Loss Cross Sections Research Articles

Slow-particle-induced kinetic electron emission from a clean metal surface: A comparison for neutral and ionized projectiles.

Electron emission from a clean gold surface bombarded by slow (v1 a.u.) neutral or singly charged atoms has been investigated both experimentally and theoretically. The determination of electron-emission statistics for 1--16-keV ${\mathrm{H}}^{+}$, ${\mathrm{H}}^{0}$, ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{He}}^{+}$, ${\mathrm{He}}^{0}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{Ne}}^{0}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{Ar}}^{0}$, respectively, delivered accurate total electron-emission yields, which are consistently higher for positively charged ions than for the corresponding isoenergetic neutral atoms. It was assured that potential emission could not be responsible for the observed differences. ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ bombardment at low impact energy causes equal yields as for ${\mathrm{H}}^{0}$, but for higher kinetic energy even the yields for ${\mathrm{H}}^{+}$ are surpassed. The results are explained with a semiempirical theory for heavy-particle-induced electron emission, assuming different screening of projectile cores by the accompanying electron(s) during the continuous change of projectile charge upon penetration of the solid. For ${\mathrm{H}}^{+}$,${\mathrm{H}}^{0}$ bombardment a quantitative description of the experimentally observed effects could be achieved by calculation of the stopping power for slow projectiles in different charge states, together with the electron-capture and -loss cross sections for these projectiles colliding with the target atoms.

Measurement of charge-changing cross sections in collisions of He and He+ with H2, O2, CH4, CO and CO2

Single- and double-electron loss cross sections of He, and single-electron capture and single-electron loss cross sections of He+ in collisions with H2, O2, CH4, CO and CO2 have been measured in the energy range 0.3-1.8 MeV. From the measured cross sections, charge-changing cross sections in collisions of He and He+ with C have been determined using the Bragg rule. Scaling is examined for electron capture cross sections.

Electron-loss cross-section measurement of 3He ions by the attenuation method

We have measured single-electron loss cross sections of 3He1+ ions for various solid targets such as C, Al, V, Cr, Cu, Ge, Nb, Ag, Sn and Au at 72 MeV by using the attenuation method. In this method residual 3He1+ fractions after charge-changing collisions were measured with a 3He1+ incident beam. Concentrations of contaminating atoms in the target were determined by an independent RBS measurement. It was found that surfaces of almost all the targets were covered with thin oxygen layers by which 3He1+ fractions were reduced by about 10%. Corrections of the observed loss cross sections are made for the surface oxygen layers.

Target dependence of electron-capture and -loss cross sections of protons in solids

The target dependence of electron capture to (and loss from) bound states of swift protons moving in solids has been evaluated. Several mechanisms have been considered. Solid-state effects are relevant at low (ν lower than the Bohr velocity ν0 = 2.18 × 108cm/s) and intermediate velocities. A comparison of the relative weight of different physical processes is presented for several materials.

Optical potential description of collisions of p and p(mean) with alkali atoms

The authors have calculated cross sections for the excitation of Na(3s) and Li(2s) atoms by proton and antiproton impact within the framework of the optical potential model. They also present results for capture into hydrogen as well as loss and ionisation cross sections and compare their results with experimental data available.

Equilibrium Charge States of Incident Uranium Ions with Relativistic Velocity

Calculations are made for charge state distributions of U-ions at energies of 200-, 437- and 962-MeV/amu passing through low and high atomic number targets. The charge states of projectile ions are determined from a local equilibrium condition between electron loss and capture processes. Radiative electron capture (REC) as well as non-radiative one (NREC) is taken into consideration in the electron capture process. Both capture and loss cross sections are calculated by relativistic formalism incorporating of a strong Coulomb distortion of an electron due to a projectile ion. Resultant equilibrium charge states of U-ions are in reasonable agreement with experimental values, in particular at the incident energy 962 MeV/amu.

Calculation of high resolution electron and helium energy loss cross sections using surface vibration spectral densities

It is shown that vibrational eigenvectors (outputs of a slab calculation) are not required for the calculation of high resolution electron energy loss spectra (EELS) or helium energy loss spectra. Instead, vibrational spectral densities (outputs of a Green's function calculation) may be input directly to such calculations. This facilitates the treatment of scattering from bulk phonons as well as from surface phonons.

Calculation of high resolution electron and helium energy loss cross sections using surface vibration spectral densities

It is shown that vibrational eigenvectors (outputs of a slab calculation) are not required for the calculation of high resolution electron energy loss spectra (EELS) or helium energy loss spectra. Instead, vibrational spectral densities (outputs of a Green's function calculation) may be input directly to such calculations. This facilitates the treatment of scattering from bulk phonons as well as from surface phonons.

Charge-exchange cross sections for 445-MeV Cl ions in solid C targets.

Nonequilibrium charge-state fractions of $^{35}\mathrm{Cl}$ ions traversing solid C targets have been measured. Absolute intensities of x rays were measured for transitions between various states of the nearly fully stripped $^{35}\mathrm{Cl}$ ions that had an energy of 445 MeV and a velocity of 12.7 MeV/u. An analysis of the data has provided estimates of a number of cross sections for electron capture, excitation, and electron loss of the projectiles. Reasonable agreement has been found between some of these experimental values and theoretical estimates.

Single-electron capture and loss cross sections versus target Z for 1 MeV/u oxygen ions incident on gases.

In an ion-atom collision electron capture and loss depend, in general, on the beam energy, projectile charge state, and target Z. While most fundamental theories of capture and loss are formulated in terms of a single electron moving in the fields of the pertinent nuclei, various scaling laws have been developed to account for partially stripped ions and multielectron targets. The purpose of the present work is to systematically examine the dependence of capture and loss cross sections on target Z. Cross sections for single-electron capture and loss for 1 MeV/u oxygen ions passing through gas targets were measured as a function of target Z for incident projectile charge states of 5+, 6+, 7+, and 8+. The targets used were ${\mathrm{D}}_{2}$, He, Ne, Ar, and Kr. The electron-capture measurements are generally in reasonable agreement with existing theoretical and empirical scaling rules. The electron-loss cross sections differ appreciably from predictions of the plane-wave Born approximation, particularly for the heaviest targets studied.

Cross sections for Ar recoil ion production by 1 MeV/amu O q+ ( q = 2–8)

Cross sections for the production of recoil ions of Ar 1+ through Ar 10+ in collisions with 1 MeV/amu O 2+ through O 8+ ions have been measured using the time-of-flight (TOP) method. Postcollision charge state analysis of the projectile was performed to distinguish between events involving pure ionization ( q = 2–8), one-electron loss ( q = 2–6), two-electron loss ( q = 2–4), one-electron capture ( q = 3–8) and two-electron capture ( q = 5–8). The total direct ionization cross section was found to increase as q 1.5. The electron capture cross sections also increased as a function of q, while at the same time the cross sections for electron loss decreased. Both of these processes exhibit a steeper q dependence than the pure ionization process. The charge state distributions are bell shaped for the electron capture process and for the electron loss process at high q. For electron loss at low q the distributions are similar to those for the pure ionization process.

Classical equations-of-motion model for high-energy heavy-ion collisions.

A classical nonrelativistic microscopic model for high-energy heavy-ion collisions is presented, based on equations-of-motion calculations, where all the nucleon trajectories are computed with suitable two-body forces between all pairs of nucleons in the target and projectile. Comparison with experiment and with the results of other models is made. The model considers both position and velocity configurations according to a nuclear structure model, the isomorphic shell model previously and independently published. Thus, its results are objective and completely reproducible. The main feature, however, relies on the properties of the two-body potential used in the model which reproduces both the transverse momentum transfer cross section and the longitudinal momentum loss cross section, and at the same time possesses good saturation properties. While the present model uses a nonrelativistic approach, its results are comparable to those of other models using relativistic approaches.

フランジ型燃料ブロックを用いた高温ガス炉の炉心有効流量

The objective of present study is to evaluate and to increase the effective coolant flow rate of VHTR (Very High Temperature gas-cooled Reactor) core whose thermal output is 50MW and core outlet gas temperature is 950°C, without changing the sizes of the core and fuel element, Four types of fuel element are discussed, they are two flange type pin-in-block fuel elements which have 18 fuel rods (P 18) and 36 fuel rods (P 36), a flange type multihole fuel element (MH 8) and a dowel type pin-in-block fuel element (P 15).The flow distribution analysis was carried out by flow network code which calculated coolant pressure, flow rate and temperature. As the result, the followings were obtained:Effective coolant flow rate (Weff) became lower in the order, MH 8, P 36, P 18 and P 15 fuels. Weff of the P 15 fuel was the lowest, because crossflow loss coefficient of dowel type fuel element was lower than that of flange type. Weff of the P 36 fuel was higher than that of the P 18 fuel, because of larger total cross section of coolant flow channels. Weff of the MH 8 fuel was higher than that of the P 36 fuel, because of larger equivalent diameter of the channels.This analysis clearly revealed that the effective coolant flow rate increased by using the fuel element with large values of crossflow loss coefficient, cross section and equivalent diameter of coolant flow channels.

Experimental electron scattering spectrum of atomic carbon

As a first step in the eventual measurement of the electron energy loss cross sections for atomic carbon, a 100 eV incident energy, 2° scattering angle electron energy loss spectrum of atomic carbon showing the 7.48 eV (1657 Å) and 7.94 eV (1561 Å) multiplets has been obtained. The carbon atoms were produced by 308 nm XeCl excimer laser vaporization of a graphite rod at a 150 Hz repetition rate. The measurement of the relative intensities of the two carbon multiplets, 2s 22p 2 3P→2s 22p3s 3P o and 2s 22p 2 3P→2s 2p 3 3D o, allows their relative oscillator strengths to be calculated. The results are in excellent agreement with theoretical values and experimental lifetime measurements.

Negative ion resonance selective mode enhancement in the hreel spectrum of C2H 2 on Pd(111)

The vibrational spectra (HREELS) of acetylene (C 2H 2) adsorbed on the Pd(111) surface have been examined with a view to rationalizing conflicting evidence regarding the low temperature (130 K) formation of benzene. These show an enhancement in the electron energy loss cross section that is dependent on the incident beam energy, E i. This enhancement occurs in the loss feature assigned to the symmetric CH bend mode (660 cm −1) at an incident beam energy − 3 eV. Selective enhancement of this vibrational mode feature is attributed to negative ion resonant scattering from the chemisorbed C 2H 2 molecule. Furthermore, the 660 cm −1 mode enhancement is observed to increase with C 2H 2 coverage. The alternative interpretation, that this mode is due to the low temperature formation of benzene (C 6H 6), is discussed in light of the energy dependence of the electron scattering results.

Charge equilibrium of relativistic uranium ions in matter

Calculations are made for the electron capture and loss cross sections and the charge state distributions of uranium ions at energies of 200 MeV/nucleon, 437 MeV/nucleon and 962 MeV/nucleon colliding with low- Z and high- Z targets. The charge states of the projectile ions are determined from the equilibrium condition between electron loss from the ion and electron capture from a target atom into the projectile ion. The electron loss cross sections are formulated using the relativistic Born approximation. The electron capture process is considered to be non-radiative electron capture (non-REC) and radiative electron capture (REC) in the relativistic impact velocity range. The non-REC cross sections are calculated by Eichler's formula based on the eikonal theory, while for the evaluation of the relativistic REC process the contributions of internal e +e − pair creation and successive e +e − pair annihilation processes are taken into account in addition to the usual REC photon emission process.

Dynamic screening: Capture and loss processes of protons moving in solids

The many-body self-energy approach combined with ordinary atomic physics has been used to calculate the charge states and the capture and loss cross sections of protons moving in solids. The results show that for high velocities the processes are atomic like, while at intermediate velocities solid-state effects are responsible for the proton charges.

Single electron loss cross sections oF 3He 1+ ions for solid targets at 52, 62 and 72 MeV

Single electron loss cross sections of 3He 1+ ions for solid targets of C, Cu, Ge, Sn and Au were measured at 52, 62 and 72 MeV using the growth method. The free electron collision model for single electron atoms has been extended to all targets and the corresponding calculations have been carried out. The results give fairly good agreement with the experimental values. Results are also compared with other current theories.

Inelastic electron scattering of surface and bulk phonons on Cu(001)-p(2 x 2)S.

We have studied the scattering of electrons by surface and bulk phonons from the $p(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{S}$ on Cu(001) system. We find four surface phonons and a group of overlayer-induced bulk modes that produce larger electron-phonon loss cross sections. Comparison between microscopic theory and experiment indicates that the S adsorption distance is 1.30\ifmmode\pm\else\textpm\fi{}0.05 \AA{} above the fourfold hollow site.

Cross sections for electron capture and loss. I. H+ and H- impact on H and H2.

The electron-capture cross sections for H/sup +/ impact on H and H/sub 2/ and the electron-loss cross sections for H/sup -/ impact on H and H/sub 2/ have been measured for projectile energies between 2.0 and 0.063 keV. Relative cross-section values for all these reactions were measured directly, and placed on an absolute scale by adopting a standard value of 6.95 x 10/sup -16/ cm/sup 2/ for the electron-capture cross section for H/sup +/+H/sub 2/ collisions at 2.0-keV H/sup +/ energy. A crossed-beam technique was used, and the reaction-product H atoms were measured by a secondary-electron-emission detector. The techniques used to make the measurements are described, and the results are compared with other experimental and theoretical data.