Theoretical Cross Section Data Research Articles

Theoretical cross sections for electron collisions relevant for ammonia discharges part 1: NH3, NH2, and NH

Besides being the worlds’ most important fertilizer precursor, ammonia could play an important role as hydrogen carrier in a decarbonized future. The efficient production and decomposition (or cracking) of ammonia are essential to this end. An electricity-driven technology of interest for both these processes are non-thermal plasmas. Plasma processes have the advantage of activating—even inert—molecules and initiating chemical reactions through electron collisions, rather than through conventional heating. However, a complete set of low-energy cross section data is not available for the electron collisions with ammonia (NH3) and its radicals, amidogen (NH2) and imidogen (NH). Here, we used the ab initio R-matrix method to determine theoretical cross sections for the low-energy electron collision processes with NH3, NH2, and NH. Additionally, we explored the contribution of the different processes towards dissociation (especially from electronic excited states). Where possible, we compared our theoretical cross section data with experimental data and/or previous recommendations. Lastly, our own recommended cross section data for the electron collisions are presented. Use of this complete set of electron collision data should contribute to a more accurate description of and better insights into the plasma-chemical kinetics behind plasma-assisted ammonia production and decomposition processes.

Experimental and theoretical cross section data of deuteron induced nuclear reactions on platinum

Additional experimental activation cross sections for deuteron induced reactions on platinum were measured in the 35–49 MeV energy range for the natPt(d,xn)191,192,193,194,195,196m2,196g,198m,198g,199Au, natPt(d,x)189,191,193m,195m,197gPt and natPt(d,x)188,189,190m2,190,192,194m2Ir reactions by using the stacked foil irradiation technique and gamma ray spectrometry. The available experimental results are compared with the calculated values based on ALICE-D and EMPIRE-D model codes and with the theoretical predictions in the TALYS based TENDL-2017 library.

Recommended Positron Scattering Cross Sections for Atomic Systems

We present a critical analysis of available experimental and theoretical cross section data for positron scattering from atomic systems. From this analysis, we present (where data are available) recommended cross sections for total scattering, positronium formation, inelastic scattering, and direct ionization processes. A complete bibliography of available measurement and theory is also presented.

Modelling low energy electron and positron tracks for biomedical applications

In order to incorporate the effect of low energy electrons and positron in radiation damage models, the simulation method proposed here is based on experimental and theoretical cross section data and energy loss spectra we have previously derived. After a summary of the main techniques used to obtain reliable input data, the basis of a Low Energy Particle Track Simulation (LEPTS) procedure is established. Single electron and positron tracks in liquid water are presented and the possibility of using these results to develop tools for nanodosimetry is discussed.

Modelling low energy electron and positron tracks for biomedical applications

Purpose: To incorporate the effects of low energy electrons and positrons into radiation interaction models.Materials and methods: The simulation method proposed here was based on experimental and theoretical cross section data and energy loss spectra we have previously derived. After a summary of the main techniques used to obtain reliable input data, the basis of a Low Energy Particle Track Simulation (LEPTS) procedure was established. The programme is specifically designed to describe electron and positron interactions below 10 keV, down to thermal energies.Results: Single electron and positron tracks in water are presented and the possibility of using these results to develop tools for nanodosimetry is discussed.Conclusions: Standard approximations based on high incident energies, such as the Born-Bethe theory, are not suitable to simulate electron and positron tracks below 10 keV. Prior to the inclusion of low-energy effects in a radiation model, an appropriate study is required to determine both the interaction cross sections and the energy loss spectra.

Modelling low energy electron interactions for biomedical uses of radiation

Current radiation based medical applications in the field of radiotherapy, radio-diagnostic and radiation protection require modelling single particle interactions at the molecular level. Due to their relevance in radiation damage to biological systems, special attention should be paid to include the effect of low energy secondary electrons. In this study we present a single track simulation procedure for photons and electrons which is based on reliable experimental and theoretical cross section data and the energy loss distribution functions derived from our experiments. The effect of including secondary electron interactions in this model will be discussed.

Database for inelastic collisions of sodium atoms with electrons, protons, and multiply charged ions

The available experimental and theoretical cross section data for inelastic collision processes of ground (3s) and excited (3p, 4s, 3d, 4p, 5s, 4d, and 4f) state Na atoms with electrons, protons, and multiply charged ions have been collected and critically assessed. In addition to existing data, electron-impact cross sections, for both excitation and ionization, have been calculated using the convergent close-coupling approach. In the case of proton-impact cross section, the database was enlarged by new atomic-orbital close-coupling calculations. Both electron-impact and proton-impact processes include excitation from the ground state and between excited states ( n = 3–5). For electron-impact, ionization from all states is also considered. In the case of proton-impact electron loss, cross sections (the sum of ionization and single-electron charge transfer) are given. Well-established analytical formulae used to fit cross sections, published by Wutte et al. and Schweinzer et al. for collisions with lithium atoms, were adapted to sodium. The “recommended cross sections” for the processes considered have been critically evaluated and fitted using the adapted analytical formulae. For each inelastic process the fit parameters determined are tabulated. We also present the assessed data in graphical form. The criteria for comprehensively evaluating the accuracy of the experimental data, theoretical calculations, and procedures used in determining the recommended cross sections are discussed.

Low-energy electron capture byNe2+ions from H(D)

Using the Oak Ridge National Laboratory (ORNL) ion-atom merged-beams apparatus, the absolute, total single-electron-capture cross section has been measured for collisions of ${\mathrm{Ne}}^{2+}$ with deuterium (D) at center-of-mass (c.m.) collision energies of $59--949\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$. With the high-velocity ion beams now available at the ORNL Multicharged Ion Research Facility, we have extended our previous merged-beams measurement to lower c.m. collision energies. The data are compared to all four previously published measurements for ${\mathrm{Ne}}^{2+}+\mathrm{H}(\mathrm{D})$ which differ considerably from one another at energies $\ensuremath{\lesssim}600\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$. We are unaware of any published theoretical cross-section data for ${\mathrm{Ne}}^{2+}+\mathrm{H}(\mathrm{D})$ at the energies studied. Early quantal rate coefficient calculations for ${\mathrm{Ne}}^{2+}+\mathrm{H}$ at eV/u energies suggest a cross section many orders of magnitude below previous measurements of the cross section at $40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$ which is the lowest collision energy for which experimental results have been published. Here we compare our measurements to recent theoretical electron-capture results for ${\mathrm{He}}^{2+}+\mathrm{H}$. Both the experimental and theoretical results show a decreasing cross section with decreasing energy.

Total cross-section measurements for electron collisions with α-tetrahydrofurfuryl alcohol (C 5H 10O 2)

The absolute total cross-section (TCS) for electron scattering from α-tetrahydrofurfuryl alcohol (C 5H 10O 2; THFA) has been measured using the linear transmission technique for energies ranging from 1 to 370 eV. The obtained TCS function has the relatively high magnitude over the whole energy range studied. That is also characterized by the broad enhancement spanned between 3.5 and 15 eV superimposed with two distinct resonant-like structures. Additional weak structures can be distinguished below 3 eV while two other features are discernible above ionization threshold. The present TCS is compared with available experimental and theoretical cross section data.

DATABASE FOR INELASTIC COLLISIONS OF LITHIUM ATOMS WITH ELECTRONS, PROTONS, AND MULTIPLY CHARGED IONS

New experimental and theoretical cross-section data for inelastic collision processes of Li atoms in the ground state and excited states (up to n = 4) with electrons, protons, and multiply charged ions have been reported since the database assembled by Wutte et al. [Atomic Data and Nuclear Data Tables65, 155, 1997] was published. These new data were included in a process of critical data assessment and led to the creation of a new database for the modeling of energetic lithium beams probing fusion edge plasmas. The electron-impact part of the present database covers excitation and ionization, the data having been extended by advanced close-coupling calculations which provide a new standard of quality especially for transitions between excited states. The heavy-particle impact processes include excitation and electron removal (the sum of ionization and electron capture). Hitherto, ion-impact excitation cross sections for lithium (except for the main Li(2s → 2p) process) were based on scaling relations using the corresponding electron-impact cross sections. We have now performed large-scale atomic orbital close-coupling calculations for a large number of excitation processes as well as new measurements toward development of the new database. The recommended cross sections for the considered processes have been fitted to simple analytic expressions. The analytic-fit expressions and the tables of the parameters entering these analytic fits are here presented. We also present the recommended cross sections in graphical form together with the underlying experimental cross section data if available.

CROSS SECTIONS FOR COLLISION PROCESSES OF Li ATOMS INTERACTING WITH ELECTRONS, PROTONS, MULTIPLY CHARGED IONS, AND HYDROGEN MOLECULES

The available experimental and theoretical cross section data for collision processes of Li atoms in the ground state and excited (up ton= 3) states with electrons, protons, and multiply charged ions have been collected and critically assessed. The electron-impact processes include excitation from the ground state, transitions between excited states withn= 2, 3, and ionization from all states considered. The heavy-particle-impact processes include excitation, ionization (for the proton case), and electron removal (the sum of ionization and electron capture). Well-established cross section scaling relationships have been used to generate the cross sections for processes for which no information was found in the literature. This approach was particularly extensively used for the collision processes involving excited Li states, and for collisions with protons and multiply charged ions. In addition, available data for collision processes of Li atoms and ions with neutral hydrogen molecules are shown. The “recommended” cross sections for the considered processes, generated either by critical assessment of available data or by a scaling procedure, have been fitted to simple analytic expressions which ensure correct asymptotic behavior of the cross sections. These recommended cross sections are presented by giving their analytic-fit expressions and tabulating the values of the parameters entering these analytic fits. For those reactions from the ground state for which there is a significant amount of cross section information, we also present the recommended cross sections in graphical form together with the cross section data used for their generation. The criteria for assessing the accuracy of the experimental data, theoretical calculations, and procedures used in determining the recommended cross sections are discussed.

Recommended Cross Sections for State-Selective Electron Capture in Collisions of C 6+ and O 8+ Ions with Atomic Hydrogen

The available theoretical cross-section data for electron capture into specific ( n, l) states in collisions of C 6+ and O 8+ ions with ground-state hydrogen atoms have been critically assessed. By applying appropriate consistency checks, including comparison with the experimental emission and total cross sections, a set of recommended state-selective electron-capture cross sections σ nl has been derived for 3 ≤ n ≤ 8 for C 6+ + H and 4 ≤ n ≤ 9 for O 8+ + H, with specified accuracy. The recommended cross sections σ nl and their sum over l, σ n , are presented in graphical form in the energy range from approximately 20 keV/amu (or lower for the dominant channels) to approximately 1 MeV/amu. Analytical fits to the recommended cross sections and fitting parameters are also presented.

Recommended Data on the Electron Impact Ionization of Atoms and Ions: Fluorine to Nickel

Experimental and theoretical cross-section data for electron impact ionization of atoms and ions from fluorine to nickel has been assessed and earlier recommendations for light atoms and ions have been revised. Based on this assessment and, in the absence of any data, on the classical scaling laws a recommended cross section has been produced for each species. This has been used to evaluate recommended Maxwellian rate coefficients over a wide range of temperatures. Convenient analytic expressions have been obtained for the recommended cross sections and rate coefficients. The data are presented in both graphical and tabular form and estimates of the reliability of the recommended data are given.

Resonance Effect on the Moderation of Slow Electrons in Diatomic Gases

A survey of stopping power, range, moderation rate, and moderation time for slow electrons in pure gases of H2, N2, CO, and O2 is reported. By employing experimental and theoretical cross-section data, contributions to these quantities from vibrational excitation, rotational excitation and deexcitation, and elastic energy transfers are included. The influence of low-energy molecular shape resonances and their effect on electron degradation processes is discussed and emphasized.

Evaluated Theoretical Cross-Section Data for Charge Exchange of Multiply Charged Ions with Atoms. III. Nonhydrogenic Target Atoms

The theoretical cross-section data for single-electron capture in collisions of multiply charged ions with nonhydrogenic atoms are compiled and their accuracy is assessed. The energy per unit mass range considered is from ∼1 eV/u to several MeV/u, u being the unified atomic mass unit. Accuracy is assessed using both pure theoretical arguments and comparison with experimental data, where available. A similar assessment is performed for the two-electron capture cross-section data in ion–atom collisions, as well as for single- and double-charge exchange in ion–ion collisions.

Evaluated Theoretical Cross Section Data for Charge Exchange of Multiply Charged Ions with Atoms. I. Hydrogen Atom-Fully Stripped Ion Systems

The existing theoretical cross section data for the charge exchange process of multiply charged fully stripped ions with hydrogen atoms are evaluated in the energy range from ∼10 eV/u to ∼103 keV/u. The evaluation has been performed on the basis of both pure theoretical arguments and comparison with the most accurate experimental cross sections. The ionic charge state ranges from Z=2 to Z=54. The theoretical methods for calculation of the charge exchange cross sections are briefly discussed, and their regions of validity and the accuracy of the produced data are assessed.

Evaluated Theoretical Cross Section Data for Charge Exchange of Multiply Charged Ions with Atoms. II. Hydrogen Atom-Partially Stripped Ion Systems

The existing theoretical cross section data for charge exchange of partially stripped ions on atomic hydrogen are evaluated in the energy range from ∼10 eV/u to ∼103 keV/u. The evaluation has been carried out by using both pure theoretical arguments and comparison with the most accurate experimental data. Ions with atomic numbers Z=3–8, 10, 12, 13, 14, 16, 18, 22, 26, 30, 36, 41, 42, 48, 54, 73, and 74, in charge states q between q=2 and q=(Z−1), have been examined. A brief discussion of the evaluation criteria is also given.

Recommended Data on the Electron Impact Ionization of Light Atoms and Ions

Experimental and theoretical cross section data for electron impact ionization of light atoms and ions have been assessed. Based on this assessment and, in some cases, on the classical scaling laws, a recommended cross section has been produced for each species. This has been used to evaluate recommended Maxwellian rate coefficients over a wide range of temperatures. Convenient analytic expressions have been obtained for the recommended cross sections and rate coefficients. The data are presented in both graphical and tabular form and estimates of the reliability of the recommended data are given.

Variational calculations of accuratee−-He cross sections below 19 eV

Variational calculations of $s$- and $p$-wave phase shifts for ${e}^{\ensuremath{-}}$-He scattering have been carried out for energies less than 19 eV. The variational wave function represents target-atom electronic correlation, electric dipole and quadrupole polarizability response, and short-range electron-atom correlation at a level of accuracy sufficient for 1% accuracy in the differential cross section. The partial-wave Born approximation is used for phase shifts $lg1$. Calculated phase shifts are corrected for estimated systematic errors, and these estimated phase shifts are interpolated as smooth functions of energy by cubic spline fits to auxiliary interpolating functions. Comparison with recent experimental and theoretical cross section data indicates compatibility with the present error estimate of no more than 1%. Data given here make it possible to compute the differential cross section from simple formulas over the energy range considered. The present value of the scattering length is $1.1835{a}_{0}$ with 0.5% error.