K-shell Ionization Research Articles

L-Shell Ionization during the Alpha Decay of Superheavy Nuclei from 117 294 Ts Tennessine Decay Chain and the Alpha Decay of the Polonium Isotope 84 210 Po

The probabilities for L-shell ionization following the alpha decay of 117 294 Ts, 113 286 Nh, 109 278 Mt, and 105 270 Db superheavy nuclei from the decay chain of tennessine, which was synthesized at the Joint Institute for Nuclear Research (JINR Dubna), and the alpha decay of the isotope 84 210 Po are calculated and analyzed. The respective calculations rely on a quantum-mechanical model that takes into account alpha-particle tunneling through the Coulomb barrier of an atom. The relativistic electron wave functions obtained by the Dirac-Fock method were employed. The probabilities for L-shell ionization that were calculated here for the isotope 84 210 Po are in better agreement with experimental data than the results of earlier calculations. In contrast to what we have for K-shell ionization, where monopole transitions make a dominant contribution to the ionization probability, a significant contribution to the probability for L-shell ionization also comes from dipole and quadrupole transitions. The results of the present study will be of use in interpreting superheavy-element spectra obtained by methods of combined alpha, gamma, and electron-conversion spectroscopy.

Charge state effect on K-shell ionization of silicon induced by iodineq+ ions

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.

Path integral Monte Carlo simulations of warm dense aluminum

We perform first-principles path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) calculations to explore warm dense matter states of aluminum. Our equation of state (EOS) simulations cover a wide density-temperature range of 0.1-32.4gcm^{-3} and 10^{4}-10^{8} K. Since PIMC and DFT-MD accurately treat effects of the atomic shell structure, we find two compression maxima along the principal Hugoniot curve attributed to K-shell and L-shell ionization. The results provide a benchmark for widely used EOS tables, such as SESAME, QEOS, and models based on Thomas-Fermi and average-atom techniques. A subsequent multishock analysis provides a quantitative assessment for how much heating occurs relative to an isentrope in multishock experiments. Finally, we compute heat capacity, pair-correlation functions, the electronic density of states, and 〈Z〉 to reveal the evolution of the plasma structure and ionization behavior.

K-Shell Ionization Cross Sections of Arsenic and Yttrium by electron impact

K-Shell Ionization Cross Sections of Arsenic and Yttrium by electron impact

Absolute Hugoniot measurements from a spherically convergent shock using x-ray radiography.

The canonical high pressure equation of state measurement is to induce a shock wave in the sample material and measure two mechanical properties of the shocked material or shock wave. For accurate measurements, the experiment is normally designed to generate a planar shock which is as steady as possible in space and time, and a single state is measured. A converging shock strengthens as it propagates, so a range of shock pressures is induced in a single experiment. However, equation of state measurements must then account for spatial and temporal gradients. We have used x-ray radiography of spherically converging shocks to determine states along the shock Hugoniot. The radius-time history of the shock, and thus its speed, was measured by radiographing the position of the shock front as a function of time using an x-ray streak camera. The density profile of the shock was then inferred from the x-ray transmission at each instant of time. Simultaneous measurement of the density at the shock front and the shock speed determines an absolute mechanical Hugoniot state. The density profile was reconstructed using the known, unshocked density which strongly constrains the density jump at the shock front. The radiographic configuration and streak camera behavior were treated in detail to reduce systematic errors. Measurements were performed on the Omega and National Ignition Facility lasers, using a hohlraum to induce a spatially uniform drive over the outside of a solid, spherical sample and a laser-heated thermal plasma as an x-ray source for radiography. Absolute shock Hugoniot measurements were demonstrated for carbon-containing samples of different composition and initial density, up to temperatures at which K-shell ionization reduced the opacity behind the shock. Here we present the experimental method using measurements of polystyrene as an example.

K-Shell Ionization Cross Sections of Chromium and Cobalt by electron impact

K-Shell Ionization Cross Sections of Chromium and Cobalt by electron impact

K -shell ionization of heavy hydrogenlike ions

A theoretical study of the K-shell ionization of hydrogen-like ions, colliding with bare nuclei, is performed within the framework of the time-dependent Dirac equation. Special emphasis is placed on the ionization probability that is investigated as a function of impact parameter, collision energy and nuclear charge. To evaluate this probability in a wide range of collisional parameters we propose a simple analytical expression for the transition amplitude. This expression contains three fitting parameters that are determined from the numerical calculations, based on the adiabatic approximation. In contrast to previous studies, our analytical expression for the transition amplitude and ionization probability accounts for the full multipole expansion of the two-center potential and allows accurate description of nonsymmetric collisions of nuclei with different atomic numbers, $Z_1 \neq Z_2$. The calculations performed for both symmetric and asymmetric collisions indicate that the ionization probability is reduced when the difference between the atomic numbers of ions increases.

Discovery of 6.4 keV line and soft X-ray emissions from G323.7−1.0 with Suzaku

Abstract In this paper, the Suzaku X-ray data of the Galactic supernova remnant (SNR) candidate G323.7−1.0 are analyzed to search for X-ray emissions. Spatially extended enhancements in the 6.4 keV line and in soft X-rays are found inside or on the radio shell. The soft X-ray enhancement would be the hottest part of the shell-like X-ray emission along the radio shell. The 6.4 keV line enhancement is detected at a significance level of 4.1 σ. The lower limit of the equivalent width (EW) is 1.2 keV. The energy centroid of the 6.4 keV line is 6.40 ± 0.04 keV, indicating that the iron is less ionized than the Ne-like state. If the 6.4 keV line originates from ionizing non-equilibrium thermal plasma, presence of iron-rich ejecta in a low-ionization state is required, which is disfavored by the relatively old age of the SNR. The 6.4 keV line enhancement would be due to K-shell ionization of iron atoms in a dense interstellar medium by high-energy particles. Since there is no irradiating X-ray source, the origin of the 6.4 keV line enhancement is not likely the photoionization. The large EW can only be explained by K-shell ionization due to cosmic-ray protons with an energy of ∼10 MeV, which might be generated by the shock acceleration in G323.7−1.0.

K-Shell ionization of chlorine and argon due to impact of alpha particles

K-Shell ionization of chlorine and argon due to impact of alpha particles

K-shell ionization during the α-decay of superheavy nuclei

The probabilities of K-shell ionization in daughter atoms during the α-decay of extensively studied 84Po isotopes and superheavy 117 294 Ts, 113 286 Nh, 109 278 Mt, 105 270 Db, 102 253 No, 100 249 Fm, and 111 272 Rg nuclei are calculated. Monopole and dipole terms are considered. More accurate expressions for α-particle tunneling through the atomic Coulomb barrier are derived. The electron wave functions are calculated using the relativistic Dirac–Fock method. The results are essential for processing the spectra analyzed in combined α-, γ-, and conversion-electron spectroscopy.

Ultrafast isomerization in acetylene dication after carbon K-shell ionization

Ultrafast proton migration and isomerization are key processes for acetylene and its ions. However, the mechanism for ultrafast isomerization of acetylene [HCCH]2+ to vinylidene [H2CC]2+ dication remains nebulous. Theoretical studies show a large potential barrier ( > 2 eV) for isomerization on low-lying dicationic states, implying picosecond or longer isomerization timescales. However, a recent experiment at a femtosecond X-ray free-electron laser suggests sub-100 fs isomerization. Here we address this contradiction with a complete theoretical study of the dynamics of acetylene dication produced by Auger decay after X-ray photoionization of the carbon atom K shell. We find no sub-100 fs isomerization, while reproducing the salient features of the time-resolved Coulomb imaging experiment. This work resolves the seeming contradiction between experiment and theory and also calls for careful interpretation of structural information from the widely applied Coulomb momentum imaging method.

Photoelectron distribution of nonresonant two-photon ionization of neutral atoms

Photoelectron angular distributions following the non-resonant two-photon K-shell ionization of neutral atoms are studied theoretically. Using the independent particle approximation and relativistic second-order perturbation theory, the contributions of screening and relativistic effects to the photoelectron angular distribution are evaluated. A simple nonrelativistic expression is presented for the angle-differential cross section in dipole approximation for two-photon ionization by elliptically polarized photons, and its limitations are analyzed numerically. Moreover, we show that screening effects of the inactive electrons can significantly affect the photoelectron distributions and can also lead to a strong elliptical dichroism. Numerical results are resented for the case of two-photon K-shell ionization of neutral Ne, Ge, Xe, and U atoms.

First-principles equation of state and shock compression predictions of warm dense hydrocarbons.

We use path integral Monte Carlo and density functional molecular dynamics to construct a coherent set of equations of state (EOS) for a series of hydrocarbon materials with various C:H ratios (2:1, 1:1, 2:3, 1:2, and 1:4) over the range of 0.07-22.4gcm^{-3} and 6.7×10^{3}-1.29×10^{8}K. The shock Hugoniot curve derived for each material displays a single compression maximum corresponding to K-shell ionization. For C:H = 1:1, the compression maximum occurs at 4.7-fold of the initial density and we show radiation effects significantly increase the shock compression ratio above 2 Gbar, surpassing relativistic effects. The single-peaked structure of the Hugoniot curves contrasts with previous work on higher-Z plasmas, which exhibit a two-peak structure corresponding to both K- and L-shell ionization. Analysis of the electronic density of states reveals that the change in Hugoniot structure is due to merging of the L-shell eigenstates in carbon, while they remain distinct for higher-Z elements. Finally, we show that the isobaric-isothermal linear mixing rule for carbon and hydrogen EOS is a reasonable approximation with errors better than 1% for stellar-core conditions.

Multi-electron processes in K-shell double and triple photodetachment of oxygen anions

SynopsisAbsolute cross sections for double and triple photodetachment of O− ions have been measured at photon energies around the threshold for K-shell ionization using the photon-ion merged-beams technique at a synchrotron light-source. In addition, corresponding large-scale ab-initio calculations were carried out at a level of complexity that has never been invoked before. From the comparison between experiment and theory it becomes apparent that the inclusion of multi-electron processes such as double shake-up in the theoretical calculations is crucial for the explanation of the experimental findings.

K-K electron transfer and K-ionization in fast ion collisions with adenine and water using KLL Auger electron technique

SynopsisIn this report, we present a study of K-shell ionization, state selective K-to-K electron capture cross sections from C and N atoms in the adenine and other gas molecules using K-LL Auger electron technique, which is applied for first time. Energy dependence of K-ionization and K-K electron capture has also been measured. The e-transfer cross section is found to be substantial compared to the K-ionization. Total σKK and σKI for the entire molecule was deduced.

Localized or delocalized K-holes in N2: Photoelectron-Auger electron coincidence experiments with high energy resolution

SynopsisFor K-shell ionization of N2 photoelectron auger electron coincident angular distributions show that pathways with gerade and ungerade K-hole state can interfere. On the other hand high resolution photoelectron spectroscopy seems to indicate that the gerade and ungerade hole state can be separated in energy. The present experiment aims to combine the high energy resolution with full angular detection of Auger and Photoelectron to resolve this seeming contradiction.

First-principles simulations of warm dense lithium fluoride.

We perform first-principles path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) calculations to explore warm dense matter states of LiF. Our simulations cover a wide density-temperature range of 2.08-15.70gcm^{-3} and 10^{4}-10^{9} K. Since PIMC and DFT-MD accurately treat effects of atomic shell structure, we find a pronounced compression maximum and a shoulder on the principal Hugoniot curve attributed to K-shell and L-shell ionization. The results provide a benchmark for widely used EOS tables, such as SESAME, LEOS, and models. In addition, we compute pair-correlation functions that reveal an evolving plasma structure and ionization process that is driven by thermal and pressure ionization. Finally, we compute electronic density of states of liquid LiF from DFT-MD simulations and find that the electronic gap can remain open with increasing density and temperature to at least 15.7 gcm^{-3}.

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.

Relativistic effects in the non-resonant two-photon K-shell ionization of neutral atoms

Relativistic effects in the non-resonant two-photon K-shell ionization of neutral atoms are studied theoretically within the framework of second-order perturbation theory. The non-relativistic results are compared with the relativistic calculations in the dipole and no-pair approximations as well as with the complete relativistic approach. The calculations are performed in both velocity and length gauges. Our results show a significant decrease of the total cross section for heavy atoms as compared to the non-relativistic treatment, which is mainly due to the relativistic wavefunction contraction. The effects of higher multipoles and negative continuum energy states counteract the relativistic contraction contribution, but are generally much weaker. While the effects beyond the dipole approximation are equally important in both gauges, the inclusion of negative continuum energy states visibly contributes to the total cross section only in the velocity gauge.

Feasibility study of thin films deposited on a self-supporting carbon grid substrate target on the measurement of atomic inner-shell ionization cross-sections impacted by 3–30 keV electrons

In this paper, we have measured the , and X-ray production cross-sections of the W element and the K-shell ionization cross-sections of the Al element impacted by 3–30 keV electrons. A new kind of target consisting of a thin film deposited on a self-supporting carbon grid substrate has been used in this work. The self-supporting carbon grid substrate is made of several layers of super-aligned carbon nanotube arrays (the mass thickness of each layer of super-aligned carbon nanotube arrays is 20 μg/cm2). As a comparison, three kinds of targets consisting of a) the studied element deposited onto four layers of super-aligned carbon nanotube arrays and separated from each other by one layer of single carbon atoms, b) the studied element deposited directly onto four layers of super-aligned carbon nanotube arrays, and c) the studied element deposited directly onto two layers of super-aligned carbon nanotube arrays, were respectively prepared to figure out which type is fit for the measurement of inner-shell ionization cross-sections induced by 3–30 keV electrons. The experimental data are compared with the distorted-wave Born approximation (DWBA) theoretical predictions and with the available experimental data from other references. The results show that the first and the second targets are both suitable for the inner-shell ionization cross-section measurements by 3–30 keV electrons, but the third target is not. Besides, we present the M-shell X-ray production cross-sections of the W element by 5–30 keV electrons in this paper for the first time.