Cross Sections For Electron Production Research Articles

Comparison of experimental and theoretical electron ejection cross sections in helium by proton impact from 5 to 100 keV

Absolute values of doubly differential cross sections are obtained for electron production in helium by 5- to 100-keV proton impact. The measured values along with earlier data at higher energies are compared with theoretical plane-wave Born-approximation functions obtained from a Hartree-Fock potential. Not only is good agreement obtained at high impact energies (above 300 keV), but fairly good agreement is found at low energies (below about 20 keV). For electrons ejected in the backward hemisphere, unexpectedly poor agreement is noted at intermediate energies where the measured cross sections dip to 50% of the calculated values in some cases. Singly differential cross sections integrated over all angles agree quite well with the theoretical calculations over all ranges of parameters studied. Singly differential cross sections integrated over all electron energies tend to be more isotropic in angle as the proton energy is decreased from 100 to 5 keV. Total cross sections for electron production are also obtained which compare reasonably well with those of Solov'ev et al. but which are higher than those of de Heer et al. It is shown that the contribution to the cross section by the mechanism of charge transfer to the continuum decreases as the impact energy decreases, contrary to the prediction of Salin's treatment.

Ne K-shell vacancy production by intermediate energy F ions

The energy dependence of the Ne K-shell Auger electron production cross section is presented for various charge states of the F projectile from 3 to 35 MeV. This spans the intermediate energy range for K-shell vacancy production from the low-energy region where molecular promotion dominates to the high-energy region where Coulomb ionization.

Ne K Auger cross sections from 1.5 MeV/amu H, O and F

Ne K-shell Auger electron production cross sections, sigma A, have been measured for Ne bombarded by 1.5 MeV/amu H, O, and sigma A is found to increase with increasing projectile charge state which is a clear indication that the K-shell vacancy production cross section, sigma , is increasing with increasing projectile charge state since the fluorescence yield, omega , is increasing with increasing charge state and since sigma = sigma A/(1- omega ). The cross sections are compared to Coulomb ionization predictions.

Dynamic charge-state dependence of the K vacancy production yield in heavy-ion atom-collisions at keV energies

The KLL Auger electron production cross section has been measured for collisions between Na+, Na2+, Ne+, Ne2+, and N+ ions and Ne and N2 targets. Over a narrow velocity range (0.3-0.9au), the data reveal a dramatic dynamic effect in the 2p pi vacancy occupation probability factor Npi . This is in contrast to current available theories which invoke a static factor Npi .

Laboratory studies of collisions of energetic H+ and hydrogen with atmospheric constituents

Laboratory studies of ionization and excitation of atmospheric gases in collisions with 0.1‐ to 1000‐kev protons and hydrogen atoms are reviewed. Recent measurements of the mixed flux of H+ and H that penetrates the auroral zone atmosphere during a hydrogen aurora indicate that particles with energies less than 10 kev are most important, which implies that energetic hydrogen atoms cause most of the observed ionization and light emission. Both H+ and H produce free electrons by collisional ionization of atmospheric constituents, and stripping of energetic H is an additional source of electrons. Reliable data are available for the cross section for production of electrons in collisions of H+ and H with all important target gases, except atomic oxygen, over the full range of auroral energies. Excitation of atmospheric gases has been widely studied for H+ collisions in the range above 10 kev, but cross sections for H+ below 10 kev and H in any energy range are still largely unknown. Data are available for calculation of expected auroral emissions in the υ′ = 0 bands of the N2+ first negative system and in the υ′ = 0 bands of the N2 second positive system. The ratio of the cross section for electron production by ionization to the cross section for emission of the 391.4‐nm band of the N2+ first negative system is found to be about 20 for energies above 10 kev and then to rise to more than 100 at 1 kev. In the case of the hydrogen emissions, laboratory data are adequate for auroral calculations of Lyman α radiation. Collisional excitation of energetic H to the 2p level, rather than charge transfer excitation involving fast H+, is the major source of Lyman α in the hydrogen aurora. Data on the production of the Balmer α line are lacking at energies below 10 kev. The available Balmer α data suggest a broad peak near 10 kev in the effective auroral cross section that is nearly an order of magnitude smaller than the peak in the Lyman α cross section, which occurs at energies less than or equal to 1 kev. Insufficient laboratory data exist for meaningful calculations of auroral Hβ intensities.

Ionization of potassium by 20-100 keV protons

A modulated crossed beam technique has been used to investigate the ionization of potassium by 20-100 keV protons. Absolute cross sections for electron production and cross sections for K+ and K2+ formation have been determined. The results are compared with recent calculations based on the classical impulse approximation and with experimental data on the ionization of potassium by electron impact.

Comparison of Experimental and Theoretical Values of Cross Sections for Electron Production by Proton Impact

Angle and energy distributions of electrons ejected from single- and multishell atoms by 50-to 300-keV protons are compared with various theoretical treatments. Partial cross sections for each subshell are calculated by scaling according to the number of electrons and the binding energy and then are added. The Born approximation fails at large and at small angles but yields fair agreement at intermediate angles. The treatments of Salin and of Macek, which take account of the influence of the projectile after the collision, yield much improved agreement at small angles. The binary-encounter model is used to calculate cross sections which are differential only in electron energy. An analytical expression is given for the binary-encounter cross section averaged over the Fock hydrogenic distribution of orbital velocities. When the average orbital energy is calculated from Slater's rules, the results agree somewhat better with experiment than when this energy is set equal to the binding energy.

Angular and energy distribution of electrons produced by 200–500 keV protons in gases

The cross beam method was used to measure double differential ionization cross sections for electron production by 200–500 keV protons incident on a molecular beam. The ejected secondary electrons were detected by an electron multiplier and an electrostatic 90 °-spectrometer which was movable in the scattering chamber from 18 °–155 ° with respect to the incident proton direction. After the elimination of disturbing electric and magnetic fields, electrons were measured at energies down to 1 eV. The absorption of the very slow electrons along their path through the spectrometer could be minimized by using a relatively low gas pressure in the scattering chamber of a few 10−5 Torr. The efficiency of the electron detector was determined with an electron source whose emission rate per solid angle was known. Absolute cross sections and their angular dependence were obtained by measuring the slow electrons—ejected with a relatively high rate—without the molecular beam; these data being used to normalize the electron spectra acquired with the molecular beam. Ionization cross sections with 300 keV protons incident on helium are discussed and except for the very slow electrons, a good agreement is found with results of Ruddet al.

Cross Sections for Positive-Ion and Electron Production in Collisions of 1-25 keV Hydrogen Atoms with Atomic and Molecular Gases

Cross sections are reported for production of positive ions and electrons in collisions of hydrogen atoms in the energy range 1-25 keV with He, Ne, A, Kr, Xe, ${\mathrm{H}}_{2}$, and ${\mathrm{O}}_{2}$. Slow positive ions are produced by capture of an electron by the fast atom from the target gas and by ionization of the target. Electrons are produced by target-gas ionization and by stripping of the fast atom. Ionization cross sections for each of the target gases are derived from the positive-ion production cross sections and previous measurements of the capture cross sections.

First Born approximation electron loss, ionization and total electron production cross sections for fast positive helium ions incident on atomic helium

The first Born length and velocity approximation is used to calculate cross sections for one-electron loss, total electron production and ionization occurring in the collision of fast singly ionized helium with neutral atomic helium. Account is taken of double transitions. Good agreement between the theoretical and experimental values of the one-electron loss, total electron production and ionization cross sections is found for impact energies greater than 1000 and 300 keV respectively.

Cross Sections for Ion and Electron Production in Gases by 0.15-1.00-MeV Hydrogen and Helium Ions and Atoms

Reported in this paper are the measurements of absolute total apparent cross sections for processes leading to slow electron and ion production in the gases He, Ar, ${\mathrm{H}}_{2}$, and ${\mathrm{N}}_{2}$ by incident beams of ${\mathrm{He}}^{++}$, ${\mathrm{He}}^{0}$, and ${\mathrm{H}}^{0}$ in the energy range 0.15 to 1.00 MeV. From these measurements absolute total apparent cross sections for ionization, electron capture, and stripping were deduced. The present results are compared with those from other experiments and with available theoretical calculations.

Cross Sections for Ion and Electron Production in Gases by Fast Helium Ions (0.133-1.0 MeV). II. Comparison with Theory

The theory of ionization of gases by fast, but nonrelativistic, ions is briefly reviewed, with emphasis on the correspondences expected at high energies among the cross sections for various projectile ions incident on a given target gas. The problem of deducing cross sections for simple ionization from experimental gross ion and electron production cross sections is discussed. The methods developed are applied to the experimental data presented in the preceding paper. Estimates are thus obtained of the simple ionization cross sections for ${\mathrm{He}}^{+}$ ions incident on ${\mathrm{H}}_{2}$, He, Ar, and ${\mathrm{N}}_{2}$ in the energy range 0.133 to 1.0 MeV, and ${\mathrm{He}}^{+}$ on Ne, ${\mathrm{O}}_{2}$, and CO in the energy range 0.6 to 1.0 MeV. Similar results are obtained for ${\mathrm{He}}^{++}$ ions incident on ${\mathrm{H}}_{2}$ and He in the energy range 0.5 to 1.0 MeV. These results are compared with semitheoretical predictions based upon empirical values of target-gas matrix elements determined from previous measurements of the ionization cross sections for protons incident on the same targets. It is shown that the ionization cross sections for ${\mathrm{He}}^{++}$ conform rather well to the predictions, and that the ionization cross sections for ${\mathrm{He}}^{+}$ ions are in good agreement with those expected for a point-charge ion with the helium mass and an "effective charge" of ${Z}^{\ensuremath{'}}e=+1.2e$. The ionization cross sections are also compared with explicit detailed calculations in the full Born approximation for the cases where such calculations are available. The agreement obtained is quite good in general.

Cross Sections for Ion and Electron Production in Gases by Fast Helium Ions (0.133-1.0 MeV). I. Experimental

This paper reports the measurement of apparent cross sections for production of slow positive ions and free electrons by ${\mathrm{He}}^{+}$ ions incident on He, Ne, Ar, ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, and CO in the energy range 0.133 to 1.0 MeV, and similar cross sections for ${\mathrm{He}}^{++}$ ions incident on He and ${\mathrm{H}}_{2}$ in the energy range 0.5 to 1.0 MeV. Direct comparisons are made with experimental results obtained by other investigators for ${\mathrm{He}}^{+}$ ions at energies up to 0.40 MeV. In the companion paper comparisons are also made with available theoretical calculations and with results predicted from the Bethe-Born approximation with the evaluation of certain parameters from earlier measurements with proton projectiles.

The direct production of electron pairs by high-energy muons underground (148 m w.e.)

Direct production of electron pairs in thin iron targets by muons of mean energy 32.6 GeV was studied with a multiplate cloud chamber at a depth of 148 m w.e underground. Showers of two or more electrons associated with each outgoing muon from the targets were selected and their energy distribution determined for the target thicknesses 0.54 and 1.6 cm. The cross-sections for direct pair production of electrons as obtained from events produced in both thick and thin targets agree satisfactorily with those given by the Murota-Ueda-Tanaka theory in the ranges of energy-transfer (35÷100), (100÷500) and (500÷1000) MeV.

Charge transfer and ionization by positive ions in the energy range 60 to 450 keV

Charge transfer and ionization by singly charged positive ions have been investigated by means of a variation of the well-known condenser method in which slow charge collection over a precisely determined path length is carried out at pressures low enough to ensure single collision conditions; a uniform axial magnetic field enables total slow ion currents to be measured. The apparent total charge transfer cross-section, the total electron production cross-section and the total slow ion production cross-section have been determined for seventeen cases involving rare gas ions in the rare gases and hydrogen.

Charge Transfer and Electron Production inH−+H Collisions

The cross sections for charge transfer and electron production in collisions between hydrogen atoms and hydrogen negative ions (${\mathrm{H}}^{\ensuremath{-}}$) have been measured over the energy range 100 to 40 000 ev using modulated atomic-beam techniques in a crossed-beam experiment. Agreement of the experimental results with the perturbed-stationary-states calculation for charge transfer of Dalgarno and McDowell is quite satisfactory.