中低能速度能区离子与H,He原子碰撞中的经典电子俘获截面（英文）

Bohr-Lindhard模型被用来描述中低能速度能区离子—原子碰撞中的经典电子俘获过程。根据离子与原子的作用时间与碰撞参数的关系,建立俘获几率对碰撞参数的依赖性,碰撞参数范围被限定在俘获半径之内。在该模型的框架内,人们试图通过电子的空间分布函数来研究所有碰撞参数的贡献,但存在较为复杂的数值计算。基于Bohr-Lindhard模型,本工作提出通过简单的指数衰减函数来描述电子俘获几率对碰撞参数的依赖性,计算了A~(q+)(q=2～6)-H碰撞中的单电子俘获截面和A~(q+)(q=3～6)-He碰撞中的双电子俘获截面,计算结果与已有实验数据符合很好,很好地描述了低能和中能区的电子俘获截面随能量和电荷态的变化,该工作还可计算其他不同电荷态离子与He和H靶的电子俘获截面。     

经典过垒模型在Xeq++He碰撞中的应用

采用位置灵敏探测和飞行时间技术研究了高电荷态Xe离子(q=15,17,19,21,23)与He原子碰撞中双电子转移截面与单俘获截面比随入射离子电荷态的变化规律.提出一步过程假定,对扩展的经典过垒(ECB)模型进行了修正,利用修正模型计算得到的单、双电子转移绝对截面与Andersson等人和Selberg等人的实验结果符合得很好,所得截面比与本实验得到的双电子转移截面与单电子俘获截面符合得比较好.     

_(18)Ar~(q~+)(q=3,4)与H和He碰撞的电荷剥离截面

采用二体碰撞近似和托马斯 -费米近似计算了多电荷离子18Arq+( q =3,4 )与中性原子H和He碰撞的电荷剥离截面以及Arq+的势函数和电子动量分布 ,计算结果与文献 [4]中的数据符合得较好。所导出的计算公式和编制的计算程序可以计算任何一个多电荷离子Aq +与H或He碰撞的电荷剥离截面。因而具有一定的普适性。     

P—He碰撞中1s—ns电子俘获截面计算

本文进一步发展了由我们提出的一种新的方法来计算离子－原子，离子－离子碰撞中１ｓ－ｎｓ电子俘获截面。在该方法中，我们用联合原子模型描述初态电子的导曲波函数及用氢原子模型的描述末态电子的波函数，在小几率及峰点近似条件下，其散射振幅为一简单的解析形式。在１０－２００ｋｅＶ能量范围，我们用此方法计算了Ｐ＋Ｈｅ碰撞中电子俘获到４ｓ态的截面。计算结果与实验结果在３０－２００ｋｅＶ能量很好地一致。特别是我们的结     

高电荷态Xe离子与He原子碰撞中的电子转移过程研究

采用位置灵敏探测和飞行时间技术研究了高电荷态Xe离子（q=15，17，19，21，23）与He原子碰撞中双电子转移截面与单电子转移截面比随入射离子电荷态的变化规律.提出一步过程假定，对扩展的经典过垒（ECB）模型进行了修正，利用修正模型计算得到的单、双电子转移绝对截面与Andersson等人和Selberg等人的实验结果很好符合，所得截面比与本实验得到的双电子转移截面与单电子俘获截面比较好符合. 关键词： 离子 原子碰撞 电荷转移 一步过程     

低能高电荷态离子(4≤q≤7)与He碰撞中双俘获与转移电离的截面反转效应

基于入射离子双俘获后势能沉积与双电离靶离子势能的比值定义了势能参数Ω,研究了低能高电荷态离子(q=4,5,6,7)与He原子碰撞系统中双俘获和转移电离反应道的选择规律.研究发现,在Ω坐标下,双俘获和转移电离存在截面反转效应,Ω1.0时双俘获为双电子转移过程主反应道,Ω≥1.0时转移电离成为双电子转移过程主反应道.     

等电荷态离子与He原子碰撞中的转移电离过程研究

采用位置灵敏探测和飞行时间技术测量了等电荷态离子Cq+、Nq+、Oq+、Neq+(q=4,5,6,7)与He原子碰撞中,转移电离截面与单电子俘获截面的比值R.研究了相同q入射的情况下,R与入射离子核电荷数Z的依赖关系,在统计蒸发模型的基础上对实验结果进行了解释.     

_(18)Ar~(q~ )(q=3,4)与H和He碰撞的电荷剥离截面

采用二体碰撞近似和托马斯 -费米近似计算了多电荷离子18Arq ( q =3,4 )与中性原子H和He碰撞的电荷剥离截面以及Arq 的势函数和电子动量分布 ,计算结果与文献 [4]中的数据符合得较好。所导出的计算公式和编制的计算程序可以计算任何一个多电荷离子Aq 与H或He碰撞的电荷剥离截面。因而具有一定的普适性。     

强扰动能区非全裸Cq+,Oq+(q=1-4)与He原子碰撞过程中截面比的实验研究

利用兰州大学2×1.7MV串列加速器离子-原子碰撞实验终端上产生的单核子能量为20-500 keV的Cq+和Oq+(q=1-4)离子与He原子碰撞.采用符合测量方法和多参数数据获取系统得到了散射离子与反冲离子电荷态的二维谱,从而分别得到直接电离、入射离子俘获电子和入射离子损失电子截面与总截面的截面比Rdirect,Rcapture和Rloss,并对强扰动能区的各个反应道之间竞争关系及同一反应道在不同碰撞体系中所表现出的实验规律进行了比较和定性分析.     

强扰动区C~(q+)离子与He原子碰撞中有效电荷研究

本文利用经典过垒电离模型(Class Over Barrier Ionization)处理100-400ke V/amu强扰动区(q/v1)的不同价态非全裸离子Cq+(q=1-4)与全裸离子H1+,He2+,Li3+与He原子碰撞过程.发现相同价态下,全裸离子的双单电离截面比R21明显低于非全裸离子,原因在于两者的电子结构明显不同.非全裸离子的外壳层电子在碰撞过程中会有一定几率过垒,这在以往的研究中并未考虑.利用模型计算结果与实验数据的比对,估计入射离子第二有效电荷,最终确定入射离子在电离过程中的第一和第二有效电荷.     

On the semiclassical impulse approximation for electron capture in asymmetric ion-atom collisions

A derivation of the impulse approximation for the capture of a targetK-shell electron by a light projectile in ion-atom collisions is given in the framework of the semiclassical approximation. The impact-parameter dependence of the capture probability is calculated numerically without further approximations, and shows good agreement with recent experimental results for protons colliding with Ne and Ar. The validity of several peaking approximations and the relation to ionisation theories is briefly discussed.     

On the effect of off-shell wavefunctions onK andL shell charge transfer in fast,asymmetric collisions

Within the semiclassical strong potential Born approximation (SPB) we have calculated the electron capture from theK andL shell of a heavy target atom by protons using two different peaking approximations. Both total capture cross sections and impact parameter distributions are compared with the impulse approximation (IA) and in the case of transfer from the ArK-shell also with an exact evaluation of the SPB and with experimental data. While for theK shell, all theories give a similar impact-parameter dependence, there is a substantial difference between IA and SPB results for the 2s subshell.     

Experimental study of structure functions and sum rules in charge-changing interactions of neutrinos and antineutrinos on nucleons

High-energy exclusive and inclusive cross sections are discussed in terms of their dependence on the transverse-position variables (impact parameters) of incident and outgoing particles. The objective is to clarify the points of conflict and agreement of various models with each other and with intuitive ideas based on macroscopic collisions. First the impact parameter representation of states and amplitudes is reviewed. New impact parameter conservation laws and sum rules are derived from Lorentz invariance. The generalized optical theorem of Mueller is extended to give the impact parameter distribution of produced particles. Mueller-Regge behaviour is shown to imply three-dimensional limiting fragmentation in (impact parameter, rapidity)- space and a specific linear structure of the final-state particle density in the central region of this space. The predictions of weak- and strong-coupling multiperipheral models, the φ³ ladder eikonal model and the dual resonance model are presented, with emphasis on the dependence of average multiplicity on impact parameter and the dependence of mean square impact parameter on multiplicity. Special techniques for strong-coupling multiperipheral models are used to study the breakdown of the random-walk impact-parameter structure of the weak-coupling case, and to show explicitly that the average multiplicity is a decreasing function of impact parameter in the strongly coupled ABFST model.     

Fusion probability of symmetric heavy,nuclear systems determined from evaporation-residue cross sections

Cross sections were measured for the formation of evaporation residues in ⁴⁸Ca-, ⁸⁶Kr- and ¹²⁴ Sn-induced reactions with Yb, Sb and Zr isotopes. For the nearly symmetric systems, the energy dependence of the fusion probability in central collisions was determined. The fusion probability at the expected fusion barrier as calculated from a one-dimensional heavy-ion potential was found to be reduced by several orders of magnitude. The fusion cross sections increase gradually, and only at energies appreciably above the expected fusion barrier the major part of the cross section of central collisions leads to fusion. The observed hindrance of the fusion process is compared with model predictions.     

Cross sections of electron capture and electron capture ionization versus the impact parameter in collisions of a proton with multielectron atoms

The absolute differential cross sections of scattering of hydrogen atoms resulting from an electron capture and an electron capture ionization are measured for collisions of 4.5- and 11-keV protons with argon and xenon atoms. The range of scattering angles is 0°–2°. From the scattering differential cross section found experimentally, the probabilities of single-electron capture and electron capture ionization as a function of the impact parameter are calculated. The dependences of the incident particle scattering angle on the impact parameter (deviation function) for interactions with Ar and Xe atoms are calculated in terms of classical mechanics using the Moliére—Yukawa potential to describe the interaction of atomic particles. Analysis is given to the probabilities of electron capture and electron capture ionization versus the impact parameter and to the distribution of the electron density on different electron shells in a target atom versus a distance to the core. It is concluded that only electrons from the outer shell of the target atom are involved in the process of electron capture ionization. The cross section of electron capture ionization is calculated in the proton energy range 5–20 keV.     

Transfer ionization in isocharge sequence ion and Ne collisions

The dependence of the ratio R1 for transfer ionization to single capture for Cq+, Nq+, Oq+, Neq+ ions on Ne target upon the electronic structure of the projectile is studied. For Aq+-Ne collisions the ratio R1 decreases as the atomic number Z of the projectile increases for q=4,5,6,7 sequences which provides strong evidence for the increase of the binding energy of the target valence electron after single electron capture. The increase in binding energy depends both upon the atomic number of the projectile and the target atom.     

Peculiarities in the cross sections of electron capture by phosphorus ions

The effect of decreasing the cross sections of electron capture by phosphorus (P⁵⁺) ions penetrating through gaseous media has been revealed experimentally. This effect is a violation of the known uniform dependence between the electron-capture cross section and the ion charge. Such an anomaly was not observed in measurements performed with argon ions under the same conditions. A possible reason of decreasing the cross sections of electron capture by P⁵⁺ ions may be autoionization of excited P⁴⁺ ions. The latter are formed during electron capture into excited states by metastable particles of a beam of P⁵⁺ ions.     

反应窗理论的适用性研究

基于低能离子与原子碰撞的分子库仑过垒模型，简要描述了与入射离子速度相关的反应窗理论.根据这一理论，计算了不同碰撞速度时O⁸⁺-H，Ar⁸⁺-H，Ar⁸⁺-He，Ne¹⁰⁺-He及Ar¹⁸⁺-He等碰撞体系单电子俘获过程的微分截面，还计算了碰撞速度为0.53 a.u.时¹⁵N⁷⁺-Ne碰撞体系单电子、双电子及三电子俘获过程的微分截面，并与他人的实验结果作了比较.研究发现，反应窗理论预言的末态电子分布与实验结果符合较好.理论和实验研究表明，随着碰撞速度的增加反应窗变宽；反应窗理论所预言的微分截面，当Q值较小时比实验结果偏大，当Q值较大时比实验结果偏小. 关键词： 反应窗理论 态选择微分截面 分子库仑过垒模型 离子与原子碰撞     

原子轨道强耦合方法研究He2+-H-碰撞的电荷转移过程

应用双中心原子轨道强耦合方法研究He²⁺-H^-碰撞的单次电荷转移过程.计算中,对入射粒子He²⁺,包含n=1~7的所有束缚态,计算的能量本征值与NIST标准数据在百分之几的精度内符合很好;对靶H^-,包括一个束缚态1s和五个连续态ns(n=2~6),束缚态能量与他人理论结果一致.在4~400 keV的入射粒子能量范围,计算单电子俘获过程的总截面及到各个壳层上的态选择截面.发现在较低的入射粒子能量,电子主要俘获到He⁺离子主量子数n=3~5的壳层,高能区俘获到n=2的壳层为主;对同一主量子数n,在低能区俘获到高角动量态(l=n-1,n-2)的电荷转移截面相对较大,在高能区主要俘获到l=1的p壳层.同时还计算入射粒子能量分别为4 keV和400 keV时,电子俘获到激发态辐射退激发产生的电荷转移发射光谱,并发现cascade效应的影响很大.     

Charge transfer in H~ H and H~ He~ collisions at intermediate and high energies using an asymptotic two-state atomic expansion method

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