730 eV电子碰撞He原子(e, 2e)电离的三重微分截面

考虑初态He原子电子间的关联效应、末态敲出电子与剩余束缚电子间的关联效应和末态屏蔽效应, 计算和分析了在共面、大能量损失和小动量转移这一特殊几何条件下730eV电子离化He原子的三重微分截面. 所得结果与Stevenson等人的相对实验数据和CCC理论计算结果进行比较发现: 所得到的理论曲线能够反映实验数据给出的三重微分截面的结构特征.     

730 eV电子碰撞He原子(e, 2e)电离的三重微分截面

考虑初态He原子电子间的关联效应、末态敲出电子与剩余束缚电子间的关联效应和末态屏蔽效应, 计算和分析了在共面、大能量损失和小动量转移这一特殊几何条件下730eV电子离化He原子的三重微分截面. 所得结果与Stevenson等人的相对实验数据和CCC理论计算结果进行比较发现: 所得到的理论曲线能够反映实验数据给出的三重微分截面的结构特征.     

64.6 eV电子碰撞电离氦原子(e, 2e)反应的理论研究

利用BBK理论及其修正模型,计算了入射能64.6 eV、 不同枪角情况下,电子碰撞电离氦原子(e, 2e)反应的三重微分散射截面. 分析了曲线结构,对其内部碰撞机制进行了详细的研究和探讨.结果表明: 在非共面几何条件下,碰撞微分截面上所呈现出来的特征是由多种效应共同作用所决定的, 随着条件的不同而相互转化.且在垂直入射几何条件下,末通道存在着极强的动力学屏蔽.     

Nonperturbative treatment of ionization with excitation of helium by electron impact

We present cross sections for electron-impact ionization and simultaneous ionization plus excitation of helium by electron impact. The results are obtained from a fully nonperturbative close-coupling formalism using our B-spline R-matrix approach. A large number of pseudostates in the expansion of the wave function represent the coupling to the ionization continuum. We obtain excellent agreement with the directly measured experimental cross section ratios (Bellm et al., Phys. Rev. A 75, 042704 (2007)) for ionization leaving the residual He? ion in either the 1s ground state or the n = 2 (2s + 2p) excited states.     

Triple ionization of lithium by electron impact

Ejection of the three electrons from lithium in a single electron collision has been observed for the first time. Triply charged lithium was observed in an ion time-of-flight spectrum following electron impact on a sample of ultracold, trapped lithium. The higher signal/background afforded by the trap environment made the observation of Li3+ possible. We measured the ratios of triple-to-double and double-to-single ionization at an impact energy of 1000 eV. The 3+/2+ ratio is approximately 0.001, a value 2 orders of magnitude lower than semiempirical predictions. We present a simple method that uses photoionization data combined with sum-rule analysis to predict the asymptotic charge-state ratios. The sum-rule predictions compare reasonably with experiment and shake calculations, but disagree sharply with the semiempirical estimates.     

Glauber amplitude for ionization of helium by electron impact

The high-energy Glauber approximation is used to derive the formula for scattering amplitude for ionization of helium atom by electron impact. The scattering amplitude is expressed as a one dimensional integral involving MeijerG-functions. This may further be expressed in a closed form as simple sums of Meijer functions by writing down the series expansion for Bessel and Meijer functions. Further, the asymptotic behaviour of these amplitudes is examined for both large and small momentum transfers.     

共面不对称条件下Ar原子(e,2e)反应的三重微分截面

采用修正的扭曲波玻恩近似(DWBA)方法,计算了共面、大能量损失和小动量转移这一特殊几何条件下电子碰撞Ar(3p6)(e,2e)反应的三重微分截面.理论方法对(e,2e)反应过程近程极化势进行了修正,并引入Gamow因子表示后碰撞相互作用(PCI).将计算结果与实验结果、标准DWBA计算结果及Gamow因子修正后的DWBA-G计算结果进行了比较,发现极化效应起着重要的作用.     

非共面几何条件下102eV电子碰撞He单电离反应的三体耦合效应

在前人工作的基础上,通过引入有效索末菲参数考虑三体耦合效应,计算了非共面几何（垂直平面与垂直动量转移平面）条件下,102eV的电子碰撞He单电离反应的全微分截面,将其计算结果与3C、DWB2、我们前期的理论结果及实验数据进行了比较。     

Quasi-elastic electron scattering (e,e′p) and (e,e′d) from 6Li in a coincidence experiment

Coincidence cross sections for the reactions ⁶Li(e, e′p) and ⁶Li(e, e′d) have been measured in the region of quasi-elastic scattering. Using incident electrons of 2.5 and 2.7 GeV, the four-momentum transfers to the proton were 6.6 fm^?2, 10.0 fm^?2 and 11.6 fm^?2. The proton coincidence data agree with shell-model distributions assuming a Woods-Saxon potential and including short-range nucleon-nucleon correlations. The best fit to the deuteron coincidence data is obtained with a cluster wave function for the p-nucleons and a harmonic oscillator wave function for the s-nucleons taking into account the deuteron yield from the s-shell. The ratio of the deuteron cross section from ⁶Li divided by the elastic e-d scattering cross section depends only slightly on the four-momentum transfer and has a value of ≈ 2.     

Triple differential cross section measurements for the electron impact ionization of helium: Comparison with a second Born approximation

Triple differential cross sections for the ionization of helium by electrons of 500 eV impact energy have been measured in a coplanar, asymmetric geometry and for energies of the ejected electrons of 2.5, 5, 10 and 20 eV. A comparison is made between experimental data and a second Born treatment of Byron, Joachain and Piraux [1] for atomic hydrogen but for corresponding momenta of the incoming and the two outgoing electrons and for corresponding momentum transfer during the collision. The second Born describes quite well the shifts of the binary peak and the recoil peak to larger angles, the asymmetry of the recoil peak and the ratios of the intensities of binary to recoil peaks for different scattering parameters. — A quantitative estimate is made (for high impact energy) of the contributions to the total cross section of those ionizing collisions, in which the recoil peak intensity represents a considerable quantity. Probably most of these events can not be described by a single collision approximation.     

Triple differential cross-sections for the fast electron/positron impact ionization of hydrogen and helium in the Glauber approximation

Triple differential cross-section for electron and positron impact ionization of hydrogen and helium are calculated by using the Glauber approximation along with post-collision interaction effects which are estimated classically. The present results are compared with the recent absolute data of Ehrhardt, Jung and coworkers for the electron impact case. The positron impact case is found to lead to a larger binary to recoil peak maxima ratio (compared to the electron impact case) which further increases when post-collision interaction effects are included.     

Triple differential cross sections for low energy electron impact ionisation of helium

Measurements are reported of the triple differential cross sections for the ionisation of helium by electron impact. Data are presented for incident energies of 100 and 80.5 eV at several scattering angles and compared with previous measurements and theoretical calculations.     

共面对称条件下Mg原子(e,2e)反应的三重微分截面的计算

采用修正的扭曲波玻恩近似(DWBA)方法,本文计算了共面对称几何条件下电子碰撞Mg(3s2) 原子(e,2e)反应的三重微分截面.理论方法通过引入Gamow因子来表示(e,2e)反应的后碰撞相互作用(PCI).将计算结果与实验结果及标准DWBA计算结果进行了比较,发现PCI效应起着重要的作用.     

Near-threshold electron impact excitation of ultraviolet-emitting levels of helium atoms

The excitation by electron impact of levels of helium atoms that decay by emission of ultraviolet light has been studied as a function of incident energy up to approximately the first ionization energy. The width (FWHM) of the energy spread of the incident beam was less than 30 meV. A crossed-beam interaction region was used and UV photons emitted approximately normally to the electron and gas beam directions were detected by a channel electron multiplier. Precautions were taken to avoid detection of scattered electrons and metastable atoms by the photon detector. The onset position of the lowest excited level was used in calibrating the incident energy scale. The energies of resonance structures in the cross-sections could therefore be obtained and are compared with the results of experiments detecting other products of the interaction.     

Electron-photon coincidence studies on electron impact excitation of lighter neutral atoms

Recently we applied non-relativistic distorted wave approximation theory to study electron impact excitations in lighter atoms (viz. hydrogen, helium and some alkalis). Excitations from the ground and (or) initially excited metastableS states to next upper excitedP andD states have been considered. Results for the differential cross-sections and electron-photon coincidence parameters are obtained. Here the theory and the calculation of various scattering parameters are described briefly and some selected results are presented and discussed.     

(e, 2e) triple differential cross section for ionization-excitation of helium

Simultaneous ionization and excitation of helium by electron impact is considered in an improved second Born approximation. The wave function of the low energy ejected electron is obtained in the field of residual He⁺ ion in 2s-state. The calculation has been done for the processe ⁻+He→e ⁻+He⁺(2s)+e ⁻ in the coplanar asymmetric geometry with Hartree-Fock wave function of Byron and Joachain for the helium ground state and the results are compared with the absolute experimental data of Dupreet al [J. Phys. B25, 259 (1992)] at ∼ 5.5 keV incident energy. Our results are found to increase the ratio of the recoil peak to binary peak intensity by about 30% over the first Born results and thus to bring it closer to the experimental data.     

(e,2e)反应三重微分截面的计算

给出了利用BBK模型计算电子碰撞电离H,He⁺,He和Li⁺三重微分截面的通用方法,适用于中、高入射能量下的各种几何条件。计算结果与其它理论结果和实验数据进行了比较,符合得很好。