高能电子碰撞电离对高空核爆炸辐射电离的影响

利用数值模拟程序模拟了不同高度核爆炸下距离爆点不同位置处大气的X射线电离及演化过程,分析了高能电子碰撞电离过程对高空核爆炸电离效应的影响.结果表明:高能电子碰撞电离过程对高空核爆炸的电离结果产生了重要影响,在80 km爆高1 kt当量高空核爆炸条件下,在距离爆点1.5 km处高能电子的碰撞电离效应使得电子的峰值数密度提高了约2个数量级;随着时间的增加,高能电子能谱逐渐向低能方向发展,在5μs后高能电子数密度随电子能量近似呈负指数分布;电子峰值时间与爆高有关,随着爆高的增加而增大,电离的影响区域也随着爆高的增加而增大.在80 km爆高1 kt当量情况下电离效应对近百千米范围内的微波通信具有严重影响.     

高空核爆炸瞬发辐射电离效应的数值模拟

采用蒙特卡罗方法模拟了高空核爆炸瞬发辐射中子、γ射线、X射线电离大气的过程,给出了几种爆炸场景下瞬发辐射产生的附加电离电子密度空间分布.针对大气密度随高度非均匀连续变化的特性,采用质量距离抽样方法取代常用的步长抽样方法,无需根据大气密度随高度的变化进行分层处理,提高了计算效率.结果表明:对于不同的爆高,瞬发辐射电离分布存在显著的差异;随着爆高的增加,瞬发辐射附加电离区范围增大,但电子密度的峰值减小. 关键词： 高空核爆炸 瞬发辐射 大气电离 蒙特卡罗方法     

高空核爆炸X射线电离的时空分布数值模拟

利用数值模拟程序模拟了高空核爆炸辐射的X射线对不同高度大气的电离及演化过程,给出了电子的时空分布曲线．结果表明：在80km爆高1kt小当量高空核爆炸情况下,电子数密度随高度只出现一个极大值,而在80kin以上爆高情况下,电子数密度出现两个极大值,一个位于爆点附近,另一个位于90km高度附近,在这个高度电离的影响范围最大;高空核爆炸辐射的X射线在70km高度附近截止,对70km以下高度没有电离影响;随着辐射角度的增加,电子数密度出现第二个极大值的高度有所上升,X射线截止高度也有所上升．     

低空核爆炸在源区产生的电磁脉冲的近似估计

本文推导了在低空核爆炸的条件下,瞬发γ光子在源区中产生的电流和电场的近似解析公式,从这些解析公式给出的计算结果可看出,电场的前沿、陡度、峰值数值和半宽度的大小主要取决于弹体释放的瞬发γ光子的强度和时间特性。     

一维大气等离子体化学过程数值模拟

用数值模拟方法研究了低空及高空环境下，大气等离子体的化学反应及一维扩散过程. 推导了三组分(电子和正负离子)的双极扩散公式，观察了扩散过程中不同组分的空间分离，以及扩散和化学反应对电子数密度演化的贡献. 关键词： 大气等离子体 化学过程 数值模拟     

强激光场中模型氢原子和真实氢原子的高次谐波与电离特性研究

利用数值方法求解含时薛定谔方程，研究了一维、二维模型氢原子和真实的三维氢原子在强激光场中产生的高次谐波和电离特性.结果表明，在多光子电离区域和过垒电离区域，模型氢原子与真实的氢原子产生的高次谐波和电离概率差别很小；在隧道电离区域，它们产生的高次谐波的平台特征和截止位置相似，电离概率随时间变化的趋势相近，但其数值有明显的差异.对产生这种差异的原因进行了分析. 关键词： 强激光场 高次谐波 电离概率     

高空核爆炸注入辐射带电子的大气扩散损失

利用辐射带电子大气倾角扩散的福克-普朗克方程,通过推导与拟合处理扩散系数表征式,构造二阶精度有限差分格式,给出辐射带捕获电子大气扩散损失的数值计算方法.计算高空核爆炸裂变β谱电子注入辐射带后在不同L壳上的通量损失和能谱变化,结果表明,当L < 1.3时,大气作用引起的扩散损失效应明显,低能电子比高能电子消失要快,电子通量初始阶段衰减很快,随后逐渐近似成时间指数函数形式衰减.     

高空核爆炸形成人工辐射带的数值模拟

基于Stmer关于带电粒子在地球磁场中运动的理论模型,分析得出高能电子在地球周围的运动区域.结合高空核爆形成放射性烟云的经验模型,推断高空核爆在地球周围形成人工辐射带的基本区域.进而利用高空核爆裂变特性和辐射带中高能粒子的分布特性,计算得到高空核爆形成人工辐射带的电子密度通量,并对高空核爆激发的人工辐射带特征与核爆炸的爆点纬度、高度及当量之间的关系作了初步的定量分析.数值模拟结果表明,在一定的条件下,0.1—1Mt TNT当量的高空核爆,预计在地球周围可形成电子通量密度比自然辐射带高3—4个量级的人工辐射带.形成的人工辐射带中心位置主要受核爆爆点地磁纬度的影响,核爆的爆高和核爆的当量则对人工辐射带的厚度及其中高能电子的通量密度有一定的影响. 关键词： 高空核爆 人工辐射带 高能电子通量 爆炸当量     

电子碰撞Ga,As, Pt,W和Au原子Lα X射线产生截面的理论计算

利用修改后的MBELL模型,研究了L壳层的相对论效应和离子效应对快电子碰撞电离Lα X射线产生截面的影响.通过在BELL模型中引入相对论效应和离子效应,基于相对论性的L壳层的电子碰撞电离截面的理论,计算了Ga,As,Pt,W和Au的L壳层电子碰撞电离截面,并将其转化成Lα X射线产生截面,计算结果表明考虑到相对论效应和离子效应后,修改后的MBELL的Lα X射线产生截面结果明显优于BELL的计算结果,并和最近的文献实验数值 关键词： 快电子 Lα射线')" href="#">Lα射线 电离截面 相对论效应     

核爆炸和核诊断中的物理问题

核爆炸是剧烈的能量释放过程，在微秒级时间内使装置变成高温高密度等离子体，向周围空气辐射，形成火球等核爆炸效应．目前各国核试验目的在改进核武器设计，都已转入地下进行．核试验中现场实时物理诊断是为了提供核装置反应的实际数据，可以分为：核反应历史诊断（ｒ测量）；核爆炸中温度参数诊断（Ｎ，Ｘ测量）；核反应区空间参数诊断（针孔照相）等．它们是在恶劣环境中进行的单次、快速测量、是特殊类型为核物理实验，所用技术可概括为脉冲射线束测量．     

Multipoint radiation induced ignition of dust explosions: turbulent clustering of particles and increased transparency

Understanding the causes and mechanisms of large explosions, especially dust explosions, is essential for minimising devastating hazards in many industrial processes. It is known that unconfined dust explosions begin as primary (turbulent) deflagrations followed by a devastating secondary explosion. The secondary explosion may propagate with a speed of up to 1000 m/s producing overpressures of over 8–10 atm, which is comparable with overpressures produced in detonation. Since detonation is the only established theory that allows rapid burning producing a high pressure that can be sustained in open areas, the generally accepted view was that the mechanism explaining the high rate of combustion in dust explosions is deflagration-to-detonation transition. In the present work we propose a theoretical substantiation of an alternative mechanism explaining the origin of the secondary explosion producing high speeds of combustion and high overpressures in unconfined dust explosions. We show that the clustering of dust particles in a turbulent flow ahead of the advancing flame front gives rise to a significant increase of the thermal radiation absorption length. This effect ensures that clusters of dust particles are exposed to and heated by radiation from hot combustion products of dust explosions for a sufficiently long time to become multi-point ignition kernels in a large volume ahead of the advancing flame. The ignition times of a fuel–air mixture caused by radiatively heated clusters of particles is considerably reduced compared with the ignition time caused by an isolated particle. Radiation-induced multipoint ignitions of a large volume of fuel–air ahead of the primary flame efficiently increase the total flame area, giving rise to the secondary explosion, which results in the high rates of combustion and overpressures required to account for the observed level of overpressures and damage in unconfined dust explosions, such as for example the 2005 Buncefield explosion and several vapour cloud explosions of severity similar to that of the Buncefield incident.     

高空核爆炸下大气的X射线电离及演化过程数值模拟

利用数值模拟程序模拟了不同高度核爆炸下大气的X射线电离及演化过程.结果表明: X射线电离产生的电子数密度在射线到达后约100 ns时刻达到峰值, 峰值数密度随着到裸核区距离的增加而减小;电子具有较长的寿命, 电子寿命随着到裸核区距离的增加而增大; X射线电离空气产生正离子O⁺, O₂⁺, N₂⁺,爆高为120 km情况下 O⁺的峰值数密度与O₂⁺的相近,能维持约1 s. X射线对空气的电离影响范围在数十千米以内,在距裸核区较近的区域, 爆高为80 km时产生的电子峰值数密度比爆高为120 km时的电子峰值数密度高, 在距裸核区较远的区域则相反.     

Numerical Study on the Whole Process of Fireball Evolution in Strong Explosion *

With the actual mean free path for radiation in air and a simplified nuclear device, a one-dimension simulation research on fireball phenomenon in a sea level atmosphere is carried out based on the multi-group radiation hydrodynamic codes (RDMG). It is shown that our theoretical calculations can describe the whole process of the fireball evolution for strong explosions from the early X-ray expansion stage to the shock wave propagation stage. The radius of the shock wave and the brightness of the fireball are in good agreement with the experimental results. The whole thermal radiation power curve of the fireball evolution for strong atmospheric explosion at sea level is plotted for the first time. The impact of radiation opacity of the nuclear device material on the early fireball phenomenon is also studied. It is found that trajectories of the radiation fronts and case shocks change with the opacity of equivalent device material. From our simulations, we find that only the early fireball depends on the details of the nuclear device, and after the formation of main shock, the evolution is determined by the properties of hot air for strong atmospheric explosion.     

氢原子束在大气长程传输中自剥离效应研究

氢原子束在大气传输时,束流粒子与大气粒子碰撞电离形成的大气剥离效应,以及和大气剥离产生次级粒子碰撞电离形成的自剥离效应,是造成氢原子束能量损失的重要机制。考虑到自剥离效应成因复杂,虽然目前已有一些理论方面的研究结果,但对其发生机理和对束流损失效果尚未有实验或数值模拟方面的工作,因此,通过对自剥离效应的发生机理和对束流损失的影响进行分析,进一步完善了自剥离效应理论,在通过束流传输方程验证了粒子云网格-蒙特卡罗法对氢原子束大气传输仿真模拟适用的基础上,将仿真结果与自剥离理论进行了对比,验证了自剥离效应理论的适用性。模拟结果表明,自剥离效应是由束流被大气电离产生的带电次级粒子团在地磁场的影响不停地穿越束流导致的,且自剥离效应的强弱与原子束的密度有关,束流密度越大,自剥离效应越强,对束流的影响越大。     

Influence of chemical kinetics on spontaneous waves and detonation initiation in highly reactive and low reactive mixtures

Understanding the mechanisms of explosions is important for minimising devastating hazards. Due to the complexity of real chemistry, a single-step reaction mechanism is usually used for theoretical and numerical studies. The purpose of this study is to look more deeply into the influence of chemistry on detonation initiated by a spontaneous wave. The results of high-resolution simulations performed for one-step models are compared with simulations for detailed chemical models for highly reactive and low reactive mixtures. The calculated induction times for H₂/air and for CH₄/air are validated against experimental measurements for a wide range of temperatures and pressures. It is found that the requirements in terms of temperature and size of the hot spots, which can produce a spontaneous wave capable to initiate detonation, are quantitatively and qualitatively different for one-step models compared to detailed chemical models. The time and locations when the exothermic reaction affects the coupling between the pressure wave and spontaneous wave are considerably different for a one-step and detailed models. The temperature gradients capable to produce detonation and the corresponding size of hot spots are much shallower and, correspondingly, larger than those predicted using one-step models. The impact of the detailed chemical model is particularly pronounced for the methane-air mixture. In this case, not only the hot spot size is much greater than that predicted by a one-step model, but even at the elevated pressure, the initiation of detonation by a temperature gradient is possible only if the temperature outside the gradient is rather high, so that can ignite a thermal explosion. The obtained results suggest that the one-step models do not reproduce correctly the transient and ignition processes, so that interpretation of the simulations performed using a one-step model for understanding mechanisms of flame acceleration, DDT and the origin of explosions must be considered with great caution.     

Double resonances upon three-photon ionization of the samarium atom

The manifestation of double resonances upon the three-photon ionization of the samarium atom has been studied in a frequency range of 17200–18400 cm⁻¹. Thirty peaks caused by double resonances have been found in the dependence of the yield of Sm⁺ ions on the laser radiation frequency. The majority of these peaks greatly exceed in amplitude the peaks associated with ordinary two-photon resonances. The influence of double resonances on the three-photon ionization has been theoretically analyzed using the density matrix approximation. The calculations show that the probability of the three-photon resonance ionization can increase by more than two orders of magnitude due to the additional one-photon population of an intermediate level. The double resonance slows down the rate of increase in the probability of ionization with an increase in the laser radiation intensity compared to ordinary two-photon resonance.     

水中有限长加肋圆柱壳体振动和声辐射近似解析解

加肋圆柱壳体是水下航行器的主要结构形式。将肋骨对壳体的作用简化为只有法向力,本文导出了水中有限长加肋圆柱壳体的振动和声辐射的近似解析解。其中肋骨的作用表现为在无肋的耦合振动方程中增加附加阻抗,因此壳体的振动和声辐射由壳体的机械阻抗、流体的辐射声阻抗和肋骨的附加阻抗所决定。数值计算例子表明,在低频情况下,加肋对辐射声功率影响不大,但将降低表面平均振速,从而增加声辐射效率。     

Electric field perturbation caused by an increase in conductivity related to seismicity-induced atmospheric radioactivity growth

The influence of conductivity perturbation in the lower atmosphere on the DC electric field over a seismic region is investigated. This perturbation is related to the emanation of radon and other radioactive elements into the lower atmosphere as the seismic activity increases. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization sources. The altitude dependence of the ion formation rate is calculated. An ionization source changes the atmospheric conductivity because of the appearance of ions with an equilibrium number density. The perturbation of the atmospheric conductivity is calculated as a function of the altitude. Lower atmosphere conductivity changes disturb the electric current that flows in the global atmosphere-ionosphere circuit. This disturbance is caused by an external current over a seismic region. DC electric field perturbations on the Earth’s surface and in the ionosphere are estimated. Published in Russian in Khimicheskaya Fizika, 2007, Vol. 26, No. 4, pp. 39–44. The text was translated by the authors.