Calculation Of Absolute Cross Sections Research Articles

Absolute cross sections for electron scattering from furan

We report results of measurements and calculations of absolute cross sections for electron scattering from furan molecules (C(4)H(4)O). The experimental absolute differential cross sections (DCSs) for elastic electron scattering were obtained for the incident energies from 50 eV to 300 eV and for scattering angles from 20° to 110°, by using a crossed electron-target beam setup and the relative flow technique for calibration to the absolute scale. The calculations of the electron interaction cross sections are based on a corrected form of the independent-atom method, known as the screening corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. The latter calculations also account for rotational excitations in the approximation of a free electric dipole and were used to obtain elastic DCSs as well as total and integral elastic cross sections which are tabulated in the energy range from 10 to 10 000 eV. All SCAR calculated cross sections agree very well with both the present and previously published experimental results. Additionally, calculations based on the first Born approximation were performed to calculate both elastic and vibrationally inelastic DCSs for all the modes of furane, in the energy range from 50 eV to 300 eV. The ratios of the summed vibrational to elastic DCSs are presented and discussed. Finally, the present results for furan are compared with previously published elastic DCSs for the tetrahydrofuran molecule and discussed.

Quasiparticle renormalization and pairing correlations in spherical superfluid nuclei

Within the framework of nuclear field theory (NFT), the spectrum of atomic nuclei is described in terms of collective and quasiparticle degrees of freedom, that is, of elementary modes of excitation that are directly related to experiment and of their coupling, whose strength and form factors are the basic ingredients entering in the calculations of absolute cross sections of inelastic and of one- and two-particle transfer reactions. We present a detailed discussion of the solution of the Dyson equation, also known as the Nambu-Gor'kov equations in the case of a superfluid system, which propagates medium polarization processes calculated making use of NFT to all orders of perturbation, resulting in the dressing of quasiparticles and in the induced pairing interaction. The formalism is applied to the superfluid nucleus ${}^{120}$Sn. Results concerning the low-energy spectrum, that is, the quasiparticle strength distribution of the neighboring odd-A nuclei ${}^{119}$Sn and ${}^{121}$Sn, are presented and compared with the experimental findings.

Absolute cross sections for elastic electron scattering from 3-hydroxytetrahydrofuran

The results of measurements and calculations of absolute cross sections for elastic electron scattering from the 3-hydroxytetrahydrofuran (3hTHF) (C4H8O2) molecule are reported. The measurements were performed using a crossed beam experimental setup, for an incident electron energy range of 40–300 eV and an overall scattering angle range of 10°–110°. Relative differential cross sections (DCSs) were measured both as a function of the angle and the incident energy and the absolute DCSs were determined using the relative flow technique. The calculations of molecular cross sections are based on a corrected form of the independent-atom method, known as the screen corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. Additional calculations are also done to investigate the influence of rotational excitations and low-angular behavior of SCAR DCSs. The calculated dataset includes differential, integral and total cross sections in the energy range from 5 eV to 10 000 eV. The present results are discussed regarding the most recent low-energy elastic DCSs for 3hTHF (Vizcaino et al 2008 New J. Phys. 10 053002), as well as the recent DCSs for molecules of similar structure (tetrahydrofuran and tetrahydrofurfuryl alcohol).

Experimental and theoretical study of electron-impact ionization of atomic ions in the Sm isonuclear sequence

Experimental measurements and theoretical calculations of absolute cross sections are carried out for the electron-impact ionization of atomic ions in the Sm rare-earth-metal isonuclear sequence. Absolute cross sections for ${\mathrm{Sm}}^{q+}$ ions for $q=1\ensuremath{-}12$ were measured using the electron-ion crossed-beam technique and calculated with the configuration-average distorted-wave method for the charge states $q=4\ensuremath{-}12.$ The theory includes both direct ionization and excitation-autoionization contributions, and includes transitions from both ground and metastable levels. We present the cross sections in an electron-impact energy range from threshold up to 1000 eV for all Sm ions up to ${\mathrm{Sm}}^{12+}.$ These systems are extremally complex, but the configuration-average method, when combined with statistical averaging of the cross sections over the many levels, provides results that are in overall good agreement with the experimental measurements. The single-ionization cross sections are dominated by contributions from indirect mechanisms of excitation-autoionization in the low-energy region.

Half-collision model for multiple ionization by photon impact

We present a simple half-collision model that allows the approximate calculation of absolute cross sections for multiple ionization by breaking this process down into a primary ionization event followed by a half-scattering event in which additional electrons are ionized. As a critical test for the feasability of this approach, we consider the double ionization of two-electron systems, which we describe in terms of the single ionization of the ``primary'' electron followed by impact ionization of the slow ``secondary'' electron. For triple ionization of lithium, the model decomposes the three-electron breakup process into a double ionization of the two inner electrons followed by electron-electron half-scattering of the receding electrons at the residual ``spectator'' $2s$ electron. We find surprisingly good agreement with recent experimental data.

Half-collision model for triple photoionization of lithium

We present a simple half-collision model that allows the approximate calculation of absolute cross sections for triple ionization as well as cross-section ratios ${\ensuremath{\sigma}}^{3+}/{\ensuremath{\sigma}}^{2+}$ of lithium by photon impact. The model decomposes the three-electron breakup process into a double ionization of the two inner electrons followed by electron-electron half-scattering of the receding electrons at the residual ``spectator'' $2s$ electron. We find surprisingly good agreement with recent experimental data.

Semiclassical calculations of the cross section for electron-impact ionization of

The semiclassical Deutsch - Märk (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of the total single ionization cross section of the fullerene . The present calculation uses a Mulliken population analysis in which the outermost 120 orbitals are represented as linear combinations of the atomic C(2s) and C(2p) orbitals and no contributions from the more tightly bound C(1s) electrons have been considered. Detailed comparisons are made with available experimental data. Calculated cross sections are considerably larger (and the cross section curve slightly different in shape) than the measured ones. This indicates that the DM formalism (along with other calculation schemes based on an additivity concept) cannot without appropriate corrections be applied to targets with a complex structure such as .

Calculated Cross Sections for Double and Triple Ionization of Atoms by Electron Impact

AbstractThe semi‐empirical Deutsch‐Märk (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of cross sections for the double and triple ionization of ground state atoms. Detailed comparisons are made with available experimental data from threshold to 200 eV. In general, we find good agreement between the present calculations and the available experimental data. On that basis, we feel confident that the present formalism can be applied to predict double and triple ionization cross sections for those atoms, for which no experimental data are currently available, with an accuracy in the 30–50% range for impact energies where direct ionization processes dominate and where contributions from tightly bound inner shells can be neglected. This level of precision should be sufficient for modelling purposes and many other practical applications.

A semi-empirical formula for calculation of absolute cross sections for ionization and excitation of atoms by electrons

A simple analytical expression for the absolute ionization and (optically allowed) excitation cross sections, as a function of the electron energy, is “derived”. In this expression there are two parameters. The first one is proportional to the optical oscillator strength and the second one is dependent on the shape of the differential cross section (generalized oscillator strength), for scattering of energetic electrons as a function of their (small) momentum loss. The analytical expression is exact for large energies of the impinging electron. For small energies of this electron, the expression gives good agreement with experiment. Ionization cross sections are calculated for H, He, Ne, Ar, Kr, Xe, H 2, N 2 and O 2. Excitation cross sections are calculated for H and He.