Breit相互作用对类氦离子亚稳态1s2s3S1电子碰撞激发截面的影响

利用新近发展的基于全相对论扭曲波方法研究电子-离子碰撞激发过程的计算程序,通过对Breit相互作用的考虑,计算了类氦等电子序列离子从亚稳态1s2s3S1激发2s电子到n=2,3壳层的电子碰撞激发截面;研究了不同入射电子能量时Breit相互作用对碰撞激发截面的影响,进一步总结了沿等电子序列变化时,Breit相互作用对截面影响的一般规律.部分计算结果与实验结果进行了比较,得到了很好的一致性.     

X-ray spectra of He-like ions of Ga and Ge,excited in the low-inductance spark plasma

The spectra of Ga XXX and Ge XXXI ions in the interval 1.2–1.4 Å excited in the low-inductance vacuum spark plasma have been obtained for the first time. The resonance line 1s²?1s2p of Ga XXX and Ge XXXI and a group of satellites, corresponding to transitions in Ga XXIX and Ge XXX can be seen distinctly in the spectra. The spectra were obtained by an electronic-optical image-intensifier tube for one discharge.     

The fine structure of excitonic levels in CdSe nanocrystals

The fine structure of the exciton ground level in a spherical nanocrystal of a zincblende or a wurtzite structure semiconductor was calculated with the inclusion of short-and long-range (nonanalytical), exchange-interaction components. The band-parameter dependence of the long-range exchange-interaction contribution to the spin Hamiltonian describing the exciton ground-level splitting was found. A study was made of the effect exerted on the exciton-level fine structure by the difference between the background dielectric permittivities of the nanocrystal and of the dielectric host in which it was grown.     

Observation of fine structure in the 1s2s2p P-1s2p S transition of core-excited O V

We have measured the absolute wavelengths of the fine structure components of the 1s2s2p^{2 5}P-1s2p^{3 5}S transition in beryllium-like oxygen using the method of fast ion spectroscopy. These results represent the first measurement of fine structure in any core-excited 4-electron ion. We have also measured the lifetime of the metastable 1s2p^{3 5}S state. The structure and lifetime results are compared with recent relativistic MCHF calculations.     

Resonant coherent excitation of Ar17+ ions taking into account a fine structure of energy levels

The effect of a fine structure of the orbital electron energy levels of an Ar¹⁷⁺ ion on the resonant coherent excitation under planar channeling has been investigated by computer simulation technique. The obtained resonance curves are characterized by two closely situated peaks due to the transitions of an electron from the ground to excited states corresponding to the different components of a fine structure of the first excited state which differ in the value of the total electron momentum (1/2 or 3/2).     

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.     

Experiments on two-step heating of a dense plasma in the GOL-3 facility

This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 10¹⁷ cm⁻³ was created in the main plasma, whose density was 10¹⁵ cm⁻³. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions. Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which is inhomogeneous in density and temperature, including the appearance of pressure waves. Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998)     

g-Factor of heavy ions: a new access to the fine structure constant

A possibility for a determination of the fine structure constant in experiments on the bound-electron g-factor is examined. It is found that studying a specific difference of the g-factors of B- and H-like ions of the same spinless isotope in the Pb region to the currently accessible experimental accuracy of 7 x 10(-10) would lead to a determination of the fine structure constant to an accuracy which is better than that of the currently accepted value. Further improvements of the experimental and theoretical accuracy could provide a value of the fine structure constant which is several times more precise than the currently accepted one.     

Quasi-binary incident electron—centre of mass collision in (e, 3e) process on He and He-like ions

We present in this communication the results of our first Born calculation in the three-Coulomb (3C) wave approach for the (e, 3e) process on He and He-like ions at an incident electron energy 5599 eV in the coplanar constant θ12 as well as out-of-plane constant φ12 modes. These two geometrical modes are such that the quasi-binary collision between the incident electron and centre of mass of the ejected electrons is in the scattering plane. The theoretical formalism has been developed using plane waves, Le Sech wave function and approximated BBK-type wave function respectively for the incident and scattered, bound and ejected electrons to calculate five-fold differential crosssection (FDCS) of the (e, 3e) process. We emphasize on the similarities and dissimilarities (asymmetries) in the angular profile of the FDCS in two modes as well as the effects of post-collision interaction (between the ejected electrons) and nuclear chargeZ on the angular profile of the FDCS. We observe that with the increment of nuclear charge the two quasi-binary collisions approach towards identical behaviour at larger mutual angles and thus bringing less asymmetry in FDCS for higherZ target.     

Spectroscopic study of the production of magnesium ions from the atomic metastable states 3s3p 3 P 0, 2 by electron impact

Spectroscopic studies of the production of MgII ions from atomic metastable states by electron impact in crossed atomic and electron beams were made. Cross sections for excitation of the strongest spectral transitions and their energy dependences were determined. The maximum value of the cross section for ionization with excitation of the 3² S _1/2–3² P _3/2 transition reached 2.4×10^?16 cm². Possible mechanisms of production of excited ions from metastable states and their contribution to the total ionization process are discussed.     

Hyperfine induced {\sf 1 s}{\sf 2 s}\ ^{\sf 1}S_{\sf 0} \rightarrow {\sf 1 s}^{\sf 2}\ ^{\sf 1}S0 M1 transition of He-like ions

Hyperfine induced $1s2s\ ^1$ S $_0 \rightarrow 1s^2\ ^1$ S₀ M1 transition probabilities of He-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. Present results for ¹⁵¹Eu and ¹⁵⁵Gd are in good agreement with previous calculations [L.N. Labzowsky et al., Phys. Rev. A 63, 054105 (2001)]. Electronic data are given in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine induced decay rates to be estimated for any isotope. The results should be helpful for future experimental investigations on QED and parity non-conservation effects.     

The structure of the Z 1 Z 2 → l + l − Z 1 Z 2 amplitude process outside the born approximation framework

Resummation of the perturbative series for the amplitude of lepton pair production in nucleus-nucleus collisions is performed based on the Watson theorem and the hypothesis of infrared stability. An explicit expression for this amplitude is obtained, which is valid to within terms of the ninth order in the fine structure constant.     

Effect of radiation on compressibility of hot dense sodium and iron plasma using improved screened hydrogenic model with l splitting

High pressure investigations of matter involve the study of strong shock wave dynamics within the materials which gives rise to many thermal effects leading to dissociation of molecules, ionization of atoms, and radiation emission, etc.The response of materials experiencing a strong shock can be determined by its shock Hugoniot calculations which are frequently applied in numerical and experimental studies in inertial confinement fusion, laboratory astrophysical plasma,etc. These studies involve high energy density plasmas in which the radiation plays an important role in determining the energy deposition and maximum compressibility achieved by the shock within material. In this study, we present an investigation for the effect of radiation pressure on the maximum compressibility of the material using shock Hugoniot calculations. In shock Hugoniot calculations, an equation of state(EOS) is developed in which electronic contributions for EOS calculations are taken from an improved screened hydrogenic model with-l splitting(I-SHML) [High Energy Density Physics(2018) 26 48] under local thermodynamic equilibrium(LTE) conditions. The thermal ionic part calculations are adopted from the state of the art Cowan model while the cold ionic contributions are adopted from the scaled binding energy model. The Shock Hugoniot calculations are carried out for sodium and iron plasmas and our calculated results show excellent agreement with published results obtained by using either sophisticated self-consistent models or the first principle study.     

Measurement of cross-section of excitation transfer from 3s2 to 4s1 and 5s1 energy levels of neon

Collision induced non-radiative transitions in neon plasma have been studied using high intra-cavity radiation field of a 633 nm He-Ne laser. The transitions, induced from 3s ₂ energy level to 4s₁ and 5s₁ groups of energy levels, have been detected as changes in intensities of the spectral lines originating from these energy levels. From these intensity measurements, the quantities governing the transitions i.e. (i)S ₃ ^e /S _3RT , the ratio of the probabilities of electronic deexcitation to the total radiative deexcitation of energy level 3 (ii) 〈r ₂₃ ^e v _e〉, rate of excitation transfer per particle and (iii)S ₂₃ ^e , the total probability for excitation transfer from level 2 to level 3 at a certain value of electron density have been calculated.     

The fine structure of the isoharic analogue resonances

The distribution of an isobaric analogue resonance over the numerous surrounding states of different isobaric spin is studied analytically in the frame of the Fano-Weidenmüller shell-model theory of nuclear reactions. The doorway state wave function is described byLane's coupled equations. The matrix element of the residual nuclear interaction between this doorway state and a complicated state of different isobaric spin exhibits a particular energy dependence. A sum rule is established: the sum of the fine structure widths is larger than the width of the doorway state, as calculated fromLane's model. The residual Coulomb interactions are neglected. When perturbation theory holds, the distribution of the fine structure peaks is shown to have a characteristic asymmetrical shape. The connection withRobson's R-matrix treatment is discussed.     

Transitions between the components of the fine structure in He and He-Like ions colliding with protons

The cross sections for the transitions between the components of the fine structure of triplet levels with n = 2 and 3 in He and He-like ions colliding with protons have been considered. The feature of the problem is the presence of a virtual level coupled with the components of the multiplet by dipole-allowed transitions. As a result, the cross section at intermediate collision velocities has a peak, which is sometimes much higher than the cross section for the transition induced by collisions with electrons. The cross sections for He and C⁴⁺ and Fe²⁴⁺ ions have been calculated by the tight-binding method.