Single ionization of helium atoms by energetic fully stripped carbon ions

A four-body distorted wave approximation is presented for theoretical investigations of the single ionization of groundstate helium atoms by fully stripped carbon ions at impact energies of 2 MeV/amu and 100 MeV/amu. The nine-dimensional integrals for the partial quantum-mechanical transition amplitudes of the specified reaction are reduced to some analytical expressions or one-dimensional integrals over real variables. Fully differential cross sections(FDCSs) are calculated and compared with their experimental values as well as the results obtained from other theories. Despite the simplicity and quickness of the proposed quadrature, the comparison shows that the obtained results are in reasonable agreement with the experiment and are compatible with those of other complicated theories.     

Al,Ti,Cu,Mo原子的K壳层电离截面的理论计算

 电子离子碰撞过程是模拟激光等离子体的超热电子的能谱和产额的主要过程之一。基于相对论性的电子离子碰撞的K壳层的电离截面理论,计算了Al,Ti,Cu,Mo原子的K壳层的电子离子碰撞截面,结果和最近的文献实验数值和其它理论数值进行了比较,计算结果可用来模拟激光等离子体的超热电子能谱和产额。     

Spin dependence of the interaction of antiprotons with the deuteron

Elastic scattering of antiprotons on the deuteron is studied within the Glauber-Sitenko theory accounting for the single and double scattering mechanisms and the full spin dependence of the transition matrix element. Differential cross sections, analyzing powers and total polarized cross sections are calculated for antiproton beam energies between 50 and 300 MeV using the Jülich models for the $\bar NN$ interaction.     

屏蔽效应对氦原子(e,2e)反应中二重微分截面和单微分截面的影响

用DS3C模型计算了入射能为32.5, 36.5, 40.7 eV时电子入射单电离氦原子的二重微分散射截面, 并把计算结果与实验结果进行了比较, 对屏蔽效应进行了分析. 通过对二重微分散射截面在全空间的角度积分得到了电子入射单电离氦原子的单微分散射截面, 利用3C模型和DS3C模型计算了入射能为32.5, 36.5, 40.7, 50 eV时氦原子的单微分散射截面, 并把计算结果与实验结果进行了比较. 对截面的结构进行了分析, 并系统研究了交换效应对截面的贡献. 关键词： DS3C模型 二重微分散射截面 单微分散射截面 屏蔽效应     

Fully differential cross sections for C6+ single ionization of helium

The three-Coulomb-wave(3C) model is applied to study the single ionization of helium by 2 MeV/amu C6+ impact.Fully differential cross sections(FDCS) are calculated in the scattering plane and the results are compared with experimental data and other theoretical predictions.It is shown that the 3C results of the recoil peak are in very good agreement with experimental observations,and variation of the position of the binary peak with increasing momentum transfer also conforms better to the experimental results.Furthermore,the contributions of different scattering amplitudes are discussed.It turns out that the cross sections are strongly influenced by the interference of these amplitudes.     

质子碰撞电离过程中程函近似效应的理论研究

分别利用连续扭曲波方法和初态程函近似-连续扭曲波方法对质子碰撞电离氖原子1s,2s,2p壳层后随电离电子能量变化的单重微分散射截面(SDCS)和二重微分散射截面(DDCS)及总截面进行了计算,所得结果与部分实验数据符合得很好.详细探讨了各壳层SDCS和DDCS的细致结构以及质子碰撞的电离机制.结果表明,对于氖原子2p壳层,随着入射质子能量的增加,SDCS的区域变长,幅度减小,在低能区以软电离为主;而DDCS出现的峰均迅速减小.此外,分析了初态程函近似对SDCS和DDCS的影响,发现该效应对截面的影响在低能入射时非常明显,随着入射能量的增大,这种影响逐渐减弱.     

L-shell vacancy production in Ag,Ta and Au for incident ionsZ 1≦10 in the energy range of 0.125–4 MeV/amu

Absolute Ag, Ta and AuL-shell X-ray cross sections were measured using protons,⁴He,¹⁴N as well as²⁰Ne ions in the energy range of 0.125–4 MeV/amu. By means of single-hole fluorescence yields experimental ionization cross sections were deduced and compared with calculations according to the corrected PWBA model — PWBA(BPCR). With decreasing asymmetry of the collision system the experimental cross sections exceed the predictions of the direct ionization theory. This is caused by an increasing contribution of a competing KL charge exchange mechanism which was investigated in detail for Ne+Ag. The Lapicki and Losonsky capture model was found to fail at energiesE<1 MeV/amu because adiabatic relaxation effects in the projectileK-shell become important. An estimation by means of the Nikitin model led to more physically comprehensible results at the lowest ion velocities investigated.     

2 MeV/amu裸碳离子碰撞氦离子单电离的全微分截面的结构(英文)

用修饰的库仑波(MCB)模型计算入射能量2 MeV/amu裸碳离子碰撞氦单电离的全微分截面,并将计算结果与相应的实验数据和其他理论结果进行比较,发现MCB理论在较小的电离电子能量和较大的动量转移条件下与实验结果符合得很好,在动量转移比较小时MCB理论结果binary峰的位置向大角方向发生了偏移。MCB理论和3CW(三体库仑波)理论相似,他们都比3DW-EIS(三体扭曲波程函初态近似)理论符合的好,说明了在微扰势中被动离子与入射粒子的相互作用是不可忽略的。与3CW理论相比,MCB模型在初态波函数和相互作用势中加入扭曲效应,比较发现扭曲效应会影响全微分截面的大小,但影响不是很明显。The modified coulomb born (MCB) model is applied to study the single ionization of helium by 2 MeV/amu C6+ ion. The fully differential cross sections are presented for a variety of momentum transfers and ejected-electron energies in the scattering plane. The MCB results are compared with the experimental data and other theoretical predictions. We find that the MCB results are similar to the 3CW (three-body coulomb wave) results and they are superior to the 3DW-EIS (three-body distorted wave-eikonal initial state) results. It turns out that the treatment of the passive electron is very important for the results and distorting effects are not obvious.     

中能区反质子与核的非弹性散射

运用多次散射理论的光学势获得反质子的扭曲波.在扭曲波冲量近似下,讨论了中能区反质子与原子核的非弹性散射.考虑了反质子能量从180MeV到1800MeV这一能区¹²C,的2+,3-态微分截面.在这一能区的低能端,(E=180MeV)DWIA能够很好的符合实验,同时,预示了更高能量可能出现的微分截面的理论结果.     

Antiproton-Nucleus Inelastic Scattering at Intermediate Energies

The distorted wave of antiproton is obtained by an optical potential derived from the multiple scattering theory In the framework of the distorted wave impulseapproximation, we discuss the antiproton-nucleus inelastic scattering at intermediate energies. The inelastic differential cross sections of 2+, 3- states at antiproton energies from 180 MeV to 1800 MeV are calculated. It is shown that DWIA fitted the experimented data quite well, and theoretical results of inelastic cross sections at higher energies are predicted.     

Atomic processes in antiproton-matter interactions

Atomic processes dominate antiproton stopping in matter at nearly all energies of interest. They significantly influence or determine the antiproton annihilation rate at all energies around or below several MeV. This article discusses what is known about the atomic processes which, through their effect on stopping and annihilation, significantly influence the spatial distribution of antiproton annihilations in a material. For stopping above about 10 eV the processes are antiproton-electron collisions, effective at medium keV through high MeV energies, and elastic collisions with atoms and adiabatic ionization of atoms, effective from medium eV through low keV energies. For annihilation above about 10 eV it is the enhancement of the antiproton annihilation rate due to the antiproton-nucleus Coulomb attraction, effective around and below a few tens of MeV. At about 10 eV and below, the atomic rearrangement/annihilation process determines both the stopping and annihilation rates. Although a fair amount of theoretical and some experimental work relevant to these processes exist, there are a number of energy ranges and material types for which experimental data does not exist and for which the theoretical information is not as well grounded or as accurate as desired. Additional experimental and theoretical work is required for accurate prediction of antiproton stopping and annihilation for energies and materials relevant to antiproton experimentation and application.     

Single and double ionization of neon 2s- and 2p-subshells by proton and electron impact

Absolute single and double ionization cross sections of neon 2s- and 2p-subshells for proton (40–900 keV) and electron impact (0.2–10 keV) have been measured using photon spectroscopy in the spectral range of the vacuum ultraviolet. Cross sections for double ionization decrease more rapidly with increasing impact energy than cross sections for single ionization. No definite asymptotic energy dependence of a Bethe-Fano-plot could be found for double ionization in contrast to single ionization. The experimental results are compared with theoretical predictions of the shake-off model and Gryzinski's classical binary encounter theory. Better agreement is found with the latter, indicating that successive binary collisions have to be considered as a strong mechanism for double ionization by protons or electrons of the investigated energy range. Comparison is made with other experimental results for double ionization by photon impact or capture ionization by proton impact.     

低能电子入射电离He原子二重微分截面的理论研究

研究了低能电子入射单电离He原子的二重微分截面(DDCS)，通过对散射电子三重微分截面在全空间的角度积分得到敲出电子的DDCS.分别用DS3C模型和BBK模型计算了入射能为26.3，28.3，30.3，32.5，34.3，36.5和40.7eV时，低能电子入射电离He原子的DDCS；研究表明：DS3C的计算结果，除在低入射能(比如26.3eV)和小敲出角之外，均能与绝对测量的实验结果较好地符合.此外，对直接和交换效应也进行了研究，给出了交换效应对截面的贡献.     

Collisions of low-energy antiprotons with molecular hydrogen: ionization, excitation and stopping power

A time-dependent coupled-channel approach was used to calculate ionization, excitation, and energy-loss cross sections as well as energy spectra for antiproton and proton collisions with molecular hydrogen for impact energies 8?<?E?<?4000 keV.     

Inner-shell ionization created by fluorine ions in nearly symmetric collisions

We have measured projectile and target X-ray cross sections for F + Si, S, Ar and Kr collisions at projectile energies from 1 to 25 MeV. The experiments were performed under single collision conditions using a differentially pumped gas target. X-rays were measured by a Si(Li) detector and a proportional counter. The experimental cross sections are compared to predictions of theoretical models for direct and quasi-molecular ionization. Effects of multiple ionization that influence theK-shell fluorescence yields were examined using experimental information from line energy shifts and intensity ratios.     

Positron-impact ionization of atoms: Experiments

This review covers the recent experimental results on positron-impact ionization as well as results which can be expected in the near future. Topics of other Workshop reviews such asPs formation andinner-shell ionization are not included here. Insingle ionization, interesting new developments are the comparison of positron/electron impact with proton/antiproton impact, cross-section measurements for atomic hydrogen, and threshold studies with H₂ and noble-gas atoms. Indouble and triple ionization, some level of completion has been reached; further work along this line is to be expected when improved energy resolution will permit studying multi-ionization threshold behavior. The above remarks concerntotal ionization cross sections, the only type measured so far. Two experiments onsingle-differential and one ondouble-differential cross sections are on the way.Triple-differential measurements would be very interesting, but are not yet feasible.     

Transfer ionization in energetic \alpha-He collisions

Total cross sections σ_if for transfer ionization α + He → He⁺ + α + e are computed at high energies by means of the four-body continuum distorted wave (CDW-4B) approximation. Comparisons between the present results σ_if and the available experimental data at E = 30-600 keV/amu yield satisfactory agreement at impact energies E > 80 keV/amu, in sharp contrast to the previous independent event model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sequential over-barrier ionization of multi-electron atoms in the tens-to-hundreds keV/u energy range

Our previous work on the classical over-barrier ionization model for helium double ionization is extended to the complex multi-electron system of Ne.The total and q-fold ionization cross sections are calculated at energies ranging from a few tens to several hundred keV/u.The calculation results are in good agreement with the experimental data,and the energy dependence of the cross sections suggests that the multi-ionization of a strong perturbated complex atom is probably the sequential over-barrier ionization process.     

二重微分散射截面中非一阶效应的理论研究

利用一级玻恩近似理论及Brauner-Briggs-Klar (BBK)理论计算了不同能量入射条件下, 电子单电离氢原子(e, 2e)反应中的二重微分散射截面, 把计算结果与实验数据及其他理论结果进行了比较, 对BBK模型和考虑动力学屏蔽的BBK模型在二重微分截面 中的非一阶效应进行了详细的分析和探讨. 关键词： 一级玻恩近似 二重微分散射截面