K-shell X-ray Emission Research Articles

Breakdown of the molecular orbital picture for X-ray emission of water

By measuring X-ray emission of the water molecule in liquid phase we establish a first example of K-shell X-ray emission spectra with strong breakdown of the molecular orbital picture. A complete splitting of the 2a1 peak into satellites is observed. A theoretical model with electronic configurations generated by coupled excitations/de-excitations, so-called semi-internal configuration interaction, captures the experimentally recorded features well. Differences with respect to the corresponding breakdown effect in ultraviolet photoelectron spectrum are highlighted. Molecular dynamics calculations indicate that solvent broadening can only make up for a small fraction of the width of the recorded 2a1 derived band.

K-shell X-Ray Emission from Lithium-like Nitrogen N v

We present laboratory measurements of n = 3 → n = 1 N v X-ray emission lines situated near 26 Å. The lines are excited by electron-impact collisions and are shown to reach a combined intensity of about a fifth of the combined strong N v 1s2s2p 2 P 1/2,3/2 → 1s 22s 2 S 1/2 resonance lines, commonly labeled q and r, at 29.4 Å. In addition, we present new experimental data for the wavelength of the blended q and r lines at 29.4 Å, as well as for that of the blended inner-shell-excited N v lines u and v at 30.0 Å. All of these collisional N v lines need to be included in astrophysical emission models in order to properly account for flux from N v in the soft X-ray region. The measured wavelengths provide benchmarks for testing atomic structure calculations and excellent agreement is found with our calculations using the many-body perturbation theory method. We provide a complete listing of the N v energy levels with valence electrons in the n = 2, 3, and 4 shells calculated with this approach. The experimental and theoretical data, thus, provide accurate rest-frame wavelengths needed for velocity determinations based on high-resolution absorption features in spectra of warm absorbers in active galactic nuclei and other astrophysical objects.

High-energy interference-free K-lines synchrotron X-ray fluorescence microscopy of rare earth elements in hyperaccumulator plants.

Synchrotron-based micro-X-ray fluorescence analysis (µXRF) is a non-destructive and highly sensitive technique. However, element mapping of rare earth elements (REEs) under standard conditions requires care, since energy-dispersive detectors are not able to differentiate accurately between REEs L-shell X-ray emission lines overlapping with K-shell X-ray emission lines of common transition elements of high concentrations. We aim to test REE element mapping with high-energy interference-free excitation of the REE K-lines on hyperaccumulator plant tissues and compare with measurements with REE L-shell excitation at the microprobe experiment of beamline P06 (PETRA III, DESY). A combination of compound refractive lens optics (CRLs) was used to obtain a micrometre sized focussed incident beam with an energy of 44 keV and an extra-thick silicon drift detector (SDD) optimised for high-energy X-ray detection to detect the K-lines of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr) and neodymium (Nd) without any interferences due to line overlaps. High-energy excitation from La to Nd in the hyperaccumulator organs was successful but compared to L-line excitation less efficient and therefore slow (∼10-fold slower than similar maps at lower incident energy) due to lower flux and detection efficiency. However, REE K-lines do not suffer significantly from self-absorption, which makes XRF-tomography of millimetre-sized frozen-hydrated plant samples possible. The K-line excitation of REEs at the P06 CRL setup has scope for application in samples that are particularly prone to REE interfering elements, such as soil samples with high concomitant Ti, Cr, Fe, Mn, Ni concentrations.

Enhancement of K-shell spectroscopy for temperature measuring of isochorically heated matter in the sub-keV range

Both K-shell x-ray emission spectroscopy and fluorescence spectroscopy are well-accepted diagnostics for experimental studies of warm dense matter and hot dense matter (HDM). Until now, however, this diagnosis has been used for the study of dense matter with temperatures lower than 100 eV or with temperatures above 1 keV. In this work, we have demonstrated the possibility of using K-shell emission spectroscopy for an intermediate temperature range of 100s eV to study dense plasma. Here, we discuss an analysis of the HDM emission spectra of a solid-state copper with temperatures up to a few hundreds of electronvolts heated by laser-accelerated charged particles.

Developing a platform for Fresnel diffractive radiography with 1 μm spatial resolution at the National Ignition Facility.

An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. We use 4.75keV Ti K-shell x-ray emission to heat a 1000 μm diameter plastic cylinder, with a central 30 μm diameter channel filled with liquid D2, up to 8eV. This leads to a cylindrical implosion of the liquid D2 column, compressing it to ∼2.3 g/cm3. After pressure equilibration, the location of the D2/plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He-α x rays at 8.3keV. Using a slit aperture of only 1 μm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D2/plastic interface.

Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments

In high-energy-density physics, including inertial fusion energy using high-power lasers, doping tracer atoms and deuteration of target materials play an important role in diagnosis. For example, a low-concentration Cu dopant acts as an x-ray source for electron temperature detection while a deuterium dopant acts as a neutron source for fusion reaction detection. However, the simultaneous achievement of Cu doping, a deuterated polymer, mechanical toughness and chemical robustness during the fabrication process is not so simple. In this study, we report the successful fabrication of a Cu-doped deuterated target. The obtained samples were characterized by inductively coupled plasma optical emission spectrometry, differential scanning calorimetry and Fourier transform infrared spectroscopy. Simultaneous measurements of Cu K-shell x-ray emission and beam fusion neutrons were demonstrated using a petawatt laser at Osaka University.

Quantifying electron temperature distributions from time-integrated x-ray emission spectra.

K-shell x-ray emission spectroscopy is a standard tool used to diagnose the plasma conditions created in high-energy-density physics experiments. In the simplest approach, the emissivity-weighted average temperature of the plasma can be extracted by fitting an emission spectrum to a single temperature condition. It is known, however, that a range of plasma conditions can contribute to the measured spectra due to a combination of the evolution of the sample and spatial gradients. In this work, we define a parameterized model of the temperature distribution and use Markov Chain Monte Carlo sampling of the input parameters, yielding uncertainties in the fit parameters to assess the uniqueness of the inferred temperature distribution. We present the analysis of time-integrated S and Fe x-ray spectroscopic data from the Orion laser facility and demonstrate that while fitting each spectral region to a single temperature yields two different temperatures, both spectra can be fit simultaneously with a single temperature distribution. We find that fitting both spectral regions together requires a maximum temperature of 1310-70 +90 eV with significant contributions from temperatures down to 200eV.

Laser energy absorption and x-ray generation in nanowire arrays irradiated by relativistically intense ultra-high contrast femtosecond laser pulses

We report here on the results of comparative experimental measurements of laser energy absorption in a bulk and different morphology nanowire arrays interacting with relativistically intense, ultra-high temporal contrast femtosecond laser pulses. We compare polished, flat bulk samples with vertically and randomly oriented nanowires made of ZnO semiconductor material. The optical absorption of the 45° incident laser pulses of ∼40 fs duration with a central wavelength of 400 nm at intensities above 1019Wcm2 was determined using an integrating Ulbricht sphere. We demonstrate an almost twofold enhancement of absorption in both nanowire morphologies with an average of (79.6±1.9)% in comparison to the flat bulk sample of (45.8±1.9)%. The observed substantially enhanced absorption in nanowire arrays is also confirmed by high-resolution x-ray emission spectroscopy. The spectral analysis of the K-shell x-ray emission lines revealed that the He-like resonance line emission from highly ionized Zn (Zn28+) is only present in the case of nanowire arrays, whereas, for the flat bulk samples, only neutral and low charge states were observed. Our numerical simulations, based on radiative-collisional kinetic code FLYCHK, well reproduce the measured He-like emission spectrum and suggest that high charge state observed in nanowire arrays is due to substantially higher plasma temperature. Our results, which were measured for the first time with femtosecond laser pulses, can be used to benchmark theoretical models and numerical codes for the relativistic interaction of ultrashort laser pulses with nanowires.

Multi-keV x-ray radiator from titanium cylindrical cavity at the Shenguang-III prototype laser facility

Great efforts have been made to create a bright K-shell source using the thin metal cylindrical cavities in the past few decades. Several metal materials such as titanium (Ti), iron, and so on have been tested for high x-ray conversion efficiency mainly at the OMEGA and NIF laser facilities. Recently, x-ray sources in Ti K-shell transition energy range were investigated at the Shenguang-III prototype laser facility with ∼5 kJ laser energy. The experiments were aimed to reproduce the previous ones at OMEGA, but with an extraordinarily small volume of cylindrical cavity and detailed characterizations of the x-ray source. The cavities were 800 μm inner diameter, 800 μm length, and 30 μm thick plastic tubes supporting 1 μm thick Ti. Seven laser beams were focused to 200 μm diameter. The combination of the small cavity volume and the focused laser spots is intended to improve the electron temperature with limited laser energy since the electron temperature is a key issue for high x-ray conversion efficiency. Thomson scattering was adopted to experimentally probe the electron temperatures at special time and space zones as well as the average temperature obtained from the Ti K-shell spectrum. The evolutions of the electron temperature and density are predicted by the radiation hydrodynamic simulation. A top view and two photon energy bands of x-ray source images provide a way to directly observe the plasma movement toward the cavity axis and distinguish the different emission mechanisms between the Ti K-shell and lower energy x rays. Six Higher-energy x-ray detectors located at different angles were used to record the Ti K-shell x-ray emission and demonstrate its isotropic feature. The characteristics of the x-ray radiate intensity including the time evolution, the angular distribution, and the total yields for both the photon energy regions above and below 4 keV are compared between the cavity and planar targets. Obviously, different behaviors were found between the two photon energy regions and the two types of targets. The x-ray conversion efficiency of the Ti cylinder was determined to be ∼4% and ∼21% in 4π sr in the Ti K-shell (4–7 keV) and <4 keV range, respectively. The Ti K-shell conversion efficiency obtained in the present experiments is between the ones driven by 13.5 and 4.5 kJ laser energy at OMEGA.

Mg K-shell x-ray emission induced by various ions

Mg K-shell x-ray production cross sections have been investigated for the impact of H+, He2+ and highly charged heavy ions Xe20+ and Eu20+ in the energy range near the Bohr velocity. The x-ray production cross sections were extracted from the yield and compared with various theoretical calculations. It is found that, with the same incident energy per nucleon, the cross section induced by light ions is lower than that produced by highly charged heavy ions by a factor of about 104. With the impact of H+ and He2+ ions, the x-ray emission cross section can be well predicted by ECPSSR theory. However, for the bombardment of highly charged heavy ions, the BEA calculation, corrected both by Coulomb repulsion and effective nuclear charge, results in a good estimation to the experimental data.

Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO3.

Ternary lanthanide indium oxides LnInO3 (Ln = La, Pr, Nd, Sm) were synthesized by high-temperature solid-state reaction and characterized by X-ray powder diffraction. Rietveld refinement of the powder patterns showed the LnInO3 materials to be orthorhombic perovskites belonging to the space group Pnma, based on almost-regular InO6 octahedra and highly distorted LnO12 polyhedra. Experimental structural data were compared with results from density functional theory (DFT) calculations employing a hybrid Hamiltonian. Valence region X-ray photoelectron and K-shell X-ray emission and absorption spectra of the LnInO3 compounds were simulated with the aid of the DFT calculations. Photoionization of lanthanide 4f orbitals gives rise to a complex final-state multiplet structure in the valence region for the 4fn compounds PrInO3, NdInO3, and SmInO3, and the overall photoemission spectral profiles were shown to be a superposition of final-state 4fn–1 terms onto the cross-section weighted partial densities of states from the other orbitals. The occupied 4f states are stabilized in moving across the series Pr–Nd–Sm. Band gaps were measured using diffuse reflectance spectroscopy. These results demonstrated that the band gap of LaInO3 is 4.32 eV, in agreement with DFT calculations. This is significantly larger than a band gap of 2.2 eV first proposed in 1967 and based on the idea that In 4d states lie above the top of the O 2p valence band. However, both DFT and X-ray spectroscopy show that In 4d is a shallow core level located well below the bottom of the valence band. Band gaps greater than 4 eV were observed for NdInO3 and SmInO3, but a lower gap of 3.6 eV for PrInO3 was shown to arise from the occupied Pr 4f states lying above the main O 2p valence band.

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 1017 and 1018 W cm-2. We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted ‘probe-before-destroy’ measurement strategy can be adopted for electronic-structure related XFEL experiments.

Target K-shell X-ray emission associated with single and double electron capture for [formula omitted] + Ar collisions

Cross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the same cross sections corresponding to projectile F K X-rays and the total cross sections for single and double capture, were determined for 1.8–2.2 MeV/u F9+,8+,7+ projectiles. This work was performed at Western Michigan University using the tandem Van de Graaff accelerator. Coincidences between emitted X-rays and their corresponding charge-changed particles were detected. The Ar K X-ray coincidence cross section ratios for double to single capture are found to depend strongly on the incident charge state, with the ratios for F9+ well exceeding unity. Possible explanations for this anomalous behavior are discussed but a conclusive explanation is not found. The results are compared to previous experiments using fully-stripped fluorine where coincidence techniques were not employed.

Single and double electron capture associated with characteristic K-shell X-ray emission for F9+,8+,7++Ar

SynopsisCross 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.

The molybdenum K-shell x-ray emission spectrum**Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

We present newly measured spectra of the x-ray emission of a molybdenum metal anode subject to electron bombardment, using a very high dispersion silicon double-crystal spectrometer. The measurement includes the dipole-allowed KL, KM, and KN emission lines, based on an energy scale traceable to the Système International definition of the meter with a systematic uncertainty below . The data are presented as parametrized multi-Lorentzian fits to the results, and as supplementary data with the complete spectrum of each line group, corrected for instrumental effects. The () line energy was in complete statistical agreement with published measurements, and it showed no asymmetry. Other lines showed varying discrepancies with the literature which lie outside the bounds of probable experimental errors.

Multiple ionization state of Arq+ ions during collisions near the Bohr velocity

In order to clarify the mechanism and the influence of the initial charge state and target atomic parameters for the formation of L-shell multiple ionization state of Arq+ ions produced by the collisions near the Bohr velocity, the k-shell x-ray emission of Ar is measured for 1.2 MeV Arq+(q=4, 6, 8, 9, 11, 12) ions impacting on V target and 3 MeV Ar11+ ions interacting with selected targets (Z2 = 23, 26, 27, 28, 29, 30). It is found that the measured Ar Kα and Kβ x-ray energies shift to the high energy side, and the relative intensity ratios of Kβ/Kα are enlarged than the atomic data, owing to the presence of out-shell multiple vacancies. The multiple ionization is almost independence of the projectile charge state, but is diminished with increasing target atomic number.

Benchmark results and theoretical treatments for valence-to-core x-ray emission spectroscopy in transition metal compounds

We report measurement of the valence-to-core (VTC) region of the K-shell x-ray emission spectra from several Zn and Fe inorganic compounds, and their critical comparison with three existing theoretical treatments. We find generally good agreement between the respective theories and experiment and in particular find an important admixture of dipole and quadrupole character for Zn materials that is much weaker in Fe-based systems. These results on materials whose simple crystal structures should not, a priori, pose deep challenges to theory, will prove useful in guiding the further development of DFT and time-dependent DFT methods for VTC-XES predictions and their comparison to experiment.

Target K-shell ionization accompanied by single and double capture in [formula omitted] collisions

Cross sections for target Ar K-shell X-ray emission accompanied by single and double electron capture, as well as the total cross sections for single and double electron capture, have been measured for incident 1.8–2.4MeV/uF9+ ions colliding with Ar. Coincidences between the detected X-rays and the charge-changed projectile ions were recorded. Preliminary analysis indicates total cross sections for single electron capture on the order 10-17cm2, with those for double capture being about an order of magnitude smaller. The corresponding cross sections for target K-shell X-ray emission accompanied by single and double electron capture, despite being about 103 times smaller, are nearly flat and approximately equal, a result that was not expected.

K-shell X-ray emission from high energy pulsed C6+ ion beam impacting on Ni target

Accurate measurement of the ionization cross section of the target atom induced by collision between ions and atoms is of great significance for studying the atomic shell process and establishing a suitable theoretical model. The experimental data and the theoretical models mostly concentrate on the cases in the low energy region at present. Only a few experimental data of high energy region are reported due to the limitation of experimental conditions. Which theory is more suitable to describe the ionization cross section of the inner shell of the target atom caused by the high energy heavy ions, is necessarily studied experimentally. The C6+ ions provided by the Heavy Ion Research Facility in Lanzhou Electron Cooling Storage Ring, are used to bombard the Ni target, in which the K-shell X-ray of Ni is measured. The incident energies of C6+ ions are 165, 300, 350 and 430 MeV/u respectively. Through analyzing the intensity ratio of K/K X-ray of Ni, it is found that the influence of incident energy on the intensity ratio of K/K X-ray is not obvious. The intensity ratios of this experiment are greater than the experimental values of incident proton and the calculated values based on the Hartree-Slater theory, which may be caused by the multiple-ionization of the L shell. The production cross sections of Ni K-shell X-ray are calculated by the binary encounter approximation (BEA) model, the plane wave Born approximation (PWBA) model and the energy-loss coulomb-repulsion perturbed-stationary-state relativistic (ECPSSR) theory respectively, which are compared with the experimental results in this paper. It is found that the experimental cross section increases with the increasing incident energy, which is consistent with the trend of BEA model estimation, but the experimental value is obviously lower than the theoretical value. We think that BEA model needs to be modified when describing the ionization process in the high energy region.

Angular distributions of differential X-ray production cross sections for Cu and Ta in photoionization

Abstract The characteristic K-shell X-ray emission of Cu and L X-rays of Ta in photoionization has been measured at excitation energy of 15.9 keV. The differential X-ray production cross sections of Kα and Kβ for Cu and Lα, Lβ1, Lβ2, Lγ1 for Ta are derived at emission angles ranging from 100° to 150°. The ratio of Kβ and Kα X-ray production cross sections, Kβ/Kα, is calculated for Cu and it is found to be consistent with other work even at different incident energy. While the ratios of Lα/Lβ, Lα/Lγ1 and Lβ/Lγ1 for Ta are found to be different with other results at different excitation energy. The reasons giving rise to this discrepancy are clarified with thorough analysis.