Results 1 - 10 of 506
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[en] Capture of a K-shell electron by bare fast ions H+, He2+ and Li3+ from multi-electron atomic targets (carbon, nitrogen, oxygen, neon and argon) is theoretically studied by means of the four-body boundary-corrected first Born approximation. In a wide impact energy interval ranging from 100 to 40 000 keV/amu, extensive tables of the obtained state-selective cross sections are presented for each individual final hydrogen-like state described by the usual quantum numbers The total cross sections , and for capture summed over the quantum numbers , and respectively, are also reported. Theoretical cross sections are found to compare favorably with the corresponding experimental data. The maximal value of the principal quantum number has been taken to be which satisfies the relationship where is the nuclear charge of the projectile. The tabulated state-selective cross sections for single-electron capture by swift nuclei from multi-electron atoms are the first results in the literature on the theory of four-body collisions. The present data for the examined capture processes are of notable interest for many fundamental and applied problems in various interdisciplinary fields ranging from fusion research, plasma physics, astrophysics to radiotherapy.
[en] We describe α-transitions to low-lying states in even–even nuclei with Z>50,N>82 using the Coherent State Model (CSM). We reproduce the energy levels and electromagnetic transition rates between the states of the ground band employing two parameters, namely the deformation parameter and the strength of the harmonic CSM Hamiltonian. The B(E2) values are described in terms of an effective charge which depends linearly on the deformation parameter. The treatment of the α-emission process is based on an α–daughter interaction containing a monopole component, calculated through a double folding procedure with a M3Y interaction plus a repulsive core simulating the Pauli principle, and a quadrupole–quadrupole (QQ) interaction. The decaying states are identified with the lowest narrow outgoing resonances obtained through the coupled channels method. The α-branching ratios to 2"+ states are reproduced by means of the QQ strength. This interaction strength can be fitted with a linear dependence on the deformation parameter, as predicted by the CSM. The theoretical intensities to 4"+ and 6"+ states are in reasonable agreement with available experimental data. Predictions are made for spherical, transitional and well deformed even–even α-emitters
[en] Effective oscillator strength distributions are systematically generated and tabulated for the alkali atoms, the alkaline-earth atoms, the alkaline-earth ions, the rare gases and some miscellaneous atoms. These effective distributions are used to compute the dipole, quadrupole and octupole static polarizabilities, and are then applied to the calculation of the dynamic polarizabilities at imaginary frequencies. These polarizabilities can be used to determine the long-range C_6, C_8 and C_1_0 atom–atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations
[en] Highlights: • Lowest 110 levels for Ba XXVI are calculated. • Radiative data for E1, E2, M1 and M2 transitions within lowest 110 levels are presented. • Lifetimes for lowest 110 fine structure levels are provided. We report an extensive and an elaborate theoretical study of atomic data for Ba XXVI by considering Singlet, Doublet and Triplet (SDT) electron excitations within N-shell and single excitations from N-shell to O-shell. We have calculated energy levels and lifetimes for lowest 110 fine structure levels by using Multi-configuration Dirac–Fock method (MCDF). We have also considered Quantum Electrodynamics (QED) and Breit corrections in our calculations. We have presented the radiative data for electric and magnetic dipole (E1, M1) and quadrupole (E2, M2) transitions among lowest 110 levels. We have made comparisons of our calculated excitation energies and EUV (Extreme Ultraviolet) transition wavelengths with experimentally observed energy levels and wavelengths and achieved good agreement. We have also computed energy levels by performing similar relativistic distorted wave calculations using Flexible Atomic Code (FAC). Additionally, we have provided new atomic data for Ba XXVI which are not published elsewhere in the literature. We believe that our results may be beneficial in fusion plasma research and astrophysical investigations and applications.
[en] The spectrum of platinum was observed in the 300–2100 Å wavelength region. The transition array of four times ionized platinum, Pt V, has been investigated and 1659 spectral lines have been classified in the region of 460–1730 Å. The analysis has led to the determination of the , and configurations. Thirty two of 34 theoretically possible levels, 45 of 74 possible levels and 181 of 214 possible levels have been established. The orthogonal operators technique was used to calculate the level structure and transition probabilities. The energy parameters have been determined by the least squares fit to the observed levels. Calculated transition probability and energy values, as well as LS-compositions obtained from the fitted parameters are presented.
[en] In this study we have extended our previous investigations of Cr II spectrum to levels of the 3d5s configuration. Once again an overall good agreement is observed for these levels between experimental oscillator strength values and our calculated data using two different approaches, namely the oscillator strength parameterization and the HFR+CPOL methods. Recurring to the latter model we have computed radiative lifetime values for 20 3d5s levels, confirming the well founded basis of recent experimental data, given in literature. From the use of the former method and with the help of a least squares fitting procedure to available experimental gf-values we have taken advantage of extracting for the first time the transition radial integral value for 3d4p3d5s, , which is confirmed favorably by ab initio results, obtained by the HFR method scaled by a factor 0.92 or directly by the HFR+CPOL approach. Finally a long list of semi-empirical oscillator strength, transition probability and branching fraction values is generated for around 500 Cr II transitions depopulating the 3d5s levels. Our new gf data are compared successfully with those given by Kurucz.
[en] Calculations for energy levels, radiative rates and lifetimes have been performed for three Ne-like ions, namely Hf LXIII, Ta LXIV and Re LXVI, for which the general-purpose relativistic atomic structure package (GRASP) has been adopted. Results are presented among the lowest 121 levels of these ions, which belong to the 2s2p, 2s2p, 2s2p, 2s2p, 2s2p, and 2s2p configurations, but CI (configuration interaction) has been considered among a much larger number of levels. No measurements for energy levels are available but comparisons have been made with the earlier similar theoretical results. Additionally, calculations have also been performed with the flexible atomic code (FAC) in order to assess the effect of (much) larger CI on energy levels.
[en] The ab initio quasirelativistic approach developed specifically for the calculation of spectral parameters of highly charged ions was used to derive transition data for the Nb-like tungsten ion W33+. The configuration interaction method was applied to include electron correlation effects. The relativistic effects were taken into account in the Breit–Pauli approximation. The level energies, radiative lifetimes , Landé -factors were determined for the ground configuration 4p64d5 and two excited configurations 4p54d6 and 4p64d44f. The radiative transition wavelengths and emission transition probabilities for the electric dipole, electric quadrupole, electric octupole, magnetic dipole, and magnetic quadrupole transitions among the levels of these configurations were produced. The uncertainties of computed spectroscopic parameters were evaluated.
[en] Using a semiclassical close-coupling approach, we have calculated electron capture, excitation and ionization cross sections for collisions of fully stripped hydrogen, helium and lithium ions with atomic hydrogen in the ground state and in all excited states up to . The cross sections for collision energies between 1 and 100 keV/u are given in table form. Furthermore, we provide estimates of the accuracy of the cross sections. The set of data presented in this work represent the first complete and consistent quantum study of these collision systems and will find use in the modeling and diagnosis of thermonuclear fusion plasma reactors.
[en] Relativistic distorted-wave collision strengths have been calculated for the 185 Δn=0 transitions with n=2 in the 67 C-like ions with nuclear charge number Z in the range 26≤Z≤92. The calculations were made for the six final, or scattered, electron energies E"′=0.03,0.08,0.20,0.42,0.80, and 1.40, where E"′ is in units of Z_e_f_f"2 Ry with Z_e_f_f=Z−4.17. In addition, electric dipole oscillator strengths are provided. In the present collision-strength calculations, an improved “top-up” method, which employs relativistic plane waves, was used to obtain the high partial-wave contribution for each transition, in contrast to the partial-relativistic Coulomb–Bethe approximation used in previous work by Zhang and Sampson [H.L. Zhang, D.H. Sampson, At. Data Nucl. Data Tables 63 (1996) 275]. In that earlier work, collision strengths were also provided for the same 185 Δn=0 transitions in C-like ions, but for the more limited list of 46 ions with Z in the range 9≤Z≤54. The collision strengths covered in the present work, particularly those for optically allowed transitions, should be more accurate than the corresponding data given by Zhang and Sampson [H.L. Zhang, D.H. Sampson, At. Data Nucl. Data Tables 63 (1996) 275] and are presented here to replace those earlier results