Coherent electron emission from O2 in collisions with fast electrons

Absolute double differential cross sections (DDCS) of low-energy electron emission from water molecule were measured upon collisions with 250-keV protons for emission angles between 30--150 degrees. The electrons having energies between 1 and 600 eV were detected by using hemispherical electrostatic analyzer. The single differential (SDCS) and total cross section (TCS) were calculated by integrating the DDCS and SDCS, respectively. The measured DDCS, SDCS, and TCS were compared with the classical trajectory Monte Carlo (CTMC) model, using a dynamical approach in which a time-dependent screening is considered. The continuum-distorted-wave eikonal-initial state (CDW-EIS) theoretical model has also been used to explain the energy and angular distribution data. The angular distribution of the DDCS are very well reproduced by the CTMC approach. The TCS calculated by the CTMC model matches better with the measured values as compared to the CDW-EIS estimation. The forward-backward angular asymmetry parameter was also estimated to test the validity of the state-of-the-art theoretical models used. Finally the recently developed CDW-EIS calculations considering a residual target dynamic charge (DC-CDW-EIS) is shown to provide an improved agreement with the experiments compared to the CDW-EIS. The present data and interpretation should provide inputs towards energy loss calculations required for the radiobiology involved in the hadron therapy of cancer.

This thesis presents a complete set of proton-impact ionization cross section data of DNA constituents determined at the Physikalisch-Technische Bundesanstalt (PTB). The cross section data describe the probabilities for the ionization of gas-phase tetrahydrofuran, pyrimidine and trimethyl phosphate that are structural analogues to the base, sugar, and phosphate residue of the DNA, respectively. Total, single-differential and double-differential ionization cross sections were determined, whereby the differential description refers to the energy or angular dependence of electron emission. Double-differential cross sections were measured for impact energies between 75 keV and 3000 keV over an angular range between 15бу and 150бу in 15бу intervals. Both single-differential and total ionization cross sections were derived by integration of the measured double-differential cross sections. The measurements of double-differential cross sections were carried out using a crossed-beam arrangement in a high-vacuum chamber. The proton beam, which perpendicularly crosses an effusive gas jet target of DNA constituents inside the chamber, was generated either by the 3.75 MV Van de Graaff accelerator of the PTB ion accelerator facility (PIAF) or a newly developed 155 kV ion accelerator. In the measurement a newly constructed electron spectrometer was used to detect the secondary electrons produced by proton collisions with the target molecules. The energy of the secondary electrons was selected by a hemispherical electron energy analyzer, which was mounted on a turntable to allow the spectrometer to rotate around the axis of the gas jet. Hence, the energy spectra could be recorded at defined observation angles with respect to the proton beam. These spectra were converted into absolute cross section values via a normalization procedure based on previously published absolute electron-impact cross section data.

Further improving our previous apparatus, we have successfully measured absolute double differential cross section (DDCS) for secondary electron emission (1 eV-10 keV and 20-160°) produced in the collision of 6.0 MeV/u C6+ ion with water vapor. The angular distributions of DDCSs disagree with the CDW-EIS theoretical calculation at the backward angles (>100°), while single differential cross section (SDCS) agrees well with the CDW-EIS, particularly in the low-energy region (<200 eV).

Doubly differential cross sections (DDCSs) for electron emission have been measured for collisions of 3.6 MeV/u Ne{sup 10+}, Xe{sup 40+} and 5.9 MeV/u U{sup 29+} on neon, xenon, water, ethanol, methanol, propanol, C{sub 2}F{sub 6}, SF{sub 6}, and C{sub 3}F{sub 8}. Electrons ejected with emission angles between 0{degree} and 180{degree} with respect to the ion beam axis have been recorded simultaneously using a toroidal electron spectrometer. We analyze the singly differential cross section (SDCS) for binary encounter electron (BE{ital e}) production as a function of target electron number and laboratory emission angle. We find that there exists a linear scaling of the BE{ital e} SDCS with the number of electrons bound in the target with an energy lower than the reduced projectile energy. The enhancement of BE{ital e} production in the forward direction in collisions with partially stripped ions is studied for the different projectiles and targets and compared to theoretical calculations. {copyright} {ital 1998} {ital The American Physical Society}

We present a theoretical study of the ionization of nitrogen atom by a singly charged sodium ion using the classical trajectory Monte Carlo method. Although we suffer from a lack of cross section data of this collision system, the knowledge of the basic cross sections is essential in fusion science, because this reaction has potential applications in the diagnostic of magnetically confined fusion plasmas. In our investigations, the Na+–N collision system is reduced to a three-body problem. The interaction between the collision partners is described by the Garvey-type model potential. The results of our study provide insight into the dynamics of singly charged sodium–nitrogen interactions. The total cross sections are presented in the impact energy range between 10 keV and 10 MeV and compared them with the available experimental data. The single and double differential cross sections are presented at 30, 40, 50 and 60 keV energies related to the energies of the plasma diagnostic used in the nuclear fusion.

The nuclear incoherent π 0 photoproduction cross section from 12C is evaluated at forward angles in the 4.0 to 6.0 GeV energy range using the multicollisional intranuclear cascade model MCMC. The model incorporates some improvements in comparison with previous versions associated with the momentum distribution (MD) for light nuclei - extracted from the available (e,e ′p) data - as well as the evaluation of the shadowing effects during the photo-nucleus interaction. The final results of the single and double differential cross sections at forward angles are very sensitive to the MD parameterizations due to the Pauli principle, which largely suppresses the cross sections for low momentum transfer. The attenuation of the nuclear cross section due to pion - nucleus final state interactions is approximately 40% (without nuclear shadowing), which is in nice agreement with the predictions from the Glauber model. The single and double π 0 differential cross sections are presented for possible applications for the interpretation of the inelastic background in the PrimEx experiment at the Jefferson Laboratory. © 2007 American Institute of Physics.

New results are reported on the measurements of absolute double differential cross sections (DDCSs) of bremsstrahlung produced from 4.0 keV electrons incident on free Ar atoms in the angular detection range of 45°–120°. A significant reduction of the thick target bremsstrahlung (TTB) of the chamber wall and of the photon transmission windows has been achieved by modifying the experimental set-up used previously; a large reduction of TTB in the present experiments is supported by the results of our model calculations for the ratio of TTB background to the normal bremsstrahlung (NB) spectrum carried out for the employed geometry of the experimental set-up. The results of photon energy distribution measured at different angles and those of angular distributions of photons of a given energy are compared with theoretical predictions of Kissel–Quarles–Pratt (KQP) theory for ordinary bremsstrahlung and with predictions of total bremsstrahlung including polarization bremsstrahlung (PBS) of the stripping approximation (SA). A satisfactory agreement observed between experiment and predictions using SA theory for absolute DDCSs of bremsstrahlung provides evidence for an appreciable contribution of polarization bremsstrahlung at the considered impact energy of electrons on one hand, while on the other hand, it exhibits a large discrepancy (about a factor of 2) in DDCSs of bremsstrahlung photons obtained by experiment and by KQP theory for photon energy distributions at all detection angles measured in these experiments. In addition, present results of the angular dependence of photons of different energies show anisotropic distributions and they are found to be in reasonable agreement with both KQP and SA theories. The satisfactory agreement between experiment and theory for angular distributions is an indication of a significant reduction of the background produced from TTB photons.

Some test calculations were carried out to demonstrate the usefulness of double-differen-tial cross sections for neutron transport calculations including anisotropic scattering. A transport code system NITRAN was applied for the purpose. In NITRAN, the anisotropy of elastic and inelastic scattering can be treated in a general form by double-differential total neutron-emission cross sections, which are generated from single-differential and/or original double-differential cross section data base.The test calculations were performed for neutron flux spectra in aluminum and lead slabs, and also f, or tritium production rates in a natural lithium sphere. Since the treat-ment free from collision kinematics is possible by using the double-differential cross sections in the Sn calculations, the discretization of secondary neutron energy distribution becomes independent of the segmentation of angular distribution. A significant improvement due to this independence can be seen in calculating the anisotropy of general inelastic scatter-ing and the extreme anisotropy of elastic scattering by heavy nuclei. For precise aniso-tropic transport calculations, it is therefore concluded that the nuclear data of double-dif-ferential type are more suitable than those of single-differential type.

We report the energy and angular distribution of electron double differential cross sections (DDCS) in collision of $6\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}\phantom{\rule{0.3em}{0ex}}{\mathrm{C}}^{6+}$ ions with molecular hydrogen. We explain the observed distributions in terms of the two-center effect and the Young-type interference effect. The secondary electrons having energies between 1 and $1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ are detected at about 10 different emission angles between $30\ifmmode^\circ\else\textdegree\fi{}$ and $150\ifmmode^\circ\else\textdegree\fi{}$. The measured data are compared with the state-of-the-art continuum distorted wave-eikonal initial state and the first Born model calculations which use molecular wave function. The single differential cross sections are derived and compared with the theoretical predictions. The oscillations due to the interference effect are derived in the DDCS ratios using theoretical cross sections for the atomic H target. The effect of the atomic parameters on the observed oscillations is discussed. An evidence of interference effect has also been shown in the single differential cross section. The electron energy dependence of the forward-backward asymmetry parameter shows a monotonically increasing behavior for an atomic target, such as He, which could be explained in terms of the two-center effect only. In contrast, for the molecular ${\mathrm{H}}_{2}$ the asymmetry parameter reveals an oscillatory behavior due to the Young-type interference effect superimposed with the two-center effect. The asymmetry parameter technique provides a self-normalized method to reveal the interference oscillation which does not require either a theoretical model or complementary measurements on the atomic H target.

The authors have measured absolute (e,2e) cross sections for electron impact ionisation of helium with a much higher accuracy than obtained before. In a coplanar symmetric geometry ( theta =45 degrees ) both outgoing electrons-with equal velocities-were detected in coincidence. The resulting experimental triple differential cross sections for incoming electrons of 200-2800 eV contain an experimental error smaller than 20%. At the same time the authors have determined the absolute double differential cross sections at 45 degrees to an accuracy of 10%. The data are compared with various theoretical results.

SynopsisIon impact induced fragmentation of H2O molecules was experimentally studied. Energy and angular distribution of the charged fragments were measured by an energy dispersive electrostatic spectrometer. The measured spectra were converted into absolute double differential cross section (DDCS). The fragment ion spectra are different for H+ and N+ projectiles. From the fragmentation spectra we deduced the cross sections for the different ionization degrees of the target molecules.

Electron impact ionization cross sections of C2H4 molecule

The fully differential cross sections (FDCSs) for ionization of hydrogen atoms, being initially in the 2s excited state, by proton and antiproton impacts are calculated in the framework of the second Born approximation. The closure relation is employed to perform the summation over the intermediate states in the second Born approximation. The calculations are performed for emission of the electron in both scattering and perpendicular planes. The dependence of calculations on the projectile’s charge is investigated at different impact energies and at small scattering angles where the significant contribution to the total cross section originates. It is noticed that the influence of the electric projectile’s charge on the FDCSs in the perpendicular plane is much greater than it is in the scattering plane, and it increases as the scattering angle decreases. Finally, we calculate the doubly differential cross section (DDCS) for proton-induced reactions.

Absolute double differential cross sections for target ionization and projectile electron loss were measured in collisions of H+, H+2, 3He+ and 3He++ (0.4 to 2.0 MeV/u) with He and Ar at electron emission angles from 0° up to 60°. The experimental results are qualitatively well described by plane wave Born approximations including projectile screening.

We have studied Young-type interference in the energy and angular distributions of double differential cross sections (DDCS) of electrons emitted in single-ionization of H2, induced by 8 keV electron impact. The first-order interference is derived from the energy distribution of DDCS and the resulting ratio-spectra (H2-to-2H) exhibit oscillating behaviour. The signature of first-order interference is also demonstrated in the DDCS-spectra as a function of emission angle. We have shown that the constructive interference prevails in soft- and binary-collision regions. The single differential cross sections obtained by integrating the DDCSs over energy and solid angle also preserve the information on interference.