Nb,Ag原子的K壳层和L壳层电离截面的理论计算

电子离子碰撞电离截面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壳层电离截面理论,计算了Nb、Ag的K壳层和L壳层电子碰撞电离截面,结果和最近的文献实验数值和其它理论数值进行了比较,计算结果比其它模型更加准确,与最近的实验结果也吻合较好,该结果可用来模拟激光等离子体的超热电子能谱和产额.     

Double atomic photoeffect in the relativistic domain: Angular and energy distributions of photoelectrons

We study the double ionization of the atomic K-shell by a single photon in the relativistic energy domain. The differential and total cross sections of the process are calculated. It is shown that the ratio of the cross sections of double and single ionization increases with the photon energy, tending to the limit 0.34/Z ², where Z is the atomic number or the nuclear charge. The formulas are found to be valid for Z≫1 and αZ≪1, where α=1/137 is the fine-structure constant. Zh. éksp. Teor. Fiz. 114, 1537–1554 (November 1998)     

Measurements of K-shell ionization cross sections of35Br,37Rb,39Y using low energy protons

K-shell ionization cross section measurements are reported for₃₅Br,₃₇Rb and₃₉Y targets caused by protons over 300–400 keV energy range in 20 keV increment. The K-shell ionization cross sections (σ _k ^l ) at different energies were deduced from the K_α and K_β X-ray production cross sections which were obtained from X-ray yields of the K_α and K_β transitions. The experimental values are compared with the calculated values of ECPSSR theory and empirical reference cross sections. The resultant K-shell ionization cross sections are found to be in reasonable agreement with the ECPSSR theory. The K_α/K_β intensity ratios are also presented and compared with other experimental values and also with the theoretical one-hole values given by Scofield.     

A scaling law for K-shell ionization by relativistic electrons

Data on K-shell ionization by relativistic electron impact have been correlated for a wide range of elements (Z=13–83) and incident electron energies (E=3–900 MeV). A semi-empirical scaling law that has been developed using the Kolbenstvedt virtual photon theory is presented.     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

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。     

Ionization of hydrogen and helium atoms by highly charged fast ions in collisions with small momentum transfer

Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v² and v≫v ₀, where Z is the ion charge, v is the collision velocity, and v ₀∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron v _e≲v ₀, where v _e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula for the cross section for single ionization of helium is proposed. Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997)     

Ionization of K-shell electrons by electron impact

We have investigated the universal scaling behavior for cross sections of the single K-shell ionization by electron impact. The calculations are performed within the framework of non-relativistic perturbation theory, taking into account the one-photon exchange diagrams. Special emphasis is laid on the near-threshold energy domain. The results obtained are applicable for wide family of atomic targets with moderate values of the nuclear charge Z.     

K-shell X-ray production for fluorine ions on target elements Ti to La

The production of target atomK-shell X-rays has been studied for 2 to 28 MeV fluorine ions incident on thin solid targets of 14 elements with atomic numbers Z₂=22 to 57. Total X-ray production cross sections, energy shifts ofK _α andK _β lines andK _α/K _β intensity ratios were measured with a Si(Li) detector. The results of cross section measurements are compared with theoretical predictions of inner shell ionization. In most cases, satisfactory agreement between measured cross sections and theoretical Coulomb ionization cross sections, corrected for the perturbation of the target atom by the projectile charge and for relativistic effects, was obtained.     

Relativistic correction to the dipole polarizability of a hydrogenic ion

The first relativistic correction of orderα ² to the dipole polarizability of a hydrogenic ion has been investigated by using mean excitation energy of the ion within the second-order perturbation theory. The density-dependent mean excitation energy is estimated via Bethe theory for the stopping cross section for a moving point charge interacting with the hydrogenic ion. In this approach only the unperturbed Dirac wavefunctions are required to evaluate the appropriate matrix elements. The first relativistic correction turns out to be − (13/12)(αZ)². This has the correct sign and is within 5% of the exact result which is −(28/27)(αZ)².     

The process of coulomb dissociation of weakly bound relativistic nuclei and hypernuclei within the two-cluster model

Using the analogy with the problem of ionization and excitation of atoms in the propagation of relativistic charged particles through a bulk of matter, the process of Coulomb dissociation of weakly bound relativistic nuclei and hypernuclei is theoretically investigated in the framework of the two-cluster deuteron-like model. Explicit expressions for the total cross section of Coulomb disintegration of weakly bound systems are derived taking into account the corrections due to the finite size of a target nucleus. Numerical estimations for the Coulomb dissociation of relativistic hypernuclei ³H_Λ and ⁶He_Λ are performed. It is shown that, owing to a sharp dependence of the Coulomb dissociation cross section on the binding energy, experimental measurements of the cross section allow one to determine the values of binding energy for these systems. The text was submitted by the authors in English.     

Electron dichroism effects in the relativistic (e, 2e) process for K-shell ionization of atoms

In this communication we present theoretical demonstration of electron dichroism in the relativistic (e, 2e) process for K-shell ionization of atoms in non-coplanar asymmetric geometry. The theoretical formalism has been developed in plane wave Born approximation and in this approximation the triple differential cross-section (TDCS) has been expressed as a product of kinematical factors and atomic structure functions. The longitudinal spin asymmetry in the relativistic (e, 2e) process on K-shell of atoms has been shown to depend on the interference between the transition charge and component of the transition current in the direction perpendicular to the scattering plane. Further, the longitudinal spin asymmetry has been shown to depend on incident electron energy, atomic number of the target, azimuthal angle of the ejected electron and scattered electron angle.     

Electronic relativistic effect on the ratios of deuteron to alpha-particle induced K-shell ionization cross sections

The ratios of the K-shell ionization cross sections induced by deuterons to those induced by α-particles with the same velocities have been calculated in the plane wave Born approximation using relativistic hydrogenic wave functions for the target electrons. The numerical results are compared with the recent experimental valus of Chang et al. The use of relativistic wave functios considerably improves the agreement with the experimental data.     

Spectral shape of the 2E1 decay from 2s state in He-like tin

The two-photon 2E1 transition from the singlet 2s state of heliumlike tin was measured. An alternative experimental approach was adopted in the present investigation where the two-photon emission results from the decay of the 2s state by selective K-shell ionization of Li-like tin ions in relativistic collisions with a low-Z gaseous target, which allowed for a measurement of the undistorted two-photon spectral shape. The measured 2E1 energy distribution was compared with fully relativistic calculations, which predict a Z dependence of the distribution. The preliminary results indicate the best agreement with the relativistic many body calculations for tin, and thus confirm the sensitivity on Z. Detailed data analysis is still in progress.     

Single photoeffect on helium-like ions in the non-relativistic region

We present a generalization of the pioneering results obtained for single K-shell photoionization of H-like ions by M. Stobbe [M. Stobbe, Ann. Phys. 7 (1930) 661] to the case of the helium isoelectronic sequence. The total cross section of the process is calculated, taking into account the correlation corrections to first order of the perturbation theory with respect to the electron–electron interaction. Predictions are made for the entire non-relativistic energy domain. The phenomenon of dynamical suppression of correlation effects in the ionization cross section is discussed.     

Ratio of single K-shell ionization cross section to double K-shell ionization cross section in heavy-ion-atom collisions

The spectra of Ti Kα X-rays induced by He, C, N and O ions were measured with the use of a Bragg crystal spectrometer. The ratios of the integrated hypersatellite to diagram-plus-satellite X-ray yields were obtained. The previously obtained data on Cr, Fe and Ni Kα X rays induced by N ions were also analysed. It is found that the double K-shell vacancy production cross section is proportional to Z⁴₁.     

Note on the kinetic energy inequality leading to Lieb's negative ionization upper bound

The kinetic energy inequality is alternatively proved which yields Lieb's boundN < 2Z + 1 on the maximum negative ionization of an atom with nucleus chargeZ andN electrons when the kinetic energy operator is the nonrelativistic or relativistic magnetic Schrödinger operator. It is seen to follow from the free case where the vector potential vanishes. The proof applies to the Weyl quantized relativistic magnetic Schrödinger operator as well.Research partially supported by Grant-in-Aid for Scientific Research Nos. 04640141 and 05640165, Ministry of Education, Science and Culture, Japanese Government.     

Double ionization and excitation ionization in the Compton scattering of high-energy photons for metastable states of heliumlike ions

Double ionization and excitation ionization in Compton scattering for heliumlike ions in metastable states are investigated. The electron energy distribution for double ionization and the total cross sections for both processes are calculated. The calculations are carried out in the zeroth order of perturbation theory with respect to electron-electron interaction, using Coulomb wave functions as the first approximation. The resulting equations are valid only in the high-energy nonrelativistic range. It is assumed that Z≫1, but αZ≪1 (Z is the charge of the nucleus, and α is the fine-structure constant). Zh. éksp. Teor. Fiz. 116, 1889–1902 (December 1999)     

高能脉冲C~(6+)离子束激发Ni靶的K壳层X射线

精确测量离子与原子碰撞引起的靶原子内壳层电离截面,对研究原子内壳层过程以及建立合适的理论模型具有重要的意义.现有的实验数据和理论模型大都集中在中低能区,高能区由于受到实验条件的限制,几乎没有相关实验数据的报道,哪种理论更适合描述高能重离子入射的靶原子内壳层电离截面,还需要进行深入的实验研究.采用电子冷却存储环提供能量分别为165,300,350,430 MeV/u的C~(6+)离子束轰击Ni靶,测量Ni的K壳层X射线.分析了实验中探测到的Ni的K_β和K_α射线强度比,发现入射粒子能量的变化对该强度比影响不明显.分别应用两体碰撞近似(BEA)、平面波玻恩近似(PWBA)和ECPSSR理论对Ni的K壳层X射线的产生截面进行理论计算,并将理论结果与实验结果进行比较.     

Photoionization of helium-like ions accompanied by the excitation of <Emphasis Type="Italic">p</Emphasis>-wave states of the residual atom

The single-photon ionization of the ground state of a helium-like multicharged ion, which is accompanied by a simultaneous excitation of the residual ion to the np states, is studied using nonrelativistic pertubation theory with respect to the electron-electron interaction. Formulas describing the cross section for the process being studied are obtained. These formulas exhibit a scaling behavior in the target-nucleus charge number Z and in the principal quantum number n. Numerical calculations are performed for nonrelativistic energies including the near-threshold region.