Near-threshold ionization of atoms and molecules by positron impact

2003 ◽  
Vol 81 (7) ◽  
pp. 919-927 ◽  
Author(s):  
R I Campeanu ◽  
L Nagy ◽  
A D Stauffer
Keyword(s):  
Power Law ◽  
Cross Sections ◽  
Experimental Results ◽  
Threshold Power ◽  
Distorted Wave ◽  
Positron Impact ◽  
Atoms And Molecules ◽  
Wave Models ◽  
Impact Energies ◽  
34.50 Fa

Distorted-wave models previously used to study the ionization of hydrogen and the noble gases by positron impact at medium kinetic energies are employed to produce cross sections for impact energies within 0.02 eV of the ionization threshold. These theoretical cross sections are compared with the Wannier–Klar threshold power-law formula and the existing experimental results. PACS Nos.: 34.50.Fa, 34.85.+x

Positron impact ionization of krypton and xenon

2000 ◽  
Vol 77 (10) ◽  
pp. 769-774 ◽  
Author(s):  
R I Campeanu ◽  
R P McEachran ◽  
A D Stauffer
Keyword(s):  
Energy Range ◽  
Cross Sections ◽  
Free Electron ◽  
Impact Ionization ◽  
Plane Waves ◽  
Distorted Wave ◽  
Positron Impact ◽  
Full Energy ◽  
Alternate Model ◽  
Wave Models

Several distorted-wave models for positron ionization of krypton and xenon are investigated. Our previous CPE (Coulomb plus Plane waves -- full Energy range) model produces reliable cross sections for krypton. For xenon, at high positron energies, the CPE results fall below experiment. We have proposed an alternate model DCPE4 that works well for both krypton and xenon. A common feature of both of these models is that the free electron and positron are treated differently.PACS No.: 34.90.+q

Electron impact ionization of the ground state of singly ionized helium

2000 ◽  
Vol 78 (10) ◽  
pp. 901-906 ◽  
Author(s):  
M Bhattacharya ◽  
N C Deb ◽  
A Z Msezane ◽  
P S Mazumdar
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
Differential Cross ◽  
Ground State ◽  
Impact Ionization ◽  
Electron Impact Ionization ◽  
Experimental Results ◽  
Distorted Wave ◽  
Wave Approximation ◽  
34.50 Fa

We calculate the total and single differential cross sections for the electron impact ionization of the ground state of singly ionized helium at various energies in a distorted wave approximation. Present results are compared with existing theoretical and experimental results. PACS Nos.: 34.80.Dp, 34.50.Fa

Multiple ionization of argon by positron impact

1996 ◽  
Vol 74 (7-8) ◽  
pp. 373-375 ◽  
Author(s):  
R. Hippler ◽  
S. Helms ◽  
U. Brinkmann ◽  
J. Deiwiks ◽  
H. Schneider ◽  
...  
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
Experimental Results ◽  
Positronium Formation ◽  
Positron Impact ◽  
Single Ionization ◽  
Multiple Ionization

Recent experimental results for the multiple ionization of argon by positron impact have been reanalysed. Absolute cross sections for the double and triple ionization of argon were obtained from measured ratios of double-to-single and triple-to-single ionization, using known cross sections for single ionization and for positronium formation. Distinct differences compared to similar results for electron impact are noted.

K-, L-, and M-shell ionization of atoms by electron and positron impact

1996 ◽  
Vol 74 (7-8) ◽  
pp. 376-383 ◽  
Author(s):  
S. P. Khare ◽  
J. M. Wadehra
Keyword(s):  
Experimental Data ◽  
Cross Sections ◽  
Positron Impact ◽  
Electrons And Positrons ◽  
Virtual Photons ◽  
Plane Wave Born Approximation ◽  
Ionization Cross Sections ◽  
Impact Energies ◽  
Shell Ionization ◽  
Good Agreement

The plane-wave Born approximation with Coulomb, relativistic, and exchange corrections is employed to obtain the K-, L1-, L2-, L3-, and M-shell ionization cross sections of a number of atoms bombarded by electrons and positrons in the energy range varying from the threshold of ionization to 1 GeV. Transverse interaction of virtual photons with atoms is also included and it is found to be of great significance for impact energies greater than about 1 MeV. For K- and L-shell ionization, good agreement between the theoretical values and various experimental data for electron-impact cross sections is obtained. However, for the M shell, the theory overestimates the experimental cross sections. For positron impact the agreement between the present results and the limited experimental data is found to be quite satisfactory.

scholarly journals Positron Scattering from Atoms and Molecules

Atoms ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 29 ◽  
Author(s):  
Sultana N. Nahar ◽  
Bobby Antony
Keyword(s):  
Cross Section ◽  
Electron Scattering ◽  
Cross Sections ◽  
Optical Potential ◽  
Inert Gases ◽  
Positron Impact ◽  
Positron Scattering ◽  
Atoms And Molecules ◽  
Section Data ◽  
Theoretical Approaches

A review on the positron scattering from atoms and molecules is presented in this article. The focus on positron scattering studies is on the rise due to their presence in various fields and application of cross section data in such environments. Positron scattering is usually investigated using theoretical approaches that are similar to those for electron scattering, being its anti-particle. However, most experimental or theoretical studies are limited to the investigation of electron and positron scattering from inert gases, single electron systems and simple or symmetric molecules. Optical potential and polarized orbital approaches are the widely used methods for investigating positron scattering from atoms. Close coupling approach has also been used for scattering from atoms, but for lighter targets with low energy projectiles. The theoretical approaches have been quite successful in predicting cross sections and agree reasonably well with experimental measurements. The comparison is generally good for electrons for both elastic and inelastic scatterings cross sections, while spin polarization has been critical due to its sensitive perturbing interaction. Positron scattering cross sections show relatively less features than that of electron scattering. The features of positron impact elastic scattering have been consistent with experiment, while total cross section requires significant improvement. For scattering from molecules, utilization of both spherical complex optical potential and R-matrix methods have proved to be efficient in predicting cross sections in their respective energy ranges. The results obtained shows reasonable comparison with most of the existing data, wherever available. In the present article we illustrate these findings with a list of comprehensive references to data sources, albeit not exhaustive.

Single ionization by positron impact

1996 ◽  
Vol 74 (7-8) ◽  
pp. 367-372 ◽  
Author(s):  
J. Moxom ◽  
P. Ashley ◽  
G. Laricchia
Keyword(s):  
Energy Range ◽  
Cross Sections ◽  
Positron Impact ◽  
Ionization Cross ◽  
Positron Scattering ◽  
Direct Ionization ◽  
Low Energies ◽  
Ionization Cross Sections ◽  
Impact Energies ◽  
Existing Data

The single direct ionization cross sections for positron scattering [Formula: see text] on He, Ar, Kr, and H2 were measured and compared with existing data and the corresponding cross sections for electron impact [Formula: see text]. At most impact energies the present data for He and H2 are in reasonable accord with other measurements and, in the case of He, with some of the available calculations. At low energies, [Formula: see text] is found to increase more slowly than [Formula: see text], probably due to the importance of Ps formation in this energy range.

scholarly journals Four-body treatment of the K-shell positronium formation from multi-electron atoms

Open Physics ◽  
2014 ◽  
Vol 12 (3) ◽  
Author(s):  
Ebrahim Ghanbari-Adivi ◽  
Azime Velayati
Keyword(s):  
Cross Sections ◽  
Bound States ◽  
Transition Amplitude ◽  
Wave Functions ◽  
Positronium Formation ◽  
Distorted Wave ◽  
Helium Atoms ◽  
Three Body ◽  
Impact Energies ◽  
Correct Boundary Conditions

AbstractThe four-body Coulomb-Born distorted-wave approximation with correct boundary conditions (CBDW-4B) is applied to the K-shell positronium formation from multi-electron atoms at intermediate and high impact energies. In the present approach, both K-shell electrons are treated as active electrons. For collisions of positrons with helium, carbon, and neon atoms, both the post and prior forms of the transition amplitude are calculated and the corresponding differential and integral cross sections are compared with the results of the three-body version of the formalism (CBDW-3B). In order to investigate the effects of the static electronic correlations on the process, initial bound states of the active electrons in helium atoms are described by Hylleraas and Silverman wave functions. Also for positronium formation from helium atoms the obtained cross sections are compared with the available experimental data and also with the results of the other theories.

scholarly journals Excitation of the lowest autoionizing level of caesium atoms by positron impact

2021 ◽  
Vol 2 (1) ◽  
pp. 77-83
Author(s):  
A. W. Munywoki ◽  
J. Okumu ◽  
C. S Singh
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
High Energy ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Distorted Wave ◽  
Positron Impact ◽  
Intermediate Energies ◽  
Threshold Energies ◽  
Determining Factor

We have obtained differential and integral cross sections for the excitation of caesium atom to the lowest autoionizing level by positron impact using the distorted wave approximation. We have also done calculations for electron impact excitation of the same level using the same method and compared our present positron/electron impact results with the available theoretical positron/ electron impact results and experimental electron impact results. It is found that the present positron impact integral cross sections are higher than the cross sections of Pangantiwar and Srivastava at low and intermediate energies, but the results converge as the energy increases in the high energy range. The disagreement at near threshold energies is due to the different distortion potentials used in the two calculations. The charge on the projectile is also a determining factor in the shape of the scattering cross section curves.

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