中低能非全裸C离子与He原子的碰撞研究

采用反冲离子飞行时间-散射离子位置灵敏符合测量技术，测量了能量范围在0.7v₀—4.4v₀(v₀为玻尔速度)的碳离子C^q+(q=1—4)与He原子碰撞过程不同出射道靶原子的双电离与单电离截面比R，包括入射离子不损失电子(直接电离)的出射道(R_q,q),入射离子俘获一个电子的出射道(R_q,q-1)和入射离子损失一个电子的出射道(R_q,q+1)，并研究了R随入射C离子的能量及电荷态的变化关系.实验表明，对给定电荷态的入射离子，靶原子的双电离与单电离截面比R与出射道有很强的依赖关系，即R_q,q<R_q,q+1<R_q,q-1.直接电离出射道截面比R_q,q与入射离子电荷态几乎无关，而入射离子俘获一个电子的出射道和损失一个电子的出射道靶原子双电离与单电离截面比R_q,q-1和R_q,q+1却与入射离子电荷态有很强的关系.采用原子极化理论和电子屏蔽与反屏蔽作用对实验结果进行了解释. 关键词： 离子-原子碰撞 电离 截面比     

Projectile electron loss in collisions of light charged ions with helium

We investigate the single-electron loss processes of light charged ions （Li^1＋,2＋, C^2＋,3＋,5＋, and O^2＋,3＋） in collisions with helium. To better understand the experimental results, we propose a theoretical model to calculate the cross section of projectile electron loss. In this model, an ionization radius of the incident ion was defined under the classical over-barrier model, and we developed ＂strings＂ to explain the processes of projectile electron loss, which is similar with the molecular over-barrier model. Theoretical calculations are in good agreement with the experimental results for the cross section of single-electron loss and the ratio of double-to-single ionization of helium associated with one-electron loss.     

Polarized electron capture by3He2+ at 20–28 keV

Nuclear polarization was measured by means of beam foil spectroscopy for a³He⁺ ion produced by an electron capture process of a³He²⁺ from a polarized sodium atom in an incident energy range from 20 to 28 keV. Assuming that a polarized electron of a sodium atom is predominantly captured to the 3d orbital of a³He⁺ ion andcascades down to the 1s ground state via the 2p orbital, an alignment factorA ₀ ^col (L=2) for the 3d orbital of a³He⁺ ion was extracted by comparing the observed initial sodium polarization andfinal nuclear polarization. The observedA ₀ ^col (L=2) showed a less pronounced energy dependence andwere qualitatively reproduced by the theoretical calculation.     

Luminescent collisions of He+ and He++ ions with H2 molecules at energies below 2 keV

Spectroscopic studies of collisions between He⁺ and He⁺⁺ ions with H₂ gas target have been performed in the 200–600 nm wavelength range. Atomic lines of hydrogen Balmer series and several helium lines were identified and their excitation functions between 50 eV and 1 keV (2 keV for He⁺⁺) were determined.     

Production of recoil ions He^i＋ accompanied by single electron loss of 0.2-7 MeV C^q＋ and 0.25-5 MeV O^q＋ （q = 1- 4） ions

Target ionization accompanied with projectile electron loss is investigated for 0.2-7 MeV C^q＋ （q = 1 - 4） with He and 0.25-5 MeV O^q＋ （q = 1 - 4） with He collisions. For projectile single-electron loss channel, the He double-to-single ionization ratio R is nearly independent of projectile charge state but dependent on the nuclear charge of projectile Zp. The results are analysed with atomic structure qualitatively. So far there have not existed the experimental data comparable with our results, to our knowledge. The ratio R is interpreted in terms of the two-step mechanism. This analysis agrees well with similar experiments in the literature.     

Charge distribution of He states, excited by electron capture in He+ (26 keV)-He collisions

Using anticrossing spectroscopy we investigated one-electron capture in He⁺ (26 keV) – He collisions. The intensity of the triplet line λ (1s4l ³D → 1s2p ³P) ≈ 447.2 nm emitted by the fast atoms was measured as a function of an external electric field in the collision volume varied from ?30 kV/cm to +30 kV/cm. The radiative decay of excited He atoms in an almost field-free region outside the collision volume was observed. The highly asymmetric intensity function could be reproduced theoretically using the density-matrix formalism. It indicates that the excited He atoms are in a state with a highly forward-backward asymmetric charge distribution, immediately after the charge-exchange collision.     

中低速C3+与He，Ne，Ar原子相互作用过程中单电子转移绝对截面的测量

实验测量了1.7v₀—4.2v₀(v₀为玻尔速度,v₀=2.19×10⁸cm/s)的C³⁺与He,Ne,Ar原子碰撞过程中单电子转移绝对截面.将实验结果与多体经典轨道蒙特卡罗模拟计算结果做了比较,发现测量结果与多体经典轨道蒙特卡罗模拟计算结果在趋势上相符.当入射离子速度在1.7v₀—2 关键词： 离子-原子碰撞 单电子转移 绝对截面     

Multiple ionization of argon accompanied by electron loss and capture of 0.22-6.35 MeV C^q＋ ions

In this paper a projectile ions recoil ions coincidence technique is employed to investigate the target ionization and projectile charge state changing processes in the collision of 0.22-6.35 MeV Cq^＋ （q = 1 - 4） ions with argon atoms. The partial cross section ratios of the double, triple, quadruplicate ionization to the single ionization （or the single capture） of argon associated with single electron loss （or single electron capture） by the projectile are measured and compared with the previous experimental results. In the present experiment, it is observed that the ratios of ionization cross sections R associated with single loss and single capture depend strongly on the projectile charge state and vary significantly with different reaction channels as impact energy increases. In addition, this paper gets empirical scaling laws for the ionization cross section ratios R corresponding to the projectile single loss and finds that the ratios of the double ionization to the single ionization associated with single electron capture remain constant in the present energy range.     

Na离子和Cl离子引起He原子直接多重电离过程的研究

利用2～8 MeV的Naq+、Clq+(q=2,3,4,5)轰击氦原子,对碰撞的直接多重电离过程进行研究.实验采用反冲离子-散射离子飞行时间符合技术,通过反冲离子飞行时间谱区分不同价态反冲离子;利用静电偏转和位置灵敏探测技术区分不同电荷态散射离子;结合CAMAC-PC多参数获取系统得到一定价态散射离子所对应的反冲离子电荷态分布谱;经分析该谱得到直接多重电离截面与直接单电离截面之比R21.讨论了R21随入射离子速度和电荷态的变化关系.     

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.     

X-ray emission for Ar11+ ions impacting on various targets in the collisions near the Bohr velocity

X-ray emission from the collisions of 3 MeV Ar¹¹⁺ ions with V, Fe, Co, Ni, Cu, and Zn is investigated. Both the x-rays of the target atom and projectile are observed simultaneously. The x-ray yield is extracted from the original count. The inner-shell ionization cross section is estimated by the binary encounter approximation model and compared with the experimental result. The remarkable result is that the Ar K-shell x-ray yield is diminished with the target atomic number increasing, which is completely opposite to the theoretical calculation. That is interpreted by the competitive consumption of the energy loss for the ionization of inner-shell electrons between the projectile and target atom.     

Effect of vibrational kinetics of He2 + ions on the afterglow of a discharge in helium

A decaying weakly ionized helium plasma [n_e=(0.2–1.1)·10¹¹ cm^–3, p=(40–70) mm Hg] was studied experimentally. It is shown that the experimental time dependences of the intensities of atomic lines and molecular bands in the afterglow phase can be explained if the vibrational kinetics of He₂ ⁺ ions is included in the analysis. Analysis of the measurements shows that for n_e 10¹¹ cm^–3 and N_a 10¹⁸ cm^–3 deexcitation of He₂ ⁺ ions occurs primarily as a result of inelastic collisions with helium atoms. Based on the experimental data, an approximate value was obtained for the rate constants of the vibrational relaxation of molecular helium ions 10^–16 cm³/sec. These results are used for making a qualitative analysis of the distribution of He₂ ⁺ ions over the vibrational states in the discharge phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–96, November, 1986.     

利用超相对论量子分子动力学模型研究交变梯度同步加速器能区Au+Au碰撞中的核阻止效应

运用修正的超相对论量子分子动力学模型研究了交变梯度同步加速器(AGS)能区Au+Au碰撞中的核阻止效应. 该模型考虑了形成和"预形成"粒子的平均场势、核子-核子弹性散射反应截面的介质修正和碎块形成的判断条件. 研究发现: 在AGS能区, 核阻止效应受到形成和“预形成”粒子的平均场势和核子-核子弹性散射反应截面介质修正的影响; 在中心快度区自由质子的产额偏大, 考虑新的碎块形成判断条件后, 此模型的理论计算结果与自由质子的实验结果符合得很好. 关键词： 超相对论量子分子动力学模型 交变梯度同步加速器能区 Au+Au碰撞 核阻止效应     

中速C3+与Ne原子靶相互作用过程中单电子转移绝对截面的测量

实验测量了2.2v₀—4.2v₀(v₀为玻尔速度,v₀=2.19×10⁸cm/s)的C³⁺与Ne原子碰撞过程中单电子转移绝对截面.将实验结果与多体经典轨道蒙特卡罗模拟计算结果进行了比较.用电离能的变化、屏蔽效应、动态关联对实验和理论计算结果间的数值差异做了分析.总体上,实验结果与多体经典轨道蒙特卡罗方法计算结果在趋势上相 关键词： 离子-原子碰撞 单电子转移 绝对截面     

Investigation of transfer ionization processes in the collision of partially stripped carbon ions on Argon

The ratios of the cross section of the transfer-ionization to the single-electron-capture of Argon induced by C ^q+ (q = 1, 2, 3) ions are measured by means of position sensitive and time-of-flight techniques. Our experimental results are compared with the data of He^q+ (q = 1, 2) − Ar of DuBois. A qualitative interpretation is presented based on the Classical-Over-Barrier Model of Bohr.     

Excitation of the 1s 2- and 1s 4-levels of neon and argon by He+-impact at energies between 100 keV and 1000 keV

The excitation of the 1s ₂- and 1s ₄-levels of neon and argon by He⁺-impact has been studied in the energy range of 100 keV to 1000 keV. The total emission cross sections for the 1s ₂ levels show pronounced maxima at about 350 keV impact energy, whereas the cross sections for the 1s ₄ levels increase with decreasing energy.     

Readjustment of the Bohr stopping force from energies of keV/n to a few tens of MeV/n ions in elemental targets

An analytical approach for the electronic stopping force for non-relativistic energies that has no adjustable parameters has been developed. The approach combines the Bohr model for the close collisions and the Firsov model for the distant collisions. In order to combine the two models, a probabilistic model was introduced. We have applied our model to ¹⁶O in ¹²C, ¹⁶O in ²⁷Al, ⁸⁴ Kr in ²⁷Al, ⁵Li in ¹²C, ¹²C in ¹²C, and ¹³²Xe in ¹²C systems and compared with SRIM/MSTAR software, the original Bohr model, the Firsov model and available experimental data. We have found that the calculated electronic stopping force values are in agreement with the general qualitative behaviour of the electronic stopping force as a function of particle velocity reported in the literature. The proposed analytical formula is expected to be valid for other projectile-target combinations but more experimental data are needed to verify this assumption.     

Single-and-double electron loss of O2+ in collisions with argon and helium

This paper reports that the ratios of double to single electron loss cross-section （R） of O^2＋ in collision with Ar and He at the velocity of 1 -4 vo（vo is the Bohr velocity） have been obtained by the coincidence technique. The trend of R - V in the experiment indicates that the effective charge varies with injected velocity. The effective charge can be obtained by the n-body classical trajectory Monte Carlo method, which is interpreted by the molecular Coulomb over barrier model.