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The K α resonance fluorescence (RFL) effect via photoabsorptions of inner shell electrons as the element goes through multiple ionization states is studied. We demonstrate that the resonances observed recently in K α (1s–2p) fluorescence in aluminum plasmas by using a high-intensity X-ray free-electron laser [1] are basically K-shell resonances in hollow atoms going through multiple ionization states at resonant energies as predicted earlier for gold and iron ions [2] . These resonances are formed below the K-shell ionization edge and shift toward higher energies with ionization states, as observed. Fluorescence emission intensities depend on transition probabilities for each ionization stage of the given element for all possible K α ( 1 s → 2 p ) transition arrays. The present calculations for resonant photoabsorptions of K α photons in Al have reproduced experimentally observed features. Resonant cross sections and absorption coefficients are presented for possible observation of K α RFL in the resonant energy ranges of 4.5–5.0 keV for Ti ions and 8.0–8.7 keV for Cu ions respectively. We suggest that theoretically the K α RFL process may be driven to enhance the Auger cycle by a twin-beam monochromatic X-ray source, tuned to the K-edge and K α energies, with potential applications such as the development of narrow-band biomedical X-ray devices. [ABSTRACT FROM AUTHOR]

Abstract: Oscillator strengths (f), line strengths (S) and radiative decay rates (A) are presented for all 1s–2p transitions in gold (Au) ions. X-ray emission from gold is extensively used, such as in fusion experiments, and in medical research for diagnostics and treatment. The 1s–2p transitions in gold are found to be in the hard X-ray region of 66–73keV (0.1888–) and are limited to from hydrogen-like to fluorine-like ions as the 2p subshell is filled beyond fluorine. While there are two 1s–2p transitions (– and –) for hydrogen-like gold, , the number varies depending on the number of electrons in the 2p subshell before and after the transition. For example, there are 35 1s–2p transitions giving the same number of lines for carbon-like Au, . The transitions can be of both types, dipole allowed and intercombination, and are in general strong, that is, . However, there are also weak transitions in the set. The present results are obtained from configuration interaction atomic structure calculations using the code SUPERSTRUCTURE which includes relativistic effects in Breit–Pauli approximation. The results have been benchmarked for a few ionic states with other detailed relativistic approaches, such as Dirac–Fock and coupled cluster. Comparisons with the very few transitions in the literature as well as those from other approaches indicate reasonable accuracy for the present results. [Copyright &y& Elsevier]

A unified scheme using the R-matrix method has been developed for electron–ion recombination subsuming heretofore separate treatments of radiative and dielectronic recombination (RR and DR). The ab initio approach within the coupled channel approximation has several inherent advantages in addition to the natural unification of resonant and non-resonant phenomena. It enables a general and self-consistent treatment of photoionization and electron–ion recombination employing identical wavefunction expansion. Detailed balance takes account of interference effects due to resonances in cross sections, calculated explicitly for a large number of recombined (e+ion) bound levels over extended energy regions. The theory of DR by Bell and Seaton is adapted for high-n resonances in the region below series limits. The R-matrix method is employed for (A) partial and total photoionization and photorecombination cross sections of (e+ion) bound levels, and (B) DR and (e+ion) scattering cross sections. Relativistic effects and fine structure are considered in the Breit–Pauli approximation. Effects such as radiation damping may be taken into account where necessary. Unified recombination cross sections are in excellent agreement with measurements on ion storage rings to about 10–20%. In addition to high accuracy, the strengths of the method are: (I) both total and level-specific cross sections and rate coefficients are obtained, and (II) a single (e+ion) recombination rate coefficient for any given atom or ion is obtained over the entire temperature range of practical importance in laboratory and astrophysical plasmas, (III) self-consistent results are obtained for the inverse processes of photoionization and recombination; comprehensive datasets have been computed for over 50 atoms and ions. Selected data are presented for iron ions. [Copyright &y& Elsevier]