A measurement of the ionization cross-section of Ne + to Ne 2+ by electron impact

1963 ◽  
Vol 274 (1359) ◽  
pp. 546-551 ◽  
Keyword(s):  
Electron Energy ◽  
Cross Section ◽  
Ionization Cross Section ◽  
Incident Electron Energy ◽  
Ionization Cross ◽  
Maximum Value ◽  
Beam Method ◽  
The Cross ◽  
Semi Empirical ◽  
Limits Of Error

The crossed-beam method described by the authors in 1961 was used to measure the cross-section of Ne + in the reaction Ne + + e → Ne 2+ + 2 e . The cross-section increases linearly with electron energy near the threshold and attains a maximum value of 3·13 x 10 -17 cm 2 at 200 eV. The errors in the measurements were estimated to be less than ± 10% and the highest incident electron energy used was 1000 eV. A semi-empirical formula proposed by Drawin in 1961 describes the measured cross-section within the above limits of error when the two adjustable parameters take the values ξf 1 = 5·25 and f 2 = 0·70.

A measurement of the cross-section for detachment of electrons from H – by electron impact

1967 ◽  
Vol 299 (1459) ◽  
pp. 525-537 ◽  
Keyword(s):  
Cross Section ◽  
Born Approximation ◽  
Theoretical Calculations ◽  
Functional Dependence ◽  
Incident Electron ◽  
Incident Electron Energy ◽  
Measured Cross Section ◽  
Neutral Particles ◽  
Beam Method ◽  
The Cross

A crossed beam method has been used to measure the cross-section for the production of neutral particles in single collisions of electrons with H - ions at incident electron energies from 9 to 500 eV. The measured cross-section reaches a maximum of 50 Å 2 at an energy of 14 eV, and may be represented by the function Q = (1-1.6/( E log 10 E ) ½ )950/ E log 10 E /0·92, where the cross-section Q is in units of Å 2 and the incident electron energy E in units of electronvolts. The magnitude and functional dependence of the cross-section agree well with theoretical calculations based on the Bethe-Born approximation at energies above 20 eV.

A measurement of the electron impact ionization cross section of atomic hydrogen in the metastable 2S state

1975 ◽  
Vol 343 (1634) ◽  
pp. 333-349 ◽  
Keyword(s):  
Electric Field ◽  
Electron Energy ◽  
Cross Section ◽  
Cross Sections ◽  
Ionization Cross Section ◽  
Impact Ionization ◽  
Weak Field ◽  
Weak Electric Field ◽  
Hydrogen Atoms ◽  
Ionization Cross

The total ionization cross section for electrons colliding with metastable 2S atoms has been measured up to 500 eV electron energy by a crossed beam technique. A beam of fast hydrogen atoms, containing about 25% in the 2S state and the rest in the IS ground state, is formed by charge capture onto protons that are passed through a caesium vapour target. Protons emerging from the target are removed from the beam by deflexion in a weak electric field. Atoms formed by capture into long-lived, high quantum states are first ionized in a topographically suitable field and then removed by deflexion in the weak field. The signal arising from electron ionization of the 2S atoms is identified by quenching them in a pulsed electric field. Contributions from other sources of extraneous ionization are eliminated by modulated beam techniques. The cross sections are determined from absolute measurements of the beam fluxes, the geometry of the interaction region and the rate at which 2S atoms are ionized. The results show that as the electron energy is raised, the ionization cross section for 2S atoms rises to a maximum at about 4 times the ionization energy of the 2S state. This maximum, about 10 -15 cm 2 , is 13 times larger than th at of the IS atoms. Comparison with various theoretical determinations indicates th at best agreement is obtained with the Born approximation which includes exchange, but below 100eV the classical Monte Carlo approximation agrees equally well with observations.

scholarly journals The quantal calculation of the photo-ionization cross-section of atomic potassium

1947 ◽  
Vol 188 (1014) ◽  
pp. 350-357 ◽  
Keyword(s):  
Cross Section ◽  
Ionization Cross Section ◽  
Great Sensitivity ◽  
Wave Functions ◽  
Laboratory Measurement ◽  
Frequency Curve ◽  
Ionization Cross ◽  
The Cross ◽  
Photo Ionization

The photo-ionization of atomic potassium is investigated using quantal methods. Emphasis is laid on the great sensitivity of the cross-section to the wave functions employed. The general features of the cross-section as revealed by the laboratory measurement can be understood. To explain the finite minimum observed in the cross-section-frequency curve it is necessary to take into account non-separability effects.

Ionization Cross Sections for Quantitative Electron Probe Microanalysis

2001 ◽  
Vol 7 (S2) ◽  
pp. 672-673
Author(s):  
C. Merlet ◽  
X. Llovet ◽  
S. Segui ◽  
J.M. Fernández-Varea ◽  
F. Salvat
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Electron Probe Microanalysis ◽  
Electron Probe ◽  
Ionization Cross Section ◽  
Ionization Cross ◽  
Quantitative Electron Probe Microanalysis ◽  
Ionization Cross Sections ◽  
Semi Empirical ◽  
Quantitative Epma

Quantitative procedures in electron probe microanalysis (EPMA) require the knowledge of various atomic parameters, the most fundamental of which is the ionization cross section. A number of semi-empirical, approximate analytical formulas have been proposed to calculate the ionization cross section. The simplicity of these formulas makes them suitable for quantitative EPMA procedures. However, it is difficult to assess their reliability because of the lack of accurate experimental data. Indeed, inspection of currently available data reveals that they are still scarce for many elements and, when they are available, one usually finds significant discrepancies between data from different authors. Fortunately, the inaccuracies in the semi-empirical cross section formulas used in EPMA have only a small effect on the analytical results when standards are used. Nonetheless, in quantitative EPMA studies at low overvoltages or using standardless methods, the evaluated compositions largely depend on the adopted ionization cross sections and, therefore, knowledge of accurate ionization cross sections is a requisite for the development of improved quantification methods.

Ionization by positive ions

1957 ◽  
Vol 240 (1222) ◽  
pp. 382-395 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Ionization Cross Section ◽  
Ion Beam ◽  
Ionization Cross ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Adiabatic Theory ◽  
The Cross ◽  
Low Pressures

We describe a method of measuring the ionization cross-section of atoms by positive ions, in which electrons are collected from single collisions of an ion beam passing through a gas at low pressures. Secondary electrons formed by the collisions of ions with surfaces are suppressed. Measurements are given for twenty-three cases, over energy ranges of ~ 5 to ~ 40 keV (§ 1) and ~ 100 to ~ 3 keV (§2). The cross-sections do not appear to conform to the simple adiabatic theory, but the size of cross-section in the adiabatic region appears to depend upon the reduced mass of the system.

Microanalysis of boundaries by AEM at different voltages

1993 ◽  
Vol 51 ◽  
pp. 600-601
Author(s):  
Anthony J. Garratt-Reed
Keyword(s):  
Electron Energy ◽  
Cross Section ◽  
Ionization Cross Section ◽  
Analytical Electron Microscopy ◽  
Relativistic Equation ◽  
Image Resolution ◽  
Electron Gun ◽  
Relativistic Electrons ◽  
Ionization Cross ◽  
Area Of Interest

It is well known that theory predicts a number of benefits for high-resolution analytical electron microscopy (AEM) in raising the electron energy. These benefits arise from three principal effects, namely, an anticipated linear decrease in the beam broadening in the foil with increasing energy, and an increase in the electron gun brightness with increasing energy, and an increase in the X-ray peak-tobackground ratio as the electron energy is raised. In addition, the decrease in the electron wavelength with increasing energy can also lead to improvement in the image resolution, although generally not in the microanalytical resolution. To set off against these benefits is the disadvantage that the ionization cross-section decreases with increasing beam voltage. However, although for the case of nonrelativistic electrons this can be a significant effect, in most cases, for relativistic electrons (those used for intermediate-voltage AEM, for example) this decrease is not severe. For example, fig. 1 plots the ionization cross-section for iron for electrons in the range 20-500kV, according to the relativistic equation of Chapman et. al. A further area of interest is the effect of radiation damage in the sample, which may increase or decrease at higher voltages.

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