原子康普顿轮廓的解析计算

利用变分原理和冲量近似,给出了原子康普顿轮廓的解析计算方法。基于该方法具体导出了第一和第二周期元素各轨道电子的康普顿轮廓解析表达式,并绘制了各轨道电子的康普顿轮廓在Q=0-4范围内的变化情况。通过与文献结果的比较,验证了本文计算方法和结论的可靠性。     

NO与C2H2的康普顿轮廓研究

基于第三代同步辐射光源, 在20 keV的入射X射线能量下测量了NO与C₂H₂分子的康普顿轮廓. 考虑到本次实验结果在p_z ≈ 0附近的统计精度达到了0.2%, 本文报道的NO和C₂H₂的康普顿轮廓可以作为严格检验理论的实验基准. 除此之外, 还分别采用HF方法及密度泛函方法选用不同的基组计算了NO 与C₂H₂康普顿轮廓. 通过对比实验结果与理论计算, 发现对于NO分子, 加入弥散函数基组理论计算结果与实验符合更好, 说明NO分子基态的电子分布较为弥散. 对于C₂H₂分子, HF方法理论计算的结果与实验符合较好.     

γ射线在大气中产生康普顿电流的快速计算方法

康普顿电流是激励核电磁脉冲的主要机制。为了提高核电磁脉冲数值模拟中γ射线产生康普顿电流过程的计算效率,发展了一种γ射线在均匀大气中产生康普顿电流的快速计算方法。首先通过计算康普顿电子在出射方向上的衰减特征,得到在电子出射方向净电子流与其射程和出射距离的拟合关系,然后结合康普顿散射微分截面,给出单能γ射线在大气中产生的康普顿电流密度的解析数值计算方法。和蒙特卡罗程序的计算结果比较,用该方法计算得到的电流密度值差异在10%以内,计算速度提高两个量级以上。该计算方法可用于大气中康普顿电流的快速估算。     

高空电磁脉冲环境计算中的自洽方法

高空电磁脉冲环境计算中包含自洽过程,康普顿电流既是产生电磁脉冲的源项,同时又受电场的影响.本文从一维模型出发,经过合理近似,推导出康普顿电流与本地电场之间的解析关系.利用等效电导率的概念,将该自洽过程加入到原有计算模型中.利用粒子模拟和时域有限差分方法,对推导出的康普顿电流和电场关系进行验证.最后给出一个考虑自洽过程的高空电磁脉冲算例.     

浅析影响康普顿谱线位置的因素

康普顿散射中影响康普顿谱线位置的因素是十分复杂的,文章主要针对影响康普顿谱线位置的几个因素作了理论探讨,得出影响因素主要在于:电子具有初速度会增大散射波长的改变量;束缚能的存在要减小峰值波长的改变量;双光子散射和二次散射与谱线峰值位置的关系不大,二者对峰值波长的改变是不确定的、复杂的、在连续的范围内变化的.最后对康普顿谱线位置和康普顿轮廓的理论研究和应用前景作了展望.     

类氢离子的相对论康普顿轮廓（英文）

基于中心场近似得到Dirac径向轨道,并使用恰当的Fourier变换系统计算了类氢离子电子动量分布和康普顿轮廓。以H原子和Xe53+离子为例,探讨了相对论效应和原子核的有限体积效应对单电子康普顿轮廓的影响。同时,详细研究了单电子康普顿轮廓对主量子数n、轨道量子数l、单电子总角动量量子数j和核电荷数Z的依赖关系。结果表明,相对论效应可以扩展康普顿轮廓的分布,并且使给定nl的轨道随着Z的增加分裂得越来越明显。然而,相对论效应也会随着主量子数n和轨道量子数l的增加而减弱。同时,对于nl_j轨道,其康普顿轮廓还具有n-l个平台的结构。另外,原子核的有限体积几乎不会影响H原子和Xe53+离子的康普顿轮廓。The Compton profiles of the electron in the ground and excited states of H-like ions have been calculated systematically with one-electron Dirac radial orbitals by using the proper Fourier transformation. Taking the H atom and Xe53+ ion as examples, the effects of relativity and finite nuclear size on Compton profile have been discussed. Furthermore, the dependence of one-electron Compton profile on the principle quantum number n, orbital quantum number l, angular quantum number j and nuclear charge Z has also been discussed. It is found that the relativistic effect can expand the distribution of the Compton profile and split the orbital more and more obviously for given nl(l=0) as increasing Z. However, the relativistic effect can gradually weaken with the increase of the principal quantum number n and orbital quantum number l. Furthermore, the Compton profile of the orbital with quantum number nl_j has certain number of platforms that is n-l. In addition, the nuclear finite size hardly affects the Compton profile for H atom and Xe53+ ion.     

高空核爆炸产生的电子数密度的近似估计

在高空核爆炸的条件下,由γ-康普顿散射产生的高能电子离化空气产生次级电子。本文推导了描述次级电子的速率方程组的解析解。并把解析解的结果与数值计算的结果作了比较,离地面的高度越高,两种方法的计算结果越接近。     

铁磁性高锰硅化物Mn_4Si_7电子特性的第一性原理计算

本文采用基于第一性原理的密度泛函理论超软雁势平面波方法,对铁磁性半导体高锰硅化合物Mn_4Si_7进行了理论计算.结果表明块体Mn_4Si_7是准直接带隙半导体材料,其价带主要是由Mn的3d轨道电子构成,导带主要是由Mn的3d及Si的3p轨道电子构成.相同自旋轨道下,自旋向下态的电子更容易占据较高的能级.而自旋向上态的电子对Mn_4Si_7的禁带宽度起主导作用. Mn_4Si_7的费米能级附近各轨道未被电子占满,且自旋向上态与自旋向下态电子的不对称分布使其具有了磁性.为Mn_4Si_7磁学特性提供主要贡献的是Mn的3d轨道电子,而Si的3p和3s轨道电子提供了一个小的贡献.     

π±介子上康普顿散射过程的重新计算

用微扰量子色动力学重新计算了π^±介子上的康普顿散射过程的截面和相位.此计算把实康普顿散射作为虚康普顿散射的一种极限情形进行了处理,重点是通过比较不同模型的分布振幅对物理可观察量的影响,说明分布振幅在端点区域的行为对康普顿散射过程截面和相位的影响,由此探索用微扰量子色动力学计算这个问题的自洽性问题.     

乙醇分子的高分辨电子动量谱学研究:单个构象异构体的轨道电子动量分布

利用高分辨电子动量谱仪测量了乙醇分子外价轨道的电离能谱,通过对一系列角度关联的电离能谱进行解谱,获得了各个电离能峰对应的分子轨道电子动量分布.利用密度泛函理论方法计算了乙醇分子两种构象异构体的轨道电子动量分布,通过与实验结果进行比较,发现实验测量的电离能为14.5和15.2 eV能峰对应的电子动量分布分别与理论计算的单个构象异构体trans 8a''和gauche 9a轨道电子动量分布符合较好.     

Electron momentum distributions and compton profiles of some molecules with FSGO model

The electron momentum distributions and the Compton profiles (within the impulse approximation) of H₂, LiH, methane, water, acetylene, ethylene, ethane cyclopropane and cyclobutane have been calculated using the floating spherical Gaussian orbital (FSGO) wavefunctions. The agreement of the single-FSGO Compton profiles with the corresponding experimental or the Hartree-Fock (HF-SCF) theoretical ones is fairly good in most of the cases examined. The advantages and drawbacks of using the FSGO model for the calculation of Compton profiles are discussed.     

Strong anisotropy in the low temperature Compton profiles of electron momentum distribution in α-Ga metal

Compton profiles of momentum distribution of conduction electrons in the orthorhombic phase of α-Ga metal at low temperature are calculated in the band model for the three crystallographic directions (100), (010), and (001). Unlike the results at room temperature, previously reported by Lengeler, Lasser and Mair, the present results show strong anisotropy in the Compton profiles with the momentum distribution along (001) direction being substantially different from the other two directions. While experimental data on Compton profiles at low temperatures are not available for comparison with theory, the resistivity data in α-Ga at low temperature strongly support this anisotropic behaviour. Besides, the electronic heat capacity constant γ available from both experiment and present calculation suggests that the conduction electron distribution at low temperature in the orthorhombic phase is markedly different from the free-electron-like-distribution at room temperature, thus lending additional support to anisotropic behaviour of Compton profiles. It would be nice to have Compton profiles data from experiment at low temperature for direct comparison with theory. It is hoped that the present work would stimulate enough interest in that direction.     

Compton profiles of multiply ionized oxygen atoms

We have calculated Compton profiles of multiply ionized oxygen atoms with electronic configurations 1s^m2sⁿ2p^q, m=1−2,n=0−2,q=0−4. The values of the Compton profiles from the present calculation can be used to determine the doubly differential electron production cross sections in recent ion-atom collision experiments with oxygen ions in the rest frame of the target atoms. The calculations have been performed in impulse approximation using numerical Hartree-Fock wave functions. Compton profiles of neutral oxygen atoms, available in the literature, are in excellent agreement with the present calculation. The variation of Compton profile with the degree of ionization is investigated.     

Effect of bcc-fcc phase transition on the compton profiles of iron

The effect of the- or bcc-fcc phase transition on the electron momentum distribution and Compton profiles of iron has been theoretically examined by a band structure calculation in the two phases. The calculated band Compton profile for the bcc phase shows a good agreement with the experimental results by Phillips and Weiss. The calculated directional Compton profiles show significant changes while going from the bcc to the fcc phase.     

Anisotropy of Compton profile found in nickel oxide single crystal

The Compton profiles have been measured on a spherical single crystal of nickel oxide along three major axes using a 100 mCi ²⁴¹ Am source and a Ge(Li) detector. The anisotropy has been detected clearly and compared with a simple calculation.     

Magnetic and electronic properties of NiAs-type chromium chalcogenides

We have computed spin-dependent energy bands, spin moments and density of states of NiAs-type CrX (X=S, Se and Te) chalcogenides using linear combination of atomic orbitals method within density functional theory as well as full potential augmented plane wave method. In addition, magnetic properties have also been computed using spin polarized relativistic Korringa-Kohn-Rostoker method. We have also obtained the first ever theoretical electron momentum densities of CrX compounds considering linear combination of atomic orbitals and compared the results with the isotropic Compton profiles measured using 20 Ci ¹³⁷Cs Compton spectrometer. The Fermi surface topology and magnetic properties are discussed in terms of majority and minority energy bands and density of states. In addition, to highlight the role of Cr (3d) electrons in such type of chalcogenides, we have also reported the magnetic Compton profile of CrTe using the Korringa-Kohn-Rostoker method.     

Self-consistent Compton profile of selenium

The valence electron Compton profile of trigonal and polycrystalline trigonal selenium has been determined using the self-consistent OPW method. The anisotropy of the Compton profile between directions parallel and perpendicular to the c-axis is discussed. The results are compared with experimental data. The difference of the Compton profiles of the amorphous and polycrystalline phases is examined.