X-ray Emission Cross Sections Research Articles

Espm: A Python library for the simulation of STEM-EDXS datasets

We present two open-source Python packages: “electron spectro-microscopy” (espm) and “electron microscopy tables” (emtables). The espm software enables the simulation of scanning transmission electron microscopy energy-dispersive X-ray spectroscopy datacubes, based on user-defined chemical compositions and spatial abundance maps of constituent phases. The simulation process uses X-ray emission cross-sections generated via state-of-the-art calculations made with emtables. These tables are designed to be easily modifiable, either manually or using espm. The simulation framework is designed to test the application of decomposition algorithms for the analysis of STEM-EDX spectrum images with access to a known ground truth. We validate our approach using the case of a complex geology-related sample, comparing raw simulated and experimental datasets and the outputs of their non-negative matrix factorization. In addition to testing machine learning algorithms, our packages will also help experimental design, for instance, predicting dataset characteristics or establishing minimum counts needed to measure nanoscale features.

K-shell x-ray of Al produced by collisions of ions with near Bohr velocities

X-ray emissionproduced by highly charged ions with the energy range near the Bohr velocity involves complicated atomic process. However, duo to the limitation of experimental conditions, the relevant researches are nearly absent. It is unclear whether the existing theory is applicable in such an energy range. This needs further exploring. In the present work, K X-ray spectra of Al excited by H<sup>+</sup>, He<sup>2+</sup> and highly charged heavy ions I<sup>22+</sup> and Xe<sup>20+</sup> are investigated by using an Si drift X-ray detector in the energy range near the Bohr velocity. The X-ray production cross sections are extracted from the X-ray counts and compared with the theoretical simulations from PWBA, ECPSSR and modified BEA model. It is indicated that the cross section increases with the augment of projectile energy. With the same incident energy per nucleon, the cross section induced by highly charged heavy ions is a factor of about 10<sup>4</sup> larger than that by light ions . With the impact of H<sup>+</sup> and He<sup>2+</sup> ions, the K-shell electrons are mainly knocked off through the direct Coulomb ionization, and the X-ray emission cross section can be well predicted by ECPSSR theory. For the bombardment of highly charged heavy ions I<sup>22+</sup> and Xe<sup>20+</sup>, except for the Coulomb ionization, the orbital electrons can also be excited by electron capture. The BEA simulation after being modified by both Coulomb repulsion and effective charge can well predict the x-ray production cross section.

K-shell X-ray of Al produced by collisions of ions with near Bohr velocities

X-ray emissionproduced by highly charged ions with the energy range near the Bohr velocity involves complicated atomic process. However, duo to the limitation of experimental conditions, the relevant researches are nearly absent. It is unclear whether the existing theory is applicable in such an energy range. This needs further exploring. In the present work, K X-ray spectra of Al excited by H<sup>+</sup>, He<sup>2+</sup> and highly charged heavy ions I<sup>22+</sup> and Xe<sup>20+</sup> are investigated by using an Si drift X-ray detector in the energy range near the Bohr velocity. The X-ray production cross sections are extracted from the X-ray counts and compared with the theoretical simulations from PWBA, ECPSSR and modified BEA model. It is indicated that the cross section increases with the augment of projectile energy. With the same incident energy per nucleon, the cross section induced by highly charged heavy ions is a factor of about 10<sup>4</sup> larger than that by light ions . With the impact of H<sup>+</sup> and He<sup>2+</sup> ions, the K-shell electrons are mainly knocked off through the direct Coulomb ionization, and the X-ray emission cross section can be well predicted by ECPSSR theory. For the bombardment of highly charged heavy ions I<sup>22+</sup> and Xe<sup>20+</sup>, except for the Coulomb ionization, the orbital electrons can also be excited by electron capture. The BEA simulation after being modified by both Coulomb repulsion and effective charge can well predict the X-ray production cross section.

X-ray emission spectroscopy: a genetic algorithm to disentangle core\u2013hole-induced dynamics

A genetic algorithm (GA) is developed and applied to make proper connections of final-state potential-energy surfaces and X-ray emission (XES) cross sections between steps in the time-propagation of H-bonded systems after a core–hole is created. We show that this modification results in significantly improved resolution of spectral features in XES with the semiclassical Kramers–Heisenberg approach which takes into account important interference effects. We demonstrate the effects on a water pentamer model as well as on two 17-molecules water clusters representing, respectively, tetrahedral (D2A2) and asymmetric (D1A1) H-bonding environments. For D2A2, the applied procedure improves significantly the obtained intensities, whereas for D1A1 the effects are smaller due to milder dynamics during the core–hole life-time as only one hydrogen is involved. We reinvestigate XES for liquid ethanol and, by properly disentangling the relevant states in the dense manifold of states using the GA, now resolve the important 3a′′ state as a peak rather than a shoulder. Furthermore, by applying the SpecSwap-RMC procedure, we reweigh the distribution of structures in the sampling of the liquid to fit to experiment and estimate the ratio between the main anti and gauche conformers in the liquid at room temperature. This combination of techniques will be generally applicable to challenging problems in liquid-phase spectroscopy.

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.

Fast calculator for X-ray emission due to Radiative Recombination and Radiative Electron Capture in relativistic heavy-ion atom collisions

In experiments with highly charged, fast heavy ions the Radiative Recombination (RR) and Radiative Electron Capture (REC) processes have significant cross sections in an energy range of up to a few GeV/u. They are some of the most important charge changing processes in collisions of heavy ions with atoms and electrons, leading to the emission of a photon along with the formation of the ground and excited atomic states. Hence, for the understanding and planning of experiments, in particular for X-ray spectroscopy studies, at accelerator ring facilities, such as FAIR, it is crucial to have a good knowledge of these cross sections and the associated radiation characteristics. In the frame of this work a fast calculator, named RECAL, for the RR and REC process is presented and its capabilities are demonstrated with the analysis of a recently conducted experiment at the Experimental Storage Ring (ESR) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. A method is presented to determine unknown X-ray emission cross sections via normalization of the recorded spectra to REC cross sections calculated by RECAL.

Reconstruction of Ge spatial distribution in ICF target using PIXE-T

Inertial confinement fusion (ICF) target is a microsphere with diameter at millimeter scale and shell thickness at micrometer scale. Ge-doped glow discharge polymer (GDP) is an ideal material for the target. The homogeneity of dopant is vital for uniform compression and minimization of Rayleigh-Taylor (RT) instabilities in ignition. However, the method of quantitative measurement of dopants’ spatial distribution is still not mature. Quantitation is not accurate and image resolution is low. Particle induced X-ray emission tomography (PIXE-T) is a suitable technique for measuring trace elements’ spatial distribution in small sample at micrometer scale. This paper demonstrates the capabilities of PIXE-T to obtain quantitative spatial distribution of dopant (Germanium) in ICF target for the first time. We also developed a program run in MATLAB to reconstruct Ge spatial distribution 3D image using Filtered Back Projection (FBP) algorithm. When ion beam is transmitted through the target, its energy is attenuated due to collisions. This energy attenuation causes decrease of X-ray emission cross section. For X-ray emitted from target inside, it will be absorbed by target itself before being collected by detector. Both effects cause loss of X-ray counts, especially at the rear of target toward beam. The program can compensate the loss of X-ray counts caused by these two effects, non-linear X-ray production (NLXP) along the path of the beam and X-ray attenuation (XA). This correction is based on a uniform mass density (1.08g/cm3) and a uniform major composition (stoichiometric ratio C:H=5:7 for GDP material) within the sample. Corrections are applied before tomographic reconstruction, producing a more accurate Ge spatial distribution image. After converting X-ray counts in every voxel to Ge concentration using standard reference material (SRM), the image shows quantitative spatial distribution.

Study of dielectronic recombination and resonance transfer and excitation with X-ray emission for Fe24++H2 collision

Based on the theory of Hartree-Fock with relativistic correction, the theoretical study is carried out on the resonance strength of dielectronic recombination (DR) of the resonance double-excited states (i.e., KLL, KLM, KLN, KLO, KLP) of Fe24+. The resonance strength and colliding cross section of KLL are investigated. By using the experimental results of Compton profiles for H2, the resonance transfer and excitation with X-ray emission cross sections during collision between Fe24+ and target molecule H2 in an energy range of 300-800 MeV are studied. Our results are compared with the recent experimental and theoretical studies. It is found that for the double-excited states of Fe24+, the Kα decay tunnel is the major decay tunnel, and the wavelengths of X-ray in this process range from 1.850 to 1.880 Å. For other decay tunnels, the wavelengths of decay wave range from 1.460 to 1.601 Å. There is no overlap between the wavelengths for two cases. Our results are in reasonable agreement with the experimental results within an estimated uncertainty.

M sub shell X-ray emission cross section measurements for Pt, Au, Hg, Pb, Th and U at 8 and 10 keV synchrotron photons

M sub shell X-ray emission cross sections of Pt, Au, Hg, Pb, Th and U at 8 and 10keV photon energies have been determined with linearly polarized photon beam from Indus-2 synchrotron source. The measured cross sections have been reported for the first time and were used to check the available theoretical Dirac–Hartree–Slater (DHS) and Dirac–Fock (DF) values reported in literature and also the presently derived Non Relativistic Hartree–Slater (NRHS), DF and DHS values for Mξ, Mδ, Mα, Mβ, Mγ, Mm1 and Mm2 group of X-rays.

Experimental determination of layers films thicknesses

The determination of particle induced x-ray emission (PIXE) cross sections and the concentration of elements in a material require the knowledge of the target sample thickness. In this aim, measurements of the thickness by three different methods have been performed. These are absorption of X-rays by a 55Fe source, transmission of alpha particles by a 241Am source and Rutherford backscattering of alpha particles produced by Van de Graff Accelerator with the use of the RUMP simulation code. The results give a thickness with uncertainties ranging from 1 to 8% according to the experimental technique used. The comparison between these methods gives an advantage for the X-rays absorption for its simplicity and accuracy, when backscattering spectrometry is preferred for thin target on backing or as a complementary technique for PIXE analysis. Key words: Thickness, particle induced x-ray emission (PIXE), Rutherford backscattered (RBS), cross section, rump.

X-ray emission cross sections following charge exchange collisions on neutral targets: the role of multiple electron capture

Line emission and charge exchange cross sections obtained from a three-active electrons CTMC code allow us to determine the role of multiple electron capture for charge exchange collisions on neutral argon and neon. The present results can be compared to recent experimental data from EBIT groups operating at Liver-more, NIST and Berlin.

Interaction of slow HCI with gaseous targets: absolute x-ray emission cross sections and contribution of multi-capture processes

Collisions of 15 keV/q Ar17+ ions with a gaseous jet have been studied by high-resolution x-ray spectroscopy techniques. Absolute x-ray emission cross sections and initial population mechanisms on singly and multiple excited states are extracted.

Shell-differential electron capture in heavy ion-atom collisions at moderate collision velocities

Electron capture cross sections have been estimated from the projectile incoming inner shell vacancy dependent K and L x-ray emission cross sections of the projectile in 69.2 MeV/u Biq+-Au collisions (77≤ q ≤ 82) measured at the GSI heavy ion synchrotron SIS18. These estimations proved to be in agreement with the values deduced from the charge exchange cross sections obtained from the target thickness dependent charge state distribution of the emerging ions. The Eikonal approximation indicates trends in consonance with the measured values and predictions according to Schlachter et al. are in reasonable agreement too.

Investigation of slow collisions for (quasi) symmetric heavy systems: what can be extracted from high resolution x-ray spectra

We present a new experiment on (quasi) symmetric collision systems at low velocity, namely Ar17 + ions (v = 0.53 au) on gaseous Ar and N2 targets, using low- and high-resolution x-ray spectroscopy. Thanks to an accurate efficiency calibration of the spectrometers, we extract absolute x-ray emission cross sections combining low-resolution x-ray spectroscopy and a complete determination of the ion beam–gas jet target overlap. Values with improved uncertainty are found in agreement with previous results (Tawara et al 2001 Phys. Rev. A 64 042712). Resolving the whole He-like Ar16 + Lyman series from n = 2–10 with our crystal spectrometer enables us to determine precisely the distribution of the electron capture probability and the preferential npref level of the selective single-electron capture. Evaluation of cross sections for this process as well as for the contribution of multiple-capture is carried out. Their sensitivity to the ℓ-distribution of n levels populated by single-electron capture is clearly demonstrated, providing a stringent benchmark for theories. In addition, the hardness ratio is extracted and the influence of the decay of the metastable 1s2s 3S1 state on this ratio is discussed.

Depth selective PIXE for surface analysis with low energy heavy ions

A low energy heavy ions PIXE setup was applied for search of trace elements in the subsurface regions. Analysis of elemental composition of standardised foils and thin films PVD evaporated on various substrates at LN2 temperature was performed with the help of SWAN and GUPIX codes. Results for the k-shell X-ray emission cross sections for selected elements were compared to results obtained with swift light ions.

Real-space Green’s function approach to resonant inelastic x-ray scattering

We present an ab initio theory of core and valence resonant inelastic x-ray scattering (RIXS) based on a real-space multiple-scattering Green's function formalism and a quasiboson model Hamiltonian. Simplifying assumptions are made that lead to an approximation of the RIXS spectrum in terms of a convolution of an effective x-ray absorption signal with the x-ray emission cross section. Additional many-body corrections are incorporated in terms of an effective energy-dependent spectral function. Example calculations of RIXS are found to give qualitative agreement with experimental data. Our approach also yields simulations of lifetime-broadening suppressed x-ray absorption, as observed in high-energy resolution fluorescence detection experiment. Finally, possible improvements to our approach are briefly discussed.

X-ray emission cross sections following Ar18+charge-exchange collisions on neutral argon: The role of the multiple electron capture

X-ray emission originating in charge-exchange collisions between Ar${}^{18+}$ and neutral argon is studied at impact energies of 5--4000 eV/amu by means of the classical trajectory Monte Carlo method (CTMC). Line emission and charge-exchange cross sections obtained from different CTMC versions based on the one-active electron approximation are contrasted among themselves and against the results obtained by means of a three-active electron code that lets us infer the role of multiple electron capture. The present results are compared to the recent experimental data available from the EBIT groups operating at Livermore, NIST, and Berlin. We were not able to reconcile the major difference in x-ray emission cross sections obtained from in situ measurements made in EBIT, versus those made in an exterior, field-free collision chamber using ions extracted from the EBIT. Our calculations support the extracted beam results.

L-shell X-ray emission cross section of tantalum by 20—45 MeV O5+ bombardment

With 20—45 MeV O5+ ion bombardment we investigate L-shell X-ray emission processes on Ta film at HI-13 tandem accelerator in the Chinese Institute of Atomic Energy (CIAE). The ratios of X-ray emission cross section: σ(Lβ)/σ(Lα),σ(Lγ)/σ(Lα), and σ(Ll)/σ(Lα) are obtained. The results are compared with the predictions by the ECPSSR theory. Reasonable agreement between the ECPSSR theory and the experiment is obtained.

Resonant Transfer Excitation of Fluorine-Like Mo33+ Ion

Dielectronic recombination (DR) cross sections (σDR) and rate coefficients (αDR) for Mo33+ are calculated using the angular momentum average scheme (AMA). Moreover, the resonant transfer excitation followed by X-ray emission (RTEX) cross sections (σ RTEX) for the collision of Mo33+ with H2 and He targets are calculated and studied. The calculations of the cross sections are performed for both K- and L-shell excitations. A smooth change with the temperatures for αDR is found for all kinds of excitations. The rates for K-shell excitation are very small in comparison with the rates for Lshell excitation. The RTEX cross sections for Mo33+ ions are obtained from their corresponding DR cross sections by the method of folding in the impulse approximation (IMA). σ RTEX for the K-shell excitation shows two overlapped peaks which may be attributed to the two groups in this excitation process. The present calculations are considered as a database for future comparison with theoretical and experimental data using other coupling schemes. Multiple Auger channels are complicating the dependence of the cross sections on principal quantum numbers.

Charge exchange and x-ray emission cross sections for multiply charged ions colliding withH2O

Total and state selective $nl$-electron capture cross sections are presented for highly charged ions $Z=4--10$, 14, 18, and 26 colliding with water molecules. The energy range investigated was from $10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{amu}$ $(v=0.02\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.})\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$ $(v=2\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.})$. An initialization for the $1B1$ and $3A1$ orbitals of the water molecule is introduced based on the one center expansion of Moccia and compared to our previous studies based on a hydrogenic approximation within the microcanonical ensemble. The $Z$ dependence of the calculated total cross sections is in reasonable agreement with the recent data of Mawhorter et al. [Phys. Rev. A 75, 032704 (2007)] and is improved over previous results. The energy dependence of the $n$- and $l$-level populations is investigated. The $K$-shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. Our results compare favorably with experimental data from the KVI-Groningen, Jet Propulsion Laboratory and Lawrence Livermore National Laboratory groups.