Osamu Sueoka

Total Cross-Section Measurements for 0.3–10 eV Positron Scattering on N2, CO, and CO2 Molecules

Total cross-sections (TCS) for 0.3–10 eV positrons scattered by N 2 , CO, and CO 2 molecules have been measured using a beam transmission technique. For TCS measurements in the very low energy range, an apparatus adapted for use in a low magnetic field for beam transportation was used. Although the data in an extended energy region from one already measured did not show drastic variations from the daa already presented, small variations were shown in three TCS-curves.

Total and positronium formation cross-sections in polyatomic molecules

Abstract Total cross-section (TCS) studies of positron and electron impacts in polyatomic molecules are presented experimentally and theoretically. The polarization interaction in the positron and electron scattering processes by polyatomic molecules is discussed. Positronium (Ps) formation cross-sections in many polyatomic molecules are also measured at 2 eV above the corresponding Ps formation thresholds. And the results are analyzed based on the physical properties of the positron–molecule interaction systematically. Comparative studies of the vibrational excitation cross-sections by positron and electron impacts are also briefly described.

Positron and electron total cross sections for collisions with C2F6 and C2H3F3 molecules

Abstract The experimental total cross sections (TCSs) data for 0.7–600 eV positrons and 0.8–600 eV electrons colliding with hexafluoroethane (C2F6) and 1,1,1-trifluoroethane (C2H3F3) molecules are presented. These data are compared with the data of ethane (C2H6) measured previously. On the positron TCS data below 5 eV, the TCS curves are quite different from each other. For energies 7–25 eV, the data for these three kinds of molecules are comparable, though above 60 eV the C2F6 TCS data are roughly twice those of C2H6. The C2H3F3 TCS data have magnitudes almost midway between those of C2F6 and C2H6. The TCS curves for electrons show the same variation with energy as the positron data above 60 eV. In the low energy region, a few weak resonant peaks are observed in the C2F6 and C2H3F3 electron TCS curves. On the electron TCS data in the range 5.5–14 eV, the C2F6 data are lower than the C2H6 data.

Production of an intense slow positron beam by using an electron LINAC and its applications

Abstract An image of reemitted positrons has been produced in a proto-type positron transmission-type reemission microscope by using the electrostatic intense slow positron beam from an electron LINAC. RHEPD experiments have then been performed on H-terminated Si(111).

Brightness enhanced intense slow positron beam produced using an electron linac

An intense pulsed slow positron beam was produced from a 100 MeV electron linac of the Japan Atomic Energy Research Institute and was extracted using solenoid transport tubes. The intensity of the obtained slow positron beam was 2–3×107 e+/s at 110 of the full power operation (at 10 μA average electron beam current). In order to use the beam for positron scattering, diffraction and microscope experiments, it was transferred from the solenoid magnetic field to a field-free region, and was then brightness-enhanced. The final beam size was reduced from 10 mm o in the solenoid magnetic field to 0.5 mm o after two stages of remoderation.

A comparative study of electron and positron scattering from molecules. IV. CH3Cl, CH3Br, and CH3I molecules

An experimental study of electron and positron scattering from CH3Cl, CH3Br, and CH3I molecules has been carried out, and total cross sections (TCSs) for both projectiles were determined. Several strong structures due to resonances in the TCSs have been observed for electron impact, while weak but not negligible structures have also been seen for positron impact. A strong variation for the dominant resonance peak seen at around 10 eV was found to depend on a type of halogen atoms, and a detailed study of this dependence on molecular species has been performed to understand the origin and nature of these resonances. The continuum multiple-scattering method has been employed for the analysis of experimental results in addition to the evaluation of the elastic cross section. For larger halogen atoms, TCSs tend to possess larger magnitudes at energies above 100 eV than for smaller halogen atoms suggesting that the halogen atoms in fact dominate the dynamics, and their magnitudes increase in the order of CH3I>...

Total and elastic cross-sections of electron and positron scattering from C3H4 molecules (allene and propyne)

Abstract Total cross-sections (TCSs) for electron and positron scattering from C3H4 isomers (allene and propyne) were measured using the linear transmission method in the range of 0.8–600 eV for electrons and 0.7–600 eV for positrons. Elastic cross-sections for electron scattering were also measured by a crossed-beam experiment in the range of 2–100 eV. Sharp resonance-like peaks were observed in the electron TCSs for propyne around 3.6 and 8 eV, and 2.5 and 11 eV for allene. The positron TCSs for these molecules were found to be smaller and much smoother than the electron TCSs. Clear differences in resonance positions and magnitudes between the two isomers can be viewed as an isomer effect.

Total cross-sections of electron and positron collisions with CHF3 molecules: a comparative study with CH4 and CF4

Abstract Total cross-sections for electron (e − ) and positron (e + ) scattering from CHF 3 have been measured from 0.7 to 600 eV and compared with the theoretical elastic cross-section. For e − scattering, the cross-sections are found to be larger by 30% than the data compiled by Christophorou et al. [L.G. Christophorou, J.K. Olthoff, M.V.V.S. Rao, J. Phys. Chem. Ref. Data 26 (1997) 1] in the entire energy range measured, but their energy dependence is in good agreement. For e + scattering, the cross-sections are smaller by at least a factor of two than those for electron scattering below 20–30 eV, but quickly approach those of electron impact beyond 100 eV. A comparative study with CH 4 and CF 4 reported in our previous papers provides detailed information on the dynamics.

Remarks on total and elastic cross sections for electron and positron scattering from CO2

There remain discrepancies in the determination of the total and elastic cross sections for electron and positron collisions with carbon dioxide at impact energies from 0.3 to 100 eV. We have carried out a joint experimental and theoretical study in an attempt to resolve the differences. Our measurements for total cross sections for electron impact agree extremely well with those of Hoffman et al. [Phys. Rev. A 25, 1393 (1982)] above 2 eV, while those for positron impact agree to better than 15% in magnitude, and are in an excellent accord for the energy-dependence. The present observations, along with an analysis using a knowledge of the dominant inelastic processes, lead us to conclude that the total cross section determined in earlier studies is a considerable underestimate at intermediate energies, where inelastic processes are not negligible. The analysis provides a rationale for understanding the discrepancies. Furthermore, we present that the total cross section by positron impact below 2 eV become...

Excitation and Ionization of He Atom by Positron Impact

The 2 1 S-excitation cross-section Q exc and the ionization cross-section Q ion of He atom by positron impact were obtained in the range of 24∼120 eV positron energies by the time spectrum in the retarding potential-TOF method. The excitation cross-section is consistent with those by Coleman and Hutton at the energies below 31 eV. The values of Q ion agreed with those by electron-collision measurements.