C60与吸氢金刚石(111)表面碰撞崐的模拟研究

用分子动力学方法研究了Ｃ６０与吸氢的金刚石（１１１）表面碰撞特性与注入能量的大系。原子间的相互作用采用半经验的Ｂｒｅｎｎｅｒ多体势函数。结果表明，当入射能量小于２００ｅＶ时，Ｃ６０只是完整地从表面反弹；当入射能量为２００－３００ｅＶ时，Ｃ６０可与底靶发生化学反应；当注入能量＞３００ｅＶ时，Ｃ６０可与表面形成多个化学键而吸附在衬底表面。此外，计算机模拟计算还给出了Ｃ６０－金刚石表面碰撞的微观过程，并从原子层次研究了Ｃ６０表面沉积的成键机制。     

Trapping coefficients of energetic hydrogen (0.3–8 keV) in Ti at high doses

The trapping coefficient for hydrogen in Ti has been measured in the energy range from 300 eV to 8 keV and was compared with the trapping coefficient of Zr. In accordance with theory the trapping coefficient for Ti is higher than for Zr in the investigated energy range. The values for both materials fairly agree with computer calculations. Deviation has been found for Ti below 1 keV and for Zr below 1.5 keV. Room temperature irradiation produced swelling in the Ti target, most probably due to hydride formation.     

Ab initio study of hydrogen diffusion in zirconium oxide

Hydrogen diffusion in monoclinic and tetragonal zirconium oxides has been studied by electronic state calculations. In both structures, the optimized hydrogen site lies near the center of a distorted fluorite structure. The activation energy was calculated to be 120–200 kJ/mol, which is similar to experimentally measured values. The effects of compressive stress, alloying elements, and oxygen defects are considered individually. Compressive stress reduces the hydrogen diffusion coefficient by 40%/GPa. Oxygen defects and substituted Fe and Cr are thought to act as trapping sites for hydrogen, which probably reduces hydrogen diffusion in zirconium oxide.     

Isotope exchange reaction between tritiated water and hydrogen on SiC

SiC has been considered as a primary candidate material for a first wall component in future fusion reactor because it has been claimed that SiC has excellent high-temperature properties, good chemical stability and low activation. However, the behavior of tritium on SiC has not been discussed yet. In this study, tritium trapping capacity on the surface of SiC was experimentally obtained at the temperature range of 25-800 °C in consideration of tritium trapping to the experimental system. The capacity, which was independent of the water vapor pressure in the gas phase and the temperature, was determined as about 10⁶ Bq/cm². The isotope exchange reaction rate between tritiated water in a gas phase and hydrogen on the surface was quantified at the temperature of 25, 500 and 700 °C in consideration of the behavior of tritium trapping at change of experimental condition by the numerical curve fitting method applying the serial reactor model. The reaction rate was observed to be constant as 3.48 × 10⁻⁵ m/s. Additionally tritium release behavior from the surface of SiC in water vapor atmosphere was predicted and compared with that for graphite and stainless steel.     

Trapping of energetic hydrogen ions in reactive metals

A model is proposed to describe the trapping of a beam of energetic ions of hydrogen isotopes by targets of reactive metals in which the incident ions dissolve exothermically. The model considers the ions free to diffuse inside the metal, and to escape from the surface at a rate determined from the known solubility data.It has been shown that in the case of semi-infinite geometry the trapping efficiency can be expressed in analytic form as a function of dose. However, in the two dimensional case appropriate for beam experiments, radial diffusion becomes important and a numerical solution has been found to be necessary. The model has been compared with experimental results on the trapping of 18 keV deuterons by targets of Nb, Zr, Ti and Pd in the temperature range 230–1000 K and in general good agreement has been obtained.     

Proton microbeam investigations on electrical properties of natural and CVD diamond

A proton microbeam has been used to obtain charge collection efficiency maps on cross sections of natural IIa diamond and CVD diamond samples with a sandwich arrangement of electrodes. Particular attention has been dedicated to the dependence of the collection efficiency profiles on bias polarity. Collection efficiency maps may be easily transformed into collection length profiles, giving information about the distribution of mobility and lifetime of carriers and the profile of the electric field.

Maps of the proton-induced luminescence have also been obtained. The results confirm the columnar distribution of the charge collection length in CVD diamond, while in natural diamond the distribution is relatively homogeneous.     

Confinement of motion of interstitial clusters and dislocation loops in BCC Fe-Cr alloys

This work is devoted to the study of the effect of Cr solutes on the mobility of self interstitial atom (SIA) clusters and small interstitial dislocation loops (of size up to a few nanometers) in concentrated Fe-Cr alloys. Atomistic simulations have been performed to characterize the variation of the free energy of interstitial loops in the Fe-15Cr alloy using the experimentally determined profile of Cr distribution along the path of a loop. It is shown that the presence of randomly distributed Cr in Fe leads to the creation of local trapping configurations for small SIA clusters. The strength (trapping energy) and density of these configurations depend on the Cr content. On the contrary, large SIA clusters (which can be described as 1/2〈1 1 1〉 dislocation loops) are strongly affected by the presence Cr-Cr pairs and larger Cr clusters, which act as barriers to their motion.     

Helium desorption in He implanted tungsten at low fluence and low energy

The behaviour of helium in polycrystalline ³He implanted tungsten at low energy (60 keV) and low fluence (2 × 10¹³ cm⁻²) has been studied as a function of post-implantation annealing temperature until 1873 K by means of Nuclear Reaction Analysis. Helium desorption has been observed only from ∼1500 K, suggesting a helium trapping at mono-vacancies. Only ∼75% of the implanted helium has been released after the annealing during 1 h at high temperature (1873 K); besides, the desorption rate decreased from 1673 K. The presence of a second type of helium trapping site is likely to explain this strong helium retention.     

Initial damage processes for diamond film exposure to hydrogen plasma

Diamond is considered to be a possible alternative to other carbon based materials as a plasma facing material in nuclear fusion devices due to its high thermal conductivity and resistance to chemical erosion. In this work CVD diamond films were exposed to hydrogen plasma in the MAGnetized Plasma Interaction Experiment (MAGPIE): a linear plasma device at the Australian National University which simulates plasma conditions relevant to nuclear fusion. Various negative sample stage biases of magnitude less than 500 V were applied to control the energies of impinging ions. Characterisation results from SEM, Raman spectroscopy and ERDA are presented. No measureable quantity of hydrogen retention was observed, this is either due to no incorporation of hydrogen into the diamond structure or due to initial incorporation as a hydrocarbon followed by subsequent etching back into the plasma. A model is presented for the initial stages of diamond erosion in fusion relevant hydrogen plasma that involves chemical erosion of non-diamond material from the surface by hydrogen radicals and damage to the subsurface region from energetic hydrogen ions. These results show that the initial damage processes in this plasma regime are comparable to previous studies of the fundamental processes as reported for less extreme plasma such as in the development of diamond films.     

An equilibrium and kinetic study of the liquid sodium-hydrogen reaction and its relevance to sodium-water leak detection in LMFBR systems

A detailed study of the thermodynamic and kinetic properties of the liquid sodium-hydrogen system has been made. The technique employed was to measure the rate of absorption to equilibrium of successive hydrogen additions by a vigorously stirred excess of liquid sodium (< 10 ppm dissolved oxygen) in an isothermal, constant volume, stainless steel (316) reaction vessel in the temperature range 610–677 K. The results have been used to estimate the variation of hydrogen pressure with time for a given, steady, water leak rate into the argon gas blanket above the liquid sodium level in a secondary heat exchanger of an LMFBR, and also to calculate solution rates of hydrogen bubbles (formed from a sodiumwater reaction under the liquid sodium surface) as a function of initial bubble radius.     

Nuclear Analysis of an ITER Blanket Module

ITER blanket system is the reactor’s plasma-facing component, it is mainly devoted to provide the thermal and nuclear shielding of the Vacuum Vessel and external ITER components, being intended also to act as plasma limiter. It consists of 440 individual modules which are located in the inboard, upper and outboard regions of the reactor. In this paper attention has been focused on to a single outboard blanket module located in the equatorial zone, whose nuclear response under irradiation has been investigated following a numerical approach based on the Monte Carlo method and adopting the MCNP5 code. The main features of this blanket module nuclear behaviour have been determined, paying particular attention to energy and spatial distribution of the neutron flux and deposited nuclear power together with the spatial distribution of its volumetric density. Moreover, the neutronic damage of the structural material has also been investigated through the evaluation of displacement per atom and helium and hydrogen production rates. Finally, an activation analysis has been performed with FISPACT inventory code using, as input, the evaluated neutron spectrum to assess the module specific activity and contact dose rate after irradiation under a specific operating scenario.     

Nonequilibrium modeling study on plasma flow features in a low-power nitrogen/hydrogen arcjet thruster

Gasdynamic flow features in an electrothermal arcjet thruster with a mixture of 1:2 nitrogen/ hydrogen as the working gas have been studied by a two-temperature numerical simulation.Seven species and 17 kinetic processes are included in the chemical kinetic model used to represent dissociation,ionization,and the corresponding recombination reactions in this nitrogen/hydrogen mixture system.Based on the gas flow characteristics inside the arcjet nozzle,a new method is introduced to define the edge of the cold boundary layer,which is more convenient to analyze the evolution and development of plasma flow in an arcjet thruster.The results show that the arcjet thruster performance is determined largely by the exchange of energy and momentum between the low-density,high-temperature arc region and the high-density,coolttow region near the nozzle wall.A significant thermal nonequilibrium is found in the cold boundary layer in the expansion portion of the nozzle.The important chemical kinetic processes determining the distribution of hydrogen and nitrogen species in different flow regions are presented.It has been shown that the reaction rate of hydrogen species ionization impacted by electrons is much higher than that of nitrogen species ionization in the center of the constrictor of the arcjet thruster.This indicates that hydrogen species is very important in the conversion of applied electric energy into thermal energy in the constrictor region of the arcjet thruster.     

α-铁中氦缺陷对氢原子的俘获

体心立方结构的金属铁(α-铁)是聚变反应堆重要的候选结构材料,受氢和氦原子的辐照后可能会发生力学性能的退化。了解氢和氦原子在铁中的聚集行为是反应堆聚变材料研究的重点。本文采用密度泛函理论计算了α-铁中HeHn集团的稳定性,揭示了替代位氦缺陷俘获氢原子的过程和机制,结果表明,1个氦原子最多可俘获4个氢原子,被俘获的氢原子占据氦原子周围的八面体间隙位,且氢原子倾向于彼此聚拢。对氢原子俘获能的计算表明,氢原子足量时,HeH4是α-铁中主要的氢氦集团构型,反之则以HeH2为主。     

Present status of energy in Japan and HTTR project

An amount of primary energy supply in Japan is increasing year by year. Much energy such as oil, coal and natural gas is imported so that the self-sufficiency ratio in Japan is only 20% even if including nuclear energy. An amount of energy consumption is also increasing especially in commercial and resident sector and transport sector. As a result, a large amount of greenhouse gas was emitted into the environment. Nuclear energy plays the important role in energy supply in Japan.Japan Atomic Energy Research Institute (JAERI) has been carried out research and development of a hydrogen production system using a high temperature gas cooled reactor (HTGR). The HTTR project aims at the establishment of the HTGR hydrogen production system. Reactor technology of the HTGR, hydrogen production technology with thermochemical water splitting process and system integration technology between the HTGR and a hydrogen production plant are developed in the HTTR project.     

腐蚀疲劳断裂前氢与缺陷相互作用的正电子湮没研究

用正电子湮没谱和加热释氢研究了低合金高强钢人工海水腐蚀疲劳断裂前经若干小时疲劳的样品。实验结果表明,腐蚀疲劳早期阶段产生的位错、空位团以及钢中晶界是氢的捕获位,其捕获氢量随疲劳时间增加。氢与空位相互作用使空位团尺寸增加,数目增多,氢与位错相互作用促使位错增殖且随疲劳时间增加。晶界与氢相互作用能随疲劳时间、晶界捕获氢量增加而降低。碳化物沿晶析出促进了晶界捕获氢。较低的晶界-氢结合能有利于氢沿晶运动,促使预裂缝沿晶发展。     

Three-dimensional elastic recoil detection analysis of hydrogen in materials for use in the Yucca Mountain nuclear waste repository

An original system has been developed capable of performing three-dimensional Energy Recoil Detection Analysis (ERDA) of hydrogen in materials with scanned and finely focused heavy-ion beams. The technique is being used at the Lawrence Livermore National Laborotory Multi-user Tandem Laboratory to measure the hydrogen content in materials under consideration for use in the Yucca Mountain nuclear waste repository. From the measurement of hydrogen concentration profiles we can extrapolate reaction rates. A critical problem is the rate of dissolution of the glass being used. The HI-ERDA (Heavy Ion-ERDA) technique can provide this information which is needed in order to predict the overall rate of nuclear waste glass degradation in a waste repository. The technique is calibrated using a silicon wafer implanted with a known concentration of hydrogen. The sample is illuminated by a ³⁵Cl ion beam that is micro-scanned across the sample. From these measurements we reconstruct three dimensional profiles of hydrogen content which can then be used to obtain spatially-resolved hydrogen depth profiles.     

Microwave Plasma Chemical Vapor Deposition of Diamond Films on Silicon From Ethanol and Hydrogen

Diamond films with very smooth surface and good optical quality have been deposited onto silicon substrate using microwave plasma chemical vapor deposition(MPCVD)from a gas mixture of ethanol and hydrogen at a low substrate temperature of 450℃.The effects of the substrate temperature on the diamond nucleation and the morphology of the diamond film have been investigated and observed with scanning electron microscopy(SEM).The microstructure and the phase of the film have been characterized using Raman spectroscopy and X-ray diffraction(XRD).The diamond nucleation density significantly decreases with the increasing of the substrate temperature.There are only sparse nuclei when the substrate temperature is higher than 800℃ although the ethanol concentration in hydrogen is very high.That the characteristic diamond peak in the Raman spectrum of a diamond film prepared at a low substrate temperature of 450℃ extends into broadban indicates that the film is of nanophase.No graphite peak appeared in the XRD pattern confirms that the film is mainly composed of SP^3 carbon.The diamond peak in the XRD pattern also broadens due to the nanocrystalline of the film.     

First-principles study of hydrogen in perfect tungsten crystal

Tungsten-based materials are used as the first wall materials in ITER. Hydrogen impurities were introduced via bombarding with the reaction plasma, which are important for the behavior and stability of the tungsten wall. Using the first-principles density functional theory and planewave pseudopotential technique, we have simulated the behaviors of hydrogen atoms inside the perfect tungsten bcc lattice. The binding energies for different interstitial sites were compared to determine the optimal trapping site for the hydrogen atom inside the tungsten lattice. The diffusion barriers for hydrogen atom between nearby trapping sites and the interaction between two interstitial hydrogen atoms were also calculated. The implication of our theoretical results on the hydrogen diffusion and accumulation behavior was discussed.     

Interaction of hydrogen isotopes with metals: Deuterium trapped at lattice defects in palladium

From an interplay between theory based on the effective-medium scheme and experiments, an extremely simple picture has evolved which is capable of describing a vast number of experimental quantities related to interaction of hydrogen with metals, especially the trapping of hydrogen at defects. It is shown that the trap strengths are determined mainly by the interstitial electron density, and any open structures in the lattice leads to a trap, with the vacancies and voids being the strongest traps. It is also found theoretically and experimentally that up to six hydrogen atoms can be accomodated in a vacancy, and the change in trap strengths with occupancy has been determined. Recent results for the trapping of deuterium to defects in Pd are discussed.     

Investigation on the Priming effect of a CVD diamond microdosimeter

CVD Diamond microdosimeter is an ideal substitute of common Si,GaAs detector for extremely strong radiation experimental environment due to its high band gap energy,fast charge collection,low dielectric constant and hardness.In order to improve its character,a CVD diamond microdosimeter was irradiated by a proton dose of 46 Gy,and a lateral micro-ion beam induced charge (IBIC)technique was utilized to characterize it in low beam current(-fA),It was clearly shown that charge collection efficinecy and energy resolution were greatly improved after proton irradiation of that dose.Moreover,the homogeneities of both its counting performance and collection efficiency were enhanced.Proton irradiation of 46Gy has been proved to be an effective way to prime a CVD diamond.