of electron irradiated PMMA in a scanning electron microscope

Charging of Polymethyl Methacrylate insulators (PMMA), in a scanning electron microscope (SEM) is studied owing to a time resolved current method. This method allows the evolution of trapped charge versus time and the charging time constant to be deduced. The effect of surface roughness change on the ability of PMMA to trapped charge is highlighted. The results show that the trapped charge at the steady state decreases when the roughness increases in the micrometer range while the time constant of charging increases with surface roughness. This behaviour is due to the increase of leakage current and/or enhanced secondary electron emission (SEE). On the one hand, surface mechanical finishes allows, the build up charge in insulators submitted to an electron bombardment to be lowered. On the other hand this treatment allows the secondary electron emission to be raised for some specific applications.