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Total L X-ray production cross sections were measured for Sr and Mo by proton impact. Proton energies ranged from 200 keV to 3 MeV. K shell cross sections of Ti and Cu samples were obtained in order to normalize our results, bearing in mind that for those elements the cross sections have been vastly measured and modeled. The cross sections were obtained using the thick sample method and the results showed general agreement in the range of energies studied. The results obtained here for Sr and Mo are in well agreement with those predicted by the ECPSSR theory in the 500–3000 keV proton energy range. In the case of Sr and proton energies lower than 500 keV, the experimental results do not agree well to the calculated with ECPSSR, differing by values greater than 30%. This discrepancy may be due to an overstimation of the stopping power in oxides or secondary emissions that are not negligible in this energy range. All measured spectra were fitted by a novel open software for PIXE semi-quantitative analysis that take into account several physical phenomena related to X-ray production, absorption and detection. Fil: Pérez, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rodriguez Cabello, Tabatha Pamela. Universidad Tecnológica Metropolitana; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Trincavelli, Jorge Carlos. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Suarez, Sergio Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

The present chapter follows part I of a series of two articles, which characterized unstable nuclei and described primary transformation pathways to stabilize a nucleus in terms of its nucleon compositions. Part II focuses on follow-up phenomena of those “primary” transformations. It first illustrates the class of secondary transitions, which all originate from an excited nuclear level of a nucleus, formed in a primary transformation. Next it discusses post-effects, which appear when nuclear transformations and transitions affect the atom as a whole, i.e. also its electron shell. Third, there are several post-effect phenomena when particular or electromagnetic radiation emitted in the course of the above-mentioned processes interact with surrounding condensed matter. Consequently, there are many specific emissions which accompany those secondary and post-effect processes, and which are not directly related to the primary transformations. A prominent example is γ-emissions as emitted in one of the three secondary transition pathways. These γ-rays, however, represent just one of the many emission which altogether are the essence of radioactivity.

The emission of X-rays in Ka and KLL Auger energy regions were analyzed for transition metals by using energy dispersive X-ray fluorescence (EDXRF) system. To acquire more information in this energy region, the semi-empirical determination of Ka, Auger line-widths and the L sub-shell level widths were performed. Since K shell is a core shell for transition metals and it is not easily be affected by valence shell electronic distributions, K shell fluorescence yields were used for the semi-empirical determinations. In the experiment, elemental form of transition metals were excited by 59.5 keV g-rays from 241Am annular source and the emitted X-ray photons were counted by Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. The obtained results were compared with the other studies in the literature

In near Bohr velocity ion-atom collisions, a dependence of target K-shell ionization cross sections upon the ionic charge states has been observed. Experiments were performed in silicon solid target with 2–5 MeV iodineq+ ions incident in charge states +20 to +25. K-shell ionization cross section of silicon for q = 20 and 22 iodine ions impact with the same incident energy are almost equal, and are well described by the theory of binding-energy-modified BEA. However, for q = 25 iodine ions collisions, 3d vacancies of projectile transfer to the 1s orbit of target atom via rotational coupling of 3dπ, δ-3dσ molecular orbits in the framework of quasi-molecular model, which results in an increase of the K-shell ionization cross section of silicon.

This paper reports co-crystallization of two atomically precise, different-size ligand-stabilized nanoclusters, a spherical (AuAg)267(SR)80 and a smaller trigonal-prismatic (AuAg)45(SR)27(PPh3)6 in 1:1 ratio, characterized fully by X-ray crystallographic analysis (SR = 2,4-SPhMe2). The larger cluster has a four concentric-shell icosahedral structure of Ag@M12@M42@M92@Ag120(SR)80 (M = Au or Ag) with the inner-core M147 icosahedron observed here for metal nanoparticles. The cluster has an open electron shell of 187 delocalized electrons, fully metallic, plasmonic behavior, and a zero HOMO-LUMO energy gap. The smaller cluster has an 18-electron shell closing, a notable HOMO-LUMO energy gap and a molecule-like optical spectrum. This is the first direct demonstration of the simultaneous presence of competing effects (closing of atom vs. electron shells) in nanocluster synthesis and growth, working together to form a co-crystal of different-sized clusters. This observation suggests a strategy that may be helpful in the design of other nanocluster systems via co-crystallization., Atomic shell closure and electronic shell closure are generally considered to be competing effects in stabilizing magic-sized metal nanoclusters. Here, the authors show, by co-crystallizing two differently-sized clusters, that both mechanisms can work concurrently during magic cluster synthesis.

We report on the radiative decay of double $K$-shell vacancy states produced in solid Ca, V, Fe, and Cu targets by impact with about 10 MeV/amu C and Ne ions. The resulting $K$ hypersatellite x-ray emission spectra were measured by means of high-energy-resolution spectroscopy using a von Hamos bent crystal spectrometer. The experiment was carried out at the Philips variable energy cyclotron of the Paul Scherrer Institute. From the fits of the x-ray spectra the energies, line widths, and relative intensities of the hypersatellite x-ray lines could be determined. The fitted intensities were corrected to account for the energy-dependent solid angle of the spectrometer, effective source size, target self-absorption, crystal reflectivity, and detector efficiency. The single-to-double $K$-shell ionization cross-section ratios were deduced from the corrected relative intensities of the hypersatellites and compared to theoretical predictions from the semiclassical approximation model using hydrogenlike and Dirac-Hartree-Fock wave functions and from classical trajectory Monte Carlo calculations.

This is the final report of a three-paper series on the K-shell photoabsorption and photoionization of trace elements, namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn. K lines and edges from such elements are observed in the X-ray spectra of supernova remnants, galaxy clusters and accreting black holes and neutron stars, their diagnostic potential being limited by poor atomic data. We are completing the previously reported radiative datasets with new photoabsorption and photoionization cross sections for isoelectronic sequences with electron number $19\leq N\leq 26$. We are also giving attention to the access, integrity and usability of the whole resulting atomic database. Target representations are obtained with the atomic structure code AUTOSTRUCTURE. Where possible, cross sections for ground-configuration states are computed with the Breit--Pauli $R$-matrix method (BPRM) in either intermediate or $LS$ coupling including damping (radiative and Auger) effects; otherwise and more generally, they are generated in the isolated-resonance approximation with AUTOSTRUCTURE. Cross sections were computed with BPRM only for the K ($N=19$) and Ca ($N=20$) isoelectronic sequences, the latter in $LS$ coupling. For the rest of the sequences ($21\leq N \leq 26$), AUTOSTRUCTURE was run in $LS$-coupling mode taking into account damping effects. Comparisons between these two methods for K-like Zn XII and Ca-like Zn XI show that, to ensure reasonable accuracy, the $LS$ calculations must be performed taking into account the non-fine-structure relativistic corrections., 7 pages, 3 figures. Accepted for publication in Astronomy & Astrophysics

We investigated the atomic structure of liquid Rb along an isothermal path at 573 K, up to 23 GPa, by X-ray diffraction measurements. By raising the pressure, we observed a liquid–liquid transformation from a simple metallic liquid to a complex one. The transition occurs at 7.5 ± 1 GPa which is slightly above the first maximum of the T–P melting line. This transformation is traced back to the density-induced hybridization of highest electronic orbitals leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals.

In this paper, a weighted k-shell method is proposed to further improve the distinction of node importance by taking advantage of the number of iterations and edge weights when the node is deleted. The weighted k-shell decomposition method is applied to simple networks and complex networks respectively. The simulation results show that the improved method has low computational complexity, high result resolution and high accuracy.

K-shell X-ray emission of Silicon induced by near-Bohr-velocity ions was systematically investigated in collision systems for which the ratio of projectile-to-target atomic numbers (Z1/Z2) ranged from 0.07 to 3.79. The results show that, in asymmetric collisions, the measured K-shell X-ray production cross sections of Silicon fit very well with the predictions of different direct ionization models depending on the atomic number of projectile. In the case of near-symmetric collisions (Z1/Z2 ∼ 1), an obvious enhancement of the X-ray production cross section was observed, which can be attributed to the vacancy transfer within the framework of quasi-molecular model.

We have studied the titanium K-shell emission spectra from multi-keV x-ray source experiments with hybrid targets on the OMEGA laser facility. Using the collisional-radiative TRANSPEC code, dedicated to K-shell spectroscopy, we reproduced the main features of the detailed spectra measured with the time-resolved MSPEC spectrometer. We have developed a general method to infer the Ne, Te and Ti characteristics of the target plasma from the spectral analysis (ratio of integrated Lyman-α to Helium-α in-band emission and the peak amplitude of individual line ratios) of the multi-keV x-ray emission. These thermodynamic conditions are compared to those calculated independently by the radiation-hydrodynamics transport code FCI2.

Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously., Colloidal systems can form bulk phases such as liquid and crystals, but they also exhibit interesting behaviours that have no atomic analogues. Here, by dispersing solid polymer microspheres in a nematic liquid crystal, Senyuk et al. demonstrate spontaneous formation of hexadecapolar nematic colloids.

We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the Sao Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24).

The adsorption and activation of NO on microsilver species provide the foundation to understand the mechanism of NO removing reactions on silver based catalysts. However, the diversiform of the geometrical structures and electronic properties of microsilver species in condensed phases has posed considerable challenges for exploring these interactions. We study the reactions of NO with bare silver clusters Agn(±) (7-69) in the gas phase using a continuous flow reactor running at low temperatures. Evidence for NO unit adsorption, the formation of (NO)2 and the reduction of NO is observed on different cluster sizes. The kinetic rates of initial NO unit adsorption are closely related to silver clusters' global electronic properties. The low electron binding energy and the unpaired electron of a silver cluster favor the adsorption and activation of NO. In particular, the clusters with one less electron than those of closing electron shells are generally inert and the sizes having one more electron outside these shells are generally quite reactive. These observations depict a general figure of interactions between NO and microsilver species, in which electron transfer from silver to NO dominates.

Using the stable number theory we calculate the best electron configurations of the elements and not from experimental data[6-8,10].We make the Jiang periodic table of the elements[10]. In studying the stability of the many-body problem we suggest two principles [1-10]. (1) The prime number principle. A prime number is irreducible in the integers, it seems therefore natural to associate it with the most stable subsystem. We prove that 1, 3, 5, 7, 11, 23, 47 are the most stable primes. (2) The symmetric principle. The most stable configuration of two prime numbers is then stable symmetric system in nature. We prove that 2, 4, 6, 10, 14, 22, 46, 94 are the most stable even numbers. By using the prime number principle and the symmetric principle we calculate the best electron configurations of the elements. Total quantum number and orbital quantum number determine the best electron configurations of the elements n l 1 2 3 4 5 6.. ... n . K L M N O P = Electron shells: Electron subshells: 2(2 1) 2 6 10 14 18 22.. ... l s p d f g h + = . ) ) An atomic subshell that contains its full quota of electrons is said to be closed. A closed subsell holds two electrons, a closed subshed s ( 0 l = p ( 1 l = six electrons, a closed subshell ten electrons, a closed d ( 2 l = f ( 3 l ) ) = subshell fourteen electrons, these subshells are the most stable, a closed subshell g ( 4 l ) = eighteen electrons is the most unstable. Using the symmetric principle it has been proved the 2(2 1) 2,6,10 l + = and 14 are stable and is unstable[1-10]. The , and 2(2 1) 18 l + = , . s p d f subshells are stable and the subshell is unstable. g From 1 to 92 of the atomic numbers every subshell is stable. It has been proved that the last stable element that occurs naturally is uranium with an atomic number of 92 and there are only 92 stable elements in nature. Since subshell is unstable, the elements 93-110 are unstable. Since is unstable, and 6 subshells are unstable. Therefore the elements 111-182 are unstable.. 5g h 5g 6 , ,6 ,6 ,6 s bp d f g Using the 1s,2s,3s,4s,and 5s of electron configurations[6-8,10] we make the Jiang periodic table of elements with five periods.The sequence of period lengths is 2,8,18,32,50.Table 1 shows

Measurements of K-shell mass attenuation coefficients are reported for the first time in Arsenic oxide (As2O3). Experiments are performed using Arsenic Oxide extended range HPGe detector. To achieve measurements at many small and regular energy intervals, secondary X-ray emission technique using “Seventeen Scatters” is employed. The results are in agreement with the proposed theoretical estimates. No evidence could, however be gained in favor of microscopic theories such as RRS and EXAFS, insofar as there are no energy points within a range of 100eV on either side of the K-edge.

Using an X-ray free electron laser (XFEL) at 960 eV to photo-ionize the 1s electron in neutral neon followed by lasing on the 2p-1s transition in singly-ionized neon, an inner-shell X-ray laser was demonstrated at 849 eV in singly-ionized neon gas several years ago. It took decades to demonstrate this scheme, because it required a very strong X-ray source that could photo-ionize the 1s (K shell) electron in neon on a timescale comparable to the intrinsic Auger lifetime in neon of 2 fs. In this paper, we model the neon inner shell X-ray laser under similar conditions to those used in the XFEL experiments at the SLAC Linac Coherent Light Source (LCLS), and show how we can improve the efficiency of the neon laser and reduce the drive requirements by tuning the XFEL to the 1s-3p transition in neutral neon in order to create gain on the 2p-1s line in neutral neon. We also show how the XFEL could be used to photo-ionize L-shell electrons to drive gain on n = 3–2 transitions in singly-ionized Ar and Cu plasmas. These bright, coherent, and monochromatic X-ray lasers may prove very useful for doing high-resolution spectroscopy and for studying non-linear process in the X-ray regime. PACS Codes: 42.55.Vc, 41.60.Cr, 32.80.Aa, 32.30.-r, Keywords: Photo-pumping, X-ray free-electron laser, X-ray laser

Durak, Ridvan/0000-0002-3935-176X; DURAK, RIDVAN/0000-0002-3935-176X; Akman, Ferdi/0000-0002-8838-1762 WOS: 000367613700014 The total attenuation cross section at the K edge, absorption jump ratio, jump factor, Davisson-Kirchner ratio, and oscillator strength parameters for the K shell were determined by measuring the total attenuation cross sections around the K edge for Pr, Nd2O3, and Sm. The measurements were performed in a secondary excitation geometry using the K alpha(2), K alpha(1), K beta(1), and K beta(2) X-rays (in the region from 31.817 to 55.293 keV) from different secondary source targets excited by the 59.54 keV gamma-photons from an Am-241 annular source. It is the first time that the Davisson-Kirchner ratio values have been determined for present samples. The experimental results were compared with the theoretically calculated and other available experimental results. Ataturk UniversityAtaturk University [2011/82] This work was done with the support of the Ataturk University Research Fund under project No. 2011/82.

Special features of the effect of the electron shell on alpha decay that have important experimental implications are studied within the adiabatic approach. The magnitude of the effect is about several tenths of a percent or smaller, depending on the transition energy and on the atomic number. A dominant role of inner shells is shown: more than 80% of the effect is saturated by 1s electrons. This circumstance plays a crucial role for experiments, making it possible to measure this small effect by a difference method in the same storage rings via a comparison of, for example, decay probabilities in bare nuclei and heliumlike ions. The reasons behind the relative success and the applicability limits of the frozen-shell model, which has been used to calculate the effect in question for more than half a century, are analyzed. An interesting experiment aimed at studying charged alpha-particle states is proposed. This experiment will furnish unique information for testing our ideas of the interplay of nonadiabatic and adiabatic processes.

MnTeMoO6 crystal was obtained by top-seeded solution growth method. Optical and nonlinear optical properties of MnTeMoO6 crystal were measured. Band structures, DOS, optical properties of MnTeMoO6 were calculated. Both calculated and experiment results of the optical properties show that a transitional absorption band is exhibited in MnTeMoO6 crystal. Second harmonic generation measurements show that the SHG response with fundamental wavelength 1.06 μm decreases to a quarter of that with fundamental wavelength 2.05 μm. The transitional absorption band has a great effect on the nonlinear optical property of MnTeMoO6 crystal. The formation of the transitional absorption band in MnTeMoO6 crystal would be attributed to the internal transitions of transition-meta ions with incomplete electron shells (Mn2+ 3d34s2). In addition, the transitional absorption band plays an important role in the coloration of MnTeMoO6 crystal, and the crystal can be made into selective optical oscillators and laser wavelength recognizing device by utilizing the characteristic of the transitional absorption band.

The K to L shell total vacancy transfer probabilities of low Z elements Co, Ni, Cu, and Zn are estimated by measuring the Kβ to Kα intensity ratio adopting the 2π-geometry. The target elements were excited by 32.86 keV barium K-shell X-rays from a weak 137Cs γ-ray source. The emitted K-shell X-rays were detected using a low energy HPGe X-ray detector coupled to a 16 k MCA. The measured intensity ratios and the total vacancy transfer probabilities are compared with theoretical results and others’ work, establishing a good agreement.

The electron density logarithm is closely connected to the Shannon information entropy characterising the spread of the electron density. It can be seen as the uncertainty to predict the position of an electron. The position uncertainty curvature, defined as the negative of the Laplacian of the electron density logarithm, describes regions of space where the uncertainty of the electron position is higher, respectively lower, than the average in the surrounding. The atomic shells can be located in regions of high-position uncertainty curvature, thus resolving the atomic shell structure of the atoms Li to Xe. The shell boundaries are given as minima of the uncertainty curvature. This indicator, based alone on the electron density, is suitable to describe the bonding situation in molecules and solids.

The K shell absorption jump ratios, jump factors, effective atomic numbers, and electron densities were derived from the measured total mass attenuation coefficient using an energy dispersive X-ray fluorescence spectrometer for Gd2O3, Gd2(CO3)3H2O, Gd2(C2O4)3H2O, and Gd2(SO4)3 compounds. The total mass attenuation coefficients were measured in the X-ray energy range from 39.52 to 57.14 keV in a transmission geometry utilizing the Kα2, Kα1, Kβ1, and Kβ2 X-rays from different secondary source targets excited by the 59.54-keV photons from an Am-241 annular source and detected by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. The energy gap, ionization energy, electron affinity, and global electrophilicity parameters of oxide, sulfate, oxalate, and carbonate ions were calculated using density functional theory (B3LYP). The experimental results are discussed based on these parameters. Copyright © 2015 John Wiley & Sons, Ltd.

While often considered to be chemically inert, the reactivity of noble gas elements at elevated pressures is an important aspect of fundamental chemistry. The discovery of Xe oxidation transformed the doctrinal boundary of chemistry by showing that a complete electron shell is not inert to reaction. However, the reductive propensity, i.e., gaining electrons and forming anions, has not been proposed or examined for noble gas elements. In this work, we demonstrate, using first-principles electronic structure calculations coupled to an efficient structure prediction method, that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high pressure (≥125, ≥250, and ≥250 GPa, respectively). The resulting compounds are metallic and the noble gas atoms are negatively charged, suggesting that chemical species with a completely filled shell can gain electrons, filling their outermost shell(s). Moreover, this work indicates that Mg2NG (NG = Xe, Kr, Ar) are high-pressure electrides with some of the electrons localized at interstitial sites enclosed by the surrounding atoms. Previous predictions showed that such electrides only form in Mg and its compounds at very high pressures (500 GPa). These calculations also demonstrate strong chemical interactions between the Xe 5d orbitals and the quantized interstitial quasiatom (ISQ) orbitals, including the strong chemical bonding and electron transfer, revealing the chemical nature of the ISQ.

The proton, alpha-particle, and He + induced X-ray emissions of Ni were measured on mono-elemental thin films in order to obtain the K-shell X-ray production cross section in the energy range of 0.7–2.0 MeV for protons, 4.0–6.5 MeV for alpha-particles, and 3.0–4.0 MeV for He + . The proton-induced X-ray production cross section for Ni agreed well with the theoretical values, endorsing the quality of the measurements. The X-ray production cross section induced with alpha-particles is in good agreement with ECPSSR theory in the complete range of energies, while for He + that quantity is systematically below. K β / K α ratios were evaluated and compared with experimental and theoretical values.

The measured K-shell fluorescence-yield values reported in the literature from 1934 to 2015 (about 737 new measurements) were used to deduce new empirical K-shell fluorescence yields for elements in the atomic range 3 ≤ Z ≤ 99. In order to deduce the empirical K-shell fluorescence yield, the experimental data were fitted using the quantity (ω K /(1 - ω K ))1/4 with respect to the atomic number Z. The results were compared to other theoretical, semi-empirical and experimental values reported in the literature. Reasonable agreement was obtained between our result and those of other works.

Hybrid K-edge densitometry (HKED) is a non-destructive analytical assay technique used to provide rapid determination of actinide concentration in tank solutions. Of special interest for HKED is the estimation, along with associated uncertainties, of the ratio of the flouresence yeilds, ω K, of uranium and plutonium. Limited experimental data for ω K(Z) as a function of atomic number, Z, exist and the data are subject to experimental uncertainty. Previous studies have provided values for ω K(Z) with uncertainty estimates but have not included covariance information. We use a phenomenological model with a bootstrapping method to generate the ratio ω K(94)/ω K(92) and associated uncertainty.

The imaginary and real parts of anomalous scattering factors of Sn atoms around the K shell binding energy are measured using K and L X-ray photons. Gamma photons of energy 59.54 keV from an Am-241 radioactive source are used to excite K and L X-ray photons of various energies. By measuring the intensities of incident and transmitted X-ray photons in Sn foil with a good geometry arrangement, the K shell photoelectric cross sections are determined around the K shell binding energy of Sn. The real and imaginary parts of anomalous scattering factors of Sn are determined from K shell photoelectric cross section values. Experimentally determined form factors are compared with the theoretical prediction and experimental data obtained with synchrotron source.

Versions of the relativistic many-body theory that make it possible to develop the theory of electronic states and spectroscopy of heavy elements have been proposed. Asymptotic estimates of the atomic terms have been made. It has been shown that the physical cause of the formation of the layered structure of electron shells is directly related to the repulsion of electrons in the electron plasma of the atom.

The exceptional stability of thiolate-protected Au25 clusters, [Au25(SR)18]−, arises from the closure of superatomic electron shells, leading to a noble-gas-like 8-electron configuration (1S21P6). Here we present that replacing the core Au atom with Pd or Pt results in stable [MAu24(SR)18]0 clusters (M = Pd, Pt) having a superatomic 6-electron configuration (1S21P4). Voltammetric studies of [PdAu24(SR)18]0 and [PtAu24(SR)18]0 reveal that the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps of these clusters are 0.32 and 0.29 eV, respectively, indicating their electronic structures are drastically altered upon doping of the foreign metal. Density functional investigations confirm that the HOMO–LUMO gaps of these clusters are indeed smaller, respectively 0.33 and 0.32 eV, than that of [Au25(SR)18]− (1.35 eV). Analysis of the optimized geometries for the 6-electron [MAu24(SR)18]0 clusters shows that the MAu12 core is slightly flattened to yield an oblate ellipsoid. The ...

The K-L vacancy transfer probability of 3d atoms such as Cr, Cu and Zn and their compounds have been measured using Indus – 2 synchrotron radiation. The emission of K X-ray photons in the elemental and compound targets are induced by 6.5 keV, 10 keV and 11 keV synchrotron radiation. The characteristic K X-ray photons are measured with a silicon drift detector spectrometer. By measuring K shell fluorescence yield and K X-ray intensity ratios, the K-L vacancy transfer probabilities have been determined and found that they depend on solid state effect.

In developing stainless-steel (SS) and copper wire-array X-ray sources on the Z machine, we consider the optimization of K-shell yield as a function of load height. Theory, numerical modeling, and experimental data suggest that an optimum exists corresponding to a tradeoff between the increase in radiating mass and the decrease in coupled current with increasing pinch height. A typical load height of 20 mm used on many previous Z wire-array X-ray sources is found to be near optimal for K-shell yield production in SS and copper implosions. Electrical data, pinhole imaging, and spectroscopy are used to study plasma conditions in wire-array z pinches corresponding to the variation in K-shell power and yield per unit length as the pinch height is changed from 12 to 24 mm.

We consider a process in which α-particles after α-decay ionize K-shell of daughter atoms and capture electrons. We first have performed similar calculations for collisions of α-particles with He+(1s) ions. This charge transfer process is studied for the collision energy region 0.04–400 keV. The transition amplitudes are calculated in the impact parameter approximation with the use of the close coupling equations method for a basis consisting of eight molecular states. Total and partial charge-transfer cross sections to the 1s and, for the first time, to the 2s and 2p 0, 2p ±1 states of the He+ ion are obtained. Angular differential cross sections for the elastic scattering and charge-transfer processes are calculated in the eikonal approximation for a wide range of scattering angles for the collision energy of 1 keV. Results of calculations are in an excellent agreement with experimental data.

Understanding the correlation between proteins' tertiary and electronic structures is a great challenge, which could possibly lead to a more efficient prediction of protein functions in living organisms. Here, we report an experimental study of the interplay between electronic and tertiary protein structure, by probing resonant core excitation and ionization over a number of charge-state selected precursors of electrically charged proteins. The dependence of the core ionization energies on the protein charge state shows that the ionization of a protonated protein is strongly correlated to its tertiary structure, which influences its effective Coulomb field. On the other hand, the electronic core-to-valence shell transition energies are not markedly affected by the unfolding of the protein, from compact to totally elongated structures, suggesting that frontier protein orbitals remain strongly localized. Nevertheless, the unfolding of a protein seems to influence the cross section ratio between different resonant electronic transitions.

K shell X-ray production cross-sections (sigma(K alpha) and sigma(K beta)) have been measured for some elements in the atomic number range 28

Structural, magnetic and adsorption properties of Nin (n = 2–16, 21, 55) clusters have been investigated based on density funciontal theory (DFT) with the spin polarized generalized gradient approximation, using the Perdew–Burke–Ernzerhof functional. The most stable isomers have been selected to study the adsorption of methane CH4 and methyl CH3. It is found that the CH4 molecule adsorbs on the top site for all clusters considered. The most selective Nin clusters are the tetrahedron (n = 4) and icosahedral clusters due to high-coordinated edge atoms (n = 13, 21, and 55). For CH3, stronger adsorption tendencies were found with similar patterns. Our results show that clusters with n = 6, 10, and 13 with complete atomic shells are relatively more stable. Besides, they perform the lowest adsorption for CH3, indicating that they possess such a desirable property of a higher carbon poisoning resistance, than for the rest of the clusters. This result can be understood in terms of the electronic stability and loc...

Energy positions and width resonances of nitrogen and oxygen atoms are reported using the Screening Constant per Unit Nuclear Charge (SCUNC) method. Calculations are performed for the 1s2s 2 2p 3 [ 5,3 S°] n p 4 P° and for the 1s2s 2 2p 3 [ 3 D°, 3 P°] n p 4 P° core-excited autoionizing resonances of atomic nitrogen converging respectively to the 5 S° and 3 S°, and to the 3 D° and 3 P° series limits of N + and for the 1s2s 2 2p 4 [ 2,4 P°] n p 3 P° Rydberg series converging to the 1s −1 4 P° and 1s −1 2 P° series limits of atomic oxygen. The results obtained agree very well with available high-resolution K -edge spectra of atomic nitrogen and of atomic oxygen. The present calculations provide benchmark data for X-ray spectra in connections with the modeling of astrophysical systems.

In this study, the effect of external magnetic field on the Kβ/Kα X-ray intensity ratios of various alloy compositions of Ni–Cr transition metal alloys has been investigated. The Kα and Kβ emission spectra of Ni, Cr and Ni x Cr 1− x ( x =0.40; 0.50; 0.60; 0.80) alloys were measured by using a Si (Li) solid-state detector. Kβ/Kα X-ray intensity ratios of Ni, Cr and Ni x Cr 1− x alloys without magnetic field and in 0.5 and 1 T external magnetic field have been measured following excitation by 59.5 keV γ-rays from a 200 mCi 241 Am radioisotope point source. When the experimental data obtained in external magnetic field have been compared with data without external magnetic field, deviations have been observed in Kβ / Kα X-ray intensity ratios for Ni and Cr in different alloy compositions. Thus, results of these measurements have shown that Kβ/Kα X-ray intensity ratios of Ni and Cr in Ni x Cr 1− x alloys are dependent on the external magnetic field. Also the total mass attenuation coefficients for pure 3d transition metals and their alloys at different compositions were measured and theoretically estimated using mixture rule for selected photon energy. Later on, total atomic and electronic cross-sections and effective atomic number for alloys are determined experimentally and theoretically using these mass attenuation coefficients. When these parameters are examined depending on the alloy compositions, thereof have been found to vary with the alloy composition.

The spectra from laser-produced plasma have been simulated by the newly developed model. The simulation agrees well with the experimental results, which can prove that the K-shell model is suitable for the application of the spectrum from laser-produced plasma. Also, the jkl satellite lines were found important for predicting the spectra.

We demonstrate that K-shell photoelectron spectroscopy is sensitive to binding motifs of cationic cores with excess electrons in solvated metals. Hereby, the satellites in core-level spectra and not the main line provide the important insight into ion-pairing effects. We found that contact ion-pairs in Li − ( NH 3 ) 1 – 3 and a solvent-separated ion-pair in Li − ( NH 3 ) 4 result in remarkably different Li1 s spectra. The former spectra have numerous intense satellites of a charge-transfer character while that of Li − ( NH 3 ) 4 contains only one strong satellite describing excitation of a solvated electron. We also explored K-shell photodetachment of the bare Li − and found that three-electron processes are essential here.

X-ray natural circular dichroism (XNCD) spectra of alanine and serine were calculated at the C, N, and O K-edges within the framework of density functional theory. Basis set and gauge dependence of d -alanine were examined as a test case. XNCD spectra of crystalline d -alanine and l -serine were obtained using cluster models of increasing size. The absolute intensities of the XNCD spectra were found to be reduced in the solid phase compared to the gas phase monomers, suggesting that a monomer model is not necessarily a good representation of the solid phase.

The origin of the complex NEXAFS features of X-Ray Absorption, XAS, spectra in transition metal complexes is analyzed and interpreted in terms of the angular momentum coupling of the open shell electrons. Especially for excited configurations where a core-electron is promoted to an open valence shell, the angular momentum coupling is intermediate between the two limits of Russell-Saunders, RS, coupling where spin-orbit splitting of the electron shells is neglected and j–j coupling, where this splitting is taken as dominant. The XAS intensities can be understood in terms of two factors: (1) The dipole selection rules that give the allowed excited RS multiplets and (2) the contributions of these allowed multiplets to the wavefunctions of the intermediate coupled levels. It is shown that the origin of the complex XAS spectra is due to the distribution of the RS allowed multiplets over several different intermediate coupled excited levels. The specific case that is analyzed is the L 2,3 edge XAS of an Fe 3+ cation, because this cation allows a focus on the angular momentum coupling to the exclusion of other effects; e.g., chemical bonding. Arguments are made that the properties identified for this atomic case are relevant for more complex materials. The analysis is based on the properties of fully relativistic, ab initio, many-body wavefunctions for the initial and final states of the XAS process. The wavefunction properties considered include the composition of the wavefunctions in terms of RS multiplets and the occupations of the spin–orbit split open shells; the latter vividly show whether the coupling is j–j or not.

© 2018 IOP Publishing Ltd. The central (Nc) and terminal (Nt) nitrogen K-shell photoelectron spectra (PESs) of N2O molecules have been measured in the σ shape resonance energy region at temperatures of ∼300 and ∼630 K. Estimating vibrational populations based on the Boltzmann distribution at these temperatures, PESs of vibrationally ground and bending-excited levels in the initial electronic ground state were extracted. Vibrationally integrated partial cross sections and asymmetry parameters for ionization from vibrationally ground and bending-excited levels were obtained as a function of the incident photon energy by integrating PESs over the vibrational levels of the core-hole states. In Ncphotoionization, the shape resonance from the bending-excited level was found to be shifted to the lower photon energy side and to become narrower than that from the ground vibrational level. In Ntphotoionization from the bending-excited level, the downward shift of the resonance is more significant than that in Ncionization. These experimental findings are qualitatively consistent with theoretical predictions and suggest that the shape resonance associated with the Ntcore hole is more sensitive to the bending angle of the initial state than is the shape resonance associated with the Nccore hole. The asymmetry parameters for photoionization from the bending-excited level, however, showed almost the same behavior as those from the ground vibrational level for both K-shell photoionization channels and in the photon energy range studied here.

International audience; The sigma phase can serve as a prototype of intermetallic phases when investigating the atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal structure), as the sigma phase bears a broad homogeneity range and there are numerous experimental site occupancy data available for the sigma phase. The present work brings new insights into the influencing factors of atomic order in the binary sigma phase. We calculated the atomic volumes and atomic charges of the constituent elements of 32 stoichiometric end-member compounds (i.e. the complete set of ordered configurations) of the binary sigma phase by using first-principles calculations. The calculation results show that besides the size factor and the number of valence electrons, the total number of electron shells is found as the third factor that affects the atomic order of the sigma phase. Moreover, the calculation results indicate that between the two constituent elements, the one with larger atomic size, smaller number of valence electrons or smaller total number of electron shells prefers occupying large coordination number (CN) sites (i.e. 4f, 8i1 and 8j) and the other prefers occupying small CN sites (i.e. 2a and 8i2). Furthermore, we dissociated the effects of individual influencing factors on atomic order of the sigma phase combining with the measured site occupancies from the literature.

We present a systematic measurement of the X-ray emission asymmetries in the K-shell dielectronic, trielectronic, and quadruelectronic recombination of free electrons into highly charged ions. Iron ions in He-like through O-like charge states were produced in an electron beam ion trap, and the electron-ion collision energy was scanned over the recombination resonances. Two identical X-ray detectors mounted head-on and side-on with respect to the electron beam propagation recorded X-rays emitted in the decay of resonantly populated states. The degrees of linear polarization of X-rays inferred from observed emission asymmetries benchmark distorted-wave predictions of the Flexible Atomic Code (FAC) for several dielectronic recombination satellite lines. The present method also demonstrates its applicability for diagnostics of energy and direction of electron beams inside hot anisotropic plasmas. Both experimental and theoretical data can be used for modeling of hot astrophysical and fusion plasmas., 22 pages, 4 figures, 10 tables, accepted for publication in The Astrophysical Journal Supplement Series

K shell X-ray fluorescence cross-sections (sigma(K alpha), sigma(K beta) and sigma(K)), and K shell fluorescence yields (omega(K)) of Ti, Ni both in pure metals and in different alloy compositions (TixNi1-x; x = 0.3, 0.4, 0.5, 0.6, 0.7) were measured by using energy dispersive X-ray fluorescence (EDXRF) technique. The samples were excited by 22.69 keV X-rays from a 10 mCi Cd-109 radioactive point source and K X rays emitted by samples were counted by a high resolution Si(Li) solid-state detector coupled to a 4 K multichannel analyzer (MCA). The alloying effects on the X-ray fluorescence (XRF) parameters of Ti-Ni shape memory alloys (SMAs) were investigated. It is clearly observed that alloying effect causes to change in K shell XRF parameter values in Ti-Ni based SMAs for different compositions of x. Also, the present investigation makes it possible to perform reliable interpretation of experimental sigma(K alpha), sigma(K beta) and omega(K) values for Ti and Ni in SMAs and can also provide quantitative information about the changes of K shell X-ray fluorescence cross sections and fluorescence yields of these metals with alloy composition. (c) 2017 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V., Ataturk University Research Fund [2015/99], This work was supported by Ataturk University Research Fund, under the Project No. 2015/99.

We present laboratory measurement and theoretical analysis of silicon K-shell lines in plasmas produced by Shenguang II laser facility, and discuss the application of line ratios to diagnose the electron density and temperature of laser plasmas. Two types of shots were carried out to interpret silicon plasma spectra under two conditions, and the spectra from 6.6 Å to 6.85 Å were measured. The radiative-collisional code based on the flexible atomic code (RCF) is used to identify the lines, and it also well simulates the experimental spectra. Satellite lines, which are populated by dielectron capture and large radiative decay rate, influence the spectrum profile significantly. Because of the blending of lines, the traditional $G$ value and $R$ value are not applicable in diagnosing electron temperature and density of plasma. We take the contribution of satellite lines into the calculation of line ratios of He-$\unicode[STIX]{x1D6FC}$ lines, and discuss their relations with the electron temperature and density.

Single crystals or glasses that are doped with light emitting atoms are used as the gain medium in solid-state lasers. In crystals, the atoms exist in the form of ions. Aside from conventional rods and slabs with lengths of several cm, technologies based on disks or fibers with thicknesses, respectively diameters of 10 to 100 µm become more and more prevalent. Most solid-state lasers are based on transition metal ions such as Ti, Cr and Co or rare-earths such as Nd, Ho, Er, Tm or Yb. For the latter group, laser operation often relies on transitions within partially filled inner electron shells that are effectively screened by the outer shells and thus only weakly influenced by the crystal field. As a result, narrowband transitions in the visible to near-infrared spectral region occur. Besides, broadband levels exist which are addressed for realizing tunable lasers.

Complex network analysis comprises a popular set of tools for the analysis of online social networks. Among these techniques, k-shell decomposition of a network is a technique that has been used for centrality analysis, for communities' discovery, for the detection of influential spreaders, and so on. The huge volume of input graphs and the environments where the algorithm needs to run, i.e., large data centers, makes none of the existing algorithms appropriate for the decomposition of graphs into shells. In this article, we develop for a distributed algorithm based on MapReduce for the k-shell decomposition of a graph. We furthermore, provide an implementation and assessment of the algorithm using real social network datasets. We analyze the tradeoffs and speedup of the proposed algorithm and conclude for its virtues and shortcomings.