Collisions of Highly Stripped Ions at MeV Energies in Gas Targets: Charge Transfer and Ionization

We have measured cross sections for charge transfer and ionization in H2 and rare-gas targets by fast, highly ionized Carbon, iron, niobium, and lead ions in charge states +3 to +59, with energies in the range 0.1-4.8 MeV/amu. Experimental results are compared with classical-trajectory calculations; agreement is generally good. For a given target, the cross sections for net ionization reduce to a common curve when plotted as cross section divided by charge state versus energy per nucleon divided by charge state.     

跨玻尔速度能区Xe~(23+)离子与Ne原子碰撞中的电子过程

本文用飞行时间符合技术实验研究了跨玻尔速度能区(入射离子速度为0.65~1.32a.u.,a.u.为玻尔速度)高电荷态离子Xe23+与Ne原子碰撞中的多电子过程,通过分析符合二维谱获得各反应道(靶原子的电子丢失、电子转移以及伴随电离的电子丢失)的相对截面,并与拓展的过垒模型及相关的经验公式进行了对比,结果与过垒模型符合相对较好。     

6—30keVB^＋,C^＋,N^＋,O^＋与H2碰撞单电子剥离的实验研究

用增长率方法首次测量６－３０ｋｅＶＢ＾＋、Ｃ＾＋、Ｎ＾＋、Ｏ＾＋与Ｈ２碰撞的单了截面，给出的Ｂ＾＋和Ｃ＾＋和６－３０ｋｅＶ能区截面随离子能量的趋势与已有的１００－２５００ｋｅＶ能区截面的变化趋势衔接很好。根据截面随入射离子能量和核电荷数的变化，对碰撞机理作了分析，Ｂ＾＋、Ｎ＾＋、Ｏ＾＋与Ｈ２碰撞的单电子剥离截面的变化规律由分子轨道模型得到很好的解释。     

Database for inelastic collisions of sodium atoms with electrons, protons, and multiply charged ions

The available experimental and theoretical cross section data for inelastic collision processes of ground (3s) and excited (3p, 4s, 3d, 4p, 5s, 4d, and 4f) state Na atoms with electrons, protons, and multiply charged ions have been collected and critically assessed. In addition to existing data, electron-impact cross sections, for both excitation and ionization, have been calculated using the convergent close-coupling approach. In the case of proton-impact cross section, the database was enlarged by new atomic-orbital close-coupling calculations. Both electron-impact and proton-impact processes include excitation from the ground state and between excited states (n = 3-5). For electron-impact, ionization from all states is also considered. In the case of proton-impact electron loss, cross sections (the sum of ionization and single-electron charge transfer) are given. Well-established analytical formulae used to fit cross sections, published by Wutte et al. and Schweinzer et al. for collisions with lithium atoms, were adapted to sodium. The “recommended cross sections” for the processes considered have been critically evaluated and fitted using the adapted analytical formulae. For each inelastic process the fit parameters determined are tabulated. We also present the assessed data in graphical form. The criteria for comprehensively evaluating the accuracy of the experimental data, theoretical calculations, and procedures used in determining the recommended cross sections are discussed.     

Molybdenum L-shell X-ray production by 350-600 keV Xe (q = 25-30) ions

Molybdenum L-shell X-rays were produced by Xe^q+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described.     

Path dependence of the charge state distributions of low-energy F ions backscattered from RbI(1 0 0)

Projectile neutralization during backscattering from RbI(1 0 0) of F multicharged ions in the keV energy range was investigated utilizing a time-of-flight technique. The energy and charge state distributions of the scattered ions were measured as a function of the polar incidence angle and the target azimuthal orientation. We found significant variations in the neutralization degree for incident projectiles of different charge states. The charge state distribution of scattered ions, including negative charge states, was found to depend on both the polar incidence and azimuthal orientation angles. These variations are attributed to the particular hard and soft encounters with neighboring lattice sites at the target surface along the path of the ion. Sample data for few-keV F²⁺ and F⁷⁺ incident projectiles are presented to illustrate the underlying concepts.     

A Penning Ion Source for Multiply Charged Ions

The ion source described in this contribution allows the production of considerable ion beam intensities of highly charged ions. The electron density is increased by an additional electron gun. The decrease-of the ratio of neighbouring charge states is similar to the decrease of the ratio of the ionization cross sections by electron impact from which one event ionization processes are assumed to be of major importance in the performance of this source.     

类锂离子与He原子碰撞中的单电子丢失

本文基于Bohr-Lindhard(B-L)模型,考虑了碰撞双方的电子密度分布,计算了能量为20~900keV/u的B2+、C3+、N4+及O5+等类锂离子与He原子碰撞中的单电子丢失(SEL)、伴随单电离的单电子丢失(SELSI)、伴随双电离的单电子丢失(SELDI)等截面对能量的依赖曲线,计算结果与已有的实验数据符合较好。分析发现,对于一给定的过程,较重的离子有较小的有效碰撞参数范围;对于同一种入射离子,SEL、SELSI和SELDI等过程对应的有效碰撞参数范围依次减小。     

Energy loss of H and He in the semiconductors GaAs, ZnSe, InP and SiC

We have theoretically studied the electronic stopping cross section and the energy loss straggling of swift light ions (H⁺ and He⁺) moving through several compound semiconductors (GaAs, ZnSe, InP and SiC) as a function of the incident projectile energy. The calculations have been done using the dielectric formalism, in which the electronic structure of the projectile is described by the modified Brandt–Kitagawa model and the energy loss function (ELF) of the semiconductors is obtained using a linear combination of Mermin-type ELF to describe the outer electron excitations and generalized oscillator strengths to take into account the excitations of the inner-shell electrons. The different charge states that the projectile can acquire during its travel through the solid, as a result of electronic capture and loss processes, has been also considered. The contributions to the projectile energy loss from both the outer- and the inner-shell electron excitations are analyzed. The comparison of our calculated stopping cross sections with available experimental data shows a good agreement in a wide range of incident projectile energies.     

Radiative Electron Capture for F8+ and F9+ Ions in Collisions with a He Gas Target

The x rays from the radiative electron capture (REC) to the projectile K-shell were investigated for F8+ and F9+ ions incident on the He target atoms in the projectile energy range from 15 to 40 MeV. The peak energies of the K-REC x-ray spectra were found to decrease linearly with a decrease of the projectile energies as expected and extrapolated to the correct ls binding energies at zero velocity. According to theory the distribution width, ?REC, of the REC energies should be independent of the binding energy of electrons in the projectile ions. However, it is found that ?REC for F8+ ions is systematically smaller by 20% than that for F9+ ions. The measured REC cross sections for F9+ ions are slightly larger than twice those for F8+ ions and the total REC cross sections for F8+ and F9+ ions were found to be more than three orders of magnitude smaller than the total electron capture cross sections and the capture cross sections into excited states.     

K X-ray emission induced by C and O ion impact on selected lanthanoids

Measurements of K-shell X-ray production cross sections by ¹²C⁴⁺ (beam energies between 12 MeV and 14 MeV), and ¹⁶O⁵⁺ ions (with energies between 12.5 MeV and 15 MeV) are presented. The target elements were selected lanthanoids (Ce, Gd, Dy, Ho and Er). The resulting measurements are evaluated through comparisons with the eECPSShsR-UA theory, the MECPSSR model and the adiabatic perturbation (also known as direct molecular orbital, MO) theory, using a scaling based on the reduced velocity parameter . Consideration is given to multiple ionization effects and electron capture contribution to K-shell ionization. An evaluation with previously published values is also given. It is shown that the behavior of the ratios of experimental to theoretical cross sections is different for both ions. The models do not seem to be accurate to predict the X-ray production cross sections for ¹²C⁴⁺ ions, while the MECPSSR theory predicts much better the experimental data for ¹⁶O⁵⁺ than the eECPSShsR-UA.     

Phenomenological level density model with hybrid parameterization of deformed and spherical state densities

A phenomenological level density model that has different level density parameter sets for the state densities of the deformed and the spherical states and the optimization of the parameters using experimental data of the average s-wave neutron resonance spacing are presented. The transition to the spherical state from the deformed one is described using the parameters derived from a microscopic nuclear structure calculation. The nuclear reaction calculation has been performed by the statistical model using the present level density. Resulting cross sections for various reactions with the spherical, deformed, and transitional target nuclei show a good agreement with the experimental data, which indicates the effectiveness of the present model. The role of the rotational collective enhancement in the calculations of those cross sections is also discussed.     

氟离子碰撞引起铅原子L壳层X射线产生截面的实验测量

实验测量了20～50MeV的F离子碰撞Pb原子产生的L壳层X射线,研究了Pb的L各支壳层X射线产生截面σ（L_l）、σ(L_α)、σ（L_β）、σ（L_γ）和σ（L_tot）与入射离子能量的关系。结果显示：在本能区范围内,Pb原子发射L壳层X射线产生截面随入射离子能量的增加而增加。利用L壳层的辐射跃迁几率、Coster Kronig跃迁率和L亚壳层的荧光产额将平面波波恩近似（PWBA）和ECPSSR理论计算的电离截面转换为L层X射线产生截面,并与实验结果相比较。结果表明,σ（L_l）、σ(L_α)、σ（L_β）、σ（L_γ）、σ（L_tot）实验测量值与PWBA理论计算值差别很大,ECPSSR理论计算值与σ(L_α)实验值符合很好,与σ（L_l)、σ（L_β）的实验值差别较小,但与σ（L_γ）的实验值差别较大。     

K- and L-shell ionization cross sections for protons and helium ions calculated in the ecpssr theory

Ionization cross sections for K and L subshells are tabulated according to target atomic number and incident ion energy. Proton and helium ion energies between 100 keV and 10 MeV and selected targets between C and Am for the K shell and between Ar and Am for the L subshells are used. The cross sections have been calculated in the plane-wave Born approximation (PWBA) with corrections for energy loss (E), Coulomb deflection (C), perturbed stationary state (PSS), and relativistic (R) effects (ECPSSR).     

SRAM单元中子单粒子翻转效应的Geant4模拟

应用Geant4工具,构造了不同特征尺寸的SRAM单元几何模型及单粒子翻转截面计算模型,分析了敏感体积和临界电荷对低能中子单粒子翻转效应的影响趋势,计算了反应堆裂变中子谱辐射环境下,不同特征尺寸SRAM的中子单粒子翻转截面,认为小尺寸SRAM器件的低能中子单粒子翻转效应更为严重。     

Production of heavy neutron-rich nuclei with radioactive beams in multinucleon transfer reactions

The production mechanism of heavy neutronrich nuclei is investigated by using the multinucleon transfer reactions of 136,148Xe+208pb and 238U+208pb in the framework of a dinuclear system model.The evaporation residual cross sections of target-like fragments are studied with the reaction system 148Xe+208pb at near barrier energies.The results show that the final isotopic production cross sections in the neutron-deficient side are very sensitive to incident energy while it is not sensitive in the neutron-rich side.Comparing the isotopic production cross sections for the reactions of 20spb bombarded with stable and radioactive projectiles,we find that neutron-rich radioactive beams can significantly increase the production cross sections of heavy neutron-rich nuclei.     

Charge Exchange between Hydrogen Atoms and Fully Stripped Heavy Ions

Charge exchange between multicharged ions and background atomic and molecular gases represents one of the limitations to the attainment of high charge states in heavy ion sources, particularly containment sources. This work is an attempt to study systematically a particularly simple but in many respects representative class of such reactions, namely, charge transfer between atomic hydrogen and fully stripped heavy ions. Approximate cross sections for these processes in the low keV range of collision energies were obtained using a multistate Landau-Zener method. The energy and Z dependences of the cross sections are discussed.     

An Experimental Apparatus for Low Energy High Charge Heavy Ions to Study Collisions on Atomic Hydrogen

The design and performance of a recoil ion source system which includes a recoil ion source, atomic hydrogen thermal oven target and an electrostatic analysis system will be discussed. The recoil ion source produces low velocity highly charged ions via collisions between heavy fast pump beams from the EN tandem accelerator and target gases. Time-of-flight techniques provide initial recoil charge state separation. Collisions of the recoils with atomic hydrogen are being studied. The atomic hydrogen is provided by a thermal oven which features long life time operation and low input power requirements. Dissociation fractions of 80% are achieved for 300 watts of input power. A hemispherical electrostatic analyzer allows the final charge states of the recoil ions to be determined thereby allowing the measurement of charge exchange processes for an energy range of 100 eV/q to 5000 eV/q for the incident recoil ions.     

Theoretical and experimental investigations of electron emission in C + H2O collisions

Theoretical differential and total cross sections for the direct ionization process of water vapour by 6 MeV/u C⁶⁺ ions are compared to new experimental measurements performed by the dedicated apparatus already used for measuring the energy and angular distributions of secondary electrons emitted from water vapour by fast heavy-ion impact [D. Ohsawa, H. Kawauchi, M. Hirabayashi, Y. Okada, T. Homma, A. Higashi, S. Amano, Y. Hashimoto, F. Soga, Y. Sato, Nucl. Instr. and Meth. B 227 (2005) 431]. In the present work, ab initio calculations have been carried out in the first Born approximation by using an accurate molecular wave function for describing the initial bound state of the target. The calculated cross sections exhibit good agreement with the present experimental measurements and compare relatively well to the existing semi-empirical results over the entire angular and energy ranges investigated here. Free from any adjustable parameter, the proposed theoretical approach describes in detail the complete kinematics of the water molecule ionization process by highly energetic carbon ions, and could therefore be easily used for modelling the heavy charged-particle transport in the biological matter.