Experimental Ionization Cross Sections Research Articles

Cross sections and other parameters ofe − − H2O scattering (E i⩾50 eV)

Our previous theoretical work one − − H2O scattering has been modified and extended to intermediate and high energiesE i. Using the Bethe plot, we compare the present inelastic cross-sections with the experimental ionization cross sections. Total cross-sections are analytically represented asQ TOT(cm2)=a.(E ieV) −b and the parameters ‘a’ and ‘b’ are discussed for molecules H2O, NH3 and CH4 in the rangeE i=100–1000eV.

M-shell X-ray production by C, N and O ions

M-shell X-ray production cross sections for Os, Au and Th targets were measured for C, N and O ions at incident energies from 1.2 MeV to about 36 MeV. Experimental M-shell ionization cross sections, derived by using the effective M-shell fluorescence yields, are compared with the prediction of the SCA calculations with relativistic hydrogenic wave functions. The calculations were performed both in the separated-atom (SA) and united-atom (UA) limits to simulate the binding effect. Generally, the data show better agreement with the SCA-UA cross sections for lower energies and with the SCA-SA predictions for higher energies. For C and O impact on the Au target at about 2 MeV/amu the present data are compared with available experimental results and theoretical predictions of the ECPSSR theory.

Absolute electron impact ionization cross sections for highly charged ions: Scaling law for hydrogen-like ions

Scaling laws are of great importance in the description of elementary processes in plasma physics and plasma chemistry. This is particularly true for electron impact induced ionization of atoms, molecules and their respective ions. The recently proposed semi-classical DM (Deutsch-Märk) approach for the calculation of the single ionization cross section of atoms is applied here to the single ionization of hydrogen-like ions and the formula derived can be used to rationalize the empirically-based scaling law for the ionization cross section of hydrogen-like ions, i.e. the Z 4 power dependence, where Z is the nuclear charge. The results obtained are compared with previous experimental and theoretical ionization cross section functions.

Present status of the experimental L-shell ionization cross sections for light ion impact

Compilations of all available experimental L-shell X-ray production and ionization cross sections for proton and light ion impact have recently been produced by the group from the National University of Singapore (I. Orlic, C.H. Sow and S.M. Tang, At. Data Nucl. Data Tables 57, in press; I. Orlic, Experimental L-shell x-ray production and ionization cross sections for light ion impact, internal report, National University of Singapore, Department of Physics, 1993 [1,2]). Together with the previous tabulations more than 9700 experimental data points for proton impact and approximately the same number of data points for heavier ion impact have become available. An overview of all available experimental data is given in this work. Discussed are annual growth and decline of published data, distribution of L-shell cross section data vs. target atomic number as well as distribution of number of data vs. incident ions. Experimental data are compared with the corresponding ECPSSR predictions in the usual manner: plotting the ratio S = σ exper./ σ theory vs. reduced velocity parameter for each individual subshell L1, L2 and L3 separately for proton and heavier ion impact. Mean experimental cross sections are obtained using the statistical procedure recommended by the Particle Data Group (Particle Data Group, Phys. Lett. B 204 (1988) 5 [3]). Statistical errors of mean values are significantly smaller than errors of individual experimental results allowing for some generalization. A brief review of the obtained results is presented.

Total cross-sections for electron scattering from iron at 10?5000 eV using a model optical potential

We report calculations on the total (elastic plus inelastic) electron-scattering cross sections in the energy range 10–5000 eV. A model complex optical potential, composed of static, exchange, polarisation and absorption terms, is employed to describe the collision system at each electron energy. The Iron atom is described by Dirac-Hartree-Fock-Slater self-consistent charge density. The complex phase shifts are computed in a variable phase approach. The absorption cross sections are compared with the experimental results. The experimental absorption cross sections are obtained by adding the experimental ionisation cross sections and available experimental excitation cross sections for electron impact of the allowed transitions a5 D → (x,y,z)5 D 0, (w,y,z)5 P 0. We have good qualitative agreement between our results and the experimental results available below 200 eV. The Born-Bethe parameters are also calculated. Elastic differential cross-sections with and without absorption are also reported at a few selected energies.

X-RAY PRODUCTION, INNER SHELL IONIZATION AND READING’S THEOREM IN ION · ATOM COLLISIONS

When a solid or gaseous target is bombarded with heavy charged particles, inner shell electrons of target atoms are ionized and characteristic x rays are produced. We can easily observe these x rays with a Si(Li) detector and derive inner-shell ionization cross section from the x-ray production cross sections. In this paper, we make a review of x-ray production, inner shell ionization and Reading’s theorem in light ion·atom collisions. This theorem is one of the most important ones in the ion·atom collision physics and permits precise discussion on comparison between experimental inner-shell ionization cross sections obtained with a Si(Li) detector and the calculations based on usual theories where the incident particle is assumed to interact with only one electron in an atom and the presence of other electrons is ignored.

Relativistic model of secondary-electron energy spectra in electron-impact ionization.

A relativistic model for differential electron-impact-ionization cross sections that allows the energy spectrum of secondary electrons to be calculated over a wide range of primary-electron energies is presented. The semiempirical method requires only experimental total ionization cross sections and optical oscillator strengths for the target species of interest, but other information, if available, can be incorporated to make the formulation still more accurate. Results for ionization of helium indicate that the lower limit on primary-electron energy for application of the model is about 100 eV. The simple analytic form of the model facilitates investigation of the regions of the secondary-electron energy spectrum where relativistic effects are important.

L-SUBSHELL IONIZATION OF Tb, Er AND Lu BY 0.2-1.2 MeV INCIDENT PROTONS

Rare earth elements Tb, Er and Lu were bombarded by protons with energies of 0.2-1.2 MeV, L-subshell ionization cross sections were obtained. Experimental ionization cross sections were compared with the predictions of the ECPSSR theory.

Experimental ionization cross-sections of phosphorus and calcium by electron spectroscopic imaging

The absolute partial electron scattering cross-section for the phosphorus L2,3-shell ionization was measured by electron spectroscopic imaging using poliovirus as a primary standard. The equivalent calcium cross-section was obtained in relation to phosphorus using the stoichiometric ratio for these two elements in hydroxyapatite, Ca10(PO4)6(OH)2. At 80 keV, the partial cross-section of phosphorus was 2.26 x 10(-20) and 2.68 x 10(-20) cm2/atom for poliovirus and hydroxyapatite, respectively, at 150 eV loss for a 15-eV energy window and an acceptance angle of 15 mrad. Under the same conditions the calcium cross-section was 0.49 x 10(-20) cm2/atom at 360 eV loss. The experimental values are slightly higher than the theoretical cross-sections calculated either by hydrogenic or Hartree-Slater approaches.

M-shell x-ray production by 0.6-4.0-MeV protons in ten elements from hafnium to thorium.

M-shell x-ray production cross sections for selected heavy elements, namely, $_{72}\mathrm{Hf}$, $_{73}\mathrm{Ta}$, $_{74}\mathrm{W}$, $_{75}\mathrm{Re}$, $_{76}\mathrm{Os}$, $_{77}\mathrm{Ir}$, $_{78}\mathrm{Pt}$, $_{79}\mathrm{Au}$, $_{83}\mathrm{Bi}$, and $_{90}\mathrm{Th}$, were measured for protons of energy 0.6--4.0 MeV. The experimental results are compared with the predictions of the first Born and semiclassical approximations for M-shell ionization; these data are also compared with the theory that accounts for the projectile's energy loss and Coulomb deflection as well as for the target's M-shell electron perturbed stationary state and relativistic nature (ECPSSR). Generally, fair agreement between the data and the ECPSSR theory is found. Some systematical discrepancies observed for the lightest elements (Hf, Ta, and W) are explained as possible ambiguities in the M-shell Coster-Kronig factors and fluorescence yields, which were used to convert theoretical M-subshell ionization cross sections to the total M-x-ray production cross sections. The experimental total M-shell ionization cross sections were obtained from measured M-x-ray cross sections using the proposed approximate average fluorescence yield \ensuremath{\omega}${\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{M}}$ that relies on two fluorescence yields and the Coster-Kronig factor for only ${\mathit{M}}_{4}$ and ${\mathit{M}}_{5}$ subshells.

L-shell ionization of Si, P, S, Cl, and Ar by 0.4-2.1-MeV He+ bombardment.

The L-shell ionization cross sections of Si, P, S, Cl, and Ar have been obtained for incident ${\mathrm{He}}^{+}$ ion energies 0.4--2.1 MeV in steps of 0.2 MeV. The cross sections were obtained from the Auger electron yields measured for ${\mathrm{SiH}}_{4}$, ${\mathrm{PH}}_{3}$, ${\mathrm{H}}_{2}$S, ${\mathrm{CH}}_{3}$Cl, and Ar gaseous targets. The present experimental L-shell ionization cross sections are compared to existing experimental L-shell ionization cross sections as well as to previous theoretical predictions.

M-shell ionization in gold by light ions

M-shell X-ray production cross sections for Au targets have been measured by 1H, 3He and 4He ions in the energy range 0.6–4.0 MeV. The Si(Li) detector efficiency in the low-energy X-ray region (1.5–4 keV) was carefully determined using the PIXE method. The elastically scattered projectiles were detected by a surface-barrier detector to normalize X-ray yields. The measured X-ray yields were converted to M-shell X-ray production cross sections and then, using average M-shell fluorescence yields evaluated according to relativistic calculations of Chen et al., the total M-shell ionization cross sections were derived. The experimental M-shell ionization cross sections are compared with results reported by other authors and with the predictions of the first-order theories, namely, the PWBA and SCA approximations and also the ECPSSR theory, which accounts for energy-loss, Coulomb deflection, binding-polarization, and relativistic effects.

Ionization of low-Rydberg-state He atoms by polar molecules. I. Velocity dependence of the cross sections.

The ionization of low-Rydberg-state He atoms in the n /sup 1/P state (n = 14) in collisions with the polar molecules NH/sub 3/, SO/sub 2/, and acetone (C/sub 3/H/sub 6/O) is carried out in a crossed-beam experiment at thermal kinetic energies. The dependence of the experimental ionization cross sections sigma/sub i//sup expt/ on the relative velocity of the reactants is obtained by a time-of-flight method. We observe that it varies mainly as 1/v/sub r//sup 2/ in a large part of the studied velocity range, while a 1/v/sub r/ velocity dependence is predicted by the free-electron model for the higher Rydberg levels.

L-subshell ionisation cross sections by proton bombardment

Experimental L-subshell ionisation cross sections are discussed. Maps of measured cross sections in atomic number and velocity parameter coordinates are presented. A dependence of ionisation cross sections on atomic number is also discussed.

Calculated molecular double-differential cross-sections for ionisation under proton impact

This paper describes an approach (DDCS-MT), based on the plane wave Born approximation, intended to calculate double-differential ionisation cross-sections (DDCS) under heavy charged particle impact. A procedure is proposed in order to adapt this formalism to the treatment of molecules, which consists essentially to break up each molecular orbital into its atomic components and to sum up the partial DDCS. The increase of the binding energies in respect to the ion energy, as well as the post-collisional interaction between the passing ion and the ejected electron were taken into account. The method proposed led generally to a satisfactory agreement with measurements from the literature for electron ejection energies larger than 10 to 20 eV, in the case of a variety of low-Z molecules (NH3, CH4, CH3NH2, N2, O2, CO2) bombarded by 0.25-to 2.0-MeV protons. The whole procedure is free from any fitting parameter and requires no experimental ionisation cross-sections as input data.

K-shell ionization by antiprotons.

We present calculations for the impact-parameter dependence of K-shell ionization rates in p-bar-Cu and in p-bar-Ag collisions at various projectile energies. We show that the effect of the attractive Coulomb potential on the Rutherford trajectory and the antibinding effect caused by the negative charge of the antiproton result in a considerable increase of the ionization probability. Total ionization cross sections for proton and antiproton projectiles are compared with each other and with experimental ionization cross sections for protons.

Polarization and binding effects in K-shell ionization by 16O and 32S ions.

The theoretical model of Montenegro and Sigaud is used for the description of the experimental total K-shell ionization cross sections for 2.2-MeV/u /sup 16/O and /sup 32/S on 24 targets from /sub 21/Sc to /sub 83/Bi obtained by Seidel et al. The predictions of the model, which considers both binding and static polarization effects within the framework of adiabatic perturbation theory, are very good for the majority of the measured data in the region of validity of the model. The electron-capture process that can contribute in the region of the largest values of relative velocity xi/sub K/ is also analyzed.

L-shell X-ray production ratios for 100–150 keV protons

Typical relative intensity ratios for X-ray production induced by 100–150 keV protons incident on thick targets of Gd ( Z 2 = 64) and Dy ( Z 2 = 66) are reported. Experimental subshell ionization cross sections for thick Dy targets bombarded by protons are also reported. The results are compared to predictions of the ECPSSR and RPWBABC theories and to other reported work in this proton energy range. Substantial discrepancies are observed and possible explanations for them are discussed.

L-shell ionisation of medium and heavy elements by 1.2-3.0 MeV incident alpha particles

Thin targets of Yb, W, Au, Pb and Bi were bombarded by 1.2-3.0 MeV alpha particles. From the resulting L X-rays experimental Li-subshell ionisation cross section were deduced. The measured cross sections are compared with the predictions of the ECPSSR theory by expressing the data in terms of ratios of experimental to theoretical values as a function of the corrected reduced velocity xi (Li)R. Disagreements of up to 50% were revealed for the L1 subshell at xi (L1)R<or=0.3. The ECPSSR theory underestimate the L2 ionisation cross sections for all elements studied by as much as a factor of 3.3 but explains the L3 data to within 30%. In general, for heavy elements, the ECPSSR is unsuccessful in explaining the velocity dependence of the cross sections. Several factors were highlighted which may explain some of the observed disagreements. The target atomic number dependence of the experimental Li subshell and total ionisation cross sections were also investigated and the results are presented.

Ionization Cross Sections of Gas Molecules for Plasma Chemistry

AbstractUsing the recently tested formula of Gryzinski electron impact ionization cross sections for several molecules are calculated. The additivity rule and the statistical approach by Fitch and Sauter are discussed. With new experimental ionization cross sections it is possible to derive the regression coefficients also for P, As, B, and Si, which are presented together with the previously obtained values as a function of the atomic number. It appears to be possible to obtain coefficients for other atoms by interpolation. First attemps to determine regression coefficients also for 20 and 35 eV electron energy are discussed.