高电荷态离子Arq+入射在金属表面形成靶原子X射线谱

本文报道低能高电荷Ar12+、Ar13+ 、Ar14+离子与金属Mo表面作用过程中Mo原子受激发射X射线和X射线强度随入射能量变化的实验结果.结果表明,低速高电荷离子与金属表面原子相互作用可有效地激发靶原子或靶离子内壳层电子而发射X射线.     

260～520 keV Krq+ (8≤q≤17)离子轰击Al靶产生的可见光辐射

低速高电荷态离子与金属表面相互作用,原子从靶材表面溅射,其中一部分处于激发态的溅射原子通过辐射退激产生可见光。在这一相互作用过程中,低速高电荷态离子从靶材表面捕获一个或多个电子进入其激发态,这些处于激发态的入射离子也会通过辐射退激产生可见光。研究表明,离子在靶材中的核阻止本领与溅射原子产额密切相关。为了更好地理解溅射原子的激发过程,认识低速高电荷态离子与金属相互作用过程中,溅射原子的激发概率与入射离子动能和势能之间的关联,研究了260～520 keV Krq+ (8≤q≤17)离子与Al靶相互作用过程中的可见光发射。给出了520 keV Kr13+ 与Al表面相互作用过程中,发射300～550 nm波长范围的发射光谱。实验结果包括溅射的Al原子在309.0和395.9 nm处的共振跃迁,Al+和Al2+分别在358.3和451.6 nm处的共振跃迁,以及Kr+在430.0,434.1,465.8和486.0 nm处的共振跃迁。还给出了谱线强度比值Y(309.0)/Y(395.9),Y(358.5)/Y(395.9),Y(452.8)/Y(395.9)随入射离子动能和势能的变化。结果表明：谱线强度比值均随入射离子动能的增加而增大,而比值Y(309.0)/Y(395.9)随势能的增加而减小。分析表明,在低速高电荷态离子与Al靶相互作用过程中,动能（电子阻止本领）和势能共同作用导致Al原子的激发,与激发态Al(4s)相比,电子布居较高激发态Al(3d)的概率随着离子电子阻止本领的增加而增大,而随着离子势能增加而减小。在低速高电荷态离子与金属表面相互作用过程中,入射离子在靶材中的核阻止本领影响溅射原子产额,而电子阻止本领与激发概率相关。在这一作用过程中,动能和势能共同决定溅射原子的激发概率,当动能和势能在同一数量级时,动能作用比势能作用小两个量级。     

高电荷态离子Arq+与不同金属靶作用产生的X射线

研究了高电荷态离子Arq+(q=16,17,18)入射金属Be,Al,Ni,Mo,Au靶表面产生的X射线谱.实验结果表明,Ar的Kα-X射线是离子在与固体表面相互作用过程中固体表面之下形成空心原子发射的.电子组态1s2的高电荷态Ar16+离子在金属表面中性化过程中,存在的多电子激发过程使Ar16+的K壳层电子激发产生空穴,级联退激发射Ar的Kα特征X射线.Ar17+离子在金属表面作用过程中产生的X射线谱形与靶材料没有明显的关联,入射离子的Kα-X射线产额与其最初的电子组态有关,靶原子的X射线产额与入射离子的动能有关.     

126Xeq+轰击Al表面产生的原子和离子光谱线

报道了高电荷态离子^126Xe^q (6≤q≤30)入射到固体Al表面产生的200～1000nm波段的发射光谱的实验结果。实验表明,在弱束流(nA量级)高电荷态的情况下,通过入射离子与固体靶的相互作用可有效地产生原子和离子的复杂组态间跃迁所形成的可见光波段的特征谱线,而且当入射离子的电荷剥离数超过一临界值后(对Al,q=26),谱线相对强度突然显著增强。根据经典过垒模型COB(The classic over-barrier model),在入射离子的动能较小(～1keV／u)的条件下．高电荷态离子与表面相互作用过程中电子的俘获或转移起着非常重要的作用,通过提高入射离子的电荷态可增强入射离子俘获电子的能力．显著增强激发粒子的光谱线的强度。     

裸核离子与中性原子碰撞电离过程的理论研究

基于处理裸核离子与中性原子碰撞电离过程的OBKN和ECPSSR理论模型,系统计算了不同裸核离子与中性原子碰撞K壳层电子俘获截面和直接电离截面,并与其它文献已有的理论和实验结果进行了比较.研究结果表明：碰撞能量较低时,电子俘获截面大于直接电离截面,随着碰撞能量的增加,电子俘获截面和直接电离截面均是先增大后减小且直接电离截面减小地非常缓慢,高能时,直接电离截面大于电子俘获截面.当入射炮弹离子速度接近0.67倍靶原子K壳层电子速度时,电子俘获截面达到最大值,而当入射炮弹离子速度接近靶原子K壳层电子速度时,直接电离截面达到最大值.     

裸核离子与中性原子碰撞电离过程的理论研究

基于处理裸核离子与中性原子碰撞电离过程的OBKN和ECPSSR理论模型,系统计算了不同裸核离子与中性原子碰撞K壳层电子俘获截面和直接电离截面,并与其它文献已有的理论和实验结果进行了比较.研究结果表明:碰撞能量较低时,电子俘获截面大于直接电离截面,随着碰撞能量的增加,电子俘获截面和直接电离截面均是先增大后减小且直接电离截面减小地非常缓慢,高能时,直接电离截面大于电子俘获截面.当入射炮弹离子速度接近0.67倍靶原子K壳层电子速度时,电子俘获截面达到最大值,而当入射炮弹离子速度接近靶原子K壳层电子速度时,直接电离截面达到最大值.     

高电荷态离子入射Al表面库仑势对靶原子特征谱线强度的影响

用同一动能(150keV)而不同电荷态的⁴⁰Ar^q+(8≤q≤16)离子入射金属Al表面,靶原子受激辐射产生特征光谱线. 实验结果表明：高电荷态离子与金属表面相互作用过程中,经过与靶原子碰撞(Penning碰撞)交换动能和共振电子俘获(resonant capture)释放库仑势能,将携带的能量沉积于靶表面,使靶原子激发. 这种激发不同于光激发,它不仅激发了原子复杂电子组态之间的跃迁,而且跃迁辐射的特征谱线强度增强的趋势与入射粒子的库 关键词： 高电荷态离子 库仑势 特征光谱 光谱强度     

高电荷态离子Arq+与不同金属靶作用产生的X射线

研究了高电荷态离子Ar^q+(q=16，17，18)入射金属Be，Al，Ni，Mo，Au靶表面产生的X射线谱.实验结果表明，Ar的Kα-X射线是离子在与固体表面相互作用过程中固体表面之下形成空心原子发射的.电子组态1s²的高电荷态Ar¹⁶⁺离子在金属表面中性化过程中，存在的多电子激发过程使Ar¹⁶⁺的K壳层电子激发产生空穴，级联退激发射Ar的Kα 特征X射线.Ar¹⁷⁺离子在金属表面作用过程中产生的X射线谱形与靶材料没有明显的关联,入射离子的Kα-X射线产额与其最初的电子组态有关，靶原子的X射线产额与入射离子的动能有关. 关键词： 高电荷态离子 空心原子 多电子激发 X射线     

高电荷态离子129Xe28+与Au和Mo表面作用产生的X射线谱

研究了高电荷态离子129Xe28+轰击金属Au和Mo表面产生的特征X射线谱.实验结果表明,在入射离子的电荷态和能量相同的条件下,对于核电荷数较小、原子质量较轻的靶原子,只有其内壳层的电子才能被激发而产生X射线,而核电荷数较大、原子质量较重的靶原子只有其较外壳层的电子能被激发而产生X射线.特征X射线的产额随入射离子动能的增加而增加.     

正负离子碰撞过程中电荷转移的理论研究

文中用渐近方法，采用未微扰的原子波函数，导出了正负离子碰撞过程中，当离子间的距离很大时，入射离子道与出射共价道之间的交换相互作用的解析表达式。利用该相互作用的解析表达式，并考虑在入射通道里Ｈ－离子核外有两个同科电子的情况，由多通道Ｌａｎｄａｕ－Ｚｅｎｅｒ模型分别计算了低能Ｈ＋＋Ｈ－和Ｄ＋＋Ｈ－碰撞过程中的电荷转移总截面。计算结果与已有的实验数据进行了比较。     

Dynamic Potential of Interaction between Nitrogen Atoms and Aluminum Crystal Surface

Specific features of the angular distributions of accelerated neutral nitrogen atoms at the grazing angles of incidence on the Al(001) crystal surface have been investigated by the computer simulation method. The N–Al pair interaction potential is approximated by the three-parameter Morse potential with the energydependent coefficients. The angular distributions of scattered atoms have been simulated taking into account the interaction between atoms and several atomic layers in the lattice and the atomic displacement during thermal oscillations. The parameters of the pair potential of accelerated neutral nitrogen atoms in the energy range from 10 to 70 keV have been determined according to the best agreement between the calculated dependence of the rainbow scattering angle on the energy of particles incident on the crystal surface and the available experimental data.

     

Fast helium nuclei in interactions induced by very heavy nuclei

Fast helium nuclei emitted in interactions between heavy cosmic ray nuclei (12≦Z≦26) and photoemulsion nuclei at energies >1 GeV/nucleon have been studied. Comparisons with interactions where the incident particles are protons, pions or light nuclei reveal some characteristic features of nucleus-nucleus interactions. The frequency of fast target helium nuclei is much larger and the high energy tail of the energy spectrum of these helium nuclei is more pronounced in nucleus-nucleus interactions than in proton-nucleus and pion-nucleus interactions. The number of helium nuclei emitted depends on the size and disintegration of the interacting nuclei. In order to explain our experimental data several possible production mechanisms have to be considered. Some characteristics of the emission of multiply-charged projectile fragments have-also been studied.     

On the low energy limit of reflection and sticking coefficients in atom surface scattering. I. Short range forces

The elastic scattering of atoms and molecules by solid surfaces is treated in a nonperturbative way using the single particle Green's function of the scattered particles. For sufficiently short ranged interactions the elastic reflection coefficient is found to approach unity in the limit of zero energy of the incident particles. Unitarity then implies zero total reaction coefficient including the sticking coefficient. The findings of the first order distorted wave Born approximation are thus generalized. The result is not in contradiction to the experimental observation of sticking coefficients increasing with decreasing energy, since quantitative approximate calculations show that the limit is reached only at extremely low energies.     

分子动力学模拟H原子与Si的表面相互作用

通过分子动力学模拟了入射能量对H原子与晶Si表面相互作用的影响. 通过模拟数据与实验数据的比较, 得到H原子吸附率随入射量的增加 呈先增加后趋于平衡的趋势. 沉积的H原子在Si表面形成一层氢化非晶硅薄膜, 刻蚀产物(H₂, SiH₂, SiH₃和SiH₄)对H原子吸附率趋于平衡有重要影响, 并且也决定了样品的表面粗糙度. 当入射能量为1 eV时, 样品表面粗糙度最小. 随着入射能量的增加, 氢化非晶硅薄膜中各成分(SiH, SiH₂, SiH₃)的量以及分布均有所变化. 关键词： 分子动力学 吸附率 表面粗糙度 氢化非晶硅薄膜     

Energy deposition,reflection and sputtering in hyperthermal rare-gas→Cu bombardment

Using molecular-dynamics simulation, we study the scattering and penetration of normally incident hyperthermal (5–400 eV) Ne, Ar, and Xe atoms off a Cu crystal. We find that between 80% and 98% of the incident energy is deposited in the solid; the fraction depends primarily on the projectile mass, and — for not too low energies — only slightly on the bombarding energy. At low energy, the major part of the non-deposited energy is carried away by the reflected projectile. At energies above the sputter threshold, an increasingly important contribution of between 2% and 6% of the incident energy is carried away by sputtered particles. These results compare well with experiment. Electronic inelastic losses show only little influence on this behaviour. We demonstrate that the inclusion of a realistic attractive interaction between the projectile and the target atoms influences the energy deposition considerably at energies below around 100 eV.     

Geant4 simulations for sedimentary grains in infinite matrix conditions: The case of alpha dosimetry

Simulations based on the Geant4 toolkit have been performed in order to reproduce the electromagnetic interactions of alpha particles in a spherical grain embedded in an infinite radioactive matrix and to assess several dosimetric parameters; updated alpha attenuation factors have thus been calculated for a clay matrix. Their sensitivity to the chemical composition of both the coating matrix and the grain, as well as to the water content of the matrix, has also been investigated. Finally, differences between the energetic spectrum of the incident alpha particles and the deposited energy spectrum in the grain have been highlighted for fine and coarse grains, and their impact in terms of alpha dosimetry has been discussed.     

Energieverteilungen bei der Festkörperzerstäubung durch Ionenbeschuß

The energy distributions of the neutral particles sputtered from polycrystalline targets of Al, Ti, Ni, Cu and Ag by normally incident Ar⁺-ions in the 1 keV region have been determined for ejection energies below 20 eV in a direction close to the normal to the target surface. The experimental method employed is strongly connected to the characteristic properties of a low pressure electrodeless hf plasma used as an effective ion source as well as an ionizing medium for the ejected target atoms. The resulting curves always show a maximum at most probable ejection energies between 1 and 5 eV, being approximately half of the surface binding energy. These curves are converted to the corresponding energy distributions for the recoil atoms within the target by an energy dependent factor. It is found that the energy distribution within the bombarded solid decreases monotonically with the inverse square of the energy of the recoils.     

连续碳纤维增强碳化硅的辐照效应

连续碳纤维增强碳化硅材料除了具有碳化硅材料固有的低中子活化性能,低衰变热性能和低氚渗透性能等优点以外,还具有密度低、线性膨胀系数小、高比强度、高比模量、耐高温、抗氧化、抗蠕变、抗热震、耐化学腐蚀、耐盐雾、优良的电磁波吸收特性等一系列优异性能,是各类核工程重要的潜在候选材料。在核聚变工程应用领域,连续碳纤维增强碳化硅材料作为第一壁材料不可避免地会受到各种辐射粒子的影响。研究清楚这些辐射粒子对它的辐照效应对其在核工程领域的安全使用至关重要。采用蒙特卡罗方法与分子动力学方法进行模拟计算,研究了氕、氘、氚和氦四种粒子对连续碳纤维增强碳化硅的辐照效应。SRIM和LAMMPS计算结果表明:当入射原子能量为100 eV,连续碳纤维增强碳化硅中碳的浓度在80%~85%时,氕、氘、氚和氦原子的溅射率存在最小值;入射粒子的种类对溅射率的影响显著,氦原子的溅射率大于氘原子和氚原子,而氘原子和氚原子的溅射率相差不大但均显著大于氕原子;溅射率随入射能量的增加先迅速增加后逐渐减小,氕、氘、氚和氦原子入射能量分别在200,400,600和800 eV时存在溅射率最大值;当氦原子入射能量为100 eV时,溅射率随入射角度的增加而逐渐减少。这些结果对连续碳纤维增强碳化硅材料在核工程上的应用具有一定的参考意义。Continuous carbon fiber reinforced silicon carbide material has the low neutron activation, low decay heat performance and tritium permeability, which are inherent performance of silicon carbide materials. It also has other advantages such as low density, small linear expansion coefficient, specific strength and specific modulus, high temperature resistance, oxidation resistance, creep resistance, thermal shock, resistance to chemical corrosion, salt fog resistance, excellent electromagnetic wave absorption properties, etc. It is an important potential candidate material in various field of nuclear engineering. In the field of nuclear fusion engineering applications, continuous carbon fiber reinforced silicon carbide as the first wall material will inevitably be bombarded by a variety of radiation particles. The radiation effect is critical to its safe use in nuclear engineering. The Monte Carlo method and the molecular dynamics method were used to study the radiation effect of protium, deuterium, tritium and helium on continuous carbon fiber reinforced silicon carbide. The SRIM and LAMMPS simulation results show that when the incident energy is 100 eV and the concentration of carbon in the continuous carbon fiber reinforced silicon carbide is about 80% ~ 85%, the sputtering yield of protium, deuterium, tritium and helium atoms have the minimum values. The kind of incident particle has a significant effect on the sputtering yield. The sputtering yield of helium atoms is larger than that of tritium atoms and deuterium atoms. There is not much difference between the sputtering yield of deuterium atoms and tritium atoms, and both the sputtering yield of deuterium atoms and tritium atoms are larger than that of protium atoms. The sputtering yield initially increases rapidly with the increase of the incident energy and then decreases gradually. The incident energy of the protium, deuterium, tritium and helium atoms has the maximum value of the sputtering yield at 200, 400, 600 and 800 eV, respectively. When the incident energy of helium atoms is 100 eV, the sputtering yield decreases while the increase of the incident angle. These results can provide a certain reference for the application of continuous carbon fiber reinforced silicon carbide materials in nuclear engineering.     

Interactions of incident H atoms with metal surfaces

Atomic hydrogen is a highly reactive species of interest because of its role in a wide range of applications and technologies. Knowledge about the interactions of incident H atoms on metal surfaces is important for our understanding of many processes such as those occurring in plasma-enhanced catalysis and nuclear fusion in tokamak reactors. Herein we review some of the numerous experimental surface science studies that have focused on the interactions of H atoms that are incident on low-Miller index metal single-crystal surfaces. We briefly summarize the different incident H atom reaction mechanisms and several of the available methods to create H atoms in UHV environments before addressing the key thermodynamic and kinetic data available on metal and modified metal surfaces. Generally, H atoms are very reactive and exhibit high sticking coefficients even on metals where H₂ molecules do not dissociate under UHV conditions. This reactivity is often reduced by adsorbates on the surface, which also create new reaction pathways. Abstraction of surface-bound D(H) adatoms by incident H(D) atoms often occurs by an Eley-Rideal mechanism, while a hot atom mechanism produces structural effects in the abstraction rates and forms homonuclear products. Additionally, incident H atoms can often induce surface reconstructions and populate subsurface and bulk absorption sites. The absorbed H atoms recombine to desorb H₂ at lower temperature and can also exhibit higher subsequent reactivity with adsorbates than surface-bound H adatoms. Incident H atoms, either directly or via sorbed hydrogen species, hydrogenate adsorbed hydrocarbons, sulfur, alkali metals, oxygen, halogens, and other adatoms and small molecules. Thus, H atoms from the gas phase incident on surfaces and adsorbed layers create new reaction channels and products beyond those found from interactions of H₂ molecules. Detailed aspects of the dynamics and energy transfer associated with these interactions and the important applications of hydrogen in plasma processing of semiconductors are beyond the scope of this review.     

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利用分子动力学方法模拟了碳原子与碳氢薄膜的作用过程。探讨了不同入射能量对碳原子与碳氢薄膜相互作用的影响。模拟结果表明碳原子与碳氢薄膜作用会在表面形成碳薄膜。随着入射能量的增加,碳薄膜厚度变薄。在碳薄膜中碳原子的成键形式主要为Csp2-Csp2和Csp2-Csp3,随入射能量的增加,碳原子键价结合形式从Csp2-Csp2向Csp2-Csp3转化。