L-shell Ionization Research Articles

L- and M-subshell ionization cross-sections of heavy atoms by electron and proton impact

Inner-shell ionization has many applications related to material analysis. However, full theoretical calculations in heavy multielectronic atoms are scarce. In this contribution, we assess proton and electron impact Li and Mi-subshell ionization cross-sections of heavy targets (72≤Z≤83) using two theoretical models. These calculations are based on the Distorted Plane Wave Born Approximation for electron impact and the shellwise local plasma approximation for the proton impact, combined with relativistic calculations of these deep subshells wave functions and binding energies. We analyze the L-shell ionization of W, Au, and Bi and the M-shell of Hf, Ta, W, Re, Os, Pt, Au, Pb, and Bi. Present values are compared with available experimental data from the literature, with disparate agreement. The convergence of proton and electron impact cross-sections at high-impact velocities is also discussed.

L-Shell Ionization Cross Sections for Silver by Low-Energy Electron Impacts

The L-subshell ionization cross sections and total L–X-ray production cross sections for the Ag atom by the electron impact near the ionization threshold were calculated with a classical-trajectory Monte Carlo method. The results were compared with experimental data, quantum mechanical calculations, and the cross sections by positron impact. It was demonstrated that the classical treatments are useful for electron–atom collisions at energies higher than about six times the binding energies of target electrons but overestimate L-shell ionization and L–X-ray production cross sections at low energies near the threshold. Possible reasons for this discrepancy are discussed.

L-shell ionisation and X-ray production cross-sections for some low Z-elements by proton impact

L-shell ionisation and x-ray production cross-sections of various targets are useful in many Proton Induced X-ray Emission (PIXE) applications. Generally, x-ray production cross sections are measured directly but ionisation cross sections are only evaluated using theoretical models. The use of ionisation models has been instrumental in the ion-atom description of the subshells which are then converted to x-ray production cross sections, however, certain limitations exist for currently available models. For instance, at extremely low energy and high energy of the incident particle, some modifications are made to these models to correctly obtain these values. While existing ionisation theory coupled with associated computed codes or data tables have been used successfully in determining cross-sections of medium Z and high Z-elements, targets of low atomic number have not been fully studied, especially when bombarded with proton energy less than 1 MeV. In this study, a revised model using computer codes and algorithm are used in obtaining cross-sections of some light elements (Neon, Magnesium and Argon) whose experimental values are difficult to measure. To verify the certainty of these values, a comparison was made with some experimental values.

Evidence for Dissociation and Ionization in Shock Compressed Nitrogen to 800GPa.

Triple bonding in the nitrogen molecule (N_{2}) is among the strongest chemical bonds with a dissociation enthalpy of 9.8 eV/molecule. Nitrogen is therefore an excellent test bed for theoretical and numerical methods aimed at understanding how bonding evolves under the influence of the extreme pressures and temperatures of the warm dense matter regime. Here, we report laser-driven shock experiments on fluid molecular nitrogen up to 800GPa and 4.0 g/cm^{3}. Line-imaging velocimetry measurements and impedance matching method with a quartz reference yield shock equation of state data of initially precompressed nitrogen. Comparison with numerical simulations using path integral MonteCarlo and density functional theory molecular dynamics reveals clear signatures of chemical dissociation and the onset of L-shell ionization. Combining data along multiple shock Hugoniot curves starting from densities between 0.76 and 1.29 g/cm^{3}, our study documents how pressure and density affect these changes in chemical bonding and provides benchmarks for future theoretical developments in this regime, with applications for planetary interior modeling, high energy density science, and inertial confinement fusion research.

Understanding the mechanisms of L-shell x-ray emission from Os atoms bombarded by 4–6 MeV/u fluorine ion

The L-subshell ionization mechanism is studied in an ultra-thin Os target bombarded by 4–6 MeV/u fluorine ions. Multiple ionization effects are considered through the change of fluorescence and Coster-Kronig yields while determining L-subshell ionization cross sections from L x-ray production cross sections. The present experimental values are compared with various theoretical approximations: (i) the relativistic semi-classical approximation (RSCA), (ii) the shellwise local plasma approximation (SLPA), and (iii) the ECUSAR theory. We also take into account the vacancy sharing among the subshells by the coupled-states model (CSM) and the electron capture (EC) by a standard formalism. We find that the ECUSAR-CSM-EC describes the measured excitation function curves the best. However, the theoretical calculations are still about a factor of two smaller than the measured values even though the recent fluorescence and Coster-Kronig yields are considered. Hence, a re-evaluation of these parameters is a challenge for the theoretical works. Whatsoever, this work leads to demonstrate that in the present energy range the heavy-ion induced inner-shell ionization of the heavy atoms can be understood by combining the direct Coulomb ionization, the electron capture, and the vacancy sharing among subshells, together with optimizing the atomic parameters. Optimization of the atomic parameters shows that our experimental results agree with theoretical vacancy production theories if the L1 fluorescence yield is nearly doubled. Such a optimization is validated by the proton induced L-shell ionization data of uranium atoms.

W L-shell X-ray emission induced by C<sup>6+</sup>ions in the energy range of several hundred MeV/u

The L-shell X-ray emissions of tungsten has been investigated under the bombardment of C<sup>6+</sup> ions in the high energy region of 154 - 424 MeV/u. Compared to the atomic data, the energy of the X-ray is enlarged, and the relative intensity ratios of Lı, Lβ<sub>1, 3, 4</sub> and Lβ<sub>2, 15</sub> to Lα<sub>1, 2</sub> X-rays are enhanced. The L-subshell and the total X-ray production cross sections were calculated by a well corrected thick target formula and compared with the theoretical estimation of BEA, PWBA and ECPSSR. On the whole, the experimental cross sections are all smaller than the prediction of PWBA and ECPSSR, but in agreement roughly with that of BEA. It is indicated that the inner-shell ionization of W can be considered to be a binary process between the high energy C<sup>6+</sup> ions acting as a point charge and the independent target electrons. With the L-shell ionization, the outer-shells are multiply ionized. The multi-ionization degree is regard to be almost constant in the present work. This results in the X-ray energy blue shift and the enhancement of the relative intensity ratios of Lı and Lβ to Lα X-ray. Using the atomic parameters corrected by multi-ionization, the X-ray production cross section can be estimated by the BEA model.

W L-shell X-ray emission induced by C<sup>6+ </sup>ions with several hundred MeV/u

The L-shell X-ray emission of tungsten is investigated under the bombardment of C<sup>6+</sup> ions in a high energy range of 154—424 MeV/u. Compared with the atomic data, the energy of the X-ray is enlarged, and the relative intensity ratio of Lι, Lβ<sub>1,3,4</sub> and Lβ<sub>2,15</sub> to Lα<sub>1,2</sub> X-rays are enhanced. The L-subshell and the total X-ray production cross section are calculated from a well corrected thick target formula and compared with the theoretical estimation of binary encounter approximation (BEA), plane-wave Born approximation (PWBA) and ECPSSR (PWBA theory modified with Energy-loss, Coulomb-repulsion, Perturbed-Stationary-State and Relativistic corrections). On the whole, the experimental cross sections are all smaller than the prediction of PWBA and ECPSSR, but in rough agreement with that of BEA. It is indicated that the inner-shell ionization of W can be considered as a binary process between the high energy C<sup>6+</sup> ions acting as a point charge and the independent target electrons. With the L-shell ionization, the outer-shells are multiply ionized. The multi-ionization degree is approximately regard as a constant in the present work. This leads the X-ray energy to be blueshifted and the relative intensity ratios of Lι and Lβ to Lα X-ray to be enhanced. Using the atomic parameters corrected by multi-ionization, the X-ray production cross section can be estimated by the BEA model.

Nd L-shell x-ray emission induced by light ions

The L-shell x-ray of Nd has been obtained for 300–600 keV He2+ ions impacting, and compared with that produced by H+ and ions. The threshold of projectile kinetic energy for L-shell ionization of Nd is crudely verified in the energy region of about 300–400 keV. It is found that the energy of the distinct L-subshell x-rays has a blue shift. The relative intensity ratios of Lβ 1, 3, 4 and Lβ 2, 15 to Lα 1, 2 x-ray are enlarged compared to the atomic data, and they decrease with the increase of the incident energy, and increase with increasing the effective nuclear charge of the incident ions. That is interpreted by the multiple ionization of outer-shells induced by light ions.

L-shell ionization of Cd: Structure of the x-ray emission spectrum

The cadmium L x-ray spectrum induced by electron impact was analyzed in detail. The measurements were performed on a bulk pure sample using a commercial wavelength dispersive spectrometer, and the spectrum was processed with a parameter optimization method previously developed. This procedure permitted the determination of characteristic energies, relative transition probabilities and natural linewidths for this element. The results obtained here were compared to the data found in the literature, when available. Spectral structures related to satellite and radiative Auger Effect emissions were also analyzed, assessing energy shifts and relative intensities. Some of these parameters were determined for the first time, even in overlapping peaks and weak transitions, which was possible due to the robustness of the spectral processing method used.

Relativistic multiconfiguration Dirac–Fock calculations of photoionization, electron-impact ionization, Auger decay, and relaxed-orbital oscillations of Cu ions

Core-hole creation and decay are of tremendous importance in both theory and applications. However, different ionization approaches and decay channels, especially at L-shell, bring many challenges to accurate simulation. In order to understand the ionization state effects on the creation and decay at L-shell hole, we performed a theoretical study of photon/electron-impact L-shell ionization of differently charged copper ions and the subsequent Auger electron and fluorescence emission by using the relativistic multiconfiguration Dirac–Fock approach. It was found that photoionization has much larger cross sections than electron-impact ionization near the ionization threshold, but smaller ones at higher impact energies. The ionization cross sections for 2s-sublevels are negligibly small compared with those for 2p-sublevels for both photon and electron impact ionizations. Additionally, the ionization cross sections decrease with the ionization state for both electron- and photon- impact L-shell ionizations. Similar to radiative (fluorescence) decay, Auger kinetic energy and yield decrease with ionization state, and the energy gaps and rate ratios between major Auger transitions change with ionization state. Furthermore, Auger rates from the L-shell decay are much larger than fluorescence rates, and the Auger-to-fluoresce decay ratio slightly decreases with increase in the ionization state of Cu ion.

Proton induced L-shell cross-sections for some post-transition metals: A comparison of ECPSSR and SCA models

The L-shell ionisation and X-ray production cross-sections of some post-transition elements: In, Sn and Tl, induced by protons of energies 1 MeV–4 MeV, have been calculated. The targets considered have few experimental cross-sections, for indium and tin, while thallium has no existing cross-section values in the database due to its radioactive and toxic nature. The cross-sections for the targets were obtained using computer codes based on the ECPSSR and SCA theories; and were subsequently validated using lead and bismuth targets whose experimental values are known within this energy range. The comparison of the experimental and calculated cross-sections showed that both models are in good agreement within certain proton energy region. However, above 2 MeV, the ECPSSR models should be employed. For the case where the SCA model is to be employed, the energy loss and Coulomb deflection factors should be taken into account.

Experimental and theoretical L-shell ionization cross sections of heavy atoms by impact of Si ions

We present a theoretical and experimental study of the subshell resolved L-shell ionization of relativistic targets such as 73Ta, 78Pt, 90Th, and 92U. The measurements of x-ray production cross sections by (84–140 MeV) Si+q ions (q = 8; 12), were held at the Inter-University Accelerator Centre of New Delhi. Multiple-hole fluorescence and Coster-Kronig yields were used to obtain the Li(i = 1–3) ionization cross sections from the measured x-ray production cross sections of Lℓ, Lα, and Lβ, Lη, and Lγ lines. The experimental results are compared with ab initio theoretical calculations by means of the shell-wise local plasma approximation (SLPA). This model uses the quantum dielectric formalism to obtain the total ionization cross sections from an initial ground state. The wave functions and binding energies of the different targets were obtained by solving the fully relativistic Dirac equation using the HULLAC code package. These calculations are based on first order perturbation theory with a central field, including Breit interaction and quantum electrodynamics corrections. The present SLPA ionization cross sections of the L-shell are found to be independent of the charge state of the Si ions. The experimental observations display also quite similar character if the correct mean projectile charge state inside the target is used for including the multiple ionization effect during ion-solid collisions. A general good agreement between the experimental measurements and full theoretical calculations supports the reliability of present results. The comparison also includes the well-known ECPSSR and ECUSAR semi empirical approximations. We noted that the ECUSAR results agree well with the SLPA, while the ECPSSR cross sections are rather low.

Coulomb explosion of CD3I induced by single photon deep inner-shell ionisation

L-shell ionisation and subsequent Coulomb explosion of fully deuterated methyl iodide, CD3I, irradiated with hard X-rays has been examined by a time-of-flight multi-ion coincidence technique. The core vacancies relax efficiently by Auger cascades, leading to charge states up to 16+. The dynamics of the Coulomb explosion process are investigated by calculating the ions’ flight times numerically based on a geometric model of the experimental apparatus, for comparison with the experimental data. A parametric model of the explosion, previously introduced for multi-photon induced Coulomb explosion, is applied in numerical simulations, giving good agreement with the experimental results for medium charge states. Deviations for higher charges suggest the need to include nuclear motion in a putatively more complete model. Detection efficiency corrections from the simulations are used to determine the true distributions of molecular charge states produced by initial L1, L2 and L3 ionisation.

Measuring the total L-Shell X-Ray production cross sections of Te element using 6–30 keV electron impact

We report the absolute measurements of X-ray production cross sections for L-shell ionization of Te element by electron impact in an energy range of 6–30 keV with a step of 1 keV. The measurements were conducted using a scanning electron microprobe with a high-resolution X-ray silicon drift detector (SDD). The measured total L-shell X-ray production cross sections of Te were compared with the theoretical results using the distorted-wave Born approximation (DWBA) and plane-wave Born approximation with Coulomb and exchange corrections (PWBA-C-Ex). Good agreement was observed between the measured and theoretical results.

L-shell X-ray production cross sections of Ag and Au induced by carbon ions between 2 MeV and 5 MeV

In this work, we experimentally determined Ag and Au L-shell X-ray production and ionization cross sections, induced by 2–5 MeV carbon ions. The experiment was performed using the standard measurement setup already used to measure M-Shell X-ray production cross sections. Ag and Au thin targets, were used to measure L-shell X-ray spectra with Si(Li) and SDD X-ray detectors simultaneously with backscattered carbon ions from the targets by surface barrier detector. Experimental values are compared to the data available in the literature, as well as to the theoretical predictions of PWBA, ECPSSR and ECUSAR models. The analysis of data shows that the ECUSAR predictions are good at low carbon ion energies while the ECPSSR and PWBA predictions agree at the higher incident energies.

Calculated proton-induced L-shell ionisation and X-ray production cross sections for Tc, Pm, Os, Po, At, Rn, Ra and Ac

The L-shell ionisation and X-ray production cross sections of the elements: Tc, Pm, Os, Po, At, Rn, Ra and Ac, whose experimental cross sections are scanty due to their radioactive, toxic and unstable nature have been calculated. Computer codes were employed in the targets cross sections calculation for incident protons of 1.00–10.00 MeV energy range. The obtained cross sections were validated in a similar procedure for Osmium (Z2=76) induced by protons of energies 0.10–1.00 MeV and were compared with experimental data. The calculated cross sections for the Osmium target were in good agreement with the experimental data. Hence, the calculated cross sections for the considered industrially relevant targets will be a valuable addition to existing database of elements induced by protons.

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.

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.

Electron impact L-subshell and total L-shell ionization cross-sections of atoms (Z = 18–92)

We propose an extension of the modified Vaisburd and Evdokimov model (MVE) (2003 Russ. Phys. J. 46 1160) incorporating the relativistic effects to investigate the L1-, L2- and L3-subshells as well as total L-shell ionization cross-sections (LSICS) of atomic targets with atomic numbers 18 ≤ Z ≤ 92 for incident energies upto 1 GeV. We also revisited our earlier XMUIBED and XMCN model for individual L-subshell ionization cross-sections and MUIBED, GKLV and XCVTS for total LSICS for 28 atomic targets. We compare our new results from the MVE model with the available experimental data and other calculations including our previously proposed models.

Calculation of L-shell ionisation and x-ray production cross sections for some trans-uranium elements induced by protons

L-shell ionisation and x-ray production cross sections of trans-uranium elements: Np, Pu and Am, induced by protons of energies 5.00–20.00 MeV, have been calculated. The cross sections for the targets were obtained using computer codes based on the ECPSSR theory. Due to the lack of experimental data of the targets considered, in view of their radioactive, toxic and unstable nature, the calculated cross sections were subsequently validated. This was achieved using the computer codes to evaluate the ionisation and x-ray production cross sections of Uranium induced by protons of energies in the 1.00–20.00 MeV range. This study also showed that the relative x-ray line intensities associated with the ionisation and x-ray productions of the targets considered are dependent on protons energies.