Irradiation of U3Si-based compounds in the high-voltage electron microscope

U₃Si and U-3.5 wt% Si-1.5 wt% Al have been irradiated in a high-voltage electron microscope (HVEM) at 500–1180 keV and 300–660 K. The creation of ‘black spot’ damage and removal of deformation twins are observed. Defects about 10 nm diameter averaging 4 × 10²¹ m^?3 are seen only in samples pre-injected with 10^?5 atomic fraction argon and are tentatively identified as voids. The atomic displacement rate during HVEM irradiation of U₃Si-based compounds is about two orders of magnitude higher than that for fuel at power reactor ratings. It is inferred that displacement of silicon, and possible uranium, atoms in U₃Si-based compounds occurred in the HVEM at accelerating voltages in the range 700–1180keV.     

Void-swelling in solution-treated FV548 steel irradiated in a high-voltage electron microscope

A study has been made of void formation and growth in 1150°C solution-treated FV548 steel irradiated with 1 MeV electrons in the Harwell AEI EM7 high-voltage microscope (HVM). Voids are observed to form in the temperature range 200–650°C and measurements have been made of the void numbers and sizes and associated swelling as a function of temperature. Over most of the temperature range the void numbers increase rapidly to a maximum value while the voids grow continuously throughout irradiation. A particularly interesting feature of the results is that the variation in void numbers with irradiation temperature is slight up to 550°C and then the numbers decrease markedly at higher temperatures. The associated swelling increases linearly with dose and the swelling rate is a function of temperature.The present results are compared and contrasted with those from other simulation experiments on stainless steels. The most prominent distinguishing features in terms of the influence exerted by gas and by the damage process occurring during irradiation on void nucleation and growth are identified and discussed.     

A study of electron irradiation damage in Zirconium using a high voltage electron microscope

Electron irradiation damage at 1 MeV has been studied in zircomium and Zircaloy-2, in the temperature range 315 to 725 K, using a high voltage microscope. At low doses, the damage takes the form of perfect prismatic dislocation loops of interstitial character, with Burgers vectors of the type $\text{1}\text{3}\text{a<11}\text{2}\text{?}\text{0>}$. The loops form in bands parallel to the trace of the basal plane, by a process of preferred nucleation. A significant proportion of the loops appear to nucleate on {112?0} planes in a pure edge configuration and reorient during growth to reduce their energy. Continued irradiation causes loop growth and interactions, resulting in the formation of a dislocation network. The results are compared with data from neutron- and ion-irradiation studies.     

Irradiation damage in reaction-bonded silicon carbide

Reaction-bonded SiC loses nearly 50% of its fracture strength when exposed to neutron irradiation. Young's modulus also decreases rapidly. The damage occurs soon after exposure and levels out with continuing exposure up to $\text{3 × 10}{}^{21}\text{n/cm}{}^2$. Both α- and β-SiC undergo a nearly Isotropic expansion that saturates with increasing irradiation. Silicon undergoes a very small expansion and mechanical property degradation. The strength reduction in SiC is explained in terms of differential lattice expansions between SiC and Si which result in misfit strains and subsequent crack growth and critical flaw size extension.     

High-precision high-voltage detuning system for HIAF-SRing electron target

The development of a detuning system for the precision control of electron energy is a major challenge when electron targets are used in ion-storage rings.Thus,a high-precision,high-voltage,detuning system was developed for the electron target of a high-intensity heavy-ion accelerator facility-spectrometer ring (HIAF-SRing) to produce accurate electron–ion relative energies during experiments.The system consists of auxiliary,and high-voltage detuning power supplies.The front stage of the auxilia...     

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.     

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.     

Irradiation damage in proton irradiated palladium-iron solid solutions

Transmission electron microscopy was used to investigate the irradiation damage, in particular irradiation induced precipitation (IIP), in Pd-base alloys containing 2, 8, 12 and 18 at % Fe. The specimens were irradiated mainly using 400 keV protons at a current density of 0.16 μA/mm² over the temperature range 110 to 750°C. A few samples containing 2 and 8% Fe were also irradiated using 3 MeV NiP⁺ ions. The irradiation microstructure of the proton irradiated alloys consists of dislocation loops over the temperature range 110 to 550°C and voids up to 650°C in all the alloys. IIP of Pd₃Fe was observed only in the Pd-18% Fe alloy between 110 and 500°C, irradiated to a dose of 0.9 dpa. Pd₃Fe was associated with dislocation loops, voids and grain boundaries. IIP was not observed in the Pd-2,8 and 12% Fe alloys proton irradiated to the same dose, nor to a higher dose of 1.5 dpa. It was also not observed in the 2 and 8% Fe alloys irradiated at 600 and 700°C by 3 MeV Ni⁺ ions.The absence of IIP in the more dilute alloys is attributed to the fast back diffusion of Fe atoms, which is due to the high mobility of vacancies in these alloys. This causes the Fe concentration at the sinks to remain below the solubility limit. Therefore, even though Fe is an undersized solute, the size effect alone is not sufficient for the production of IIP at point defect sinks in most Pd-Fe alloys. It is proposed that IIP can occur only when the alloy concentration is high enough to minimize the rate of back diffusion, which depends not only on the vacancy mobility but also on the concentration gradient near point defect sinks.     

The temperature dependence of nickel-ion damage in nickel

The temperature dependence of void and dislocation structures was studied in high-purity nickel irradiated with 2.8 MeV ⁵⁸Ni⁺ ions to a displacement density of 13 displacements per atom (dpa) at a displacement rate of $\text{7 × 10}{}^{\mathrm{?2}}\text{dpa/sec}$ over the temperature range 325 to 625°C. Dislocation loops, with no significant concentrations of voids, were observed in specimens irradiated at 475°C and below. Specimens irradiated between 525 and 725°C contained both voids and dislocations. The maximum swelling was measured as 1.2% at 625°C. Analysis of the data by theoretical models for void nucleation and growth indicated that the swelling in the present experiment was principally limited by void growth at low temperatures and by void nucleation at high temperatures. The data were also compared with previously reported neutron and nickel-ion irradiation results.     

Performance of the SIRAD ion electron emission microscope

An axial ion electron emission microscope (IEEM) is now working at the SIRAD irradiation facility of the INFN Laboratories of Legnaro (Italy). The IEEM is used to precisely reconstruct the impact points of single ions, information that may be used to determine the areas of a microelectronic device under test that are sensitive to single event effects (SEE). After describing the setup briefly reviewing its working principles, we show our first time resolved ion induced electron emission images of standard calibration targets. We also discuss a preliminary measurement of ion impact detection efficiency of the IEEM system and the available trigger signals for SEE studies. We finally make an assessment of ion electron emission microscopy at SIRAD and indicate future developments.     

Irradiation damage studies of high power accelerator materials

High-performance production targets and other critical accelerator components intercepting intense, energetic proton beams are essential as the accelerator community envisions the next generation, multi-MW accelerators. Materials that have served the nuclear sector well may not be suitable to play such a role which demands that the material comprising the beam-intercepting element must, in addition to the long exposure which leads to accumulated irradiation damage, also endure short exposure that manifests itself as thermo-mechanical shock. The ability of materials to resist irradiation-induced degradation of its properties that control shock and fatigue is of primary interest. The need for such materials that extend beyond resistance to the neutron-driven irradiation damage of reactor components has led to an extensive search and experimentation with new alloys and composites. These new high-performance materials, which appear to possess the right combination of mechanical and physical properties, are explored through a multi-phased experimental study at Brookhaven National Laboratory (BNL). This study, which brings together the interest in accelerator targets of different facilities around the world, seeks to simulate conditions of both short and long exposure to proton beams to assess the survivability potential of these new alloys and composite materials. While thermo-mechanical shock effects have been studied in the early stages of this comprehensive effort, it is irradiation damage that is currently the focus of the study and results to-date are presented in this paper along with the status and objectives of on-going studies. Of special interest are results depicting damage reversal through post-irradiation annealing in some of the materials. High fluences of 200 and/or 117 MeV protons provided by the BNL Linac beam that serves the Isotope Production Facility were used to assess irradiation damage in these new composites and alloys.     

Internal friction and electron microscope studies of strain-ageing in zirconium

Internal friction experiments and transmission electron microscopy have been used to throw further light on the mechanism of strain-ageing which occurs at about 300 °C in zirconium and zirconium-oxygen alloys. Internal friction specimens which have been heat-treated and deformed in a manner which leads to a discontinuous yield point in a tensile test show only logarithmic damping and the implication is that under these conditions the dislocations are strongly pinned. On the other hand in internal friction specimens treated in such a way that discontinuous yielding is not observed a transition from logarithmic to non-logarithmic damping takes place.     

Dose-rate dependence of swelling and damage in ion-irradiated nickel

The results of an irradiation experiment using 46 MeV Ni⁶⁺ ions from the Variable-Energy Cyclotron facility in Harwell are presented. The dose rate was varied, at a constant total dose, by a factor of 20 and the damage produced examined in the peak region of damage and at smaller depths. The temperature range 450–700°C was investigated. It was found that the temperature dependence of swelling varies with both the dose rate and the dose.     

大功率电子束轰击炉高压PWM电源的研制

介绍高压PWM-BUCK DC/DC变换器的工作原理,分析其工作特点,给出了应用于大功率轰击炉加速电源工程实践的技术路线.运行结果证明,高压PWM电源较之晶闸管移相调压控制的高压电源,具有输入电流谐波小、功率因素高及运行效率高等优点.     

Comparison of secondary electron emission in helium ion microscope with gallium ion and electron microscopes

To evaluate secondary electron (SE) image characteristics in helium ion microscope, Si surfaces with a rod and step structures is scanned by 30 keV He and Ga ion beams and 1 keV electron beam. The topographic sensitivity of He ions is in principle higher than that for scanning electron microscope (SEM) because of the stronger dependency of SE yield versus incident angle for He ions. As shrinking to sub nm patterns, the pseudo-images constructed from line profile of SE intensity by the electron beam lose their sharpness, however, the images for the He and Ga ion beams keep clearness due to darkening the bottom corners of the pattern. Here, the sputter erosion for Ga ions must be considered. Furthermore, trajectories of emitted SEs are simulated for a rectangular Al surface scanned by the beams to study voltage contrast, where positive and negative voltages are applied to the small area of the sample. Both less high energy component in the energy distribution of SEs and dominant contribution of direct SE excitation by a projectile He ion keep a high voltage contrast down to a sub nm sized area positively biased against the zero-potential surroundings.     

Void swelling of an oxide dispersion strengthened ferritic alloy in a high voltage electron microscope

An oxide dispersion strengthened ferritic alloy with nominal composition Fe-13Cr-3.5Ti-1.5Mo-2TiO₂ and a cast alloy with a composition close to that of the matrix of the oxide dispersion strengthened alloy are irradiated in a high voltage electron microscope in the temperature range 380–550°C. The alloys are doped with 0–30 ppm helium. For alloys containing 10 ppm He a peak swelling temperature at 450°C is found. A maximum swelling of 1.1% is found at an irradiation dose of 20 dpa. In the absence of He no swelling is found in the temperature range 430–470°C. The swelling rate is highest at the onset of swelling. The results obtained here are quite similar to those for some ferritic steels such as FV607, EM 12 and HT9, except for the influence of He and for the dose dependence.