Oscillator strengths and lifetimes for the S V spectrum

The semi-empirical weighted oscillator strengths (gf) and the lifetimes presented in this work for all experimentally known electric dipole S V spectral lines and energy levels were carried out in a multiconfiguration Hartree–Fock relativistic (HFR) approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure, in order to improve the adjustment to experimental energy levels. This method produces lifetime values and gf values that are in agreement with intensity observations used for the interpretation of spectrograms of solar and laboratory plasmas.     

Extended analysis of the Kr V spectrum

The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s²4p5d, 4s²4p5s, 4s²4p6s, 4s²4p5p and 4s4p²4d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions.     

Relativistic core binding energies of selected atoms: Comparison with experiment and other calculations

Single-configuration Dirac—Fock binding energies are reported for K 2p, Rb 3p, Cs 3d, Mg 1s, Zn 2p, and Cd 3d as well as for the corresponding levels in the cations of these elements and the neighboring rare gases. The results are compared with similar Dirac—Slater and Hartree—Fock calculations, and with experiment. It is found that the calculated binding energies are generally in very good agreement with experiment and are superior to the Dirac—Slater and Hartree—Fock results. The relativistic contribution is shown to be significant even for lighter atoms.     

Energy levels and probabilities of radiative transitions in the Kr IX ion

The energy levels of the 3d ⁹4l (l = 1–3) and 3p ⁵3d ¹⁰4l (l = 0, 1) configurations in the Kr IX ion and the probabilities of radiative transitions to the ground state from these excited states have been calculated within the relativistic perturbation theory using a zero-approximation model potential. The results are shown to be stable within this approximation. The well-known problem of anomalously low accuracy of the calculations of some higher lying singlet levels is considered.     

Autoionization resonances in the photoabsorption spectra of Fe<Superscript><Emphasis Type="Italic">n</Emphasis>+</Superscript> iron ions

The photoabsorption cross sections of a neutral iron atom, as well as positive Fe⁺ and Fe²⁺ ions, are calculated in the relativistic random-phase approximation with exchange in the energy range 20–160 eV. The wavefunctions of the ground and excited states are calculated in the single-configuration Hartree–Fock–Dirac approximation. The resultant photoabsorption spectra are compared with experimental data and with the results of calculations based on the nonrelativistic spin-polarized version of the random-phase approximation with exchange. Series of autoionization resonance peaks, as well as giant autoionization resonance lines corresponding to discrete transitions 3p → 3d, are clearly observed in the photoabsorption cross sections. The conformity of the positions of calculated peaks of giant autoionization resonances with experimental data is substantially improved by taking into account additionally the correlation electron–electron interaction based on the model of the dynamic polarization potential.     

Lineshapes of the even mp1/2 5n(p′/f′) autoionizing resonances of Ar, Kr and Xe

The even parity mp_1/2 ⁵np^′ and mp_1/2 ⁵nf^′ autoionizing resonances of Ar, Kr, and Xe (m=3,4,5) were investigated experimentally and theoretically by one-photon excitation from lower-lying intermediate levels. In particular, high resolution measurements for the Ar(nf^′), Kr(12p^′,8f^′), and Xe(8p^′) resonances are reported; lineshape parameters for these resonances have been derived by a Fano-type analysis, thus yielding reduced resonance widths. The experimental spectra and the resonance parameters are compared with theoretical calculations which are based on the configuration interaction Pauli–Fock approach including core polarization. The measured and calculated lineshapes are in good agreement. In addition, theoretical predictions are presented for other resonances, which have not yet been observed experimentally, and some systematic trends are elucidated.     

Electron shake probabilities of heavy elements as a result of M‐shell vacancy production

The electron shakeup‐plus‐shakeoff probabilities accompanying M‐shell vacancy creation have been calculated for elements between Z = 72 and 92. The calculations were performed relativistically in the sudden approximation by the use of the Dirac–Fock–Slater wave functions. The relativistic effects are demonstrated in comparison with the nonrelativistic calculations, and the validity of the approximation method based on the difference in the effective nuclear charge is discussed. The dependence of different initial M‐subshell vacancies on the shake probability is studied. Copyright © 2014 John Wiley & Sons, Ltd.     

Weighted oscillator strengths and lifetimes for the S XIV spectrum

The weighted oscillator strengths gf and the lifetimes for S XIV presented in this work have been calculated in a multiconfigurational Hartree–Fock relativistic approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure in order to improve the adjustment to experimental energy levels. This method produces gf values that are in better agreement with observed line intensities and lifetime values closer to the experimentally determined ones. In this work we presented all the experimentally known electric dipole S XIV spectral lines. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 473–476, 2009.     

Ground-state properties of neutron magic nuclei

A systematic study of the ground-state properties of the entire chains of even–even neutron magic nuclei represented by isotones of traditional neutron magic numbers N = 8, 20, 40, 50, 82, and 126 has been carried out using relativistic mean-field plus Bardeen–Cooper–Schrieffer approach. Our present investigation includes deformation, binding energy, two-proton separation energy, single-particle energy, rms radii along with proton and neutron density profiles, etc. Several of these results are compared with the results calculated using nonrelativistic approach (Skyrme–Hartree–Fock method) along with available experimental data and indeed they are found with excellent agreement. In addition, the possible locations of the proton and neutron drip-lines, the (Z, N) values for the new shell closures, disappearance of traditional shell closures as suggested by the detailed analyzes of results are also discussed in detail.     

Independent yields of Kr and Xe isotopes in the photofission of heavy nuclei

The yields of Kr (A = 87–93) and Xe (A = 138–143) primary fission fragments produced in ²³²Th, ²³⁸U, and ²⁴⁴Pu photofission upon the scission of a target nucleus and neutron emission were measured in an experiment with bremsstrahlung from electrons accelerated to 25 MeV by a microtron, and the results of these measurements are presented. The experimental procedure used involved the transportation of fragments that escaped from the target by a gas flow through a capillary and the condensation of Kr and Xe inert gases in a cryostat at liquid-nitrogen temperature. The fragments of all other elements were retained with a filter at the capillary inlet. The isotopes of Kr and Xe were identified by the γ spectra of their daughter products. The mass-number distributions of the independent yields of Kr and Xe isotopes are obtained and compared with similar data on fission induced by thermal and fast neutrons; the shifts of the fragment charges with respect to the undistorted charge distribution are determined. Prospects for using photofission fragments in studying the structure of highly neutron-rich nuclei are discussed.     

Free-free radiation in electron-neutral atom collisions

Free-free absorption coefficients are calculated for the electron-neutral atom systems involving He, C, N, O, Ne, Ar, Kr and Xe. The calculations are based upon model atomic potentials which have been adjusted to fit experimental scattering cross sections or electron affinities. Some angular distributions are presented and thermal averages are evaluated in the ranges λ = 0.5–20 μm and T = 500–20,000°K.     

Calculations of the EPR g-tensor using unrestricted two- and four-component relativistic approaches within the HF and DFT frameworks

ABSTRACT

Approaches and programs for calculations of the EPR g-tensor in the framework of the two- and four-component methods are still very rare. There are three main reasons for this: the wider community's unawareness of the importance of second- and higher order spin–orbit effects on the g-tensor, the methodological problems associated with performing such calculations and the lack of understanding of these problems. This paper reports on the implementation of a method for calculation of the g-tensor in the framework of the relativistic unrestricted two- and four-component Hartree–Fock and density functional theory approaches based on the Kramers pair formalism. This implementation allows us to analyse problems which arise when the g-tensor is calculated via Kramers pairs in the unrestricted framework.     

Flow effects in high-energy nucleus collisions with Ag(Br) in emulsion

Various flow phenomena observed by a unique emulsion method are reviewed. The experimental data of the emission of projectile and target fragments and relativistic particles in collisions of 1–160 A GeV/c ¹⁶O, ²²Ne, ²⁸Si, ³²S, ⁸⁴Kr, ¹⁹⁷Au, and ²⁰⁸Pb nuclei with ¹⁰⁸Ag (⁸⁰Br) targets are investigated. The transverse-momentum approach, the flow-angle analysis using principal vectors, the azimuthal correlation functions, the method of azimuthal correlations between charged secondaries, and the method of Fourier expansion of the azimuthal angle distributions are applied. Evidence of the directed flow of spectators has been obtained in the medium-impact nuclear interactions. In azimuthal distributions, with respect to the reaction plane, the signal of the elliptic flow of participants has been observed.     

Determination of the S and P° Rydberg energy levels of rubidium-like ions by the method of interpolation of relativistic quantum defects

The method of interpolation of relativistic quantum defects is used for determining the energies of Rydberg levels of rubidium-like ions. For this purpose, the values of relativistic quantum defects calculated by the Dirac-Fock method at three points, two of which correspond to discrete levels and the third, to the ionization threshold, are approximated by a second-degree polynomial. By using the continuous function μ(E) thus obtained, one can readily determine the energy value for any discrete level. A formula for calculating the threshold value of the quantum defect μ(0) (the phase shift δ(0)) is given. The approximation coefficients corresponding to the nS _1/2, nP°_1/2, and nP°_3/2 levels are presented. For better agreement with the experimental results, an empirical correction to the quantum defect is introduced, which weakly depends on energy. The calculations were performed for 17 members of the rubidium isoelectronic sequence (from Rb to Fr⁵⁰⁺).     

Relativistic Hartree-Bogoliubov description of the lithium isotopes

Here we report the development of the relativistic Hartree-Bogoliubov theory in coordinate space. Pairing correlations are taken into account by both density dependent force of zero range and finite range Gogny force. As a primary application the relativistic HB theory is used to describe the chain of Lithium isotopes reaching from ⁶Li to ¹¹Li. In contrast to earlier investigations within a relativistic mean field theory and a density dependent Hartree Fock theory, where the halo in ¹¹Li could only be reproduced by an artificial shift of the 1p _1/2 level close to the continuum limit, the halo is now reproduced in a self-consistent way without further modifications using the scattering of Cooper pairs to the 2s _1/2 level in the continuum. Excellent agreement with recent experimental data is observed.     

Accurate potential energy curves for Tl+–Rg (Rg=He–Rn): spectroscopy and transport coefficients

High-quality ab initio potential energy curves are presented for the Tl⁺–Rg series (Rg=He–Rn). Calculations are performed at the CCSD(T) level of theory, employing aug-cc-pV5Z quality basis sets, with ‘small core' relativistic effective core potentials being used for Tl⁺ and Kr–Rn. The curves are shown to be in excellent agreement with experimental mobility data for the systems Tl⁺–Rg (Rg=He–Xe), and generally excellent agreement is also obtained with longitudinal diffusion data. An exception to the latter is Tl⁺ in He, which is attributed to the experimental data not being obtained under steady state conditions. Spectroscopic information is also presented for the titular species, derived from potential energy curves, and the results are compared with previous potentials inferred from the ion transport data.     

Unrestricted Dirac-Fock theory: Relativistic determination of core polarization hyperfine interactions

The unrestricted Dirac-Fock (UDF) method is developed for determining relativistic contributions to the hyperfine interaction, notably that due to core polarization. Radial core-polarization of the one-electron (jj-coupled) spin orbitals is obtained by relaxing the restraint in restricted Dirac-Fock (RDF) theory that the radial part be independent of the magnetic quantum number, the projection m_j of j. Relativistic effects on the core polarization are obtained by comparison with results obtained from the non-relativistic spin polarized Hartree-Fock (m_s unrestricted) and spin plus orbital polarized Hartree- Fock (m_s plus m_j unrestricted) calculations. For the 5d transition series ions, the relativistic core polarization enhancement factor, S_s(z), is determined to be about a factor of two and so is much smaller than the isomer shift charge density enhancement factor (≈6) found earlier for these same ions. Comparison is made with limited experimental data available to date; for the case of atomic Re, excellent agreement is obtained with experiment.     

Relativistic coupled cluster calculation of Mössbauer isomer shifts of iodine compounds

ABSTRACT

Mössbauer isomer shifts of ¹²⁹I and ¹²⁷I in the ICl, IBr and I₂ molecules are studied. Filatov's formulation is used, based on calculating the electronic energy change of the two systems involved in the Mössbauer γ transition, the source and absorber. The energy difference between the transitions in the two systems determines the shift. The effects of relativity and electron correlation on the shifts are investigated. The exact two-component (X2C) and the four-component relativistic schemes give virtually identical results; the non-relativistic approach yields about 50% of the relativistic shifts. Electron correlation is included by coupled-cluster singles-and-doubles with perturbative triples [CCSD(T)]; it reduces Hartree–Fock shifts by 15%–20%. Basis sets are increased until the isomer shifts converge. The final results, calculated with the converged basis in the framework of the X2C Hamiltonian and CCSD(T) correlation, give an agreement of 10% or better with experimental data.