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The VIP collaboration is performing high precision tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the Underground Gran Sasso Laboratories of INFN (Italy). The experimental technique consists in introducing a DC current in a copper conductor, searching for the X-rays emission due to a PEP-forbidden atomic transition from the L shell to the K shell of copper when the K shell is already occupied by two electrons. VIP set un upper limit on the PEP violation probability 1 2 β 2 < 4.7 × 10 − 29 , the aim of the upgraded VIP-2 experiment is to improve this result by two orders of magnitude at least. The experimental setup and the results of preliminary data analyses will be presented.

As a part of the investigation of the entire Si isonuclear sequence for x-ray spectral diagnostics, we use the Li-like Si11+ ion, a stable component that thus features prominently in x-ray astrophysical spectra. We perform R-matrix calculations for the photoabsorption cross section of Si11+ including relativistic contributions via the use of a Breit-Pauli Hamiltonian. Relativistic effects — predominantly spin-orbit splitting of resonances and mass-velocity and one-body Darwin shifts of relative energies — are shown to be tractable and worthy of consideration in final x-ray spectral modeling data banks.

The high-order harmonic generation (HHG) in xenon is studied by using the time-dependent density-functional theory. The dynamics of all electrons on the outer 4th and 5th atomic shells is considered with subsequent separation of contributions of different atomic orbitals to the HHG amplitude. It is shown that giant enhancement of HHG yield in a spectral region near 100 eV is caused by perturbation of the electron–electron interaction potential induced by recolliding photoelectron wavepacket originated from the 5p 0 orbital. This perturbation leads to the collective oscillations of all orbitals on the 4th shell closely localized in space and strongly interacting with each other. The resulting HHG yield is enhanced by more than an order of magnitude compared with the response of the single 5p 0 orbital. The high accuracy of the numerical results is confirmed by comparing the calculated HHG spectra and photoionization cross-sections with experimental results and an analytical parameterization of the HHG yield.

The K-shell ionization cross sections of titanium and copper atoms were determined by analyzing the spectra of characteristic X-ray radiation generated by an electron beam with energies of 1 and 2 GeV in metal foils. New data obtained for these energies demonstrate the influence of the density effect on the ionization cross sections values. The results were compared with previous experimental data and calculations based on pure theoretical and semi-empirical models.

Single photon simultaneous core ionization/core excitation (K−2V) of the Benzene molecule has been observed experimentally, using synchrotron radiation, by electron coincidence spectroscopy with a magnetic bottle time-of-flight electron spectrometer and reveals a rich spectrum. DFT and Post–Hartree–Fock calculations provide detailed assignments of K−2V states. The specific Auger decay of these states has also been determined experimentally with a new technique to improve the energy resolution.

In order to maximize the influence of commodity profits in e-commerce platforms, designing and improving the K-shell algorithm to select the more influential seed node sets in this paper. The new algorithm improves the number of active nodes by setting node threshold and edge weight attributes. To obtain more commodity profits, a strategy IRDSN (Strategy for Improving Repeat Degree of Seed Nodes) is proposed to select initial seed nodes and improve the repeat degree of seed nodes. The profit maximization based on linear threshold model is realized by setting different propagation modes. The improved algorithm and strategy IRDSN are analysed and verified in real data set and e-commerce platform. The results show that the algorithm effectively improves the profit of commodities.

We report oxygen K-shell photoabsorption measurements in CO2 plasmas, using a table-top laser produced plasma soft X-ray and extreme ultraviolet (EUV) source. Significant differences are observed between the photoabsorption spectra of the neutral CO2 molecule and photoionized CO2 plasmas, as new spectral features emerge in the case of the latter. These features are attributed to 1s → 2p photoexcitation in O, O+ , O 2+ species identified with the aid of calculations performed with the Cowan suite of atomic structure codes. Such signatures of atomic ions in the photoionized plasma point to the fragmentation of the parent molecule upon absorption of a soft X-ray photon.

The paper investigates theoretically the optimization of the doped ablator layers for the plastic ignition capsule. The high-resolved one-dimensional implosion simulations show that the inner pure CH layer of the Si-doped design is excessively preheated by the hard x-ray, leading to the unstable ablator-fuel interface compared to the Ge-doped capsule. This is because that the Si K-shell absorption edge (1.8 keV) is higher than the Ge L-edge (1.3 keV), and Si dopant makes more hard x-ray penetrate through the doped ablator layers to preheat the inner pure CH layer. So an optimization of the doped ablator layers (called "Si/Ge capsule") is performed: an Si-doped CH layer is placed next to the outer pure CH layer to keep the high implosion velocity; next to the Si-doped layer is a thin Ge-doped layer, in order to absorb the hard x-ray and protect the inner undoped CH-layer from excessively preheating. The simulations show that the Si/Ge capsule can effectively improve hydrodynamic stability at the ablator-fuel interface while keeping the high implosion velocity.

Synopsis Cross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the corresponding cross sections for total electron capture and the projectile F K x rays, were determined for 1.8-2.2 MeV/u F9+,8+,7+ projectiles. The Ar K x-ray coincidence cross section ratios for double to single capture are found to vary strongly with the incident charge state, with the ratios for F9+ well exceeding unity.

31st International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC XXXI, Deauville, France, 23 Jul 2019 - 30 Jul 2019; Journal of physics / Conference series 1412, 152072 (2020). doi:10.1088/1742-6596/1412/15/152072, Published by IOP Publ., Bristol

Synopsis The total and magnetic cross sections for K-shell electron impact excitation (EIE) of Fe20+ have been calculated using the fully relativistic distorted-wave approach. Degrees of linear polarization of x-ray emission following EIE are presented for several stronger 2p→1s transitions, and compared with the values for the same transition lines but from dielectronic recombination process of Fe21+ in the ground state, obvious differences are found that can be employed in diagnosing the formation mechanism of corresponding x-ray lines.

Measurements were performed of K-shell ionization cross sections of Ti element by 10~30 keV positron impact using the thick-target method. The effects of multiple scattering of incident positron and from bremsstrahlung photons and annihilation photons with the thick-target method are discussed with the Monte Carlo code PENELOPE. Meanwhile, the Monte Carlo method is also applied to determine the detection efficiencies of X- and γ-ray detectors. Our experimental K-shell ionization cross sections for Ti element are compared with the distorted-wave Born approximation (DWBA) theoretical predictions, and it is found that the agreement of the experimental data and theoretical values is good and this indicates that the experimental method adopted in this study is applicable.

The energies, electric dipole rates and oscillator strengths of K α x-ray satellites from 1s–2p transitions in platinum with a single vacancy in the K shell and variously ionized L shell are calculated using multi-configuration Dirac Fock wavefunctions with the inclusion of Breit interaction and quantum electrodynamics effects. The computations have been performed for low ionized (Pt1+–Pt6+) and also for highly ionized (Pt69+–Pt77+) Pt. As K α x-ray satellites with spectator vacancies only in the L shell, to the best of our knowledge, have been studied for the first time, to check the accuracy of the present work, calculations have also been performed for H-, He-, Li-, Be-, B- and F-like Pt for which theoretical data for comparison exist. The purpose of choosing a high Z element is that the detailed decay properties of heavy ions due to systematic 1s–2p transitions with spectator vacancies in the L shell using fully relativistic treatment are unexplored and the increasing need for reliable data from such ions in various applications that are under investigations in recent years. Also, for heavy ions like Pt, the contribution from the competing non-radiative transitions is less and hence the atomic properties are largely due to radiative transitions. The K X ray satellite energies, rates and resonance photo- ionization cross sections from H-, He-, Li-, Be-, B- and F-like Pt are compared with available data.

The Auger decay of single and double K-shell hole and hollow states of Al4+–Al11+ was theoretically investigated in the framework of perturbation theory implemented by the distorted wave approximation. The natural lifetime widths of the hollow states x + are found to be 1.3–1.9 times larger than those of corresponding hole states x + . The maximal ratio is found originating from the hollow states of , which is ~2.9 times as large as the hole states of . The calculated energy levels and natural lifetime widths are compared with the experimental and other theoretical results wherever available in the literature. The Auger decay rates and natural lifetime widths presented in this work are useful in the modeling of ultra-intensive x-ray laser interaction with aluminum.

This paper reports that the K x-ray spectra of the thin target (47)Ag, (48)Cd, (49)In and (50)Sn were measured by an HPGe semi-conductor detector in collisions with 84.5 MeV (6)C(4+) ions. Our experiment revealed the K alpha x-ray energy shifts were not obvious and the K beta(1) x-ray energy shifts were about 90 similar to 110 eV. The simple model of Burch et al has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model.

We consider the electron loss from the ground state of hydrogen- and helium-like uranium ions in collisions with neutral atoms in the domain of impact energies where the collision velocity is close to but does not yet exceed the typical electron velocities in the K-shell of the uranium ions. Since in such collisions the loss process is caused practically only by the interaction of the electron with the (unscreened) atomic nucleus, it can be treated as a three-body problem. We show that in collisions with heavy atoms, where the first Born approximation strongly fails, a very substantial improvement in the description of the loss cross sections is obtained when the symmetric eikonal and continuum-distorted-wave-eikonal-initial-state models are employed. Our consideration also emphasizes the importance of the relativistic electron description in the initial and final undistorted states of the ions.

Close-coupling calculations based on an R-matrix formalism are performed for the 1s?2p resonance photoionizations from the low-lying states of boron-like carbon ions. The resonance energies, widths and oscillator strengths of 1s?2p core excitations are determined by analysing the calculated photoionization cross sections. Our calculations are in reasonable agreement with the experimental and theoretical results presented by other authors. The present numerical values may help to analyse the astrophysical and laboratory plasmas.

We describe in this paper a new method for measuring the K shell photoelectric cross sections of high-Z elemental targets at a K absorption edge. In this method the external bremsstrahlung (EB) photons produced in the Ni target foil by beta particles from a weak 90Sr-90Y beta source are passed through an elemental target and the spectrum of transmitted EB photons is measured with a HPGe detector coupled to a 2K ORTEC multichannel analyser spectrometer. The measured spectrum shows a sharp decrease in transmitted intensity at the K absorption edge of the element. Such a sharp decrease is used to determine the K shell photoelectric cross section at the K edge as well as the K absorption edge of the element. We report the data for Gd, Hf, Ta, Au and Pb targets.

K shell fluorescence parameters such as fluorescence yield, fluorescence cross section and absorption jump factor for pure elemental targets of Mo, Ag, Cd, In and Sn have been determined by adopting a 2π geometrical configuration. The K x-ray photons are excited in the target using 123.6 keV gamma rays from a weak 57Co source, and detected with a GMX 10P HPGe detector coupled to an 8K multichannel analyser. Measured values of these parameters have been compared with theoretical and others' experimental values.

The possibility of using x-radiation from bare and hydrogen-like highly charged ions as a driver for a proposed form of cancer therapy is discussed. This proposed form of therapy, called resonant combination therapy, benefits from a very high contrast ratio between dose to the tumour and dose to the surrounding healthy tissue as is illustrated by some simple model calculations of isodose/ion distributions. The need for further radiobiological measurements and ion source developments in order to make this form of therapy feasible are highlighted.

Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.

Hollow Li2+(2s) production in a collision between a fast electron and a neutral lithium target is studied theoretically by a procedure which determines the fully-differential cross section of the corresponding (e, 3e) process. The calculated cross sections are obtained within the framework of the first Born approximation. The two slow emitted electrons in the continuum are described by the fully correlated three Coulomb interactions (3C). The results are compared to those of the double ionization of lithium resulting in a residual Li2+(1s). The comparison between these two channels is essential to get precious indication of the different mechanisms in double ionization of a three-electron target and to observe directly electronic correlation, which is the main cause of the double ionization by fast electron impact.

Fully relativistic calculations on the energies and electric dipole rates of x-ray multiplets arising from states of 2pq, 2s2pq and 2s2 2pq configurations of variously ionized neon with q ranging from 6 to 1 have been performed. The calculations have been carried out using multi-configuration Dirac–Fock wavefunctions with the inclusion of Breit interaction, quantum electrodynamics contributions and finite nuclear mass and size corrections. An attempt has been made to take into account the dominant contributions to correlation effects. Using a scaling procedure on the already available relativistic radial matrix elements for a single vacancy in the K shell, the Auger rates have been calculated. The numerical results for the x-ray and Auger transitions of double vacancy states of neon ionized to different degrees in the L shell have been compared with other available theoretical and experimental values. Due to the influence of both relativity and configuration interaction, the configuration average x-ray rates obtained from individual multiplet rates were seen to substantially differ from non-relativistic rates for many transitions.

The K-shell jump ratio, jump factor and the ratio of total to K-shell photoelectric cross section at K edge have been determined for Hf, Ta, Au and Pb by adopting a novel method. In this method, continuous external bremsstrahlung (EB) photons are produced in a thin nickel elemental converter by beta particles from a 90Sr–90Y weak beta source. The spectrum of EB photons transmitted through the elemental targets of Hf, Ta, Au and Pb is recorded with an HPGe detector coupled to an 8K multichannel analyser. The transmitted spectrum shows a sharp decrease in intensity at the K-shell binding energy of the target atom. The region of sharp decrease is fitted to a sigmoidal function and the K-shell jump ratio, jump factor and the ratio of total to the K-shell photoelectric cross section at K edge are determined. The measured values are compared with the theoretical values.

The ratios of photoionization cross sections of the 1σg and 1σu shells of the N2 molecule for the vibrational transitions to the v' = 0 and v' = 1 core-ionized states in the photon energy region between 440 and 550 eV have been measured. The calculations in the random phase approximation well reproduce the experimental data. The variation of the ratio with photon energy is attributed to the interference modulation that is caused by coherent photoemission from the two atoms, as an analogue of the Young's double-slit experiment. The calculations extended up to 1.8 keV allow connecting the modulation with the onset of transitions to the states of increasing orbital angular momentum which occurs at increasing photon energies and demonstrate that the main contribution to these modulations comes from the σ continuum states.

L x-ray production cross sections have been measured for highly charged 2.5 MeV/u Cuq+ (q = 20–26) ions colliding with H2, Ne, Ar, Kr and Xe target atoms. The observed Cu L x-rays are due to the excitation and electron-transfer processes. The charge state dependence of the projectile L x-rays has been studied with Ar and Kr targets. We have derived the subshell resolved K-L1, K-L2 and K-L3 electron-transfer cross sections from the measured Ar K x-ray yields as a function of L vacancies in Cu ion. The measured projectile L x-ray production cross sections arising from the excitation and electron capture are found to saturate as target atomic number Zt increases. Similarly, a saturation has also been found in the Ar K-shell ionization cross sections as a function of Zp.

By using the space-resolved spectrograph, the K-shell emission from laser-produced plasma was investigated. Electron density profiles along the normal direction of the target surface in aluminum laser-plasmas were obtained by two different diagnostic methods and compared with the profiles from the theoretical simulation of hydrodynamics code MULTI1D. The results corroborate the feasibility to obtain the electron density above the critical surface by the diagnostic method based on the Stark-broadened wings in the intermediately coupled plasmas.

Simple correlated wavefunctions considering two K-shell active electrons of neutral atoms from He to Xe are presented in this paper, describing a variational method subject to a local Hartree potential representing the presence of outer shell electrons. Three kinds of electron–electron correlation functions have been studied with rigorous observation of the exact behaviour of the wavefunctions at the electron–electron and electron–nucleus coalescence points (Kato cusp conditions). Global properties, such as the energies and virial coefficients, as well as local properties, such as spatial mean values, together with scaling laws with the nuclear charge for the variational parameters, are also analysed. We calculated the expansion of the functions in terms of bipolar spherical harmonics. Finally, comparisons are made with a more rigorous, fully quantal close-coupling method, which also includes the same Hartree potential for the outer electrons. Fil: Mitnik, Dario Marcelo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Miraglia, Jorge Esteban. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Absolute cross-section measurements for K-shell photoionization of Be-like C2+ ions have been performed in the photon energy range 292 325 eV. These measurements have been made using the photon ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory. Absolute measurements compared with theoretical results from the R-matrix method indicate that the primary C2+ ion beam consisted of 62 percent ground-state (1s22s2 1S) and 38 percent metastable state (1s22s2p 3Po) ions. Reasonable agreement is seen between theory and experiment for absolute photoionization cross sections, resonance energies and autoionization line widths of K-shell-vacancy Auger states.

A comparative study of high harmonic generation (HHG) by atoms and ions with active p-electrons is carried out in the theoretical framework of the rescattering mechanism. The substate with ml = 0, i.e. zero orbital momentum projection along the electric vector of a linearly polarized laser wave, is found to give the major contribution to the HHG rate. Our calculations for HHG by an H atom in an excited 2p-state demonstrate that the rate for recombination into a final state with a different value of ml (=±1), is higher for lower harmonic orders N, while for higher N (beyond the plateau domain) the difference vanishes. For species with closed electron shells, the ml-changing transitions are forbidden by the Pauli exclusion principle. We report absolute HHG rates for halogen ions and noble gas atoms at various intensities. These results demonstrate that the Coulomb binding potential of the atoms considerably enhances both the ionization and recombination steps in the rescattering process. However, the weak binding energy of the anions allows lower orders of HHG to be efficiently produced at relatively low intensities, from which we conclude that observation of HHG by an anion is experimentally feasible.

In the non-relativistic approximation for the wavefunctions of the one-electron states and in the dipole approximation for the scattering amplitude, the effect of radial monopole rearrangement of electron shells within the field of a vacancy and of the processes of one-photon double excitation/ionization on the absolute values and the shapes of the differential cross sections of anomalous non-zero-angle elastic scattering of linearly polarized x-ray photons by the Ne atom and by the neon-like Si4+ and Ar8+ ions in the vicinity of K- and KL23-ionization thresholds is studied. The results of calculations for the Ne atom were found to be in agreement with the high-precision synchrotron radiation experiments by Coreno et al (1999 Phys. Rev. A 59 2494; K-ionization threshold) and by Avaldi et al (1996 J. Phys. B: At. Mol. Opt. Phys. 29 L737; KL23-ionization threshold). The results of calculations for the Si4+ and Ar8+ ions are predictions.

We report x-ray absorption and magnetic circular dichroism measurements performed at the M4,5 edges of uranium in the ferromagnetic superconductor UGe2. The spectra are described with the LSDA +U electronic structure computation method. Combined with the analysis of the published (i) x-ray photoemission spectrum, (ii) electron–positron momentum density, and (iii) angular dependence of the de Haas–van Alphen frequencies, we infer for the Coulomb repulsion energy within the 5f electron shell eV. This leads to where W is the bandwidth.

Cross sections for the double K-shell vacancy production of lithium atoms in collision with fast charged projectiles are calculated. For these ionization– excitation processes, the relative importance of the different first- and secondorder mechanisms and the dependence of the cross sections on the sign of projectile charge are investigated. Our studies confirm the strong influence of electron–electron correlations on the behaviour of the cross sections. The obtained results are in reasonable agreement with the data as observed in recent experiments.

Photoionization cross sections, dipole matrix elements and phase shifts are calculated for the O K-shell of the CO molecule using two theoretical models. One of them is a new version of the relaxed core Hartree–Fock approximation with a fractional charge. The value of this charge is considered as a fitting parameter. In this paper, the fractional charge 0.7 was used which gives a correct position of the maximum of the σ* shape resonance in the photoionization cross section. The other model is a modification of the multiple scattering method with overlapping atomic spheres. The dipole matrix elements and phase shift differences calculated by these two methods are compared with the corresponding values determined from the complete experiment by Cherepkov et al (2000 J. Phys. B: At. Mol. Opt. Phys. 33 4213).

Radiation energy deposition results are presented from a Monte Carlo code simulating the lower part of a leg during an in vivo 109Cd K-shell x-ray fluorescence (KXRF) bone lead measurement. The simulations were run for a leg phantom model representing an adult subject, assuming concentrations of 10 microg Pb per gram bone mineral and tracing 500 million photons in each simulation. Trials were performed over a range (0.5-6.0 cm) of source-to-sample (S-S) distances. Energies deposited due to Compton and photoelectric processes occurring in the bone and the soft tissue were obtained. The data show an increase in the amount of energy deposited in the bone as the sample is moved closer to the source (from 2.0 cm to 0.5 cm). However, there is a decrease in the amount of energy deposited in the soft tissue as the sample is moved closer to the source over the same distance interval. In decreasing the S-S distance from 2.0 cm to 0.5 cm, the amount of energy deposited in the sample as a whole was found to increase by 11%. By calculating the energy deposition in the bone and in the soft tissue as a fraction of the total energy deposited in the sample, the corresponding changes are quantified as a function of S-S distance. Similarly, the proportions of energy deposited via the photoelectric effect and Compton scattering are presented as a function of S-S distance.

A dynamic model of electron orbitals deformation (EODD) has been developed making it possible to allow for dynamic effects of outer electron shells screening on deuterons interactions. Computer simulation based on the EODD model revealed that deuterons in the palladium crystalline structure can approach each other so that the distance between them can be less than 0.01 A and gave estimated probability of such an approach. Assuming deuterium be completely mobile in palladium, the calculated rate of the fusion reaction at 300 K is 10−10–10−12 s−1 per the D-D pair. This value corresponds to the energy release of 1–100 W per gram of palladium β-deuteride and is in good agreement with experimental data for excess heat measurements within an order of magnitude.

In the non-relativistic approximation for the wavefunctions of the one-electron states and in the dipole approximation for the scattering amplitude the effect of relaxation of atomic shells in the field of core vacancies, multiplet splitting, Auger and radiative vacancy decays and virtual processes of one-photon double excitation/ionization from the atomic ground state on the differential cross section of anomalous elastic scattering of the linearly polarized x-ray photon by the copper atom near its 1s-shell ionization threshold are studied. The results of calculations are found to be in agreement with the high-precision synchrotron radiation experiment by Arp et al (1993 J. Phys. B: At. Mol. Opt. Phys. 26 4381).

Relative L-shell radiative transition rates were obtained for a number of decays in Gd, Dy, Er, Yb, Hf, Ta and Re by means of a method for refining atomic and experimental parameters involved in the spectral analysis of x-ray irradiated samples. For this purpose, pure samples were bombarded with monochromatic synchrotron radiation tuning the incident x-ray energy in order to allow selective ionization of the different atomic shells. The results presented are compared to experimental and theoretical values published by other authors. A good general agreement was found and some particular discrepancies are discussed. Fil: Bonetto, Rita Dominga. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina Fil: Carreras, Alejo Cristian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Trincavelli, Jorge Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina Fil: Castellano, Gustavo Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina

Partial photoionization cross sections and the angular asymmetry parameter β for the C K-shell of the CO molecule have been calculated in the relaxed core Hartree–Fock approximation. In contrast with all previous calculations, we introduced the relaxed core potential with a fractional charge of the ion which was fitted from the condition to get an agreement with the experimental position of the σ ∗ shape resonance for the K-shell cross section. We found the optimal value of the fractional charge to be 0.5. After performing calculations within the Born–Oppenheimer approximation for several fixed internuclear distances R, we averaged the R-dependent dipole amplitudes over R with the vibrational wavefunctions of the initial and final states. Transitions from the ground vibrational level to several vibrationally excited states of the residual molecular ion have been studied within this approximation. A good agreement was found with the recently published vibrationally resolved experimental data.

Lifetimes for K-shell vacancy states in atomic carbon have been determined by measurement of the natural linewidth of the 1s → 2p photoexcited states of C + ions. The K-shell vacancy states produced by photoionization of atomic carbon are identical to those produced by 1s → 2p photoexcitation of a C + ion: 1s2s 2 2p 22 D, 2 P, and 2 S autoionizing states occur in both cases. These vacancy states stabilize by emission of an electron to produce C 2+ ions. Measurements are reported for the lifetime of the 1s2s 2 2p 22 D, 2 P and 2 S autoionizing states of C + :6 .3± 0.9 fs, 11.2 ± 1.1 fs and 5.9 ± 1.3 fs respectively. Knowledge of such lifetimes is important for comparative studies of the lifetimes of Kshell vacancies in carbon-containing molecules, benchmarking theory, and interpreting satellite x-ray spectra from astrophysical sources such as x-ray binaries. Absolute cross sections were measured for both ground-state and metastable-state ions providing a stringent test of state-of-the-art theoretical calculations. Carbon is ubiquitous in nature and is the building block of life. This atom in its various stages of ionization has relatively few electrons, and is thus amenable to theoretical study. Lifetimes

A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, for the description of single-electron capture in ion–atom collisions involving multielectronic targets is presented. This approximation is developed within the framework of the independent electron model taking particular care of the representation of the bound and continuum target states. Total cross sections for single-electron capture from the K-shell of He, Ne and Ar noble gases by impact of bare ions are calculated. Present results are compared to previous CDW-EIS ones and to experimental data.

Multiconfiguration Dirac–Fock calculations have been carried out in the Extended Optimal Level (EOL) scheme on the energies, transition probabilities and weighted absorption oscillator strengths of intercombination lines of highly ionized argon. The calculations have been carried out in intermediate coupling with empty K shell, varying degrees of ionization in the L shell and open outer shells. The radiative transition rates have been calculated in both length and velocity gauges and an analysis on the accuracy of the orbital functions used in this work has been attempted by comparing the length form and velocity form transition rates.

The partial and total cross sections for photodetachment of the metastable 1s22s2p2 4Pe bound state of the negative ion of beryllium are presented for a range of initial photon energies across and beyond the 1s detachment threshold. The cross sections are computed using a multichannel close-coupling R-matrix approximation, where sophisticated configuration-interaction wavefunctions are used to represent the initial and final states. Twelve target eigenstates with configurations 1s22s2p, 1s22p2, 1s2s22p, 1s2s2p2 and 1s2p3 are included in the expansion of the total wavefunction describing the neutral Be atom. A number of prominent resonance structures have been identified in the partial cross sections for the three total system symmetry transitions of interest: 4Pe–4So, 4Po and 4Do. No comparison can be made at this stage with other theoretical or experimental measurements due to a lack of data describing the inner shell photodetachment of the negative ion of beryllium.

K-shell vacancy production in low-atomic-number (Z t = 17–29) solid targets ha sb een measured in collisions of highly charged carbon ions with energies of 1.5–6 MeV u −1 .T he K-shel li onization cross sections of Cl, K, Ti, Fe and Cu are derived from the measured K x-ray cross sections. The present data-set has been used to test the predictions of a theoretical model based on the local plasma approximation (LPA). This theory takes into account the response of solid core electrons working within the dielectric formalism. We find that this ab initio ion–solid model gives very good agreement with the measured data for Fe and Cu targets, while it tends to under-estimate the data for the most symmetric collision systems studied here. We discuss the range of validity of the LPA in terms of the symmetry parameter and the impact velocity. On the other hand, am odel based on the perturbed stationary state approximation, designed for ion–atom collisions (ECPSSR) is found to give excellent agreement with the measured data for all target elements over the whole energy range. All the measured cross sections for different targets are found to follow a universal scaling rule predicted by the ECPSSR.