用正电子湮没寿命谱研究凝聚态甲烷的温度关系

在30—150K温度范围内,测量了高纯凝聚态甲烷中的正电子寿命谱随温度的变化。在固态甲烷中,正电子素(简称Ps)在自由体积中形成,形成率为²7%。正-正电子素(其符号为o-Ps)的寿命随温度变化的特征可用o-Ps在热激活空位型缺陷中的捕获来说明,且由Ps捕获模型和实验测得的o-Ps寿命求得缺陷激活能E_a=0.10±0.02eV。在液态甲烷中,Ps形成率高达36%,且o-Ps寿命长达5—7ns,这表明液态甲烷中形成了Ps气泡态。我们用经验公式估算了这种气泡的尺寸及其微观表面张力。 关键词：     

正电子寿命-动量关联技术

评述了国际正电子领域的新探测技术———寿命 动量关联技术.介绍了该技术的发展过程,讨论了该技术的分析方法,详细阐述了该技术在Ps形成和热化过程中的应用,并讨论了该技术在Ps化学上的应用.A new detection technique--age momentum correlation in international positron field is reviewed. The recent development is described and the analysis methods are discussed for the technique. The application of the technique in the positronium formation and thermalization processes are systematically summarized. Besides the application of the technique in Ps chemistry is discussed.     

电子偶素物理学

电子偶素(positronium),又称正电子素,其符号为Ps,是由电子及其反粒子──正电子组成的准束缚系统.自从 Deutsch[1]在1951年发现Ps以来的三十年间,人们已对Ps的特性及其与物质的相互作用进行了广泛的研究.这不仅加深了人们对Ps本身的了解,也导致了它在原子物理学、化学及固体物理学等领域中获得广泛应用.然而,由于Ps是一个二体、纯轻子的电磁束缚体系,因而是研究量子电动力学的理想对象.特别是近十余年,由于理论和实验两方面的进展,在测量基态Ps的超精细结构和衰变率,以及激发态Ps的探索方面均取得了引人注目的成就.此外,在用Ps研究弱相…     

快放电激励下准分子ArF*和Ar2F*时间谱的研究

本文通过对快放电激励下He/Ar/F₂混合气体中ArF^*,Ar₂F^*时间分辨谱的研究,探讨了准分子ArF^*和Ar₂F^*的形成和猝灭动力学过程。分析表明,ArF^*的时间衰减过程由生成它的主要前态Ar^*的时间变化过程决定,而Ar₂F^*的时间衰减过程则取决于它自己的有效寿命 关键词：     

He2+离子和H2,O2分子碰撞过程中电子俘获和靶激发的发射截面

实验结果表明:在He²⁺和H₂,O₂碰撞过程中存在着双电子俘获而产生激发态的过程,同时也存在着单电子俘获而产生激发态的过程。在靶H₂,O₂直接激发过程中,测量到了巴耳末系H_α,H_β,H_γ和OI的发射谱。本文给出随入射离子速度变化的Hel,Hell和H_α,H_β,H_γ,O 关键词：     

PbCl2分子的光解离

用YAG激光的四次谐波光解离PbCl₂分子。实验确认了这种光解过程是双光子过程。通过对激光诱导荧光的测量,发现这一光解过程造成了Pb原子的亚稳态6p^{2 3}P₂与基态6p^{2 3}P。间的粒子数反分布。同时观察到基于6p^{2 3}P₂能级的受激共振辐射及受激喇曼散射。 关键词：     

改进的反Stokes能量传递对ErP5O14非晶中荧光动力学研究的影响

本文通过建立不同浓度五磷酸盐非晶材料(Er_xLa_1-xP₅O₁₄)动力学过程的速率方程,特别是引入了改进系数exp{hc _k/kT}以区别能量传递Stokes过程和反Stokes过程,分别对Er_0.01La_0.99P₅O₁₄,Er_0.1La_{关键词： 反Stokes能量传递改进系数 动力学过程 五磷酸盐非晶 红外量子剪裁}     

非晶钛酸铋的晶化过程

利用差热分析、X射线衍射和透射电子显微镜等技术对溶胶-凝胶法合成的凝胶的晶化过程进行了分析，实验结果表明，Bi₄Ti₃O₁₂非晶凝胶晶化过程经历了四个过程：首先在433℃先形成了Bi₂O₃和TiO₂亚稳相，然后在488℃时TiO₂亚稳相与Bi₂O₃反应形成Bi，Ti复合氧化物亚稳相Bi₂T 关键词： 钛酸铋 铁电材料 溶胶凝胶 非晶 晶化过程     

Pr3+、Tb3+共掺的NaGdF4和GdB3O6的VUV荧光性质

分别制备了单掺和双掺Pr³⁺和Tb³⁺的NaGdF₄和GdB₃O₆等材料,研究了其真空紫外荧光性质。发现在VUV光的激发下,Gd³⁺离子在Pr³⁺和Tb³⁺的能量传递过程中起着重要的作用。Gd³⁺离子不存在时,Pr³⁺和Tb³⁺之间没有明显的能量传递过程。当体系中加入Gd³⁺离子后,Pr³⁺将大部分能量传递给中间体Gd³⁺,Gd³⁺再将能量传递给Tb³⁺,实现了将Pr³⁺的近紫外光转化为Tb³⁺的绿色光的转换过程。     

BaFCl0.5Br0.5:Sm2+的荧光特性分析

本文是对无机光谱烧孔的典型材料BaFCl_0.5Br_0.5:Sm²⁺的发光动力学过程进行的探索。通过实验得到了⁵D₂、⁵D₁、⁵D₀→⁷F₀的荧光强度、荧光衰减曲线随温度的变化关系,对⁵D₂→4f5d带的热激活、⁵D_J间的无辐射弛豫,⁵D_J→⁷F₀的辐射跃迁等过程进行了分析。     

Two-phase state in Mg3Cd alloy

The kinetics of order-disorder processes in alloys of type Mg₃Cd and MgCd₃ in the single-phase and two-phase regions are investigated by measuring the electrical resistance of the material directly at the temperatures at which tests are carried out. It is shown that in a MgCd₃-type alloy the processes involved in an order-disorder transition proceed much more slowly in the two-phase region than in the single-phase region. The Mg₃Cd alloy, on the other hand, exhibits no such delay effects. The difference in the behavior of the investigated alloys is due to the fact that the lattice distortions accompanying transitions in the two-phase region are greater for MgCd₃ than for Mg₃Cd.     

Farinfrared absorption in Al2O3 and MgO

Far-infrared absorption measurements performed in Al₂O₃ and MgO between 300 and 1 500 K with a Fourier scanning interferometer are reported. A temperature analysis of results based on a phonon self-energy model allows to assign the absorption in this region to 2- and 3-phonon difference processes. The contributions of these processes are separated and discussed. In Al₂O₃, the frequency dependence of the absorption is also analyzed. A good overall agreement between theory and experiment is evidenced.     

Kinetics of energy deactivation in the O2(1Δ)-I medium

The kinetics of energy-exchange and quenching processes in the O₂(¹Δ)-I medium plays an important role in the operation of the chemical oxygen-iodine laser. However, up to now, many of the key processes in this medium are not fully understood. In this work, the flow tube technique is used to determine the rate of excitation energy deactivation in the O₂(¹Δ)-I medium in the presence of small concentrations of water and carbon dioxide. The concentrations of electronically excited species are measured with spectrometers calibrated in absolute spectral responsivity. The effective rate constant for the deactivation of O₂(¹Δ) molecules in processes involving iodine atoms is determined. The results are compared to those obtained in previous works.     

New surface ionization processes

The results of analysis of processes including surface ionization are presented. It is found that these processes do not fit into the classical theory of surface ionization. This concerns the processes with diffusion exchange of particles between the adsorbed layer and the bulk of the emitter, catalytic processes on the emitter surface involving individual centers, as well as processes occurring in the adsorbed layers under illumination, electron bombardment, and in electric fields. We consider the results of analysis of surface ionization of alkali metal atoms and organic molecules on the surface of gold intermetallide (Na _x Au _y ), considerably extending information about this phenomenon.     

Effect of hadronization on the form of correlation moments for instanton processes and possibility of discovering them experimentally

The possibility of discovering QCD instantons in deep-inelastic scattering by analyzing correlations in final states is studied. The correlation moments F _q and H _q for instanton processes are calculated at the parton and at the hadron level. Hadronization is taken into account by the Monte Carlo method. The moments for instanton and for usual processes are found to behave differently, which can be used to identify experimentally instantons.     

Ho2Fe14B化合物的高场磁化过程

基于单离子模型,详细分析了Ho₂Fe₁₄B化合物在T=0K沿[100],[110]和[001]轴磁化时,Ho和Fe次晶格的磁化过程。预测了该化合物在T=0K高达2000 kOe的磁场中沿主晶轴的磁化曲线。 关键词：     

Kinetic and thermodynamic investigation of cBN formation in the system BN-Mg3N2

3 N₂BN system are presented and discussed. In particular, a temperature region slightly above the lower limit of the formation region characterized by fast transformation processes and submicron cBN grains strongly agglomerated is investigated in more detail concerning thermodynamics and kinetics. The catalyst/solvent active in that temperature interval is Mg₃BN₃ previously formed at about 5.5 G Pa and 1170 K in a solid state reaction. The cBN formation proceeds as precipitation from a eutectic melt formed by the intermediate compound and BN. These results are used to improve the previously proposed phase diagram for the Mg₃N₂BN system. The kinetics is discussed based on the usual Avrami theory. It follows that the processes may be described by nearly instantaneous nucleation at the beginning of the reaction with large rate. Growth processes are soon inhibited due to strong impingement of the formed nuclei and grains so that an Avrami exponent n in the neighbourhood of 1 results. This exponent, as well as the rate constant k summarizing the physical mechanisms of nucleation and growth, show a temperature dependence. Received: 6 January 1997/Accepted: 16 May 1997     

Coupled channel analysis of inner-shell vacancy formation in superheavy quasimolecules

We calculate the ionization probability of the quasimolecular 1sσ-state in collisions of very heavy ions with (Z ₁+Z ₂) α?1. Multistep excitation processes between bound and continuum states are investigated. Due to the multistep processes the number of created 1sσ-vacancies is typically increased by a factor 2–5 over that obtained within time-dependent perturbation theory (i.e. the one-step processes). Some implications of the many-electron problem and the Pauli principle are discussed. The δ-electron distribution is compared with recent experimental data.     

The N45N67X Coster-Kronig transitions of gold

An experimental and theoretical study of the N₄₅N₆₇N₆₇ super-Coster-Kronig and the N₄₅N₆₇O Coster-Kronig transitions of gold has been undertaken. The results are analysed within an intermediate coupling framework on the basis of the semi-empirical Auger electron model developed by Larkins. The most significant finding is that the transition probability calculations by McGuire based on an atomic system overestimate the relative importance of the N₄₅N₆₇N₆₇ processes in the solid system. The main de-excitation processes are the N₄₅N₆₇ V transitions involving the conduction band of gold.